Physics
Scientific paper
Dec 2005
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005agufmsa53b1172p&link_type=abstract
American Geophysical Union, Fall Meeting 2005, abstract #SA53B-1172
Physics
0310 Airglow And Aurora, 0343 Planetary Atmospheres (5210, 5405, 5704), 0355 Thermosphere: Composition And Chemistry, 5405 Atmospheres (0343, 1060), 5408 Aurorae And Airglow
Scientific paper
Three-body recombination of O-atoms, O + O + M → O_2* + M is one of the most important reactions in the upper atmospheres of Earth, Venus, and Mars. It is the only source for O2 nightglow, and the resulting emissions of electronically excited O2 are key tracers for photochemical and wave activity near the mesopause. Thus, knowledge of the rate coefficient for recombination of atomic oxygen is essential for modeling atmospheric composition. However, there exists a large discrepancy in the published estimates for this rate coefficient. For M = N2, the room temperature coefficient varies between about 3 × 10-33 cm6s-1, which is the value used in the combustion science community, and 5 × 10-33 cm6s-1, a value adopted in the atmospheric modeling community. We report measurements of the rate coefficient for O-atom recombination with N2 as the third body by two different experimental approaches. In the first experiment, we employ the pulsed output of a F2 laser at 157 nm to achieve high levels of photodissociation of molecular oxygen. In a high-pressure (760 Torr) background of N2 the produced O-atoms recombine in a time scale of several milliseconds. Oxygen atom population is monitored by observing fluorescence at 845 nm, induced by the output of a second laser near 226 nm. In the second experiment, the focused output of a KrF excimer laser at 248 nm is used to achieve complete photodissociation of measured amounts of ozone (0.2--0.9 Torr) in a background of ~500 Torr of N2, producing known initial concentrations of O-atoms. Their population decay is monitored by laser-induced fluorescence excited by the 226 nm radiation from a delayed frequency-doubled OPO system. The reaction cell can be cooled by dry ice or liquid nitrogen baths. The preliminary results of the O2 photolysis experiments give a room-temperature value for the rate coefficient of about 2.8 × 10-33 cm6s-1. The ozone photolysis experiments at 316 K (including effects of laser and kinetic heating of the gas) give a preliminary value of ~2.5 × 10-33 cm6s-1, in a good agreement with the O2 photolysis result. Preliminary results show faster recombination at lower temperatures: k(260 K) ~ 4.5 × 10-33 cm6s-1, and k(170 K) ~ 20 × 10-33 cm6s-1. The temperature dependence of k is in a good agreement with the recommendation of Baulch et al. [1], which has been adopted by the combustion modeling community. The O2 photolysis experiments were supported by the NASA Geospace Sciences Program under grant NAG5-12992. The F2 laser was purchased under grant ATM-0216583 from the NSF Major Research Instrumentation Program. The ozone photolysis experiments were supported by the NSF Grant ATM-0233523. [1] D. L. Baulch, D. D. Drysdale, J. Duxbury, and S. J. Grant, Evaluated Kinetic Data for High Temperature Reactions Vol. 3 (Butterworths, London, 1976).
Copeland Richard A.
Huestis David L.
Kalogerakis Konstantinos S.
Pejaković Dušan A.
Robertson Rae M.
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