Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

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Phosphorus, P, is one of the main biogenic elements, a group which, along with H, C, O, N, and S, is present in all known life forms. Compounds of phosphorus appear profusely in biological systems, where they are involved in many fundamental biological functions, including replication, information transfer, and metabolism.(1) Despite its biological importance, P is relatively scarce on a cosmic scale. With an elemental abundance of 3.4 × 10–7 relative to H in the Sun’s atmosphere,(2) it is the least abundant of the main biogenic elements. Ortho-phosphate (oxidation state +5) is the dominant form of inorganic P at the Earth’s surface. However, P(V) salts typically exhibit poor bioavailability due to their low water solubility and low reactivity. Indeed, low concentrations of dissolved P make it a limiting reaction in many ecosystems, as well as giving rise to the “phosphorus problem” in the origin of life.(3,4) In contrast, the salts of more reduced forms of P (oxidation state ≤ +3) are far more soluble and reactive and thus have improved bioavailability.

One possible source of these reduced forms of P is from extra-terrestrial material that fell to Earth during the heavy bombardment period. A study by Pasek(5) demonstrated how phosphides, delivered directly to the surface of the Earth in iron nickel meteorites, can be processed by aqueous phase chemistry to form several prebiotic P species. However, of the total annual mass influx of exogenous material entering the Earth’s atmosphere, iron nickel meteorites only account for ∼1%, with interplanetary dust particles (IDPs) accounting for the other 99%.(6) An alternative entry route for reduced forms of exogenous P is the atmospheric processing of P that ablates in the upper atmosphere. In two previous publications, we have demonstrated that the meteoric ablation of IDPs is a significant source of atmospheric P, PO, and PO2 to the terrestrial planets(7) and how any P atoms will be rapidly oxidized to PO.(8) Continued atmospheric processing of PO and PO2 will then result in a variety of compounds in which P may exist in different oxidation states, due to the presence of both oxidizing and reducing agents in these atmospheres. Figure 1 shows a schematic diagram of the likely chemistry of meteor-ablated P species. This scheme was constructed by performing high-level electronic structure calculations (at the CBS-QB3 level of theory(9)) of P species reacting with atmospherically relevant species to determine energetically viable reaction pathways. Following initial oxidation of P and PO to PO2 (via reactions R1 and R2a), there appears to be two main channels: the formation of phosphoric acid (H3PO4) via the species HOPO2 (reactions R6 and R7) or the formation of the bioavailable compound phosphonic acid (H3PO3) via HPO2 (reactions R8 and R9):Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

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Figure 1

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Figure 1. Proposed reaction scheme for the neutral chemistry of P in the upper atmosphere of a terrestrial planet.

At present, only two reactions from this scheme have been previously investigated (R1 and R2). The temperature dependence of reaction R1 was reported in a previous publication from this group, in which the reactions of both ground and excited state P atoms with atmospherically relevant species were investigated.(8) Prior to this, only room temperature determinations of the rate of R1 were available, and the literature rate coefficients reported disagreed by over an order of magnitude.(10−13) For reaction R2, there is similar disagreement in the literature, with four previous room temperature rate coefficients reported. Two of the studies(14,15) put the rate at around 2 × 10–13 cm3 molecule–1 s–1, while the other two studies(16,17) put the rate at around 60 times faster than this, with a value of ∼1.3 × 10–11 cm3 molecule–1 s–1. This poor characterization of the gas-phase chemistry of phosphorus is not only of consequence to planetary atmospheres, as P-bearing compounds, including PO,(18−20) have been detected in a range of astrochemical environments. Many current chemical models are using the isovalence between nitrogen and phosphorus to derive chemical rates for P-bearing species, the validity of which is questionable, as these models tend to significantly underpredict the observed abundances of PO. Indeed, modeled and observed abundances of PO in a stellar outflow, in which PO is formed from the reaction of P + OH → PO + H, disagree by greater than 3 orders of magnitude.(21) Understanding the oxidation chemistry of elemental phosphorus and its oxides is also of importance to combustion chemistry, as phosphorus-containing compounds may be useful as potential fire suppression agents.(22−24) An understanding of the combustion of organophosphate compounds is of particular importance in the destruction of chemical warfare agents.(25,26)

The PO radical has been studied extensively by spectroscopic methods, with a brief history of the experimental work given by Moussaoui et al.(27) Studies investigating the A2Σ+X2Π transition include those by Coquart et al.,(28) Sausa et al.,(17) and Wong et al.(29) There have also been numerous theoretical studies, with a good overview of these given by Liu et al.(30) These theoretical studies have provided potential energy curves for the ground and many excited states of PO and also transition dipole moments for electric dipole transitions. However, as the A2Σ+ state is a low-lying Rydberg state, it is completely missed by the ab initio calculations employed in the majority of these theoretical studies, making the available literature on the A2Σ+ state rather sparse.(31)

In this paper, we present results from the second part of our investigation into the reactions of meteor-ablated phosphorus, reporting temperature-dependent rate coefficients for reactions R2 and R3. Rate coefficients were determined using a pulsed laser photolysis-laser induced fluorescence (PLP-LIF) technique, which is described in section 2. Using the same experimental setup, LIF spectra of PO over the wavelength range 245–248 nm were also collected. These spectra are then assigned and new spectroscopic constants for the X2Π and A2Σ+ states of PO reported.

2. Experimental Procedure


2.1. Reaction Kinetics

The experimental apparatus employed in this study has been discussed in detail in recent publications,(8,32−34) so only a brief synopsis is given here. All experiments were carried out in a slow flow reaction cell, using a PLP-LIF technique, with detection of either PO or PO2 radicals. The reaction cell consists of a cylindrical stainless steel chamber with four orthogonal horizontal side arms and a fifth vertical side arm. The chamber was enclosed in a thermally insulated container, which can be operated as a furnace or filled with dry ice, providing a temperature range from 190 to 800 K. Temperatures inside the reactor were monitored by a shielded K-type thermocouple inserted directly into the center of the chamber. Radical precursors, reagents, and bath gases were introduced to the chamber via the five side arms, after being combined in a mixing manifold to ensure homogeneous mixing. Radical precursors were prepared as dilute mixtures of between 0.5 and 5% in N2 (the total precursor concentrations in the cell were typically around 0.1%). Flow rates were controlled using calibrated mass flow controllers (MKS instruments), with total flow rates ranging from 100 to 400 standard cm–3 min–1. These flow rates were sufficient to ensure a fresh flow of gas through the interaction region for each photolysis laser pulse. The pressure inside the reaction chamber was measured by a calibrated capacitance manometer (Baratron MKS PR 4000) and controlled by a needle valve on the exit line to the pump. The photolysis and probe laser beams were introduced collinearly on opposite sides of the cell and the fluorescence signal collected using a photomultiplier tube (PMT) (Electron Tubes, model 9816QB) mounted orthogonally to the laser beams. To increase the solid angle of collected fluorescence, a glass tube of ∼1.5 cm diameter was positioned ∼1 cm above the interaction region to act as a waveguide to transport the fluorescence light along the vertical side arm to the PMT.

For reaction R2, PO radicals were produced from the multiphoton dissociation of POCl3 at 248 nm (R10). For reaction R3, PO2 radicals were produced by the photolysis of either POCl3 or PCl3 at 248 nm, in the presence of O3. O3 was produced by passing a flow of O2 though a corona discharge in an ozonizer (Edwards, E28), with a typical conversion efficiency of ∼2%. O3 concentrations were monitored downstream of the reactor, by either UV or green light absorption spectroscopy. UV absorption spectroscopy was carried out at 253.7 nm from a Hg Pen-ray lamp, using a 1 m absorption cell with a PMT (Hamamatsu type H9306-13) fitted with a monochromator set at 257.3 nm (Minichrom, 300 μm slits). Green light absorption spectroscopy was carried out using a multipass Herriott cell,(35) with a total pass length of 1.38 m. Green light at 532 nm was produced using a solid state laser and monitored using a photodiode detector (Thorlabs SM05PD3A) connected to a digital oscilloscope (LeCroy, LT262). Ozone concentrations were determined using absorption cross sections taken from the MPI-Mainz Spectral Atlas(updating × 10–17 cm2 at 253.7 nm and 3.0 × 10–21 cm2 at 532 nm). Corrections were made to the measured ozone concentrations to account for photolysis by the 248 nm photolysis laser in the reaction chamber. This was done by first determining the intensity of 248 nm light entering the reaction cell (as measured by a Gentec UP19-VR power meter) and reaching the interaction region, after accounting for losses due to windows and attenuation by O3 in the 15 cm side arm. Then, using the intensity of light reaching the interaction region, the number of photons of 248 nm light absorbed by O3 over the 1 cm interaction region was calculated. Assuming that each photon of 248 nm light absorbed led to the photodissociation of one O3 molecule,(37) the remaining concentration of O3 in the interaction region could then be determined. In a typical experiment, at high ozone concentrations of ∼6 × 1015 molecules cm–3, around 10% of the O3 within the 1 cm3 interaction region was removed, while, at lower ozone concentrations of ∼6 × 1014 molecules cm–3, around 20% of the ozone was removed. To validate this method of correcting the ozone concentration, the reduction in the intensity of the 248 nm light due to absorption by O3 as it passed through the entire cell was also calculated and shown to be in good agreement with measured reductions in the 248 nm light intensity exiting the cell.

In all experiments, the 248 nm photolysis light was generated from a KrF excimer laser (Lambda Physik COMPEX 102). In experiments requiring multiphoton dissociation of the precursor, the excimer beam was loosely focused using a 50 cm focal length lens, with the focal point positioned approximately 10 cm beyond the center of the reaction chamber, giving a beam cross section in the interaction region of ∼8 mm2. The KrF laser fluence at the interaction region ranged between 10 and 20 mJ cm–2 for experiments in which no focusing was required and between 270 and 650 mJ cm–2 for experiments in which focusing was required. PO and PO2 radicals were observed by time-resolved LIF spectroscopy, using the frequency doubled output of a Nd:YAG pumped dye laser (a Quantel Q-smart 850 pumping a Sirah Cobra-Stretch with a BBO doubling crystal). PO(X2Π) was probed using the A2Σ+ (ν′ = 0) ← X2Π (ν″ = 0) transition at ∼246.3 nm.(17) The nonresonant (ν′, ν″ 0, 1) fluorescence at ∼255.4 nm was collected using a PMT fitted with an appropriate filter (Laser2000 Brightline Bandpass filter, λmax - 255 nm, fwhm - 8 nm) and recorded using a digital oscilloscope (LeCroy, LT262). PO2 was probed using either the B2B1(2, 7, 0) ← X2A1(0, 0, 0) transition at ∼286.1 nm or the B2B1(4, 2, 0) ← X2A1(0, 0, 0) at 287.0 nm and the nonresonant fluorescence at λ > 350 nm discriminated using a 350 nm cut on filter. The temporal evolution of the LIF signal was recorded by varying the time delay between the photolysis and probe laser. A typical time-resolved LIF profile (Figures 2 and 4) consisted of between 150 and 250 delay steps and resulted from the average of between 5 and 10 individual delay scans.

Figure 2

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Figure 2. PO LIF signal following PLP of POCl3 at a total pressure of 19.8 Torr and [O2] = 8.35 × 1014 molecules cm–3, at T = 335 K. Inset: a bimolecular plot for reaction R2 at T = 335 K, giving k2 = (1.44 ± 0.03) × 10–11 cm3 molecule–1 s–1.

In the experiments monitoring LIF from PO2, the raw PMT signal needed to be corrected for chemiluminescence produced following the photolysis of POCl3 and PCl3 in the presence of O3. Although this chemiluminescence has been observed in other studies involving oxygen–phosphorus systems,(38−41) the precise reactions producing it are unknown, although two studies(38,41) do suggest it arises from PO2 itself. Indeed, the observed loss of the chemiluminescence signal with [O3] was consistent with the observed loss of the PO2 LIF signal with [O3], suggesting PO2* as a possible source. However, of the possible reactions forming PO2 explored in section 3.2 below, only the reaction between PO and O3 is sufficiently exothermic to populate the first excited state of PO2, which lies ∼250 kJ mol–1 above the ground state.(42) As PO may only be produced in experiments using PCl3 as a precursor (see Scheme 3 in section 3.2), this reaction cannot explain the chemiluminescence observed when using POCl3 as a precursor. Furthermore, the observed growth of the chemiluminescence signal with [O3] was typically only around half the observed growth of the PO2 LIF signal with [O3], suggesting a species other than PO2 as the source of the chemiluminescence. As the exact nature of the chemiluminescence signal is uncertain, its contribution to the raw PMT signal was removed. To do this, back-to-back experiments were conducted, one with the probe laser on and one with the probe laser off (Figure 4a). In the experiment with the probe laser off, all signal measured by the PMT results from chemiluminescence initiated by the photolysis laser. In the experiment with the probe laser on, the measured signal contained both chemiluminescence initiated by the photolysis laser and the signal from the LIF of PO2. The PO2 LIF signal (Figure 4) is then obtained by subtraction. Note that, although chemiluminescence would also have been produced in the experiments monitoring the PO LIF signal, no correction to the raw PMT signal was required, as the chemiluminescence was effectively excluded by the interference filter used in those experiments.

2.2. PO LIF Spectrum

PO LIF spectra were collected using the same experimental setup as the kinetics experiments. PO radicals were generated either by the reaction with O2 of ground and excited state P atoms produced from the multiphoton dissociation of PCl3 or PBr3 at 248 nm or directly from the multiphoton dissociation of POCl3 at 248 nm. These three regimes were used to ensure a positive identification of PO. In the experiments in which LIF spectra were collected, the delay between the photolysis and probe lasers was fixed, while the probe laser wavelength was linearly scanned between 245 and 248 nm. In this manner, each new laser pulse produced the PO LIF signal at a new wavelength, rather than at a later delay time. The pulse width of the probe laser employed is 6 ns, with a line width of 0.003 nm. The output of the probe laser was calibrated using a wavemeter (Bristol Wavemeter 871).

