Quantum Mechanical Investigation of the Energetics of Proton Transfer along Hydrogen Bonds

Proton transfer along hydrogen bonds is examined using medium and large basis set ab initio quantum mechanical calculations. Post Hartree−Fock analysis is applied to the results. The model systems for these studies are clusters containing three or four water molecules. The proton in the hydrogen bond chosen for study belongs to a molecule which is involved in at least two hydrogen bonds and serves as both a donor and an acceptor in those bonds. The transfer of the proton along the bond between adjacent oxygen atoms thus creates an ion pair in the model system. For comparison similar calculations were undertaken in which the proton in question was associated with a H3O+ ion. These latter calculations model the energy of proton migration without the initial formation of an ion pair.