State-specific rate constants for the relaxation of O2(X3Σg–, ν= 8–11) in collisions with O2, N2, NO2, CO2, N2O, CH4and 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 3Σu––X3Σg– 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.