Kinetic Study of the Reactions PO + O and PO + O and Spectroscopy of the PO Radical.

The kinetics of the reactions of PO with O and PO with O were studied at temperatures ranging from ∼190 to 340 K, using a pulsed laser photolysis-laser induced fluorescence technique. For the reaction of PO + O, there is evidence of both a two- and three-body exit channel, producing PO + O and PO, respectively. Potential energy surfaces of both the PO + O and PO + O systems were calculated using electronic structure theory and combined with RRKM calculations to explain the observed pressure and temperature dependences. For PO + O, 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 PO + O of >99%; the rate coefficient can be expressed by log(, 120-500 K, cm molecule s) = -13.915 + 2.470 log() - 0.5020(log()), with an uncertainty of ±10% over the experimental temperature range (191-339 K). With increasing pressure, the yield of PO increases, reaching ∼90% at a pressure of 1 atm and = 300 K. For PO + O, (188-339 K) = 3.7 × 10 exp cm molecule s, with an uncertainty of ±26% over the stated temperature range. Laser-induced fluorescence spectra of PO over the wavelength range 245-248 nm were collected and simulated using pgopher to obtain new spectroscopic constants for the ground and = 1 vibrational levels of the Π and Σ states of PO.