Rotation-vibration interactions in (HF)(2). II. Rotation-vibration interactions in low-lying vibrational states

Results of a six-dimensional treatment of the rotation-vibration Hamiltonia n for (HF)(2) are presented. Energies of 40(J + 1) states for J less than o r equal to 4 are reported. These energies and the corresponding wave functi ons are used to analyze rotation-vibration interactions in (HF)(2). Over th e range of energies probed in this study, Coriolis couplings are found to b e relatively unimportant and for 94% of the states the wave functions and e nergies can be approximated by the solutions to a Hamiltonian in which the Coriolis coupling terms are neglected. Rotation-vibration interactions are investigated in greater detail for the ground state and for states with one and two quanta of excitation in the intermolecular stretching vibration up silon(4). Specifically, we study the K and n(4) dependencies of the tunneli ng splitting and the effective rotational constant that corresponds to rota tion about the intermolecular axis. Based on an analysis of the wave functi ons and the potential, we find that the observed trends can be attributed t o the fact that (HF)(2) behaves like a quasilinear molecule whose large amp litude bending motions lead to significant wave amplitude in linear configu rations, even in the vibrational ground state. (C) 1999 American Institute of Physics. [S0021-9606(99)02505- 2].