Formation and vibrational relaxation of OH (X 2Πi,v) by O2 and CO2

Abstract

Time‐resolved OH(X ²Π_i,v=1–9) populations have been measured and analyzed to determine parameters relating to formation mechanisms and vibrational relaxation. OH(v) was formed in electron‐irradiated Ar/H₂/O₃ mixtures containing added O₂ or CO₂ as relaxer species. OH(v→v−1,v−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(v) production via H+O₃→OH(v)+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_v=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_v=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)+H₂→OH+H is also discussed.