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

The kinetics of the reactions of PO with O 2 and PO 2 with O 3 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 2 , there is evidence of both a two- and three-body exit channel, producing PO 2 + O and PO 3 , respectively. Potential energy surfaces of both the PO + O 2 and PO 2 + O 3 systems were calculated using electronic structure theory and combined with RRKM calculations to explain the observed pressure and temperature dependences. For PO + O 2 , 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 2 + O of >99%; the rate coefficient can be expressed by log 10 ( k , 120-500 K, cm 3 molecule -1 s -1 ) = -13.915 + 2.470 log 10 ( T ) - 0.5020(log 10 ( T )) 2 , with an uncertainty of ±10% over the experimental temperature range (191-339 K). With increasing pressure, the yield of PO 3 increases, reaching ∼90% at a pressure of 1 atm and T = 300 K. For PO 2 + O 3 , k (188-339 K) = 3.7 × 10 -11 exp (-1131/ T ) cm 3 molecule -1 s -1 , 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 v = 1 vibrational levels of the X 2 Π and A 2 Σ + states of PO.