Potential energy surface and energy levels of (HF)₂ and its D isotopomers

Abstract

A new six-dimensional analytical potential energy surface for the hydrogen bonded dimer (HF)₂ is presented. It is based on the ab initio study by Kofranek et al., and uses 1070 points with energies up to 500 kJ mol^-1 as well as recent correlated dispersion coefficients from a perturbation treatment by Rijks and Wormer, and the experimental Morse parameters for the HF monomer. The fit to the ab initio points contains 29 free and several constrained parameters and has a weighted standard deviation of 29·5 cm^-1. A brief description of some properties of the new surface is given. Preliminary results of a diffusion quantum Monte Carlo (QMC) study for vibrational energy levels on the new surface as well as on a surface published by Bunker et al. are given. An interesting anharmonic isotope effect in the v ₆ fundamental is discussed and explained.