Materials

He (99.999%, BOC), N2 (99.9995%, BOC), O2 (99.999%, BOC), and CO2 (99.999%, BOC) were used without further purification. PCl3 (≥99.0%, VWR), POCl3 (99%, Sigma-Aldrich), PBr3 (99%, Sigma-Aldrich), and dimethyl methylphosphonate (DMMP) (97%, Sigma-Aldrich) were initially degassed by freeze–pump–thawing to remove volatile contaminants and then made up as dilute vapors in N2 or He.


3.1. PO + O2

We initially thought that the rate of the reaction between PO and O2 (R2) could be determined from the PO LIF profiles produced following PLP of PCl3 in the presence of O2, via the following reaction scheme:Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R1)Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R2a)However, as discussed previously,(8) the multiphoton dissociation of PCl3 produces significant amounts of the first two excited states of P (the 2D and 2P states, hereafter collectively referred to as P*). The formation of P* together with ground state P(4S) complicated the reaction scheme so that information regarding the removal of PO could not be extracted. Therefore, in order to measure the rate of reaction R2, a photolytic source of PO was used. Previous studies into the rate of reaction R2 employed DMMP as a PO precursor.(15−17) However, we observed that photolysis of DMMP at 248 nm produced substantial amounts of P*. Indeed, photolysis of DMMP produced so much P(2P) that we were able to use it as a precursor when measuring the rate of P(2P) with O2.(8) The formation of P* from the multiphoton dissociation of DMMP resulted in the reaction scheme for PO formation and removal becoming over complicated, making information regarding the removal of PO difficult to extract. This led us to investigate a cleaner source of photolytic PO. Tests on the PLP of phosphoryl chloride, POCl3, indicated that it was a good source of PO and did not produce any evidence of P* formation, even when using concentrations of POCl3 and photolysis energies substantially higher than required for the kinetics experiments. We cannot rule out the significant formation of ground state P(4S), as we are unable to observe this species directly. However, as the formation of PO from the reaction of P(4S) and O2 (R1) would occur on a much longer time scale than the removal of the photolytically produced PO with O2,(16) this would not affect the measurement of the rate of R2. Numerical simulations of the system (using the chemical kinetics software Kintecus(43)), involving reactions R1 and R2, indicate that 5 times more P(4S) than PO would need to be produced from the photolysis of POCl3 in order to reduce the measured rate of R2 by only 6%, a scenario that is unlikely to occur due to the large amount of energy required to produce P(4S) from POCl3.

A typical PO LIF profile produced following PLP of POCl3 in the presence of O2 is shown in Figure 2, which demonstrates a small growth of the PO LIF signal at short times. We attribute this small growth to the formation of rotationally excited PO* during photolysis, which is then rapidly relaxed to the chamber temperature by the N2 bath gas. No consideration of vibrational relaxation is required, first as vibrational relaxation has been shown to be much slower than reactive removal of PO (v = 0)(16) and second as PO LIF spectra collected when using POCl3 as a precursor indicate no vibrationally excited (v = 1) PO is formed (Figure 6). Thus, the reaction scheme for the formation and removal of PO (v = 0) is given byKinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R10)Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R11)Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R2)where PO* is an initially rotationally excited PO molecule formed from the photolysis of POCl3, krel is the combined rate coefficient for relaxation of any rotationally excited PO, and k2 is the bimolecular rate coefficient for the reaction of ground state PO with O2. As experiments were carried out under pseudo-first-order conditions ([PO] ≪ [O2]), the temporal evolution of the PO is given byKinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(E1)andKinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(E2)where [PO] and [PO*] are the initial concentrations of PO and PO* produced from reaction R10, respectively, t is the time delay between the photolysis and probe lasers, k′ is the pseudo-first-order rate constant for the removal of PO (i.e., k2[O2]), and kdiff is the total rate coefficient for other minor loss processes of PO (such as diffusion out of the probe laser beam and reaction with the POCl3 precursor). Equation E1 was fitted to the PO profiles to extract the parameters krel, k′, [PO], and [PO*]. A plot of k′ vs [O2] then yields a straight line of gradient k2 and intercept kdiff. The inset in Figure 2 shows an example of such a plot, and the small intercept (relative to the total removal rate) demonstrates that reaction with O2 dominates PO removal. For a given experimental run (in which the temperature and total pressure are kept constant), the parameter krel was found to be effectively independent of [O2], over the range employed (typically (0–2) × 1015 molecules cm–3). This allowed us to do a global fit of the PO traces from an experimental run, with a single fitted value for krel. For different experimental runs, krel varied linearly with pressure (see Table 1), as would be expected of rotational relaxation processes. When fitting a biexponential growth and loss, if the growth and loss rates are approaching one another, the fitting procedure is sometimes unable to find a unique solution and returns a result in which the growth and loss rates are equal, meaning one rate has been artificially inflated and the other decreased. This can be a source of error when analyzing biexponential profiles. To minimize the possibility of this affecting our results, for a given pressure (and thus krel), the [O2] range was selected to ensure that, even at the highest [O2], the removal rate was around 4 times lower than the growth rate.

Figure 3

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Figure 3. Experimentally determined rate coefficients for the reaction of PO + O2 vs temperature (a). Pressure dependence of the PO + O2 reaction at (b) T = 294 K and (c) T = 337 K. Open symbols are experimental data from this study (black downward facing triangles); Long et al.(16) (dark blue pentagon); Sausa et al.(17) (dark green star). Solid symbols and lines are rates calculated by MESMER(44) for PO + O2 → PO2 + O (channel R2a, red squares); PO + O2 (+N2) → PO3 (channel R2b, blue diamonds); and total reaction PO + O2 (R2, green upward facing triangles). The dotted line is an Arrhenius fit to the experimental data. At temperatures of 294 and 337 K, experimental errors have been increased to 10% of their mean value to avoid any one point being overly weighted.

Table 1. Rate Coefficients for the Reaction of PO + O2 and Relevant Experimental Conditions (Errors Are Statistical at the 1σ Level)

The bimolecular rate coefficients for the reaction of PO with O2 (R2) are presented as a function of temperature in Table 1 and Figure 3a and compared with available literature. No effects were observed on the bimolecular rate coefficients determined in this study as the radical concentration and photolysis energy were varied by around a factor of 2. The temperature range over which R2 could be studied was limited by thermal decomposition of the POCl3 precursor at temperatures higher than ∼350 K, which resulted in a large background signal of PO and a PO removal rate with O2 that appeared to be ∼1000 times slower than that measured at ∼340 K. At the lowest temperature that we investigated (∼191 K), loss of PO signal indicated significant freezing out of POCl3 on the walls of the reaction chamber. As PO fluorescence is also quenched by the N2 bath gas, we were unable to go above pressures of ∼6 Torr at this temperature, due to loss of the PO signal. At temperatures of ∼294 and 338 K, rate coefficients were measured over the pressure range of ∼10–40 Torr. At both of these temperatures, plotting the biexponential rate coefficients vs the total bath gas concentration (Figure 3b and c) suggests evidence for a small positive pressure dependence, which would be due to a three-body removal channel:Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R2b)An Arrhenius fit to the experimental data (dotted line in Figure 3a) yields k2 (PO + O2, 191–339 K) = (1.91 ± 0.33) × 10–11 × exp(−84±52)/T. This fit was determined after increasing the errors at temperatures of 294 and 338 K to 10% of their mean value to avoid the fit being overly weighted to some of the rate coefficients with smaller statistical errors.

In addition to monitoring the loss of PO, experiments were also carried out in which the growth of the PO2 product from R2 was monitored. These experiments confirmed PO2 as a product of reaction R2, and the observed rise of PO2 was consistent with the measured rate of removal of PO with O2. However, due to the poor signal-to-noise of these experiments, no rate coefficients for reaction R2 were determined monitoring the growth of the PO2 product.

3.2. PO2 + O3

A typical PO2 LIF profile produced following the photolysis of POCl3 in the presence of O3 can be seen in Figure 4b. Unlike the experiments monitoring PO fluorescence, the 248 nm photolysis laser did not need to be focused in order to observe PO2, suggesting only a single photon is required to initiate the reaction leading to PO2. Energetically, a single 248 nm photon has enough energy to remove either one Cl atom (R12), or two atoms as Cl2, from POCl3. However, using the time-dependent density functional (TD-DFT) excited states method,(45) within the Gaussian 16 suite of programs,(46) shows that, at the TD//B3LYP/6-311+g(2d,p) level of theory, following vertical excitation of POCl3 to its first excited state (relevant for a 248 nm photon), and then allowing the molecule to relax, there is clear dissociation to POCl2 + Cl. Thus, we propose the following reaction scheme for the formation of PO2Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R12)Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R13)where k13 is the bimolecular rate coefficient for the reaction of POCl2 with O3. Together with the reaction for the removal of PO2 (R3)Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R3)and as experiments were carried out under pseudo-first-order conditions ([PO2] ≪ [O3]), the temporal evolution of PO2 is given byKinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(E3)where kgrowth and kloss are the pseudo-first-order rate coefficients for the reactions producing and removing PO2 and [POCl2] is the initial amount of POCl2 formed following photolysis of POCl3. Equation E3 was fitted to the PO2 profiles (Figure 4b) and the parameters kgrowth and kloss, and [POCl2] was extracted. Plots of the parameters kgrowth and kloss should then yield straight lines, with gradients equal to the bimolecular rate coefficients for reactions R3 and R13 (eq E2). As we have discussed previously,(8) when analyzing biexponential traces, some prior knowledge about the system is required to determine whether kgrowth, and thus the plot of kgrowth vs [O3], relates to the reaction producing or removing PO2, and vice versa for kloss; i.e., we need to know which reaction is faster than the other one. As there have been no previous studies of either reaction R3 or R13, this problem was solved by carrying out some additional experiments using PCl3 as a precursor. This second set of experiments would again yield two bimolecular rate coefficients, one for the production and one for the removal of PO2. Comparing the two pairs of rate coefficients, one rate coefficient (for the removal of PO2 by O3, R3) should be common to both and thus identifiable.

Figure 4

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Figure 4. (a) PMT signal detected following the photolysis of POCl3 in the presence of O3, both with (black circles) and without (red squares) the probe laser. The PO2 LIF signal (green triangles) is then the difference of the two traces. (b) PO2 LIF signal following PLP of the POCl3 precursor at a total pressure of 10.6 Torr and [O3] = 1.6 × 1015 molecules cm–3, at T = 337 K. Inset: bimolecular plot for reaction R3 at T = 337 K, giving k3 = (9.32 ± 1.37) × 10–13 cm3 molecule–1 s–1. (c) PO2 LIF signal following PLP of the PCl3 precursor at a total pressure of 9.36 Torr and [O3] = 3.8 × 1015 molecules cm–3, at T = 292 K. Inset: bimolecular plot for reaction R3 at T = 291 K, giving k3 = (9.51 ± 2.79) × 10–13 cm3 molecule–1 s–1.

A typical PO2 LIF profile produced following the photolysis of PCl3 in the presence of O3 can be seen in Figure 4c. As with the experiments conducted using POCl3 as a precursor, the 248 nm photolysis laser did not need to be focused in order to observe PO2, suggesting that only a single photon is required to initiate the reaction leading to PO2. Energetically, a single 248 nm photon has enough energy to remove either one Cl atom, or two Cl atoms as Cl2, from PCl3. The first excited state of PCl3 is 480 kJ mol–1 vertically above the ground state (at the TD//B3LYP/6-311+g(2d,p) level of theory(9)), which is very close to the energy of a single 248 nm photon. A relaxed scan of the potential surface of this excited state shows that it should dissociate to PCl2 + Cl. We therefore propose one of the two following reaction schemes for the formation of PO2 when using PCl3 as a precursor:

Scheme 1:

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Scheme 2:

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

From our experiments, we are unable to tell definitively whether one or the other (or both) of these schemes forms the observed PO2. Nevertheless, the PO2 traces can be satisfactorily fit using a biexponential (Figure 4c), where the formation of PO2 is treated as a single process, described by the term kPO2. With the substitution of the [POCl2] term with the term [PCl2] (the initial amount of PCl2 formed following photolysis of PCl3), we were able to fit the PO2 traces using eq E3 and extract the parameters, kgrowth, kloss, and [PCl2]. Plots of kgrowth and kloss vs [O3] then yielded straight lines with gradients equal to the bimolecular rate coefficients kPO2 and k3 and intercepts kdiff (eq E2).

Figure 5 shows the rate coefficients obtained when using both POCl3 and PCl3 as a precursor. At T ∼ 293 K, the rate coefficients obtained by plotting kgrowth vs [O3] for the different precursors differ significantly (Figure 5a), ranging from (7.11 ± 0.74) × 10–12 cm3 molecule–1 s–1 for POCl3 to only (1.54 ± 0.37) × 10–12 cm3 molecule–1 s–1 for PCl3. In contrast, there is quite good agreement between the rate coefficients obtained by plotting kloss vs [O3] for the different precursors (Figure 5b): (8.93 ± 0.19) × 10–13 cm3 molecule–1 s–1 for POCl3 vs (7.58 ± 0.50) × 10–13 cm3 molecule–1 s–1 for PCl3. This implies that kgrowth describes the reactions forming PO2, while kloss describes the reaction removing PO2, R3. With this assignment, k3 was determined over a range of temperatures and pressures (Figure 5 and Table 2). k3 did not vary significantly as radical concentrations and photolysis energies were varied by a factor of ∼2 or pressures varied by a factor of ∼6. The upper temperature limit at which k3 could be studied was set by the thermal decomposition of O3 on the reactor walls at temperatures higher than 380 K. An Arrhenius fit (dotted line in Figure 5b) to the experimental data yields k3(PO2 + O3, 186–339 K) = (2.2 ± 0.7) × 10–11 exp(−990±81)/T cm3 molecule–1 s–1.

