Raman Scattering Studies of Liquids and Glasses. I. Liquid and Supercooled Liquid Glycerol

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Abstract
The Raman scattering technique was used to investigate the low-lying intermolecular modes in liquid and vitreous glycerol from 65–353°K. It was found that while the integrated intensity of the polarized spectrum decreases with decreasing temperature, the depolarization ratio remains more or less constant (≅ 0.68). A large decrease in the scattering intensity occurs near the glass transition temperature. Considering that a normal mode of vibration is responsible for both the ir absorption and the Raman scattering, we have derived an expression which relates the absorption coefficient to the scattering power spectrum. The derivation was obtained with a similar technique used by Kubo and Tomita in their theory of magnetic resonance absorption and relaxation. The derived expression was used to calculate the ωχ″(ω) function (the absorption coefficient divided by the frequency ω) from the measured Raman spectrum. It was shown that the so obtained ωχ″(ω) curves can be fitted to within experimental uncertainty by a simple damped-harmonic oscillator function with a temperature-dependent damping constant. Except for a transition region at 260–280°K, the temperature behavior of the damping constant derived from the depolarized Raman spectrum can be described in terms of two activation energies. For the temperature region above 285°K, the activation energy corresponds to the hydrogen bond energy, and for the region below 280°K the activation energy is considered to arise from the anharmonicity in the hydrogen bond potential. The reason for the temperature insensitive Raman scattering cross section in vitreous materials is also given.