Vibrational Relaxation of OH(υ = 7) with O, O2, and H

Details Vibrational Relaxation of OH(υ = 7) with O, O2, and H Vibrational Relaxation of OH(υ = 7) with O, O2, and H

Dec 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufmsa43a1752t&link_type=abstract

American Geophysical Union, Fall Meeting 2010, abstract #SA43A-1752

Physics

[0317] Atmospheric Composition And Structure / Chemical Kinetic And Photochemical Properties, [0340] Atmospheric Composition And Structure / Middle Atmosphere: Composition And Chemistry, [0394] Atmospheric Composition And Structure / Instruments And Techniques

Scientific paper

The hydroxyl radical is a key species in the energy budget of the terrestrial atmospheres. In the Earth's upper atmosphere, 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 and internal energy via collisions with ambient gases, particularly O, O2, and N2. Accurate rates for the deactivation of the OH high υ states at mesospheric temperatures are essential in the modeling of both the atmospheric OH emission and the heating efficiency of the H + O3 reaction. In spite of the central importance of OH energy transfer for understanding the energy balance in the atmosphere, no data exists for the vibrational relaxation of OH(υ = 5 - 8) by O atoms and for the temperature dependence of these processes by O2. Laboratory experiments are underway to study the relaxation of OH(υ = 7) with important atmospheric colliders. To make these measurements, we developed a novel three-laser approach using the following steps: 1. Generation of OH(υ ≤ 4) by the O(1D) + H2 reaction following ozone photolysis at 248 nm by an excimer laser in a mixture containing nitrogen and hydrogen, 2. Infrared overtone excitation of the OH(υ = 4) radicals to υ = 7 at 1.21 μm using the pulsed output from an Optical Parametric Oscillator system, 3. Probing the temporal evolution of the OH(υ = 7) population by laser induced fluorescence using the B-X (0,7) band at 213 nm. The experimental set-up will be described and initial measurements on OH(υ = 7) relaxation by O-atoms, O2, and H-atoms will be presented. Preliminary measurements at room temperature find a rate constant for O-atoms on the order of 2-3 × 10-10 cm3 s-1. We will discuss the atmospheric implications of these results based on the most current modeling calculations. This work was supported by the NASA Geospace Science Program under grant NNX08AM47G.

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