Search

We report a laboratory measurement of the rate coefficient for the collisional removal of O2(X3Σg-,υ=1) by O(3P) atoms. In the experiments, 266-nm laser light photodissociates ozone in a mixture of molecular oxygen and ozone. The photolysis step produces vibrationally excited O2(a1Δg) that is rapidly converted to O2(X3Σg-,υ=1–3) in a near-resonant electronic energy-transfer process with ground-state O2. In parallel, a large amount of O(1D) atoms is generated that promptly relaxes to O(3P). Under the conditions of the experiments, only collisions with the photolytically produced O(3P) atoms control the lifetime of O2(X3Σg-,υ=1), because its removal by molecular oxygen at room temperature is extremely slow. Tunable 193-nm laser light monitors the temporal evolution of the O2(X3Σg-,υ=1) population by detection of laser-induced fluorescence near 360 nm. The removal rate coefficient for O2(X3Σg-,υ=1) by O(3P) atoms is (3.2±1.0)×10-12 cm3 s-1 (2σ) at a temperature of 315±15 K (2σ). This result is essential for the analysis and correct interpretation of the 6.3-μm H2O(ν2) band emission in the Earth’s mesosphere and indicates that the deactivation of O2(X 3Σg-,υ=1) by O(3P) atoms is significantly faster than the nominal values recently used in atmospheric models. [ABSTRACT FROM AUTHOR]

Vibrational relaxation of O2(X 3Σg-,υ=2,3) by O2 molecules is studied via a two-laser approach. Laser radiation at 266 nm photodissociates ozone in a mixture of molecular oxygen and ozone. The photolysis step produces vibrationally excited O2(a 1Δg) that is rapidly converted to O2(X 3Σg-,υ=2,3) in a near-resonant adiabatic electronic energy-transfer process involving collisions with ground-state O2. The output of a tunable 193-nm ArF laser monitors the temporal evolution of the O2(X 3Σg-,υ=2,3) population via laser-induced fluorescence detected near 360 nm. The rate coefficients for the vibrational relaxation of O2(X 3Σg-,υ=2,3) in collision with O2 are 2.0-0.4+0.6×10-13 cm3 s-1 and (2.6±0.4)×10-13 cm3 s-1, respectively. These rate coefficients agree well with other experimental work but are significantly larger than those produced by various semiclassical theoretical calculations. [ABSTRACT FROM AUTHOR]