Figure 5

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Figure 5. Bimolecular rate coefficients determined by plotting (a) kgrowth vs [O3] and determined to relate to reactions R13 and/or R14b (for POCl3 as a precursor) and the summed processes forming PO2 (for PCl3 as a precursor) and (b) kloss vs [O3] and determined to relate to reaction R3. Black circles are experiments using POCl3 as a precursor, while red triangles are those using PCl3 as a precursor. The dotted line is an Arrhenius fit.

Table 2. Rate Coefficients for Reaction of PO2 + O3 and Relevant Experimental Conditions (Uncertainties Reported at the 1σ Level for the Linear Least-Squares Fitting of the Pseudo-First-Order Coefficients as a Function of [O3])

A possible source of error in the determination of k3 is interference from O atoms produced from the photolysis of O3. These O atoms may react with either the precursors or other photolysis products to form PO2. As discussed above, between 10 and 20% of the O3 at the interaction region is photolyzed by the 248 nm photolysis laser. Photolysis of O3 at 248 nm produces either excited state O(1D) + O2 with a quantum yield of 0.9 or ground state O(3P) + O2 with a quantum yield of 0.1.(37) The excited O(1D) atoms will be rapidly relaxed down to ground state O(3P) by collisions with the N2 bath gas. This relaxation occurs on a significantly faster time scale than the observed growth of PO2 when using either precursor (∼200 times faster at a pressure of 5 Torr), suggesting that reaction of O(1D), either with the precursors or other photolysis products, is not a significant source of PO2. With regard to reaction of the relaxed O(3P) with the precursors, with POCl3, the reaction to PO2 + Cl2 + Cl is thermodynamically unfavorable, being endothermic by ∼120 kJ mol–1. In contrast, for the reaction of O(3P) with POCl2, there are two energetically viable reactions:Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R14a)Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical(R14b)The more exothermic channel (R14b), which also involves a single bond cleavage, should be favored, suggesting the contribution of reaction R14a to the PO2 observed in our experiments is likely to minor. However, as we are not able to unequivocally rule out contribution from reaction R14a, numerical simulations using Kintecus(43) have been conducted, in which for a range of experimentally applicable [O3] and [O], the rates of R13 and R14a were varied and their effect on the determined rate of R3 evaluated. In these simulations, k13 was varied between 0 and 8 × 10–12 cm3 molecule–1 s–1, while k14a was varied from 0 up to 1 × 10–10 cm3 molecule–1 s–1 (using values higher than these upper limits results in the gradient of a plot of kgrowth vs [O3] being larger than that observed experimentally). The numerical simulations showed that the rate coefficient determined for R3 was unaffected by varying either k13 or k14a between the ranges given. Thus, the occurrence of the side reaction R14a producing PO2 in our experiments would not have affected the value determined for k3. The reason for this is due to the approximately linear relationship between [O3] and [O] in our experiments (at high [O3], the percentage of O3 photolysis at the interaction region is smaller than that at low [O3], so the relationship is not precisely linear). Whether PO2 is produced from the reaction of POCl2 with O3 (R13), from the reaction of POCl2 with O(3P) (R14a), or from a combination of both, as a doubling of the concentration of O3 will be mirrored by an approximately doubling of the concentration of O(3P), the rate of PO2 formation will also be doubled. As such, we are able to fit a biexponential (rather than a triexponential or higher exponential) to our PO2 LIF traces to extract the pseudo-first-order rate coefficients, and the value determined for k3 is unaffected.

With regard to the reaction of O(3P) with the PCl3 precursor, there are energetically viable pathways to POCl2 and POCl, both of which could go on to react with O3 or another O(3P) to produce PO2. However, there are two reasons we can rule out O(3P) reacting with the PCl3 precursor as a source of PO2. First, if this were the case, as PCl3, O(3P), and O3 are all in excess in our experiments, we would expect to see vastly more PO2 LIF signal in experiments using PCl3 as a precursor than in experiments using POCl3, in which PO2 is only produced from reaction of the deficient POCl2 photolysis product. Second, if a reaction between O(3P) and PCl3 was generating PO2, we would expect the PO2 LIF signal to be directly proportional to [O(3P)] (and thus [O3]). As neither of these cases are true, the reaction between O(3P) and PCl3 can be ruled out as a source of PO2. For the reaction of O(3P) with PCl2, there are energetically viable product channels, producing either PO or POCl. This leads us to suggest a further two reaction schemes for the formation of PO2 when using PCl3 as a precursor:

Scheme 3:

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Scheme 4:

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

From our experiments, we are unable to tell which of the four reaction schemes involving PCl2 reacting with O3 or O(3P), or a combination thereof, are generating PO2 in our experiments. Nevertheless, as stated above, the PO2 traces were satisfactorily fit using the biexponential given in eq E3 (Figure 4c). Furthermore, the numerical simulations on the POCl2 with O3 and O(3P) system indicated that, whether PO2 is generated from reactions of O3 or O(3P), the rate coefficient determined for R3 was unaffected due to the approximately linear relationship between [O3] and [O(3P)]. As such, we expect any contribution from Schemes 3 and 4 to the production of PO2 to have little effect on k3.

3.3. PO LIF Spectra

LIF spectra of PO, collected using different PO production regimes, are shown in Figure 6. The good agreement between spectra produced using different precursors allows for a positive identification of PO, while comparison of line positions to earlier emission and fluorescence studies allows for positive identification of the A–X system.(17,28,29,47) The spectra have been baseline corrected to remove any contribution from scattered probe laser light. No corrections were made to account for laser dye efficiency, or the spectral efficiency of the PMT, as neither of these change significantly over the narrow spectral range of the measurements.

Figure 6

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Figure 6. PO LIF spectra taken using three different precursors, together with labels indicating the X2Π3/2 and X2Π1/2 sub-bands and the upper and lower vibrational levels: blue upper trace, PCl3; red middle trace, PBr3; gray lower trace, POCl3.

Figure 6 illustrates that there is a significant population of vibrationally excited PO (v = 1) when using PCl3 or PBr3 as a precursor, indicating that the reaction of P* + O2 (and possibly P(4S) + O2) produces both ground and vibrationally excited PO (v = 1). As with the detection of PO (v = 0), PO (v = 1) is also detected by nonresonant fluorescence via the (ν′, ν″ 1, 2) transition at ∼253.6 nm. This is due to the resonant fluorescence being excluded by our interference filter. When using POCl3 as a precursor, we see no evidence of vibrationally excited PO, even at very short delay times (30 μs), indicating that the small growth in PO signal observed in the kinetic traces of PO (Figure 2) is due to rotational relaxation, rather than relaxation of higher vibrational states.


4.1. Comparison with Previous Work

The bimolecular rate coefficients for the removal of PO with O2 (R2) determined in this study are compared with the literature values in Table 1 and Figure 3. As discussed above, there is significant discrepancy in the literature over the room temperature rate of reaction R2, with two studies reporting a rate constant of ∼2 × 10–13 cm3 molecule–1 s–1 (14,15) and two others reporting a rate constant 60 times faster, of ∼1.3 × 10–11 cm3 molecule–1 s–1.(16,17) Taking an average of our room temperature measurements, we determine a value of k2 = (1.44 ± 0.11) × 10–11 cm3 molecule–1 s–1 at T = 294 K, putting the rate toward the top end of the available literature, in good agreement with the value reported by Long et al.(16) and lying slightly above (just outside mutual error limits) the value reported by Sausa et al.(17) The probable reason for the large discrepancy between the measured values of k2 is the different experimental techniques employed. The two lower values were measured in fast flow tubes, using a microwave discharge of DMMP to produce PO, the loss of which was then monitored using LIF. The two larger rate coefficients were measured by the PLP-LIF technique, similar to that employed in this study, with the exception that DMMP rather than POCl3 was used as the PO precursor. As in the present work, Sausa et al.(17) used a KrF excimer laser (248 nm) as the photolysis source. They discuss in their paper that the focused KrF radiation may result in the dissociation of O2, so that they observed the reaction of PO with O rather than PO + O2. Indeed, they do note a significant deviation from exponential decay of PO when the photolysis source is a shorter wavelength ArF laser (193 nm), which would have generated a much larger fraction of O atoms. However, interference from O atoms can in fact be ruled out, because Long et al.(16) produced PO from the infrared multiphoton dissociation of DMMP, a method which cannot generate O atoms from O2, and they obtained a value for k2 in good agreement with that obtained with the KrF lasers employed in the present study and that by Sausa et al.(17)

Another possible source of error in measurements of k2 is interference from P atoms, which has not been discussed in the previous studies. As we have demonstrated previously,(8) multiphoton dissociation of DMMP by focused 248 nm light produces significant amounts of P*. Although not directly detectable in our experiments, we also presume the presence of ground state P(4S), formed either directly from the multiphoton dissociation of DMMP or from the relaxation of P*. These excited state P* atoms react with O2 to form PO on a time scale similar to that at which PO is removed by O2.(8) Thus, if significant amounts of these excited states are present, the observed removal of PO would be slower, resulting in a smaller rate coefficient for the reaction. This may be less of a problem in the study by Long et al.(16) in which the photolysis source is 10.6 μm light from an infrared CO2 laser. At this wavelength, many more photons would need to be absorbed to excite PO to a high enough level in which it may dissociate to ground or excited state P atoms. Indeed, the rate constant measured by Long et al.(16) agrees well with that determined in our study where we used a PO precursor that does not produce P* when photolyzed. P(4S) atoms also react with O2 to produce PO (R1); however, the time scale of this reaction is around 50 times slower than the removal of PO by O2, and as such, the formation of any ground state P atoms should only have a minor effect on the measurement of k2 (see section 3.1).

Figure 3 indicates that there is a small pressure dependence for reaction R2, which is evidence for both a two- and three-body channel for this reaction (R2a and R2b, respectively), which are explored using theoretical calculations in section 4.2. The presence of the three-body channel forming PO3 has not previously been reported in the literature, presumably as the previous studies did not measure the removal of PO2 over a range of pressures.

There has been no previous investigation into the kinetics of the reaction between PO2 and O3. Taking the average of our room temperature measurements, we determine that k3 = (8.47 ± 0.30) × 10–13 cm3 molecule–1 s–1 at T = 293 K. This is over 4 orders of magnitude faster than the reaction between the isovalent NO2 with O3 (∼3.5 × 10–17 cm3 molecule–1 s–1 at T = 298 K).(48) Although this reaction is unlikely to be important astrochemically, the fact that many current chemical models are using the isovalence between nitrogen and phosphorus to derive rate coefficients for P-bearing species is called into question and highlights the importance of experimentally determined rate coefficients.

4.2. Theoretical Calculations

Electronic structure calculations were carried out using the Gaussian 16 suite of the programs.(9) Vibrational frequencies, rotational constants, and energies were calculated with the complete basis set (CBS-QB3) method of Montgomery et al.(49) The Cartesian coordinates, molecular parameters, and heats of formation of the phosphorus oxides are listed in Table 3.

Table 3. Molecular Properties of the Stationary Points on the Potential Energy Surfaces for PO + O2 and PO2 + O3a

The resulting potential energy surfaces for PO + O2 (R2) and PO2 + O3 (R3) are shown in parts a and b of Figure 7, respectively, which also illustrate the geometries of the stationary points. RRKM calculations were then performed for these two reactions using the Master Equation Solver for Multi-Energy well Reactions (MESMER) program.(44)R2 initially involves addition of O2 to PO, forming the cis-OPO2 complex. This can either dissociate directly to PO2 + O via TS3 or first rearrange to trans-OPO2 via TS1 followed by rearrangement to PO3 via TS2. PO3 will then either be quenched by collision with the third body (N2) or dissociate to PO2 + O.

Figure 7

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Figure 7. Potential energy surfaces for (a) PO + O2 (R2), determined at the CBS-QB3 level of theory, and (b) PO2 + O3 (R3), determined at the CBS-QB3 level of theory apart from barrier TS1 which is a CCSD(T)//MP2/6-311+g(2d,p) calculation with respect to the reactants.

The internal energy of each species on the potential energy surface was divided into a contiguous set of grains (width 200 cm–1), each containing a bundle of rovibrational states. Each grain was then assigned a set of microcanonical rate coefficients for dissociation back to the reactants (PO + O2) and forward to the products (PO2 + O), using an inverse Laplace transformation to link them directly to the high-pressure limiting recombination coefficients (k). An Arrhenius expression was optimized by floating both the pre-exponential factor and the activation energy to give the best fit of the RRKM model to the experimental data, yielding k(PO + O2) = 3.5 × 10–11 exp(−168/T) cm3 molecule–1 s–1. For the reaction of PO2 + O, the rate coefficient was set to be reasonably fast with a small T-dependence, k(PO2 + O) = 2.4 × 10–11 exp(−25/T) cm3 molecule–1 s–1. The exponential down model was used to estimate the probability of collisional transfer between grains. For N2 as the third body, the average energy for downward transitions ⟨ΔEdown was set to 300 cm–1 at 300 K, with a temperature dependence of T0.25.(51)

Figure 3 shows a satisfactory fit to the experimental data at 294 and 337 K. Figure 8 illustrates the RRKM-predicted overall rate coefficient k2 (Figure 8a) and the branching ratio to produce PO3, as a function of [N2] and T (Figure 8b). Figure 8 shows that the variation of the total rate coefficient and the branching ratio to form the two products OPO and PO3 have relatively complex dependences on P and T. This arises from the nature of the PES for the reaction (Figure 7a). As a result, a Troe-type falloff expression(52) does not give a good fit to the rate coefficient for the recombination reaction forming PO3. Nevertheless, the data plotted in Figure 8 can be used to estimate the rate coefficients for both reaction channels at a selected P and T. As shown in Figure 8a, k2 is predicted to have a rather small T and P dependence. At [N2] < 1017 cm–3, over the temperature range 120–500 K, the fraction of PO3 formed is below 1%. At pressures typical of planetary upper atmospheres where meteoric ablation of P will occur,(7) the reaction should essentially be pressure-independent and can be fitted to the following expression: log10(k2, 120–500 K, cm3 molecule–1 s–1) = −updating log10(T) – 0.5020(log10(T))2, with an uncertainty of ±10% within the experimental temperature range (191–339 K).

