Hardness and Polarizability Profiles for Intramolecular Proton Transfer in Water Dimer Radical Cation

Abstract

In view of the recently reported discrepancies in the prediction of minimum energy structure (proton-transferred vs hemibonded) for the water dimer on ionization, we have performed complete active-space self-consistent field calculations followed by total energy evaluation using multiconfigurational quasi-degenerate perturbation theory to obtain very accurate relative energies of different structures and predicted the proton-transferred structure to be the most stable ones. The variations of hardness, polarizability, chemical potential, and energy for the proton-transfer process in this weakly interacting system (ionized water dimer species) are investigated through calculations using Hartree−Fock theory. It is observed that the transition state corresponding to the proton-transfer process is associated with maximum polarizability at different O−O distances for the water dimer cation, although the hardness minimum does not exactly correspond to the transition state. However, the hardness profiles scaled suitably with chemical potential are found to have minima at the transition states.