Collisional removal of O2 (c 1Σ−u, ν=9) by O2, N2, and He

The collisional removal of O2 molecules in selected vibrational levels of the c 1Σ−u state is studied using a two-laser double-resonance technique. The output of the first laser excites the O2 to ν=9 or 10 of the c 1Σ−u state, and the ultraviolet output of the second laser monitors specific rovibrational levels via resonance-enhanced ionization. The temporal evolution of the c 1Σ−u state vibrational level is observed by scanning the time delay between the two pulsed lasers. Collisional removal rate constants for c 1Σ−u, ν=9 colliding with O2, N2, and He are (5.2±0.6)×10−12, (3.2±0.4)×10−12, and (7.5±0.9)×10−12 cm3 s−1, respectively. As the rate constants for O2 and N2 are similar in magnitude, N2 collisions dominate the removal rate in the earth’s atmosphere. For ν=10 colliding with O2, we find a removal rate constant that is 2–5 times that for ν=9 and that single quantum collision cascade is an important pathway for removal.