Figure 8

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Figure 8. RRKM calculations for the reaction PO + O2 on the surface in Figure 7a: (a) the overall rate coefficient, k2; (b) the branching ratio to PO3. Both are plotted as a function of [N2] and T.

For the reaction between PO2 and O3, the RRKM fit using the potential energy surface in Figure 7b was used. The measured positive temperature dependence of the reaction (Figure 5) implies that there is a barrier in the entrance channel. Initial exploration of the reaction entrance channel using the B3LYP/6-311+g(2d,p) level of theory did not indicate the presence of a barrier. However, this DFT functional is not appropriate for long-range interactions; guided by previous work on the analogous reaction between NO2 and O3 (which has a significantly larger barrier in the entrance channel),(53) we used the MP2 level of theory to determine that a small barrier exists at a PO2–O3 separation of 2.7 Å. An accurate coupled cluster calculation at the CCSD(T)//MP2/6-311+g(2d,p) level of theory(54) gave a barrier height of 9.4 kJ mol–1 (Figure 7b and Table 3), in good agreement with the 8.2 ± 0.7 kJ mol–1 activation energy determined from the Arrhenius fit to the experimental data. A satisfactory fit to the experimental data was then obtained by optimizing the pre-exponential factor in an Arrhenius expression for the inverse Laplace transformation, yielding k(PO2 + O3, 180–370 K) = 3.7 × 10–11 exp(−1131/T) cm3 molecule–1 s–1 (σ = ± 26% over the experimental temperature range, 188–339 K), where the activation energy is set to 9.4 kJ mol–1.

4.3. Fitting the PO Spectra

To simulate the PO spectra obtained in this study, we have used the pgopher spectral simulator,(55) together with the molecular constants provided by Verma and Singhal(47) for the X2Π state and by Coquart et al.(28) for the A2Σ+ state. The simulated PO spectrum was then compared to the experimental spectrum obtained using PCl3 as a precursor, which was chosen as it has the best signal-to-noise (although it should be noted that, for the lines that are visible in the spectra produced using PBr3 and POCl3 as precursors, there is excellent agreement between the line positions; Figure 6). Next, the simulated spectrum was refined by first assigning simulated lines to the corresponding peaks in the experimental spectra and then refitting the simulated spectrum to the experimental spectrum allowing the molecular constants to float. This process was iterative, with more peaks being able to be assigned and fitted as the agreement between the simulated and experimental spectra improved. Both the (0,0) and (1,1) bands were fit simultaneously.

When fitting the spectra, we encountered some difficulty in obtaining a good fit to sections of the fine structure within the (0,0) bands. Verma and Singhal(47) reported that the A2Σ+ (v = 0) level of PO is perturbed by the 4Σ (v = 4) level. By including this perturbing state in our simulation, we were able to obtain a good fit to the data. Figure 9 shows the simulated spectrum overlaid on the experimental spectrum, as well as the residual for the contour fit, while Tables 4–

6 give the molecular constants employed in the simulation. The best match was obtained using a rotational temperature of 350 K and by convolving the simulated spectra with a Gaussian with 0.6 cm–1 fwhm, which accounts for Doppler broadening and spectral resolution. In addition to allowing the molecular constants to float, the relative intensities of the A2Σ+ (v = 0) ← X2Π (v = 0) and the A2Σ+ (v = 1) ← X2Π (v = 1) transitions were also floated. The 4Σ (v = 4) ← A2Σ+ (v = 0) matrix element was 4.593 ± 0.011.

Figure 9

Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radical

Figure 9. Measured and calculated A2Σ+X2Π band of PO, together with the residual (experimental – simulated). Plot a shows the X2Π3/2 sub-band, while plot b shows the X2Π1/2 sub-band.

Table 4. Molecular Constants of the X2Π State Employed in the Simulation of the PO Spectruma

Table 5. Molecular Constants of the A2Σ+ State Employed in the Simulation of the PO Spectruma

Table 6. Molecular Constants of the 4Σ (v = 4) Perturbing Level Employed in the Simulation of the PO Spectruma

As can be seen from Figure 9, there is good agreement between the line positions of the simulated and experimental spectra, for both the (0,0) and (1,1) bands. In general, there is also satisfactory agreement between the simulated and experimental line intensities. There does, however, seem to be some systematic differences between branches, implying some additional Ω (but not J) dependent mixing between branches. Comparing the molecular constants obtained in this study with the literature values (Tables 4–6) shows that all of the values are essentially consistent, with the differences most likely arising from minor differences in the definitions of the constants.

4.4. Atmospheric Implications

Interplanetary dust particles entering the upper atmosphere of a terrestrial planet will undergo meteoric ablation at around the 1 μbar pressure region.(56) Phosphorus will ablate from these particles as either PO or PO2,(7) and these molecules will mostly dissociate to form ground and excited state P atoms following hyperthermal collisions with atmospheric molecules. Peak ablation in the Earth’s atmosphere occurs around 85 km,(56) and the P atoms formed in this region will be quickly oxidized by O2 to PO.(8) These PO molecules will then react with O2, with an e-folding lifetime of around 2.5 ms. At the low pressure at this altitude (<10–5 bar), the reaction will proceed via the two-body bimolecular channel to form PO2 and O. As the concentration of O3 at this altitude is around 105 times lower than that of O2,(57) removal of PO2 by O3 to PO3 will be a very slow process: if this were the only process removing PO2, it would have a lifetime of ∼7.5 days. This suggests PO3 will not be a major reservoir of meteor-ablated P. As there are no exothermic processes to convert PO2 back to PO, the speciation of phosphorus should essentially depend on the reactions converting PO2 into HPO2, HOPO, and HOPO2, as illustrated in Figure 1.


The reactions of PO with O2 (R2) and PO2 with O3 (R3) have been studied both experimentally and theoretically, with this being the first study to our knowledge of reaction R3. For reaction R2, there are significant discrepancies in the literature values reported for k2 at room temperature, with values varying by around a factor of 60. We have determined with the PLP-LIF technique a rate coefficient at the top end of the literature values, with k2(294 K) = (1.44 ± 0.11) × 10–11 cm3 molecule–1 s–1 at P ∼ 10 Torr. Rate coefficients for R2 determined over a range of pressures also indicate the presence of a three-body channel, in which PO + O2 combine to form PO3 (R2b). The potential energy surfaces of both the PO + O2 and PO2 + O3 systems were determined using electronic structure theory, and these calculations combined with RRKM theory to explain the observed pressure and temperature dependences. For PO + O2, at pressures typical of a planetary upper atmosphere where meteoric ablation of P will occur, the reaction is effectively pressure independent with a yield of PO2 + O of >99% and can be expressed by log10(k2, 120–500 K, cm3 molecule–1 s–1) = −updating log10(T) – 0.5020(log10(T))2, with an uncertainty of ±10% over the experimental temperature range (191–339 K). With increasing pressure, the yield of PO3 increases, reaching ∼90% at a pressure of 1 atm and T = 300 K. For PO2 + O3, k3(PO2 + O3) = 3.7 × 10–11 exp(−1131/T) cm3 molecule–1 s–1, with an uncertainty of ±26% over the experimental temperature range (188–339 K). Laser-induced fluorescence spectra of PO over the wavelength range 245–248 nm were collected and fitted using the pgopher program, which yields new spectroscopic constants for the ground and v = 1 vibrational levels of the X2Π and A2Π+ states of PO.


    • Mark A. Blitz - School of Chemistry, University of Leeds, Leeds, LS2 9JT, U.K.National Centre for Atmospheric Science (NCAS), University of Leeds, Leeds, LS2 9JT, U.K.Kinetic Study of the Reactions PO + O2 and PO2 + O3 and Spectroscopy of the PO Radicalhttp://orcid.org/updating

    • Thomas P. Mangan - School of Chemistry, University of Leeds, Leeds, LS2 9JT, U.K.

    • Colin M. Western - School of Chemistry, University of Bristol, Bristol, BS8 1TS, U.K.

  • The authors declare no competing financial interest.


This study was supported by funding from the UK Science and Technology Facilities Council (grant ST/P000517/1). The raw and processed data produced by this study is archived at Leeds University and is available upon request to J.M.C.P.

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    Phosphorus is a key biol. element, and a prebiotic pathway leading to its incorporation into biomols. has been difficult to ascertain. Most potentially prebiotic phosphorylation reactions have relied on orthophosphate as the source of phosphorus. It is suggested here that the geochem. of phosphorus on the early Earth was instead controlled by reduced oxidn. state phosphorus compds. such as phosphite (HPO2-3), which are more sol. and reactive than orthophosphates. This reduced oxidn. state phosphorus originated from extraterrestrial material that fell during the heavy bombardment period or was produced during impacts, and persisted in the mildly reducing atm. This alternate view of early Earth phosphorus geochem. provides an unexplored route to the formation of pertinent prebiotic phosphorus compds., suggests a facile reaction pathway to condensed phosphates, and is consistent with the biochem. usage of reduced oxidn. state phosphorus compds. in life today. Possible studies are suggested that may detect reduced oxidn. state phosphorus compds. in ancient Archean rocks.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD1cXht1Onu7g%253D&md5=71eb3914ff0245a0fa3d6b9e26292f12

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    Plane, J. M. C.; Flynn, G. J.; Määttänen, A.; Moores, J. E.; Poppe, A. R.; Carrillo-Sanchez, J. D.; Listowski, C. Impacts of cosmic dust on planetary atmospheres and surfaces. Space Sci. Rev. 2018, 214, 23,  DOI: 10.1007/s11214-017-0458-1

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    Carrillo-Sánchez, J. D.; Bones, D. L.; Douglas, K. M.; Flynn, G. J.; Wirick, S.; Fegley, B.; Araki, T.; Kaulich, B.; Plane, J. M. C. Injection of meteoric phosphorus into planetary atmospheres. Planet. Space Sci. 2020, 187, 104926,  DOI: 10.1016/j.pss.updating

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    Injection of meteoric phosphorus into planetary atmospheres

    Carrillo-Sanchez, Juan Diego; Bones, David L.; Douglas, Kevin M.; Flynn, George J.; Wirick, Sue; Fegley, Bruce Jr.; Araki, Tohru; Kaulich, Burkhard; Plane, John M. C.

    Planetary and Space Science (2020), 187 (), 104926CODEN: PLSSAE; ISSN:updating. (Elsevier Ltd.)

    This study explores the delivery of phosphorus to the upper atmospheres of Earth, Mars, and Venus via the ablation of cosmic dust particles. Micron-size meteoritic particles were flash heated to temps. as high as 2900 K in a Meteor Ablation Simulator (MASI), and the ablation of PO and Ca recorded simultaneously by laser induced fluorescence. Apatite grains were also ablated as a ref. The speciation of P in anhyd. chondritic porous Interplanetary Dust Particles was made by K-edge X-ray absorption near edge structure (XANES) spectroscopy, demonstrating that P mainly occurs in phosphate-like domains. A thermodn. model of P in a silicate melt was then developed for inclusion in the Leeds Chem. Ablation Model (CABMOD). A Regular Soln. model used to describe the distribution of P between molten stainless steel and a multicomponent slag is shown to provide the most accurate soln. for a chondritic-compn., and reproduces satisfactorily the PO ablation profiles obsd. in the MASI. Meteoritic P is moderately volatile and ablates before refractory metals such as Ca; its ablation efficiency in the upper atm. is similar to Ni and Fe. The speciation of evapd. P depends significantly on the oxygen fugacity, and P should mainly be injected into planetary upper atmospheres as PO2, which will then likely undergo dissocn. to PO (and possibly P) through hyperthermal collisions with air mols. The global P ablation rates are estd. to be 0.017 t d-1 (tonnes per Earth day), 1.15 x 10-3 t d-1 and 0.024 t d-1 for Earth, Mars and Venus, resp.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BB3cXpt1GmsLY%253D&md5=c7488b7525996ceec317593ef7c0b69b

  8. 8

    Douglas, K. M.; Blitz, M. A.; Mangan, T. P.; Plane, J. M. C. Experimental Study of the Removal of Ground- and Excited-State Phosphorus Atoms by Atmospherically Relevant Species. J. Phys. Chem. A 2019, 123, 94699478,  DOI: 10.1021/acs.jpca.9b07855

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    8

    Experimental Study of the Removal of Ground- and Excited-State Phosphorus Atoms by Atmospherically Relevant Species

    [external_link offset=1]

    Douglas, Kevin M.; Blitz, Mark A.; Mangan, Thomas P.; Plane, John M. C.

    Journal of Physical Chemistry A (2019), 123 (44), updatingCODEN: JPCAFH; ISSN:updating. (American Chemical Society)

    The reaction kinetics of the ground and first two excited states of at. phosphorus, P, with atmospherically relevant species were studied at temps. ranging from ∼200 to 750 K using a pulsed laser photolysis-laser-induced fluorescence technique. The temp. dependence of the rate coeffs. is parametrized as follows (units: cm3mol.-1s-1, 1σ errors): k(P(2P)+O2)(189 ≤ T/K ≤ 701) = (7.10 ± 1.03) × 10-12 × (T/updating±0.13×exp[(374 ± 41)/T]; k(P(2D)+O2)(188 ≤ T/K ≤ 714) = (1.20 ± 0.29)×10-11×(T/updating±0.207×exp[(177 ± 70)/T]; k(P(2D)+CO2)(296 ≤ T/K ≤ 748) = (5.68 ± 0.36)×10-12×(T/updating±0.103; k(P(2D)+N2)(188 ≤ T/K ≤ 748) = (1.42 ± 0.03)×10-12×(T/updating±0.04; k(P(4S)+O2)(187 ≤ T/K ≤ 732) = (3.08 ± 0.31)×10-13×(T/updating±0.29. Electronic structure theory combined with RRKM calcns. have been used to explain the unusual temp. dependence of P(4S) + O2. The small pre-exponential factor for the reaction results from a tight steric constraint, together with the requirement that the reaction occurs on doublet rather than sextet electronic surfaces.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1MXhvFClurrO&md5=40c086dupdatingc8ca7033b466d5ca9

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    Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson, G. A.; Nakatsuji, H.; Gaussian 16, rev. B.01; Gaussian, Inc.: Wallingford, CT, 2016.

