Infrared Spectroscopy of Solvation in Small Zn⁺(H₂O)_<i>n</i> Complexes

Abstract

Singly charged zinc-water cations are produced in a pulsed supersonic expansion source using laser vaporization. Zn⁺(H₂O)_<i>n</i> (<i>n</i> = 1–4) complexes are mass selected and studied with infrared laser photodissociation spectroscopy, employing the method of argon tagging. Density functional theory (DFT) computations are used to obtain the structures and vibrational frequencies of these complexes and their isomers. Spectra in the O–H stretching region show sharp bands corresponding to the symmetric and asymmetric stretches, whose frequencies are lower than those in the isolated water molecule. Zn⁺(H₂O)_<i>n</i>Ar complexes with <i>n</i> = 1–3 have O–H stretches only in the higher frequency region, indicating direct coordination to the metal. The Zn⁺(H₂O)_2–4Ar complexes have multiple bands here, indicating the presence of multiple low energy isomers differing in the attachment position of argon. The Zn⁺(H₂O)₄Ar cluster uniquely exhibits a broad band in the hydrogen bonded stretch region, indicating the presence of a second sphere water molecule. The coordination of the Zn⁺(H₂O)_<i>n</i> complexes is therefore completed with three water molecules