VIBRATIONAL DYNAMICS OF H5+ - ABINITIO CALCULATION OF THE LOW-LYING VIBRATIONAL-STATES

The full nine-dimensional vibrational problem of the H+5 complex is reduced to a five-dimensional subproblem in which all molecular rearrangements among the four low-lying stationary points on the total potential energy hypersurface of the ion can be described. Following the general idea of the Hougen-Bunker-Johns approach and using appropriate vibrational coordinates, a nonrigid reference configuration is defined which covers all motions on the low-lying part of the potential surface and which facilitates the derivation of a suitable model Hamiltonian. The relevant sections of the potential energy and electric dipole moment surfaces are determined ab initio at the configuration interaction level of theory and analytic potential energy and dipole moment functions are obtained by fitting to the ab initio data. These functions are used to calculate vibrational energy levels and dipole transition moments within the limitations of an extended adiabatic approximation. The calculations are in good agreement with the experimental photo-dissociation spectrum. Predicted energies can therefore be expected to be reliable. © 1993 Academic Press, Inc.