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

Abstract

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.