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    Henshaw, T. L.; MacDonald, M. A.; Stedman, D. H.; Coombe, R. D. The P(4Su) + N3(2Πg) reaction: chemical generation of a new metastable state of PN. J. Phys. Chem. 1987, 91, 28382842,  DOI: 10.1021/j100295a037

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    10

    The P(4Su) + N3(2IIg) reaction: chemical generation of a new metastable state of PN

    Henshaw, T. L.; MacDonald, M. A.; Stedman, D. H.; Coombe, R. D.

    Journal of Physical Chemistry (1987), 91 (11), 2838-42CODEN: JPCHAX; ISSN:updating.

    The kinetics and spectroscopy of the chemiluminescent reaction between P(4Su) atoms and N3(2Πg) radicals were studied with a discharge-flow app. The chemiluminescence exhibited 3 band systems, which were identified as PN (A1Π → X1Σ+), PF (B3Π → X3Σ-), and a previously unobserved system in PN. From the spectrum of the new system, mol. consts. of the excited state were found. This excited state is significantly Franck-Condon shifted from the ground state, with 0,3 being the most intense band of the spectrum. From comparison of this system with the analogous N(4Su) + N3(2Πg) reaction, the new excited state of PN is a triplet metastable. Anal. of the removal of P atoms from the system indicated a rate const. of (4.7 ± 0.4) × 10-11 cm3 s-1 for the P + N3 reaction. The lifetime of the excited metastable state of PN is >4 ms.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXitVamtr8%253D&md5=a3cdbbc5cfddd8159aee7cc5fbafc530

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    Clyne, M. A. A.; Ono, Y. Kinetic studies of ground-state phosphorus atoms. J. Chem. Soc., Faraday Trans. 2 1982, 78, 11491164,  DOI: 10.1039/fupdating

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    Kinetic studies of ground-state phosphorus atoms

    Clyne, Michael A. A.; Ono, Yoko

    Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics (1982), 78 (8), 1149-64CODEN: JCFTBS; ISSN:updating.

    The kinetics of reactions at 293 K involving ground-state P atoms, P(4S3/2), were studied by using resonance-fluorescence detection in a discharge-flow system. P atoms were formed by a discharge in He contg. a trace of P trihalide. Rate consts. were detd. by using pseudofirst-order kinetic anal. for the reactions of P with NO2, O2, Cl2, NO, and PCl3.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL38Xls12kt7s%253D&md5=70931e4a74607e9c4902b0e4c5ded75a

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    Husain, D.; Slater, N. K. H. Time-resolved resonance fluorescence studies of ground state phosphorus atoms, P[3p3(4S3/2)]. J. Chem. Soc., Faraday Trans. 2 1978, 74, 16271643,  DOI: 10.1039/Fupdating

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    Time-resolved resonance fluorescence studies of ground state phosphorus atoms, P[3p3(4S3/2)]

    Husain, David; Slater, Nigel K. H.

    Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics (1978), 74 (9), 1627-43CODEN: JCFTBS; ISSN:updating.

    The 2nd order rate consts. for the quenching reactions of ground state P[3p3(4S3/2)] atoms with 6 gases, e.g. O2 and C2H4, were detd. by time-resolved resonance fluorescence measurements. The results were compared with those obtained using time-resolved resonance line absorption measurements. Radiation trapping calcns. for the systems P[3p24s(4PJ) → and P[3p4(4PJ)] → P[3p3(4S3/2)] were performed using the diffusion theory of radiation. The calcd. relations between the fluorexence intensity and the concn of P[3p3(4S3/2)] for various boundary conditions of the diffusion equation were compared with the empirical calibration.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE1MXjtFartg%253D%253D&md5=9baupdatingc1c8ada7e5345ed7bbed3

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    Husain, D.; Norris, P. E. Reactions of phosphorus atoms, P(34S3/2), studied by attenuation of atomic resonance radiation in vacuum ultraviolet. J. Chem. Soc., Faraday Trans. 2 1977, 73, 11071115,  DOI: 10.1039/Fupdating

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    13

    Reactions of phosphorus atoms, P(34S3/2), studied by attenuation of atomic resonance radiation in the vacuum ultraviolet

    Husain, David; Norris, Peter E.

    Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics (1977), 73 (8), 1107-15CODEN: JCFTBS; ISSN:updating.

    The kinetics are reported of the reactions of P(34S3/2) with 10 gases, e.g. H2, NH3, and CO2. P(34S3/2) was generated by repetitive pulsed photolysis of PCl3 in the presence of excess He and was monitored photoelec. in absorption by time-resolved attenuation of at. resonance radiation at 177.50 nm, {P[4s(4P5/2)] ← P[3p3(4S3/2)]}. The rate data are compared with data for P(32DJ), P(32PJ), and N(24S3/2) and are discussed in relation to potential surfaces derived from symmetry arguments using the weak spin-orbit coupling approxn. The enthalpies of the reactions are also discussed.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2sXlvV2qur8%253D&md5=9ce9a2f8a4c7fc77e9fe393fde36fc4f

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    Aleksandrov, E. N.; Arutyunov, V. S.; Dubrovina, I. V.; Kozlov, S. N. On the role of PO radicals in the reaction of phosphorus oxidation. Dokl. Akad. Nauk SSSR 1982, 267, 110113

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    Role of phosphorus oxide (PO) radicals in the oxidation of phosphorus

    Aleksandrov, E. N.; Arutyunov, V. S.; Dubrovina, S. N.; Kozlov, S. N.

    Doklady Akademii Nauk SSSR (1982), 267 (1), 110-13 [Phys. Chem.]CODEN: DANKAS; ISSN:updating.

    PO forms by reaction of at. O with P4 mols. Rate consts. are given for PO reactions with O2 and P4. Concns. of PO in the P combustion zone were calcd. These results confirm a published reaction scheme for P4 combustion.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL3sXktFCiuw%253D%253D&md5=a8c08db1f87084b878cd54c7cc6015c5

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    Wong, K. N.; Anderson, W. R.; Kotlar, A. J.; Dewilde, M. A.; Decker, L. J. Lifetimes and quenching of the B 2Σ+ PO by atmospheric gases. J. Chem. Phys. 1986, 84, 8190,  DOI: 10.1063/updating

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    Lifetimes and quenching of B2Σ+ phosphorus monoxide by atmospheric gases

    Wong, Koon Ng; Anderson, William R.; Kotlar, Anthony J.; DeWilde, Mark A.; Decker, Leon J.

    Journal of Chemical Physics (1986), 84 (1), 81-90CODEN: JCPSA6; ISSN:updating.

    Pulsed laser excited fluorescence in the B2Σ+ ← X2π system of gas phase PO was used to measure the lifetime of v' = 0 of the B state. Rotationally resolved measurements for a few selected J' levels, at Ar or He carrier gas pressures of ∼2 torr, reveal no dependence of the lifetime on the rotational level excited. Earlier measurements of relative fluorescence intensities in the v' = 0 vibrational progression were reinterpreted to ext. the dependence of the electronic transition moment on internuclear distance. By using this transition moment, no lifetime dependence on rotational level is to be expected, even at low pressures. Rate consts. for quenching of the B state PO by N2, O2, CO2, and H2O, and upper limits thereof for He and Ar are reported. O2 reacts with ground state PO. A crude measurement of the rate const. was performed. The result was compared to 2 other known measurements. The rate const. is in excellent agreement with the previous measurement, but in poor agreement with that of a concurrent study.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XlvVOqtw%253D%253D&md5=b9a7c6754f1ff7b9364ec957a6be1729

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    Long, S. R.; Christesen, S. D.; Force, A. P.; Bernstein, J. S. Rate constant for the reaction of PO radical with oxygen. J. Chem. Phys. 1986, 84, 59655966,  DOI: 10.1063/updating

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    Rate constant for the reaction of phosphorus oxide (PO) radical with oxygen

    Long, S. Randolph; Christesen, Steven D.; Force, Alan P.; Bernstein, Jeffrey S.

    Journal of Chemical Physics (1986), 84 (10), 5965-6CODEN: JCPSA6; ISSN:updating.

    A CO2 transversely excited atm. laser was used to produce PO by IR multiphoton dissocn. of (Me)2-Me phosphonate. The loss of PO was monitored at O2 pressures of updating Torr. The rate const. is linearly dependent on O2 pressure, with the decay of PO being pseudo-1st order.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XktFaqsL8%253D&md5=55e602d79d0ceb59141c296dd3b75705

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    Sausa, R. C.; Miziolek, A. W.; Long, S. R. State distributions, quenching, and reaction of the PO radical generated in Excimer laser photofragmentation of dimethyl methylphosphonate. J. Phys. Chem. 1986, 90, 39943998,  DOI: 10.1021/j100408a033

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    17

    State distributions, quenching, and reaction of the phosphorus monoxide radical generated in excimer laser photofragmentation of dimethyl methylphosphonate

    Sausa, Rosario C.; Miziolek, Andrzej W.; Long, S. Randolph

    Journal of Physical Chemistry (1986), 90 (17), 3994-8CODEN: JPCHAX; ISSN:updating.

    Focused KrF and ArF excimer laser radiation acting on di-Me methylphosphonate (DMMP) produces ground electronic state PO radicals via an initial two-photon absorption by the DMMP parent followed by a sequence of daughter photofragmentations. Probing the PO radical by laser-induced fluorescence, utilizing the A2Σ+ - X2Π transition near 247 nm, reveals that the nascent PO rotational population has a distribution characterized by a temp. considerably greater than 300 K, while at least 95% of the PO radicals are formed in the lowest vibrational state. The nascent spin-orbital distribution in the 2Π1/2,3/2 state is near that characteristic of 300 K; quenching of the A state of PO by both N and O occurs with a rate const. of ∼1.8 (±0.5) × 10-10 cm3/mol.-s. Ground state PO reacts bimolecularly with mol. O with a rate const. of 1.2 (± 0.2) x 10-11 cm3/mol-s, equiv. to approx. 1/40 the hard sphere collision rate.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28XltVGmt7g%253D&md5=f2f9ab403ce09e758fde23708aa6403f

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    De Beck, E.; Kaminski, T.; Patel, N. A.; Young, K. H.; Gottlieb, C. A.; Menten, K. M.; Decin, L. PO and PN in the wind of the oxygen-rich AGB star IK Tauri. Astron. Astrophys. 2013, 558, A132,  DOI: 10.1051/updating/updating

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    18

    PO and PN in the wind of the oxygen-rich AGB star IK Tauri

    De Beck, E.; Kaminski, T.; Patel, N. A.; Young, K. H.; Gottlieb, C. A.; Menten, K. M.; Decin, L.

    Astronomy & Astrophysics (2013), 558 (Pt. 2), A132/1-A132/9CODEN: AAEJAF; ISSN:updating. (EDP Sciences)

    Context. Phosphorus-bearing compds. have only been studied in the circumstellar environments of the asymptotic giant branch star IRC +10216 and the protoplanetary nebula CRL 2688, both carbon-rich objects, and the oxygen-rich red supergiant VY CMa. The current chem. models cannot reproduce the high abundances of PO and PN derived from observations of VY CMa. No observations have been reported of phosphorus in the circumstellar envelopes of oxygen-rich asymptotic giant branch stars. Aims. We aim to set observational constraints on the phosphorous chem. in the circumstellar envelopes of oxygen-rich asymptotic giant branch stars, by focussing on the Mira-type variable star IK Tau. Methods. Using the IRAM 30 m telescope and the Submillimeter Array, we obsd. four rotational transitions of PN (J = 2-1, 3-2, 6-5, 7-6) and four of PO (J = 5/2-3/2, 7/2-5/2, 13/2-11/2, 15/2-13/2). The IRAM 30 m observations were dedicated line observations, while the Submillimeter Array data come from an unbiased spectral survey in the frequency range 279-355 GHz. Results. We present the first detections of PN and PO in an oxygen-rich asymptotic giant branch star and est. abundances X(PN/H2) ≈ 3 × 10-7 and X(PO/H2) in the range 0.5-6.0 × 10-7. This is several orders of magnitude higher than what is found for the carbon-rich asymptotic giant branch star IRC +10216. The diam. (.ltorsim.0.''7) of the PN and PO emission distributions measured in the interferometric data corresponds to a max. radial extent of about 40 stellar radii. The abundances and the spatial occurrence of the mols. are in very good agreement with the results reported for VY CMa. We did not detect PS or PH3 in the survey. Conclusions. We suggest that PN and PO are the main carriers of phosphorus in the gas phase, with abundances possibly up to several 10-7. The current chem. models cannot account for this, underlining the strong need for updated chem. models that include phosphorous compds.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXisFejsLY%253D&md5=6e4899c0d15dbeac44796c9eedf3daa2

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    Tenenbaum, E. D.; Dodd, J. L.; Milam, S. N.; Woolf, N. J.; Ziurys, L. M. Comparatie spectra of oxygen-rich versus carbon-rich circumstellar shells: VY Cannis Majoris and IRC + 10216 at 215–285 GHz. Astrophys. J., Lett. 2010, 720, L102L107,  DOI: 10.1088/updating/720/1/L102

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    Ziurys, L. M.; Milam, S. N.; Apponi, A. J.; Woolf, N. J. Chemical complexity in the winds of the oxygen-rich supergiant star VY Canis Majoris. Nature 2007, 447, 10941097,  DOI: 10.1038/nature05905

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    Chemical complexity in the winds of the oxygen-rich supergiant star VY Canis Majoris

    Ziurys, L. M.; Milam, S. N.; Apponi, A. J.; Woolf, N. J.

