AN AB-INITIO CALCULATION OF THE LOW-FREQUENCY VIBRATIONAL ENERGIES OF THE HCL DIMER

With the two HCl bond lengths held fixed at the monomer vibrational ground state value (r0 = 1.284 Angstrom) we have calculated a four-dimensional ab initio potential energy surface of the HCl dimer at 400 nuclear geometries covering energies within 1000 cm-1 of the minimum. The electronic basis set is larger than that used earlier (A. Karpfen, P.R. Bunker, and P. Jensen, Chem. Phys. 149, 299-309, (1991) to obtain a surface on which dynamical calculations were carried out. We calculate the lowest 33 vibrational energies (up to 230 cm-1) involving the four large-amplitude modes on this surface using an adiabatic separation of the van der Waals stretching coordinate from the three large-amplitude bending coordinates (following S.C. Althorpe, D.C. Clary, and P. R. Bunker, Chem, Phys. Lett. 187, 345-353, (1991), and we contrast the results with those obtained using electrostatic potentials. (C) 1994 Academic Press, Inc.