AN ABINITIO CLOSE-COUPLING CALCULATION OF THE LOWER VIBRATIONAL ENERGIES OF THE HCL DIMER

We have previously determined an analytical ab initio six-dimensional Potential energy surface for the HCI dimer, and in the present paper we use this potential, with the HCI 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 nu-4, the trans-bend tunneling vibration nu-5, and the torsion nu-6. The highest of the 24 levels is the (nu-4-nu-5-nu-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 5-nu-5 = 183 cm-1, we determine nu-4 = 49 cm-1, 2-nu-4 = 93 cm-2, 3-nu-4 = 134 cm-1, 4-nu-4 = 172 cm-1, nu-6 = 137 cm-1 and nu-4 + nu-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 D0 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 1 62 vibrational (J = K = 0) states, for this potential surface.