Spin–orbit corrected potential energy surface features for the I (2P3/2) + H2O → HI + OH forward and reverse reactions

Abstract

Using the CCSD(T) method with relativistic correlation consistent basis sets up to cc-pVQZ-PP, the entrance complex, transition state, and exit complex for the endothermic reaction I + H₂O → HI + OH have been studied. The vibrational frequencies and the zero-point vibrational energies of the five stationary points for the title reaction are reported and compared with the limited available experimental results. Opposite to the valence isoelectronic F + H₂O system, but similar to the Cl + H₂O and Br + H₂O reactions, the I + H₂O reaction is endothermic, in this case by 46 kcal mol⁻¹. After the zero-point vibrational energy and spin–orbit coupling corrections, the endothermic reaction energy is predicted to be 48 kcal mol⁻¹, which agrees well with experimental values. For the reverse reaction HI + OH → I + H₂O the transition state lies below the reactants, consistent with the experimental negative temperature dependence for the rate constants.