Vibrational Relaxation of OH(υ = 1, 2) by O, O2, and CO2

Details Vibrational Relaxation of OH(υ = 1, 2) by O, O2, and CO2 Vibrational Relaxation of OH(υ = 1, 2) by O, O2, and CO2

Dec 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agufmsa31a1600r&link_type=abstract

American Geophysical Union, Fall Meeting 2008, abstract #SA31A-1600

Astronomy and Astrophysics

Astrophysics

0300 Atmospheric Composition And Structure, 0310 Airglow And Aurora, 0317 Chemical Kinetic And Photochemical Properties, 0340 Middle Atmosphere: Composition And Chemistry, 0343 Planetary Atmospheres (5210, 5405, 5704)

Scientific paper

The hydroxyl radical is a key reactant in the energy budget of the terrestrial atmospheres. In the Earth's upper atmosphere the vibrationally excited OH radicals (υ ≤ 9) are formed by the H + O3 reaction. The non-thermal vibrational energy is either emitted as an infrared or visible photon, or converted into translational or internal energy via collisions with ambient gases, particularly O, N2, and O2. Recently OH(υ = 2 and 1) emission has been observed by Piccioni et al. in the atmosphere of Venus,1 and the magnitude of the emission is controlled by the competition between radiative decay and vibrational relaxation by the most abundant constituent, CO2. Considerable disagreement exists among the OH(υ) removal rate constants measured by different laboratories for OH(υ = 2 and 1), and data at lower temperatures of atmospheric relevance are lacking, especially for υ = 2. Given the importance of these rate constants for understanding of behavior in atmospheric OH on both Earth and Venus, we applied a two-laser approach to determine the rate constants for vibrational relaxation of OH(υ = 1, 2) by O-atoms, O2, and CO2. The product pathways for relaxation of OH(υ = 2) were also examined. In the experiments, ozone is almost completely photolysed at 248 nm and most of the resulting O(1D) atoms are quenched to O(3P) by collisions with N2 and CO2. A small fraction of O(1D) reacts with H2O, forming OH with up to two vibrational quanta. The temporal evolutions of OH(υ = 1, 2) are measured using laser induced fluorescence; and kinetic simulations are used to extract the rate constants and the product pathways. Experiments were performed at temperatures between 240 and 295 K. The experimental results and their relevance for current atmospheric modeling calculations will be discussed. This work was supported by the NASA Geospace Science and Planetary Atmospheres Programs. The participation of H. Timmers was supported by an NSF Research Experiences for Undergraduates (REU) Program. Reference List (1.) Piccioni, G.; Drossart, P.; Zasova, L.; Migliorini, A.; Gerard, J.-C.; Mills, F. P.; Shakun, A.; Garcia Munoz, A.; Ignatiev, N.; Grassi, D.; Cottini, V.; Taylor, F. W.; Erard, S.; VIRTIS-Venus Express Technical Team Astronomy and Astrophysics 2008, 483, L29-L33.

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