VIBRATIONAL DYNAMICS OF THE BIFLUORIDE ION .1. CONSTRUCTION OF A MODEL POTENTIAL SURFACE

Construction of an extended model potential surface for the bifluoride ion FHF-] is described, based on ab initio calculations for the free ion at the CID (configuration interaction, double replacement) level with a Huzinaga-Dunning double-zeta basis set. 710 data points were generated, for displacements in the three noncyclic vibrational coordinates exploring the potential surface to a height at least 30 000 cm-1 above its minimum, and giving a realistic account of the dissociation into HF + F-. Analogous calculations were made for HF and F-using the same basis. The predicted hydrogen bond energy (De) is 48.13 kcal/mol, with equilibrium F-F separation Re = 4.2905 a.u., in good agreement with other recent calculations. A model potential has been constructed, based on a superposition of Morse potentials associated with each H-F distance plus a fairly structureless correction function expressible as a 36-term least-squares polynomial in the prolate spheroidal coordinates used to describe vibrational displacements. The resulting model surface fits all 710 ab initio data points with an r.m.s. deviation of 65.6 cm-1, and points less than 15 000 cm-1 above the minimum with a deviation of 26.3 cm-1. This surface provides the basis for a series of vibrational dynamics studies on the FHF - system being done in this laboratory. © 1990 American Institute of Physics.