Morphing of ab initio-based interaction potentials to spectroscopic accuracy:: Application to Cl-(H2O)

We present anharmonic vibrational calculations for the Cl-(H2O) cluster and their convergence with the n-mode representation of the interaction potential. Extension of this representation up to 4-mode couplings produces results that appear to be converged to within 10 cm(-1) or less relative to the exact 6-mode representation for this system. This methodology, in conjunction with the "morphing" technique, which is based on the scaling of the internal coordinates, provides an effective means of fitting intermolecular potentials to measured vibrational spectra. Application of this approach to the chloride-water interaction produces a revision of a previously developed empirical interaction potential which now reproduces the measured fundamental and first overtone frequencies to within an average absolute deviation of 1.75 cm(-1) in the 4-mode coupling representation.