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

The reaction H + O3 → OH + O2 yields OH in vOH = 7–9. We report equilibration of OH vOH = 7 and vOH = 9 in baths of N2 + O2 in v = 0 at 300 K. Each relaxes initially by near-resonant, coupled, vibrational energy exchange with bath gas molecules, followed by further, slower, phases of energy transfer. Single (first) collision cross-sections are calculated to be 1.42; 1.51; 1.52 ± 0.21 Å2 for depopulation of vOH = 7; 8; 9 respectively. ‘Equilibrated’ OH rotation becomes the lowest of all nine possible modal temperatures in OH and the two bath gases, despite an initial sharp rise.