    Nature (London, United Kingdom) (2007), 447 (7148), updatingCODEN: NATUAS; ISSN:updating. (Nature Publishing Group)

    The interstellar medium is enriched primarily by matter ejected from old, evolved stars. The outflows from these stars create spherical envelopes, which foster gas-phase chem. The chem. complexity in circumstellar shells was originally thought to be dominated by the elemental carbon to oxygen ratio. Observations have suggested that envelopes with more carbon than oxygen have a significantly greater abundance of mols. than their oxygen-rich analogs. Here we report observations of mols. in the oxygen-rich shell of the red supergiant star VY Canis Majoris (VY CMa). A variety of unexpected chem. compds. have been identified, including NaCl, PN, HNC and HCO+. From the spectral line profiles, the mols. can be distinguished as arising from three distinct kinematic regions: a spherical outflow, a tightly collimated, blue-shifted expansion, and a directed, red-shifted flow. Certain species (SiO, PN and NaCl) exclusively trace the spherical flow, whereas HNC and sulfur-bearing mols. (amongst others) are selectively created in the two expansions, perhaps arising from shock waves. CO, HCN, CS and HCO+ exist in all three components. Despite the oxygen-rich environment, HCN seems to be as abundant as CO. These results suggest that oxygen-rich shells may be as chem. diverse as their carbon counterparts.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2sXmvFKmu7o%253D&md5=3e6b1ce387396bc276ee04f482dbc03c

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    Gobrecht, D.; Cherchneff, I.; Sarangi, A.; Plane, J. M. C.; Bromley, S. T. Dust formation in the oxygen-rich AGB star IK Tauri. Astron. Astrophys. 2016, 585, A6,  DOI: 10.1051/updating/updating

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    21

    Dust formation in the oxygen-rich AGB star IK Tauri

    Gobrecht, D.; Cherchneff, I.; Sarangi, A.; Plane, J. M. C.; Bromley, S. T.

    Astronomy & Astrophysics (2016), 585 (), A6/1-A6/15CODEN: AAEJAF; ISSN:updating. (EDP Sciences)

    Aims. We model the synthesis of mols. and dust in the inner wind of the oxygen-rich Mira-type star IK Tau by considering the effects of periodic shocks induced by the stellar pulsation on the gas and by following the non-equil. chem. in the shocked gas layers between 1 R* and 10 R*. We consider a very complete set of mols. and dust clusters, and combine the nucleation phase of dust formation with the condensation of these clusters into dust grains. We also test the impact of increasing the local gas d. Our derived mol. abundances and dust properties are compared to the most recent observational data. Methods. A semi-anal. formalism based on parameterized fluid equations is used to describe the gas d., velocity, and temp. in the inner wind. The chem. is described by using a chem. kinetic network of reactions and the condensation mechanism is described by a Brownian formalism. A set of stiff, ordinary, coupled differential equations is solved, and mol. abundances, dust cluster abundances, grain size distributions and dust masses are derived. Results. The shocks drive an active non-equil. chem. in the dust formation zone of IK Tau where the collision destruction of CO in the post-shock gas triggers the formation of C-bearing species such as HCN and CS. Most of the modelled mol. abundances agree well with the latest values derived from Herschel data, except for SO2 and NH3, whose formation may not occur in the inner wind. Clusters of alumina, Al2O3, are produced within 2 R* and lead to a population of alumina grains close to the stellar surface. Clusters of silicates (Mg2SiO4) form at larger radii (r > 3 R*), where their nucleation is triggered by the formation of HSiO and H2SiO. They efficiently condense and reach their final grain size distribution between ∼6 R* and 8 R* with a major population of medium size grains peaking at ∼200 Å. This two dust-shell configuration agrees with recent interferometric observations. The derived dust-to-gas mass ratio for IK Tau is in the range 1-6 × 10-3 and agrees with values derived from observations of O-rich Mira-type stars. Conclusions. Our results confirm the importance of periodic shocks in chem. shaping the inner wind of AGB stars and providing gas conditions conducive to the efficient synthesis of mols. and dust by non-equil. processes. They indicate that the wind acceleration will possibly develop in the radius range 4-8 R* in IK Tau.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC28XoslemtrY%253D&md5=972d7567f8e8d598e19bedupdatinga

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    Jayaweera, T. M.; Melius, C. F.; Pitz, W. J.; Westbrook, C. K.; Korobeinichev, O. P.; Shvartsberg, V. M.; Shmakov, A. G.; Rybitskaya, I. V.; Curran, H. J. Flame inhibition by phosphorus-containing compounds over a range of equivalence ratios. Combust. Flame 2005, 140, 103115,  DOI: 10.1016/j.combustflame.updating

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    Flame inhibition by phosphorus-containing compounds over a range of equivalence ratios

    Jayaweera, T. M.; Melius, C. F.; Pitz, W. J.; Westbrook, C. K.; Korobeinichev, O. P.; Shvartsberg, V. M.; Shmakov, A. G.; Rybitskaya, I. V.; Curran, H. J.

    Combustion and Flame (2005), 140 (1/2), 103-115CODEN: CBFMAO; ISSN:updating. (Elsevier)

    There is much interest in the combustion mechanism of organophosphorus compds. (OPCs) due to their role as potential halon replacements in fire suppression. A continuing investigation of the inhibition activity of organophosphorus compds. under a range of equivalence ratios was performed exptl. and computationally, as measured by the burning velocity. Updates to a previous mechanism were made by the addn. and modification of reactions in the mechanism for a more complete description of the inhibition reactions. Reaction pathways for HOPO2 + H and HOPO + H are analyzed by using the BAC-G2 approach. A new reaction pathway for HOPO2 + H = PO2 + H2O was identified which results in a higher rate const. than that reported in the literature. In this work, the laminar flame speed is measured exptl. and calcd. numerically for a premixed propane/air flame at 1 atm, under a range of equivalence ratios, undoped and doped with di-Me methylphosphonate (DMMP). A detailed investigation of the catalytic cycles involved in the recombination of key flame radicals is made for two equivalence ratios, fuel lean and fuel rich. From this, the importance of different catalytic cycles involved in the lean vs. rich case is discussed. The chem. kinetic model indicates that the HOPO2 ↔ PO2 inhibition cycle is more important in the lean flame than the rich. The OPCs are similarly effective across the range, demonstrating the robustness of OPCs as flame suppressants. In addn., it is shown that the phosphorus compds. are most active in the high-temp. region of the flame. This may, in part, explain their high level of inhibition effectiveness.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD2cXhtFejsLbP&md5=86ec12fcdupdatinge320d877db1

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    Korobeinichev, O. P.; Shvartsberg, V. M.; Bol’shova, T. A.; Shmakov, A. G.; Knyaz’kov, D. A. Inhibition of methane-oxygen flames by organophosphorus compounds. Combust., Explos. Shock Waves 2002, 38, 127133,  DOI: 10.1023/A:1014937428678

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    MacDonald, M. A.; Jayaweera, T. M.; Fisher, E. M.; Gouldin, F. C. Inhibition of nonpremixed flames by phosphorus-containing compounds. Combust. Flame 1999, 116, 166176,  DOI: 10.1016/Supdating(98)00034-0

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    Inhibition of nonpremixed flames by phosphorus-containing compounds

    Macdonald, M. A.; Jayaweera, T. M.; Fisher, E. M.; Gouldin, F. C.

    Combustion and Flame (1998), 116 (1/2), 166-176CODEN: CBFMAO; ISSN:updating. (Elsevier Science Inc.)

    Phosphorus-contg. compds. (PCCs) are proposed as viable alternatives to current, ozone-destroying, flame-inhibiting agents. An opposed-jet burner app. was used to study the effectiveness of two low-vapor-pressure PCCs, di-Me methylphosphonate (DMMP) and tri-Me phosphate (TMP), in extinguishing a nonpremixed methane-air flame. The global extinction strain rate was detd. as a function of dopant loadings. Tests were also conducted using nitrogen as an inert additive for ref. Results demonstrate that these phosphorus-contg. compds. are significant inhibitors of nonpremixed methane-air flames when introduced into the oxidizer stream, 40 times more effective than nitrogen on a molar basis. A novel technique for measuring the extinction strain rate while maintaining a const. dopant level in one gas stream was developed.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXlvFWlsLo%253D&md5=3042e475fb3a48449d8352efe8bd8cdd

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    Korobeinichev, O. P.; Shvartsberg, V. M.; Shmakov, A. G. The chemistry of combustion of organophosphorus compounds. Russ. Chem. Rev. 2007, 76, 1094,  DOI: 10.1070/RC2007v076n11ABEH003713

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    Zegers, E. J. P.; Fisher, E. M. Gas-phase pyrolysis of diisopropyl methylphosphonate. Combust. Flame 1998, 115, 230240,  DOI: 10.1016/Supdating(98)00003-0

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    Gas-phase pyrolysis of diisopropyl methylphosphonate

    Zegers, E. J. P.; Fisher, E. M.

    Combustion and Flame (1998), 115 (1/2), 230-240CODEN: CBFMAO; ISSN:updating. (Elsevier Science Inc.)

    Gas-phase pyrolysis studies of diisopropyl methylphosphonate (DIMP) in nitrogen have been conducted to gain insight into the decompn. behavior of organophosphorus chem. warfare nerve agents. Expts. were conducted in a quartz-lined atm. flow reactor between 700 and 800 K, at residence times ranging from 15 to 90 ms. Propylene, isopropanol, iso-Pr methylphosphonate (IMP), and methylphosphonic acid (MPA) were identified as decompn. products of DIMP. FTIR spectrometry was used to quantify parent, propylene, and isopropanol mole fractions in the reactor. The proposed pyrolysis mechanism for DIMP comprises two stages. The first corresponds to the unimol. decompn. of the parent into IMP and propylene. The second involves two competing pathways for the unimol. decompn. of IMP, one leading to isopropanol and the very reactive Me dioxophosphorane; the other to propylene once again and MPA. In the range of temps. studied, an isopropanol to propylene mole fraction ratio close to 0.25 suggests a branching ratio of 1.5 between these two pathways in favor of propylene prodn. The Arrhenius expression for the unimol. decompn. of DIMP was found to be: k[s-1]=10(12.0±1.5)[s-1] exp(-36.7±4.9[kcal.mole-1]/(RT)). Pyrolysis expts. with iso-Pr and t-Bu acetates, which have well-known decompn. rates, were performed to illustrate the ability of the app. to produce valid chem. kinetic data. An investigation of the effects of surface to vol. ratio on the DIMP decompn. process shows that wall reactions are significant in a 4-mm i.d. quartz tube, but less important in an 8-mm i.d. tube. Their effects are expected to be small in the 45-mm i.d. reactor.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaK1cXjslOmsLk%253D&md5=fddd10ffe487f3d6534c5d9e622b6a5a

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    Moussaoui, Y.; Ouamerali, O.; De Mare, G. R. Properties of the phosphorus oxide radical, PO, its cation and anion in their ground electronic states: comparison of theoretical and experimental data. Int. Rev. Phys. Chem. 2003, 22, 641675,  DOI: 10.1080/updating

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    Properties of the phosphorus oxide radical, PO, its cation and anion in their ground electronic states: comparison of theoretical and experimental data

    Moussaoui, Yahia; Ouamerali, Ourida; De Mare, George R.

    International Reviews in Physical Chemistry (2003), 22 (4), 641-675CODEN: IRPCDL; ISSN:updatingX. (Taylor & Francis Ltd.)

    Exptl. and theor. data for the phosphorus oxide radical (PO), its cation (PO+) and anion (PO-) in their electronic ground states are reviewed. The internuclear distances, fundamental vibrational frequencies, bond orders, partial at. charges, free valences, dipole moments, dissocn. energies, ionization potential and electron affinity are discussed. The literature data are augmented by the results of a theor. study including computations using RHF closed- and open-shell, generalized valence bond-perfect pairing, Moller-Plesset perturbation theory, complete active space SCF, coupled-cluster with single and double substitutions up to the level augmented by a perturbative est. of triple excitations and d. functional theory methods.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXhtVShtr7O&md5=2cbce6e8125eac9f4160e6cb08718331

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    Coquart, B.; Paz, M. D.; Prudhomme, J. C. Transition A2Σ+X2 Π des molécules P16O et P18O. Perturbations de l’état A2Σ+. Can. J. Phys. 1975, 53, 377384,  DOI: 10.1139/p75-048

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    Α2Σ+-X2Π transition of phosphorus oxide (oxygen-16, -18) molecules. Perturbations of the Α2Σ+ state

    Coquart, B.; Da Paz, M.; Prudhomme, J. C.

    Canadian Journal of Physics (1975), 53 (4), 377-84CODEN: CJPHAD; ISSN:updating.

    New emission bands of the A2Σ+-X2II system of the P16O mol. were analyzed and this transition for P18O was studied for the 1st time, with a mean dispersion of 0.30 Å/mm. The levels 0, 1, 2, 3, 4, 5, and 6 of the A2Σ+ state for P16O and the levels 0, 1, 2, 3, and 4 of this state for P18O show perturbations from various species, some of which, studied previously for P16O, are attributable to a 4Σ- state and to the C2Σ- state. A vibrational quantification of the 4Σ- state is tried.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaE2MXhslOmtb4%253D&md5=286f370fb23e38f6c21ee0996433b154

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    Wong, K. N.; Anderson, W. R.; Kotlar, A. J. Radiative processes following laser excitation of the A 2Σ+ state of PO. J. Chem. Phys. 1986, 85, 24062413,  DOI: 10.1063/updating

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    Radiative processes following laser excitation of the A2Σ+ state of phosphorus oxide (PO)

    Wong, Koon Ng; Anderson, William R.; Kotlar, Anthony J.

