Effects of confinement on small water clusters structure and proton transport.

Analyses of the structure of two to four water molecule clusters confined between two benzene and between two naphthalene molecules have been performed using ab initio methods. The water clusters tend to maximize the number of hydrogen bonds via formation of a cyclic network. The oxygen atoms locate approximately in the middle of the confined geometry, and the dipole vectors arrange either parallel or pointing to the surfaces. Energy barriers for proton transfer calculated for H3O+-(H2O) complexes in the same confined geometries suggest that there is a specific range of confinement that helps to lower the energy barriers of the proton transfer. When the walls are too close to each other, at a separation of 4 A, the energy barriers are extremely high. Confinement does not lower the barrier energies of proton transfer when the H3O+-(H2O) complexes are located further from each of the surfaces by more than approximately 8 A.