Microscopic hydration of the fluoride anion

A combined experimental and theoretical investigation of the step-wise hydr ation of the fluoride ion has been performed in order to characterize the d etails of its solvation at the microscopic level. The comparable anion-wate r and water-water interactions pose a challenging experimental/theoretical problem due to competing intermolecular forces in these small ionic cluster s. Vibrational spectra of size-selected F-(H2O)(3-5) in the O-H stretching region, coupled with high level ab initio calculations, have been used to a nalyze the spectra and assign the structures of these species. The interact ion between the fluoride anion and water plays the dominant role, resulting in internally solvated clusters. The microhydration of fluoride ion is thu s qualitatively different from the other halide ions. (C) 1999 American Ins titute of Physics. [S0021-9606(99)04501-8].