    Journal of Chemical Physics (1986), 85 (5), 2406-13CODEN: JCPSA6; ISSN:updating.

    Laser induced fluorescence in the (0,0) band of the A2Σ+-X2Π system of the PO radical (∼2470 Å) was used to study the radiative properties of the A state. A laser excitation scan of the (0,0) band and a fluorescence scan of the emission are given. Fluorescence from the B2Σ+ state to the X state was obsd. (∼3250 Å) when the A state was pumped by the laser. The branching ratio for emission from the A state to the lower B and X states was indirectly detd. The A state has a very short free radiative lifetime, 9.68 ± 0.47 ns. In the absence of quenching, the excited state decay is primarily due to radiative processes. Upper limits were detd. for the quenching rates of Ar and He carrier gases. Relative intensities of emission of the v' = 0 progression in the A-X system were also measured. These intensities were used to det. the electronic transition moment function in the region of the equil. internuclear distance.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL28Xls1Wgt7Y%253D&md5=2c509c3bbe246383d99e66594d0e4fc0

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    Liu, H.; Shi, D. H.; Sun, J. F.; Zhu, Z. L. Accurate potential energy curves and spectroscopic properties of the 27 Lambda-S states and 73 Omega states of the PO radical. Mol. Phys. 2017, 115, 714730,  DOI: 10.1080/updating

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    Accurate potential energy curves and spectroscopic properties of the 27 Λ-S states and 73 Ω states of the PO radical

    Liu, Hui; Shi, Deheng; Sun, Jinfeng; Zhu, Zunlue

    Molecular Physics (2017), 115 (6), 714-730CODEN: MOPHAM; ISSN:updating. (Taylor & Francis Ltd.)

    The potential energy curves (PECs) were calcd. for the 27 Λ-S states and 73 Ω states of PO radical. The calcns. were done using the CASSCF method, which was followed by the internally contracted multireference CI (icMRCI) approach. To improve the quality of PECs, core-valence correlation and scalar relativistic corrections as well as Davidson correction were included. Of the 27 Λ-S states, the 16Σ+ state was repulsive at any case. The 14Φ and 16Π states were bound, but they became repulsive with the spin-orbit coupling (SOC) effect accounted for. The 34Σ+, a4Π, C'2Δ, D'2Π, 14Δ, 12Φ, 16Σ+ and 16Π states were inverted with the SOC effect included. The F2Σ+ state had double wells. The avoided crossings existed between the B2Σ+ and F2Σ+ states, the F2Σ+ and 32Σ+ states, the C'2Δ and 22Δ states, the 14Δ and 24Δ states, the 24Δ and 34Δ states, the 24Π and 34Π states and the 34Π and 44Π states. The c4Σ+, 24Σ+, 34Σ+, 34Π, 44Π, 54Π, 34Δ, 14Φ and 16Π states were weakly bound, which well depths were within several hundred cm-1. The spectroscopic parameters were derived. The SOC effect on the spectroscopic properties was evaluated. The spectroscopic results obtained here could be expected to be reliably predicted ones.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2sXjtlyksrw%253D&md5=1d837f6e84d1e405055eb4ed17ff795d

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    Izzaouihda, S.; El Makarim, H. A.; Komiha, N.; Lahmar, S.; Ghalila, H. Ab-initio potential energy curves of valence and Rydberg electronic states of the PO radical. Comput. Theor. Chem. 2014, 1049, 102108,  DOI: 10.1016/j.comptc.updating

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    Ab-initio potential energy curves of valence and Rydberg electronic states of the PO radical

    Izzaouihda, Safia; Abou El Makarim, Hassna; Komiha, Najia; Lahmar, Souad; Ghalila, Hassen

    Computational & Theoretical Chemistry (2014), 1049 (), 102-108CODEN: CTCOA5; ISSN:updatingX. (Elsevier B.V.)

    This paper reports a theor. study of the electronic states of PO radical. Highly correlated ab initio methods were used for mapping the potential energy curves. Internally contracted multi-ref. CI method with the augmented correlation-consistent basis set (aV5Z) has been employed to carry out the study. After the nuclear motion treatment, the spectroscopic consts. and the vibrational energy levels of the doublet and quartet electronic states are detd. The calcd. values have been found in a good agreement with the existing exptl. and theor. results. The spin-orbit couplings between interacting states were also detd. in the region where the crossings of the potential energy curves occurs. These couplings are capable to induce predissocn. processes involving quartet states and producing P and O atoms at their ground and low lying excited electronic states. The theor. vibrational spectrum was predicted using the Franck Condon factors and the transition moments integrals. The calcd. spectrum shows intense peaks involving the Rydberg states in complete accordance with the expt.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXhslOru7fL&md5=da46518bf9c7c879cb1ffa7007ea6a60

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    Gómez Martín, J. C.; Blitz, M. A.; Plane, J. M. C. Kinetic studies of atmospherically relevant silicon chemistry Part I: Silicon atom reactions. Phys. Chem. Chem. Phys. 2009, 11, 671678,  DOI: 10.1039/B812946K

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    Kinetic studies of atmospherically relevant silicon chemistry part I: silicon atom reactions

    Gomez Martin Juan C; Blitz Mark A; Plane John M C

    Physical chemistry chemical physics : PCCP (2009), 11 (4), 671-8 ISSN:updating.

    Atomic silicon is generated by meteoric ablation in the Earth's upper atmosphere (70-110 km). The reactions of Si(3P(J)) atoms with several atmospherically relevant species were studied by the pulsed laser photolysis of a Si atom precursor (typically PheSiH3), followed by time-resolved laser induced fluorescence at 251.43 nm (Si(3p2 3P0 --> 4s 3P1)). This yielded: k(Si + O2, 190-500 K) = 9.49 x updating x 10(-10) x exp(-T/115 K) cm3 molecule(-1) s(-1) (uncertainty < or = +/- 15%), in good accord with recent high-level theoretical calculations but in marked disagreement with previous experimental work; k(Si + O3, 190-293 K) = (4.0 +/- 0.5) x 10(-10) cm3 molecule(-1) s(-1); k(Si + CO2, 293 K) < or = 1.2 x 10(-14) cm3 molecule(-1) s(-1); and k(Si + H2O, 293 K) < or = 2.6 x 10(-13) cm3 molecule(-1) s(-1). These results are explained using a combination of quantum chemistry calculations and long-range capture theory. The quenching rate coefficients k(Si(1D2) + N2, 293 K) = (4.0 +/- 0.7) x 10(-11) cm3 molecule(-1) s(-1) and k(Si(1D2) + H2O, 293 K) = (2.3 +/- 0.3) x 10(-10) cm3 molecule(-1) s(-1) were also determined.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A280%3ADC%252BD1MnpvVCiug%253D%253D&md5=ea2d93712aab7c7204365ed03f68b27e

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    Mangan, T. P.; McAdam, N.; Daly, S. M.; Plane, J. M. C. Kinetic study of Ni and NiO reactions pertinent to the Earth’s upper atmosphere. J. Phys. Chem. A 2019, 123, 601610,  DOI: 10.1021/acs.jpca.8b11382

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    Kinetic Study of Ni and NiO Reactions Pertinent to the Earth's Upper Atmosphere

    Mangan, Thomas P.; McAdam, Nathanial; Daly, Shane M.; Plane, John M. C.

    Journal of Physical Chemistry A (2019), 123 (2), 601-610CODEN: JPCAFH; ISSN:updating. (American Chemical Society)

    Nickel atoms are injected into the Earth's mesosphere by meteoric ablation, producing a Ni layer between 70 and 105 km in altitude. The subsequent reactions of Ni and NiO with atmospherically relevant species were studied using the time-resolved pulsed laser photolysis-laser-induced fluorescence technique, combined with electronic structure calcns. and RRKM theory where appropriate. Results for bimol. reactions (in cm3 mol.-1 s-1): k(Ni + O3, 293 K) = (6.5 ± 0.7) × 10-10; k(NiO + O3 → Ni + 2O2, 293 K) = (1.4 ± 0.5) × 10-10; k(NiO + O3 → NiO2 + O2, 293 K) = (2.5 ± 0.7) × 10-10; k(NiO + CO, 190-377 K) = (3.2 ± 0.6) × 10-11 (T/updating±0.05. For termol. reactions (in cm6 mol.-2 s-1, uncertainty ± σ over the stated temp. range): log10(krec,0(Ni + O2 + N2, 190-455 K)) = -updatinglog10(T) - 1.5650(log10(T))2, σ = 11%; log10(krec,0(NiO + O2 + N2, 293-380 K)) = -updatinglog10(T) - 2.2610(log10(T))2, σ = 22%; and log10(krec,0(NiO + CO2 + N2, 191-375 K)) = -updatinglog10(T) - 2.5287(log10(T))2, σ = 15%. The faster recombination reaction NiO + H2O + N2, which is clearly in the falloff region over the exptl. pressure range (3-10 Torr), is best described by log10(krec,0/cm6 mol.-2 s-1) = -updatinglog10(T) - 1.7118(log10(T))2, krec,∞ = 6.0 × 10-10 exp(-171/T) cm3 mol.-1 s-1, broadening factor Fc = 0.84, σ = 16%. The implications of these results in the atm. are then discussed.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXisFCjtb3N&md5=c40e517b13c89cd6a0d103cb1f3bc098

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    Totterdill, A.; Gómez Martín, J. C.; Kovács, T.; Feng, W.; Plane, J. M. C. Experimental Study of the Mesospheric Removal of NF3 by Neutral Meteoric Metals and Lyman-α Radiation. J. Phys. Chem. A 2014, 118, 41204129,  DOI: 10.1021/jp503003e

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    Experimental study of the mesospheric removal of NF3 by neutral meteoric metals and Lyman-α radiation

    Totterdill, Anna; Gomez Martin, J. C.; Kovacs, Tamas; Feng, Wuhu; Plane, John M. C.

    Journal of Physical Chemistry A (2014), 118 (23), updatingCODEN: JPCAFH; ISSN:updating. (American Chemical Society)

    [external_link offset=2]

    NF3 is a potent anthropogenic greenhouse gas with increasing industrial usage. It is characterized by a large global warming potential due in part to its large atm. lifetime. The estd. lifetime of about 550 years means that potential mesospheric destruction processes of NF3 should also be considered. The reactions of NF3 with the neutral metal atoms Na, K, Mg and Fe, which are produced by meteoric ablation in the upper mesosphere, were therefore studied. The obsd. non-Arrhenius temp. dependences of the reactions between about 190 and 800 K are interpreted using quantum chem. calcns. of the relevant potential energy surfaces. The NF3 absorption cross section at the prominent Lyman-α solar emission line (121.6 nm) was detd. to be (1.59 ± 0.10) × 10-18 cm2 mol.-1 (at 300 K). In the mesosphere above 60 km, Lyman-α photolysis is the dominant removal process of NF3; the reactions with K and Na are 1-2 orders of magnitude slower. However, the atm. lifetime of NF3 is largely controlled by reaction with O(1D) and photolysis at wavelengths shorter than 190 nm; these processes dominate below 60 km.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC2cXotFCru7s%253D&md5=4e56523c03e509ad378f3163d70bf08f

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    Lewis, T.; Heard, D. E.; Blitz, M. A. A novel multiplex absorption spectrometer for time-resolved studies. Rev. Sci. Instrum. 2018, 89, 024101,  DOI: 10.1063/updating

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    A novel multiplex absorption spectrometer for time-resolved studies

    Lewis, Thomas; Heard, Dwayne E.; Blitz, Mark A.

    Review of Scientific Instruments (2018), 89 (2), 024101/updating/8CODEN: RSINAK; ISSN:updating. (American Institute of Physics)

    A Time-Resolved UV/Visible (UV/Vis) Absorption Spectrometer (TRUVAS) has been developed that can simultaneously monitor absorption at all wavelengths between 200 and 800 nm with millisecond time resoln. A pulsed photolysis laser (KrF 248 nm) is used to initiate chem. reactions that create the target species. The absorption signals from these species evolve as the compn. of the gas in the photolysis region changes over time. The instrument can operate at pressures over the range ∼10-800 Torr and can measure time-resolved absorbances <10-4 in the UV (300 nm) and even lower in the visible (580 nm) 2.3 × 10-5, with the peak of sensitivity at ∼500 nm. The novelty of this setup lies in the arrangement of the multipass optics. Although appearing similar to other multipass optical systems (in particular the Herriott cell), there are fundamental differences, most notably the ability to adjust each mirror to maximise the overlap between the probe beam and the photolysis laser. Another feature which aids the sensitivity and versatility of the system is the use of 2 high-throughput spectrographs coupled with sensitive line-array CCDs, which can measure absorbance from ∼200 to 800 nm simultaneously. The capability of the instrument is demonstrated via measurements of the absorption spectrum of the peroxy radical, HOCH2CH2O2, and its self-reaction kinetics. (c) 2018 American Institute of Physics.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BC1cXitFGmt7s%253D&md5=a41cfdc5c54e8fff215c6332ab1e7276

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    Keller-Rudek, H.; Moortgat, G. K.; Sander, R.; Sörensen, R. The MPI-Mainz UV/VIS Spectral Atlas of Gaseous Molecules of Atmospheric Interest. Earth Syst. Sci. Data 2013, 5, 365373,  DOI: 10.5194/essd-5-365-2013

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    Matsumi, Y.; Kawasaki, M. Photolysis of Atmospheric Ozone in the Ultraviolet Region. Chem. Rev. 2003, 103, 47674782,  DOI: 10.1021/cr0205255

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    Photolysis of Atmospheric Ozone in the Ultraviolet Region

    Matsumi, Yutaka; Kawasaki, Masahiro

    Chemical Reviews (Washington, DC, United States) (2003), 103 (12), updatingCODEN: CHREAY; ISSN:updating. (American Chemical Society)

    A review concerning UV photodissocn. of O3 and its effect on stratospheric and tropospheric chem. is given. Topics discussed include: absorption spectrum and its assignment; O(1D) formation from O3 photolysis (O(1D) formation in the atm., O(1D) quantum yield measurements, exptl. methods to measure O(1D) yield, abs. values of the O(1D) quantum yield, O(1D) quantum yield between 306 and 328 nm, O(1D) quantum yield at <306 nm and >328 nm, phys. processes of O(1D) formation [photodissocn. of vibrationally-excited O3, spin-forbidden processes]); and atm. chem. implications (formation of O2(v) in O3 photolysis and subsequent reactions, O2(A1Δg) and O2(b1Σ+g) detection from O3 photolysis, non-local thermal equil. translational distribution produced by UV photolysis of O3, N2O formation assocd. with UV photodissocn. of O3).

