The Raman Spectra of Some Simple Molecules in Solution

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Abstract
The Raman spectra of HCl, HBr, SO2 and NH3 in various nonionizing solvents indicate vibrational frequencies in the solute molecules of lower value than in the corresponding gaseous states, the relative diminution amounting, in the hydrogen halides dissolved in some solvents, to 3 percent of the gas frequencies. The frequency shift is smaller for the two polyatomic molecules. There seems to be a definite relation between the relative frequency displacement and the dielectric constant of the solvent for the dissolved molecules of HCl and HBr. Δv/v increases with solvent dielectric constant to a limiting value of 0.03. A similar trend is shown in SO2 and for NH3 it seems that other factors than the dielectric constant of the solvent are effective in determining the frequency displacement. Concentrated solutions of HCl and HBr in several ionizing solvents have no features in their Raman spectra which can be identified as vibrations in HCl or HBr molecules. The bearing of these results on the dissociation process of HCl in solvents is discussed.

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