Temperature Dependence of the Vibrational Relaxation of OH(υ = 1 and 2) by CO2

Details Temperature Dependence of the Vibrational Relaxation of OH(υ = 1 and 2) by CO2 Temperature Dependence of the Vibrational Relaxation of OH(υ = 1 and 2) by CO2

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p33a1270r&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P33A-1270

Astronomy and Astrophysics

Astrophysics

[0317] Atmospheric Composition And Structure / Chemical Kinetic And Photochemical Properties, [0343] Atmospheric Composition And Structure / Planetary Atmospheres, [3359] Atmospheric Processes / Radiative Processes, [6295] Planetary Sciences: Solar System Objects / Venus

Scientific paper

The hydroxyl radical is a key species in the energy budget of the terrestrial atmospheres. The main source of OH, the reaction between H-atoms and ozone, produces OH radicals with up to nine quanta of vibrational energy. The energy of OH(υ ≥ 1) is either transferred to an ambient species via collisional relaxation or is emitted as an infrared or visible photon. The relative intensities of the OH emission bands depend strongly on the planet’s atmospheric composition and temperature. Recently, the Venus Express mission detected IR emissions corresponding to the (1-0) and (2-0) bands of ground state of OH at an altitude of around 95 km.1 In the atmosphere of Venus, the dynamics of the OH vibrational populations are controlled mainly by collisions with CO2 molecules. Therefore, the key input parameters to the OH kinetic models are the vibrational quenching rate constants by CO2 and the fractions of single- and multi-quantum relaxation steps at temperatures relevant to the altitudes where these emissions occur. Currently, there are no available data for the vibrational relaxation of OH(υ = 1, 2) by CO2 below 300 K. Given the importance of these rate constants for the understanding the OH radical emissions on Venus, we applied a two-laser approach to extract the rate constants for the vibrational relaxation of OH(υ = 1, 2) by CO2. The pathways for relaxation of OH((υ = 2) were also examined. Ozone is photolysed at 248 nm and a small fraction of resulting O(1D) reacts with H2O and form OH(υ ≤ 2). The remaining O(1D) atoms are quenched to O(3P) by collisions with N2 and CO2. The OH(υ = 1, 2) populations are monitored by using LIF. The transients corresponding to the decay of OH(υ) and kinetic simulations are used to extract the rate constants and the relaxation pathways. Experiments were performed at temperatures between 210 - 295 K. The results indicate that the rate constant increases as the temperature decreases. This temperature dependence needs to be included for quantitative models of the Venus emission. This work was supported by the NASA Planetary Atmospheres Program. The participation of A. Marakov and H. Timmers was supported by the 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 & Astrophysics 2008, 483, L29-L33.

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