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADC%252BD3sXoslWiu78%253D&md5=96ffffupdatingc2c9d1880560

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    Hamilton, P. A. The laser-induced fluorescence-spectrum and radiative lifetime of PO2. J. Chem. Phys. 1987, 86, 3341,  DOI: 10.1063/updating

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    The laser induced fluorescence spectrum and radiative lifetime of phosphorus oxide (PO2)

    Hamilton, Peter A.

    Journal of Chemical Physics (1987), 86 (1), 33-41CODEN: JCPSA6; ISSN:updating.

    The UV spectrum of PO2 1st obsd. in absorption by R. D. Verma and C. F. McCarthy (1983) was studied by laser induced fluorescence for the 1st time. The spectra are similar in many respects to those obsd. in the visible system of NO2 and no predissocn. is obsd. The loss of rotational structure is attributed instead to mixing with one or more near continuous background states, with the amt. of mixing apparently related to excitation of the bending vibration. The radiative decays are nonexponential but are accurately described by a double exponential form. This gives collision free radiative lifetimes of ∼0.5 and 4.5 μs for the structured and continuous states, resp., with the effective lifetime of the structured state varying strongly with the amt. of mixing. Collisional quenching rate consts., are roughly const. at (6 ± 1) × 10-10 and (4 ± 1) × 10-1 cm3 mol.-1 s-1 for the 2 states, with the very rapid quenching rate of the structured state probably being for nonradiative transfer to the background continuum. From observations of the wavelength dependence of the fluorescence the ground state ν2 and ν1 frequencies are about 387 and 1117 cm-1, resp. The emission is very extensive and strongly red shifted and lends further evidence that these states of PO2 are responsible for the chemiluminescence obsd. in phosphorus/oxygen reactions.

    https://chemport.cas.org/services/resolver?origin=ACS&resolution=options&coi=1%3ACAS%3A528%3ADyaL2sXnsFeltQ%253D%253D&md5=b1b8a5aeb13c34df65914eed049a996b

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    Hamilton, P. A.; Murrells, T. P. Kinetics and mechanism of the reactions of PH3 with O(3P) and N(4S) atoms. J. Chem. Soc., Faraday Trans. 2 1985, 81, 15311541,  DOI: 10.1039/fupdating

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    Kinetics and mechanism of the reactions of phosphine with oxygen(3P) and nitrogen(4S) atoms

    Hamilton, Peter A.; Murrells, Timothy P.

    Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics (1985), 81 (10), 1531-41CODEN: JCFTBS; ISSN:updating.

    The reactions of ground-state O and N atoms with PH3 were studied by using a discharge-flow system with detection of both radical and mol. species by mol.-beam sampling mass spectrometry. The rate const. for the O-PH3 reaction is 4.6 × 10-11 cm3 mol.-1 s-1, and the main products are H2PO and H with <10% of the reaction proceeding to PH2 and OH. H3PO, HPO, and PO were also detected, and a new mechanism is proposed. The N-PH3 reaction is very slow with an upper limit for the rate const. of 4.0 × 10-14 cm3 mol.-1 s-1.

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    The chemiluminescent reactions of O with a variety of P-contg. compds. were examd. in a discharge-flow/mass spectrometer system. Various qual. tests and the correlation of the chemiluminescence with the mass spectrometric signals lends strong support to the suggestion that the green emitter is PO2, formed in the reaction O + PO → PO2 + hν. The results cannot be explained in terms of the PO excimer model. The blue emission seen in the phosphine system is not from the reaction of OH + PO as previously suggested but is tentatively assigned to the reaction O + POH → PO2H + hν.

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    MESMER: An Open-Source Master Equation Solver for Multi-Energy Well Reactions

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    Journal of Physical Chemistry A (2012), 116 (38), updatingCODEN: JPCAFH; ISSN:updating. (American Chemical Society)

    The most commonly used theor. models for describing chem. kinetics are accurate in two limits. When relaxation is fast with respect to reaction time scales, thermal transition state theory (TST) is the theor. tool of choice. In the limit of slow relaxation, an energy resolved description like RRKM theory is more appropriate. For intermediate relaxation regimes, where much of the chem. in nature occurs, theor. approaches are somewhat less well established. However, in recent years master equation approaches were successfully used to analyze and predict nonequil. chem. kinetics across a range of intermediate relaxation regimes spanning atm., combustion, and (very recently) soln. phase org. chem. In this article, a Master Equation Solver is described for multi-energy well reactions (MESMER), a user-friendly, object-oriented, open-source code designed to facilitate kinetic simulations over multi-well mol. energy topologies where energy transfer with an external bath impacts phenomenol. kinetics. MESMER offers users a range of user options specified via keywords and also includes some unique statistical mechanics approaches like contracted basis set methods and nonadiabatic RRKM theory for modeling spin-hopping. The design principles implemented in MESMER will facilitate its development and usage by workers across a range of fields concerned with chem. kinetics. As accurate thermodn. data become more widely available, electronic structure theory is increasingly reliable, and as the fundamental understanding of energy transfer improves, it is envisioned that tools like MESMER will eventually enable routine and reliable prediction of nonequil. kinetics in arbitrary systems.

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    Journal of Chemical Physics (1998), 109 (19), updatingCODEN: JCPSA6; ISSN:updating. (American Institute of Physics)

    Time-dependent d.-functional (TDDFT) methods are applied within the adiabatic approxn. to a series of mols. including C70. Our implementation provides an efficient approach for treating frequency-dependent response properties and electronic excitation spectra of large mols. We also present a new algorithm for the diagonalization of large non-Hermitian matrixes which is needed for hybrid functionals and is also faster than the widely used Davidson algorithm when employed for the Hermitian case appearing in excited energy calcns. Results for a few selected mols. using local, gradient-cor., and hybrid functionals are discussed. We find that for mols. with low lying excited states TDDFT constitutes a considerable improvement over Hartree-Fock based methods (like the RPA) which require comparable computational effort.

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    An extensive study of the β system of the PO mol. was carried out. The rotational anal. of 23 bands yielded the consts. of the v = 0-9 levels of the B2Σ+ state and of the v = 0-11 levels of the X2Π state with a precision higher than previous measurements. The spin coupling const., Av, evaluated for the 12 levels of X2Π, follows the equation Av = updatingv - 0.013v2. The perturbations obsd. in the B2Σ (v = 6 and 7) levels were interpreted as being caused by a 4Σ- state and the B'2Π state. A deperturbation calcn. was carried out to evaluate the mol. consts. of the PO mol. in the 4Σ- state. Several new bands were also obsd.; some of these belong to the β and B'-X systems and others are left unassigned.

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    This review article, the first in the series, presents kinetic and photochem. data evaluated by the IUPAC Subcommittee on Gas Kinetic Data Evaluation for Atm. Chem. It covers the gas phase and photochem. reactions of Ox, HOx, NOx and SOx species, which were last published in 1997, and were updated on the IUPAC website in late 2001. The article consists of a summary sheet, contg. the recommended kinetic parameters for the evaluated reactions, and five appendices contg. the data sheets, which provide information upon which the recommendations are made.

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    The atm. reaction NO2 + O3 → NO3 + O2 (1) has been investigated theor. by using the MP2, G2, G2Q, QCISD, QCISD(T), CCSD(T), CASSCF, and CASPT2 methods with various basis sets. The results show that the reaction pathway can be divided in two different parts at the MP2 level of theory. At this level, the mechanism proceeds along two transition states (TS1 and TS2) sepd. by an intermediate, designated as A. However, when the single-ref. higher correlated QCISD methodol. has been employed, the min. A and the transition state TS2 are not found on the hypersurface of potential energy, which confirms a direct reaction mechanism. Single-ref. high correlated and multiconfigurational methods consistently predict the barrier height of reaction (1) to be within the range 2.5-6.1 kcal mol-1, in reasonable agreement with exptl. data. The calcd. reaction enthalpy is -24.6 kcal mol-1 and the reaction rate calcd. at the highest CASPT2 level, of k = 6.9 × 10-18 cm3 mol.-1 s-1. Both results can be regarded also as accurate predictions of the methodol. employed in this article.

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    The closed-shell CCSD equations are reformulated to achieve superior computational efficiency. Using a spin adaptation scheme based on the unitary group approach (UGA), a new set of equations is obtained that greatly improves a previous formulation. Based on this scheme, equations are derived for the closed-shell CI including all single and double excitations (CISD) case. Both methods have been implemented and tested. For a range of test cases the new CCSD procedure is faster than the shape-driven graphical (SDG) UGA algorithm; the new CCSD scheme is less than two times more computationally intensive than SDGUGA CISD per iteration.

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    PGOPHER: A program for simulating rotational, vibrational and electronic spectra

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    The PGOPHER program is a general purpose program for simulating and fitting mol. spectra, particularly the rotational structure. The current version can handle linear mols., sym. tops and asym. tops and many possible transitions, both allowed and forbidden, including multiphoton and Raman spectra in addn. to the common elec. dipole absorptions. Many different interactions can be included in the calcn., including those arising from electron and nuclear spin, and external elec. and magnetic fields. Multiple states and interactions between them can also be accounted for, limited only by available memory. Fitting of exptl. data can be to line positions (in many common formats), intensities or band contours and the parameters detd. can be level populations as well as rotational consts. PGOPHER is provided with a powerful and flexible graphical user interface to simplify many of the tasks required in simulating, understanding and fitting mol. spectra, including Fortrat diagrams and energy level plots in addn. to overlaying exptl. and simulated spectra. The program is open source, and can be compiled with open source tools. This paper provides a formal description of the operation of version 9.1.

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    Plane, J. M. C.; Feng, W. H.; Gómez Martín, J. C.; Gerding, M.; Raizada, S. A new model of meteoric calcium in the mesosphere and lower thermosphere. Atmos. Chem. Phys. 2018, 18, 1479914811,  DOI: 10.5194/acp-updating

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    A new model of meteoric calcium in the mesosphere and lower thermosphere

    Plane, John M. C.; Feng, Wuhu; Gomez Martin, Juan Carlos; Gerding, Michael; Raizada, Shikha

    Atmospheric Chemistry and Physics (2018), 18 (20), updatingCODEN: ACPTCE; ISSN:updating. (Copernicus Publications)

    Meteoric ablation produces layers of metal atoms in the mesosphere and lower thermosphere (MLT). It has been known for more than 30 years that the Ca atom layer is depleted by over 2 orders of magnitude compared with Na, despite these elements having nearly the same elemental abundance in chondritic meteorites. In contrast, the Ca+ ion abundance is depleted by less than a factor of 10. To explain these observations, a large database of neutral and ion-mol. reaction kinetics of Ca species, measured over the past decade, was incorporated into the Whole Atm. Community Climate Model (WACCM). A new meteoric input function for Ca and Na, derived using a chem. ablation model that has been tested exptl. with a Meteoric Ablation Simulator, shows that Ca ablates almost 1 order of magnitude less efficiently than Na. WACCM-Ca simulates the seasonal Ca layer satisfactorily when compared with lidar observations, but tends to overestimate Ca+ measurements made by rocket mass spectrometry and lidar. A key finding is that CaOH and CaCO3 are very stable reservoir species because they are involved in essentially closed reaction cycles with O2 and O. This has been demonstrated exptl. for CaOH, and in this study for CaCO3 using electronic structure and statistical rate theory. Most of the neutral Ca is therefore locked in these reservoirs, enabling rapid loss through polymn. into meteoric smoke particles, and this explains the extreme depletion of Ca.

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    Atmospheric chemistry of meteoric metals

    Plane, John M. C.

    Chemical Reviews (Washington, DC, United States) (2003), 103 (12), updatingCODEN: CHREAY; ISSN:updating. (American Chemical Society)

    A review with refs. is presented on the atm. chem. of metals that ablate from meteoroids at altitudes 70-120 km. Other topics include meteoric ablation as the source of metals in the mesosphere, atm. modeling of the metal atom layers, and meteor smoke in the middle and lower atm.

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This article is cited by 1 publications.

  1. Juan C. Zapata Trujillo, Anna-Maree Syme, Keiran N. Rowell, Brendan P. Burns, Ebubekir S. Clark, Maire N. Gorman, Lorrie S. D. Jacob, Panayioti Kapodistrias, David J. Kedziora, Felix A. R. Lempriere, Chris Medcraft, Jensen O'Sullivan, Evan G. Robertson, Georgia G. Soares, Luke Steller, Bronwyn L. Teece, Chenoa D. Tremblay, Clara Sousa-Silva, Laura K. McKemmish. Computational Infrared Spectroscopy of 958 Phosphorus-Bearing Molecules. Frontiers in Astronomy and Space Sciences 2021, 8 https://doi.org/10.3389/fspas.updating
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