Raman studies of the depolarized rayleigh wing of liquids and solutions

Abstract

Raman spectra of the depolarized Rayleigh wing region of a number of liquids and solutions have been recorded in digital form employing signal averaging techniques. The symraetrized I (γ) spectra have been recast in an I (γ).γ2 form which corrects for thermal population effects and transforms the spectra into a form directly comparable to far infrared absorption. This procedure suppresses the Rayleigh line and emphasizes the weak low frequency “peaks” which have been reported by numerous workers.Relative intensity studies of C6H6-CCl4 mixtures indicate that the low frequency benzene peak (78 cm−) is monomolecular and appears to originate in hindered librational oscillations. Temperature variation studies revealed that the peak maximum decreased with increased temperature.Studies of water and aqueous fluoride and perchlorate solutions suggest that the peak at 191 cm−1 has its origin in the hydrogen bonded water structure. Temperature and isotopic substitution (D2O,H218O) measurements support this conclusion. Anisotropic ions such as NO−3 and CN− superimpose an intense librational peak on the water spectrum.