Potential Energy Surface and the Rates of the Reaction OH + OH → H2O + O

Abstract

The intrinsic paths of the disproportionation reactions OH + OH → H2O + O(3P) and OH + OH → H2O +O(1D) have been calculated by the 4-31G UHF SCF procedure, and MRD-CI calculations have been carried out at several points along the paths. Both reactions are found to proceed through the initial formation of hydrogen-bonded complex OH·OH followed by the attainment of coplanar transition states. The net activation barrier heights obtained for the triplet and singlet channels of the reaction are ca. 3 and 35 kcal/mol, respectively. On the basis of the transition state characteristics deduced from the ab initio computations, the bimolecular rate constants have been evaluated from the conventional transition state theory. The results obtained in the temperature range 300-2000 K are found to be in good agreement with the experimental data which apparently exhibit a strong non-Arrhenius behavior.