An infrared study of the competition between hydrogen-bond networking and ionic solvation: Halide-dependent distortions of the water trimer in the X−⋅(H2O)3, (X=Cl, Br, I) systems

Vibrational spectra of the water trimers solvating the halide anions (Cl−, Br−, I−) have been acquired in the OH stretching region by predissociation spectroscopy of the X−⋅(H2O)3⋅Ar3 complexes. These “wet” ions display two groups of bands assigned to normal modes of the (C3) pyramidal structure. We interpret the evolution of the spectra down the halogens in the context of the rings closing up toward the structure of the bare (H2O)3 neutral. This trend is discussed in terms of the disruptive effect of the ionic H bonds on the water network.