An ab initio close-coupling calculation of the lower vibrational energies of the HF dimer

Abstract

We have previously determined an analytical ab initio six-dimensional potential energy surface for the HF dimer, and in the present paper we use this potential with the HF bond lengths held fixed in a full (four-dimensional) close-coupling calculation to determine the energies of 18 low-lying vibrational states. These vibrational states involve the intermolecular stretch ν 4, the transbend tunneling vibration ν 5, and the torsion ν 6. As well as determining tunneling energies up to 5ν 5 = 341 cm −1, we determine ν 4 = 122 cm −1, 2ν 4 = 236 cm −1, 3ν 4 = 342 cm −1, ν 6 = 378 cm −1 and ν 4 + ν 6 = 491 cm −1,together with the tunneling splittings in all these states. A strong perturbation between 4ν 5 and ν 4 + 2ν 5 is found for this ab initio potential. Making allowance for the HF stretching zero-point energy, we determine the dissociation energy D 0 as 1012 cm −1. We hope that these energies provide benchmark vibrational energies for this ab initio surface for the purpose of testing the accuracy of other more-approximate calculations.We also hope that our results will be of help in assigning experimental spectra and in identifying perturbations.