Quantum Calculation of Atmospherically Important Radical-Molecules Complexes
Date
2013-08-01
Authors
Voglozin, David
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Abstract
Atmospheric free radicals play an important role in the chemistry of the Earth atmosphere. Yet, there is limited knowledge of the physical and chemical properties of complexes such radicals can form with other components of the atmosphere. The topical and controversial issue of "global warming" on the one hand, and the health problems posed by the presence of hundreds of man-made materials in the atmosphere on the other hand, provide motivation for researchers to investigate free radicals atmospheric processes and energetics. This work strengthens and extends our knowledge of radical complexes, starting with the most important radical of the troposphere, the hydroxyl radical (OH), and then, extending to the mercapto (or sulfhydryl) radical (SH).The goal was to determine optimal geometries of OH- and SH-containing complexes as well as accurate vibrational frequencies of the stretch of these radicals in the complexes, by using high-level ab initio quantum mechanical calculations. Our computational method is fully applicable to all complexes of OH and SH, in which these radicals act, either as hydrogen donor, or as hydrogen acceptor. In order to obtain highly accurate vibrational frequencies, the effects of anharmonicity were directly accounted for by fitting Morse potentials to the theoretically calculated potential energy curves for vibrations of interest. The primary species investigated herein are H2O.HO, (H2O)2.HO, N2.HO, O2.HO, CO2.HO, H2O.HS, and H2S.HS. The work I have successfully performed will directly support future laboratory experiments to isolate and identify such complexes, so their detection in the atmosphere may become possible, for modeling of atmospheric processes.
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Keywords
Physical chemistry, Atmospheric chemistry, Anharmonic frequency, HCAO local mode model, Morse potential, OH and SH complexes, Perturbative triple methods, Potential energy surface