Raman light scattering studies of the depolarized Rayleigh wing of liquids and solutions

Abstract

Raman spectra of the depolarized Rayleigh wing region (10–300 cm−1) of a number of liquids and solutions have been recorded in digital form employing signal averaging techniques. The symmetrized I(?) spectra have been recast in an I(?)?2 format which transforms the Rayleigh spectra into forms directly comparable to far-infrared absorption. The major advantage of this procedure is that it suppresses the exciting line and emphasizes the weak low frequency peaks. As a result, the basic characteristics of the ’’peaks’’ previously reported are confirmed with improved precision. Peaks have also been observed for the first time for cyclohexane, acetone, and n-tetradecane. These peaks appear to reflect the short-time behavior of the external coordinates of individual anisotropic molecules and should not be confused with fundamental vibrational or negative combination modes. For liquid benzene, studies of the effects of concentration change (in carbon tetrachloride), temperature change, and isotopic substitution clearly showed that the peak originates in hindered librational oscillations of individual benzene molecules. Temperature variation studies revealed that the peak maximum decreased with increased temperature, which was exactly the opposite of that reported from infrared studies.