An abinitio study of the singlet potential-energy surface for the reaction of NO3 with HO2

Abstract

The geometries of transition states and intermediates on the singlet potential-energy surfaces for the reactions NO₃ + HO₂ → OH + NO₂ + O₂ (1) and NO₃ + HO₂ → HNO₃ + O₂ (2) have been optimised in MP2 calculations with a 6-31G* basis set. Energetics have been derived from single point MP4/6-311G** calculations at the MP2/6-31G* geometries. Reaction (1) proceeds without an overall activation barrier other than the reaction endothermicity via three O₂NO···OOH rotational isomers. Reaction (2), which is exothermic, has no overall activation energy and involves hydrogen atom transfer in a NO₃···HO₂ complex which then yields products via a HNO₃···O₂ adduct. No evidence was found for a cyclic transition state.