Equilibration of OH (v7; v9) in air-like gas ensembles

► Equilibration of ensembles is a multistage process not a single exponential decay. ► Initial relaxation is via near resonant V-V exchange with bath molecules. ► OH initially becomes rotationally hot from quasi-resonant vibration-rotation transfer. ► Rotational equilibration only begins once vibrational quasi-equilibrium is reached. ► At equilibrium OH rotational temperature is the lowest of all modes of all species present.