Theoretical study of the H+O3↔OH+O2↔O+HO2 system

Abstract

The key features of the H+O3 potential energy surface have been determined using ab initio quantum mechanical methods. The electronic wave function used is a multiconfiguration Hartree–Fock wave function which provides a qualitatively correct description of various reactive channels. It is found that the H+O3→HO+O2 reaction proceeds along a nonplanar pathway in which the H atom descends vertically to the plane containing the ozone molecule to form an HO3 intermediate which then undergoes fragmentation. No planar transition state for a direct O-atom abstraction could be located. The radical–radical O+HO2 reaction was found to have no energy barrier to formation of HO3 which was determined to subsequently decompose to HO+O2. The H-atom abstraction reaction O+HO2→OH+O2 was found to have a small activation energy. The dynamical implications of these findings are discussed. The results are consistent with the observed vibrational excitation of the OH product in the H+O3 reaction. The key features of the H+O3 potential energy surface are expected to be transferable to the X+O3 systems where X=Cl, OH, NO, and NH2.