Concentration Raman study of intramolecular, intermolecular and Fermi resonance interactions in the OH stretching spectra of dilute solutions of HDO in D₂O using Fourier deconvolution technique

Abstract

The Raman OH stretching spectra of dilute solutions of H₂0 in D₂0, from 100 mole per cent to 10 mole per cent concentration, are studied. For the first time the decoupled OH spectra are treated by means of Fourier deconvolution technique. The resolved components in the isotropic and anisotropic spectra are analysed in terms of a model. The frequency and intensity behaviour of the components confirm the suggestion, that strong decoupling of all vibrations with dilution takes place. It is shown that intramolecular and Fermi resonance interactions are negligibly small under 20 mole per cent concentration. On the contrary, a significant intermolecular interaction, with a coupling constant equal to 42 cm⁻¹, is observed down to concentrations of 10 mole per cent. The latter is explained with the significant number of the HDO molecules, which have at least one HDO, or H₂0 neighbour at this concentration. In respect to intermolecular interaction a dilution of H₂0 in D₂0 down to 10 mole per cent concentration is equivalent to an increase of the temperature of liquid water to 90°C.

The frequency and intensity behaviour of the resolved components in the OH stretching spectra of dilute solutions of H₂0 in D₂0 can be understood by a model including intramolecular, intermolecular and Fermi resonance interactions. The results support the continuous model for water structure.