The Symmetric Exchange Reaction OH + H2O → H2O + OH: Convergent Quantum Mechanical Predictions

The symmetric hydrogen exchange reaction OH + H2O -> H2O + OH has been studied using the "gold standard" CCSD(T) method with the correlation-consistent basis sets up to aug-cc-pVSZ. The CCSDT and CCSDT(Q) methods were used for the final energic predictions. Two entrance complexes and two transition states on the H3O2 potential surface were located. The vibrational frequencies and the zero-point vibrational energies of these stationary points for the reaction are reported. The entrance complex H2O center dot center dot center dot HO is predicted to lie 3.7 kcal mol(-1) below the separated reactants, whereas the second complex HOH center dot center dot center dot OH lies only 2.1 kcal mol(-1) below the separated reactants. The classical barrier height for the title reaction is predicted to be 8.4 kcal mol(-1), and the transition state between the two complexes is only slightly higher than the second complex. We estimate a reliability of +/- 0.2 kcal mol(-1) for these predictions. The capabilities of different density functional theory methods is also tested for this reaction.