Ab initio study of the fluoride-ammonia clusters:: F--(NH3)n, n=1-3

Fluoride-ammonia clusters have been investigated via ab initio calculations at the MP2 level of theory, using Dunning's augmented correlation consistent basis sets. Optimised geometries, vibrational frequencies, and enthalpy changes for the ligand association reactions are presented for clusters with one, two, and three ammonias bound to a fluoride anion. The minimum energy structure for the F--NH3 complex, with C-s symmetry, displays a single hydrogen bond between the ammonia and fluoride anion. For the F--(NH3)(2) cluster, two closely lying minima with C-2 and C-1 symmetry were predicted. For F--(NH3)(3), four minima were located, with the minimum energy structure having C-3h symmetry. Calculated infrared spectra for the minima are presented to aid in assigning spectra from future experimental studies.