Low-frequency Raman investigation of the liquid-glass transition in glycerol

The low-frequency response of glycerol has been studied by polarized Raman scattering. The ‘‘boson peak’’ always appear far above ${\mathit{T}}_{\mathit{g}}$=193 K, whereas the depolarization ratio is nearly constant between 5 ${\mathrm{cm}}^{\mathrm{-}1}$ and 200 ${\mathrm{cm}}^{\mathrm{-}1}$ at temperatures from 333 to 90 K. In the analysis of the boson peak, comparisons are made between experimental results and calculations based on the two types of structural correlation function. The typical behavior of line shape and depolarization ratio of the spectra is fitted with an exponential structural correlation function. The structural correlation length is estimated to be about 14 Å. It may be associated with the mean size of the clusters of hydrogen-bonded molecules.