HR: 1340h
AN: SA53B-1172    [Abstracts]
TI: Rate Coefficients for O-Atom Three-Body Recombination in N₂ at Temperatures in the Range 170--320 K
AU: * Pejakovic, D A
EM: dusan.pejakovic@sri.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025 United States
AU: Kalogerakis, K S
EM: ksk@sri.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025 United States
AU: Copeland, R A
EM: richard.copeland@sri.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025 United States
AU: Huestis, D L
EM: david.huestis@sri.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025 United States
AU: Robertson, R M
EM: robert.robertson@sri.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025 United States
AU: Smith, G P
EM: gregory.smith@sri.com
AF: Molecular Physics Laboratory, SRI International, 333 Ravenswood Ave., Menlo Park, CA 94025 United States
AB: 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).
DE: 0310 Airglow and aurora
DE: 0343 Planetary atmospheres (5210, 5405, 5704)
DE: 0355 Thermosphere: composition and chemistry
DE: 5405 Atmospheres (0343, 1060)
DE: 5408 Aurorae and airglow
SC: SPA-Aeronomy [SA]
MN: Fall Meeting 2005