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

Abstract

We have previously determined an analytical ab initio six-dimensional potential energy surface for the HCl dimer, and in the present paper we use this potential, with the HCl bond lengths held fixed, in a full (four-dimensional) close-coupling calculation to determine the energies of the lowest 24 vibrational states. These vibrational states involve the intermolecular stretch ν 4, the trans-bend tunneling vibration ν 5, and the torsion ν 6. The highest of the 24 levels is the (ν 4ν 5ν 6)=(111) state, for which we calculate an energy of 200 cm −1 above the (000) state. As well as determining tunneling energies up to 5ν 5=183 cm −1, we determine ν 4=49 cm −1, 2ν 4=93 cm −1, 3ν 4=134 cm −1, 4ν 4=172 cm −1, ν 6=137 cm −1 and ν 4+ν 6=178 cm −1, together with tunneling energies in all these states. Making allowance for the HCl stretching zero-point energy we determine the dissociation energy D 0 as 390 cm −1 on this analytical surface. We determine that below 300 cm −1 there are 72 vibrational ( J=K=0) states, and below dissociation there are 162 vibrational ( J=K=0) states, for this potential surface.