Non-Thermal Rate Constants of Quenching and Vibrational Relaxation in the OH(A2Σ+; ν’ = 0,1) Manifold

Knowledge of molecular energy-transfer processes is a key ingredient for using laser-induced fluorescence, LIF, as a quantitative optical diagnostic method at high pressure. At present, rate constants of electronic quenching and vibrational energy transfer in the OH$left({mathrm{A}}^{2}{{Sigma}}^{+},{\upsilon }^{prime }=0,1 ight)$ manifold for many colliders are known only in the condition of thermal equilibrium of the rotational population of the A electronic state. However, this condition is seldom met in molecular gases. Therefore, the rotational distributions in the OH$left({mathrm{A}}^{2}{{Sigma}}^{+},{\upsilon }^{prime }=0,1 ight)$ manifold are often non-thermal and close to the nascent ones. In the present work, a new set of rate constants has been measured in the condition of non-thermal rotational distribution, for the excitation of three rotational levels, N' = 0, 1, 2, of OH$left({mathrm{A}}^{2}{{Sigma}}^{+},{\upsilon }^{prime }=1 ight)$ with CO2, CO, O2, CH4 and H2 as colliders. For N' = 2 the temperature dependence of the rate constants has also been measured for the first time from 300 to over 2000 K. These new data are crucial for the quantification of OH by LIF in gas discharges at high pressure and to fully exploit the CET-LIF (collision energy transfer LIF) technique for measuring the CO2 dissociation as a function of time in a nanosecond repetitively pulsed discharge.