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

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.