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G. Lendvay
Ab Initio Studies of Complexes of HO2 Radicals with NH3, H2O, and HF
A comparative ab initio study was performed to determine the properties of the complexes of HO2 with three nucleophile additives. At the QCISD(T)/6-311++G(2d,2p)//MP2/6-311++G(2d,2p) level including CP correction binding energies D0 of 7.94 kcal mol-1, 5.12 kcal mol-1, and 3.58 kcal mol-1 was obtained for HO2·NH3, HO2·H2O, and HO2·HF, respectively. The vibrational frequencies of the HO2 fragment are shifted by several hundred wavenumbers due to the influence of NH3, together with a two order of magnitude increase of the IR intensity, making the complex a good candidate for experimental detection. Lower shift is caused by H2O and negligible shift by HF. The additive and the radical in the HO2·NH3 as well as in the HO2·H2O complexes are bound together by a hydrogen bond between the nucleophile atom of NH3 and H2O and the H atom of HO2. In HO2·HF the H atom of HF is oriented towards the radical center of HO2 and an additional hydrogen bond is formed between F and the H of HO2. The self-reaction of the HO2 radicals is significantly modified by the presence of the additives. An important factor may be the formation of the complexes studied in this work. While the stability of the complex itself does not explain the complicated influence of the additive on the kinetics of the H2O+HO2 reaction, the study of the properties of the complexes allows one to derive some conclusions on the mechanism of the reaction.
Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag
Print ISSN: 0942-9352
Volume: 215, 03/2001
Pages: 377