Translational hydrodynamics and light scattering from molecular fluids

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Abstract:

The density fluctuations in a molecular fluid are studied by treating the fluid as a multicomponent reacting mixture. The ordinary hydrodynamic equations for a reacting mixture form the starting point of the present derivation. The description is then contracted to that appropriate for the one-component molecular fluid. The resulting translational hydrodynamics theory contains memory effects due to the internal relaxation process. The results are compared with a recent kinetic model and with two previous theories of Mountain. The dynamic structure factor S(k, ω) and the roots of the dispersion relation are computed for parahydrogen gas and studied as a function of density. The results indicate that the treatment of the thermal-diffusivity mode in the theories by Mountain breaks down in the low-density region. It is suggested that Rayleigh-Brillouin scattering experiments on dilute parahydrogen gas at room temperature and densities between 5 and 30 amagats can quantitatively verify the predictions of translational hydrodynamics. © 1972 The American Physical Society.