Theoretical Investigations of OH/HO2 Chemistry in the Middle Atmosphere

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In this project, a number of outstanding issues related to the OH/HO2 chemistry in the upper stratosphere and lower mesophere will be investigated. Current understanding of the HOx chemistry in this region of the atmosphere is complicated because standard photochemical models or any modifications of them are unable to consistently account for the odd hydrogen abundance above and below the stratopause. This is due, in part, to uncertainties in the rate coefficients of the reactions that determine the OH/HO2 ratio in the stratosphere and mesosphere, and or due to the lack of full understanding of the HOx chemistry. The key reactions that partition the OH/HO2 abundance in the stratosphere and mesosphere whose rate coefficients have come under increased scrutiny in recent years will be investigated. Rate coefficients for the reaction between vibrationally excited H2 and O(3P) atoms which has recently been proposed as a novel source of OH in the mesosphere will be evaluated using explicit quantum mechanical calculations. Nonthermal energy distribution functions of O(3P) atoms in the mesosphere and their contributions to OH formation in O(3P)+H2 collisions will be determined. Further, quenching of vibrationally excited OH produced by the reaction between hydrogen atoms and ozone will be investigated.