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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]

Abstract: Observations of CO emissions in the visible and near-infrared (NIR) have been rare for comets, and no measurements from orbiters are currently available in the visible for the dayglows of Mars or Venus. Analysis of the ultraviolet CO(a–X) Cameron bands from Mars Express dayglow observations supports the conclusion that these bands have very high rotational temperatures, some thousands of kelvins. The most plausible source for the CO rotational excitation is its generation by CO2 photodissociation. Recent laboratory measurements investigating the photodissociation of CO2 in the extreme ultraviolet (EUV) reveal strong emissions in the visible and NIR region by the triplet CO(a′, d, e) states, which we take to be a primary source for the UV CO(a–X) Cameron bands. Thus, detection of visible emissions from the triplet CO states in planetary dayglows and comets provides an upper limit to the CO2 density. The presence of CO high rotational excitation along with the intense visible and NIR band emissions should be considered as a practical way by which planetary dayglow and cometary spectra provide information on the presence of CO2. Finally, we report on existing observations of cometary atmospheres and estimate the altitude for the emitting layer of the CO triplet states in Mars and Venus. [Copyright &y& Elsevier]