The spectral distribution of scattered light is calculated for the model of a liquid in which the bulk and shear relaxation processes are each characterized by a multiplicity, or a continuous set, of relaxation times. The treatment is a generalization of that given by the authors previously [Phys. Rev. 173, 231 (1968)] in which bulk relaxation was ascribed to the relaxation of a thermodynamic order parameter relaxing with a single relaxation time. It is found that, in general, one has to introduce two independent distribution functions associated with the bulk relaxation times. Only when all the bulk relaxation processes are of the same type (pressure induced, temperature induced, etc.), does the expression for the spectral function contain just one distribution for bulk relaxations. This is in contrast to the results obtained by previous workers and may have significance in relation to a reported discrepancy in interpreting (in terms of a single distribution function for bulk relaxation) experimental data on Brillouin scattering and ultrasonic absorption in glycerine.
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Bhatia et al. (1971) studied this question.