Structure of the rayleigh line wing in highly viscous liquids

An experimental investigation has been performed of the Rayleigh line wing in glass-forming liquids in the temperature range from the melting point down to the glass-transition point. The so-called boson peak is found to contribute substantially to the Rayleigh line wing, and to determine the spectral profile of the high-energy part of the wing. A model is constructed which readily describes the spectral profile of the Rayleigh line wing in the above specified temperature range and its dependence on the chemical composition of the liquid. The model is based on the effect of the structural relaxation of the material on the process of light scattering from quasi-local vibrational excitations which give rise to the boson peak in the spectrum. An analogy is found between the boson peak and the side mode in Raman scattering near the phase transition in ferroelectrics. Within the framework of this model, the temperature dependence of the lifetime of the quasi-local modes has been derived from spectral variations in the Rayleigh line wing.