Light scattering by a fluid in a nonequilibrium steady state. II. Large gradients

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Abstract
The equations derived in the first paper of this series for the correlation functions of mass, momentum, and energy densities are solved for a fluid subject to a large temperature gradient. The shape and intensity of the Rayleigh line show deviations from equilibrium that are proportional to the square of the temperature gradient. The deviations of the intensity of each Brillouin line from its equilibrium value as a function of the temperature gradient is obtained for the optimal scattering geometry. The intensity of one of these two Brillouin lines shows a maximum or minimum as a function of the temperature gradient, depending on the sign of the temperature derivatives of the coefficient of sound attenuation and thermal conductivity and on the orientation of the momentum transfer between fluid and light with respect to the temperature gradient. Further, the difference in intensity of the two Brillouin lines is found to be about three times smaller than predicted by the linear theory, consistent with the experiments of Beysens et al. Since all these results are due to mode-coupling effects, an experimental verification would constitute the first observation of mode-coupling effects away from criticality. The connection between (a) the mode-coupling effects responsible for the changes in the intensities of the Rayleigh and Brillouin lines, (b) the long-time tail contributions to the transport coefficients, and (c) the nonexistence of a virial expansion of the transport coefficients is discussed.