Vibrational dynamics of hydrogen bonds: The system OH −·H 2O

Abstract

A complete vibration-(internal rotation) Hamiltonian for the hydrogen bonded ionic system OH −·H 2O is developed following the general idea of the Hougen-Bunker-Johns approach [J. T. Hougen, P. R. Bunker, and W. W. C. Johns, J. Mol. Spectrosc. 34, 136–172 (1970)]. In this formulation the large-amplitude antisymmetric O⋯H⋯O stretching mode (hydrogen tunneling motion) and the internal rotation are removed from the vibrational problem by defining a molecular reference configuration as a function of the antisymmetric stretching and the internal rotation coordinates. Ab initio configuration interaction calculations are performed to investigate the molecular structure of the H 3O 2 − ion and to determine certain sections of the multi-dimensional potential energy hypersurface. An analytic potential function is obtained by fitting to the ab initio energy points and this function is used to calculate symmetric and antisymmetric O⋯H⋯O stretching and internal rotation energy levels within the limitations of an extended adiabatic approximation. In addition, using a presently calculated electric dipole moment function and the approximate vibrational eigenfunctions, dipole transition moments are evaluated for the symmetric and antisymmetric O⋯H⋯O stretching states.