FORMATION AND VIBRATIONAL-RELAXATION OF OH (X2-PI-I,V) BY O2 AND CO2

Time-resolved OH (X2-PI-i, upsilon = 1-9) populations have been measured and analyzed to determine parameters relating to formation mechanisms and vibrational relaxation. OH(upsilon) was formed in electron-irradiated Ar/H-2/O3 mixtures containing added O2 or CO2 as relaxer species. OH(upsilon --> upsilon - 1,upsilon - 2) emission was observed using time-resolved Fourier spectroscopy. Spectra were then fit to determine time-dependent populations. Population data were analyzed using a single-quantum relaxation model, but the possible effects of multiquantum relaxation were also considered. The model includes provision for OH(upsilon) production via H + O3 --> OH(upsilon) + O2 after e-beam termination, which has been found to have a significant effect on the results. The following relaxation rate constants are obtained: k-upsilon = 1-6(O2) = 1.3 +/- 0.4, 2.7 +/- 0.8, 5.2 +/- 1.5, 8.8 +/- 3.0, 17 +/- 7, 30 +/- 15 (10(-13) cm3s-1) and k-upsilon = 1-4 (CO2) = 1.8 +/- 0.5, 4.8 +/- 1.5, 14 +/- 5, 28 +/- 10 (10(-13) cm3s-1), respectively. Two different exponential decay rates are necessary to characterize the time dependence of the inferred H atom concentration. The role of O(1D) + H-2 --> OH + H is also discussed.