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

Abstract

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 C₂ and C₁ 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.