Infrared Spectra of HDO in Water and Ionic Solutions

Abstract

The infrared spectra of HDO in water and saturated metal halide solutions were investigated to study the interactions between ions and solvent molecules and the nature of hydrogen bonding in aqueous systems. The fundamental and overtone bands of the OH and OD stretching vibrations are shifted to lower frequencies and the bending vibration shifts to higher frequencies as one passes from the gaseous to the liquid state. Similar shifts occur for the metal halide solutions, the magnitudes of which are sensitive to the anion species but relatively independent of the cations. The frequency shifts for ionic solutions increase in the order I-, Cl-, F-, with the shift in ion-free water about equal to that for Cl-. The data are analyzed in terms of four probable nearest-neighbor configurations in these solutions. The vibrational anharmonicity of the OH stretching vibration in solution is nearly independent of the frequency shift and only slightly larger than the gas value. The dependence of frequency shift on the shortening of hydrogen bonds (volume contraction) and H-bond energy were studied and gave qualitative agreement with other systems previously investigated.