State-specific rate constants for the relaxation of O2(X 3Σg–, ν= 8–11) in collisions with O2, N2, NO2, CO2, N2O, CH4 and He

Abstract

Rate constants have been measured at 295 K for the state-specific vibrational relaxation of O₂(8 ⩽ν⩽ 11) by several gases, M = NO₂, O₂, CO₂, N₂O, CH₄ and He. Upper limits are reported for the rate constants for relaxation by N₂. Vibrationally excited O₂ was formed in levels up to ν= 11 by the reaction of O(³P) atoms with NO₂. The O(³P) atoms were created by partial photolysis of NO₂ at 355 nm using a frequency-tripled Nd: YAG laser, and the kinetics of O₂ in individual ν levels observed by laser-induced fluorescence in the (0, ν) bands of the B ³Σ_u^––X³Σ_g^– system. Except with He as collision partner, it appears that relaxation occurs by single quantum, intermolecular, vibration–vibration (V–V) energy exchange. Comparison of the rate constants for relaxation by different collision partners demonstrates again the importance of near-resonance and long-range forces in facilitating V–V exchange, with IR active modes accepting vibrational quanta more readily than IR inactive modes. The results are compared with those obtained previously for higher vibrational levels of O₂, with estimates of the relaxation rates estimated according to a version of Sharma–Brau theory, and the implications of the results for atmospheric chemistry are discussed briefly.