Temperature variation of polarized and depolarized scattered light spectra from liquid benzene derivatives

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Abstract
The spectra of polarized and depolarized light scattered from liquid chlorobenzene, bromobenzene, nitrobenzene, aniline, benzonitrile and benzoyl chloride have been measured over a temperature range from the melting point to 160°c or the boiling point. The sources were He-Ne lasers of power 20 and 40 mw, operating in uniphase Tem0, 0, n at 6328 å. The spectra were analysed using pressure-scanning and piezo-electrically scanning Fabry-Pérot interferometers giving free spectral ranges from 0·5 to 30 cm-1 (1·5 × 1010 to 9 × 1011 hz). The hypersonic velocity decreases linearly with temperature in all these liquids except aniline at low temperatures, where the deviation from linearity is attributed to a structural dispersion. The depolarized spectra may be described by the superposition of at least two lorentzians, corresponding to two relaxation times. The longer time only could be measured accurately here, and shows an Arrhenius temperature dependence. The variation with temperature of the total depolarized intensity, the depolarization ratios and the relaxation times suggest that shear waves account for only a small proportion of the depolarized intensity in the central region of the spectra for these liquids except for nitrobenzene, where they may decay by a process related to molecular reorientation.

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