Ab initio quantum chemistry study of the gas-phase reaction of CIO with HO2

Abstract

The reaction of CIO with HO2 has been studied using ab initio molecular orbital theory with electron correlation being taken into account by Møller–Plesset (MP) perturbation theory. Saddle-point geometries, energies and harmonic vibrational wavenumbers have been calculated at the MP2/6-31G** level and barrier heights at the MP4/6-311G** level. The study shows that the products and mechanism depend on which potential-energy surface the reaction occurs. If the reaction proceeds along the triplet reaction surface, ground-state HOCl (1A′) and ground-state O2(3Σg–) are formed. If the reaction takes place on the singlet reaction surface the same products are formed, but in this case the molecular oxygen is formed in a singlet state. The CIO + HO2 reaction proceeds via a multi-step reaction mechanism on the singlet surface and via a direct hydrogen-abstraction mechanism on the triplet surface.