Rayleigh and Raman scattering near the critical point of carbon dioxide

Abstract

An experimental study of the behavior of depolarized Rayleigh and Raman spectra of carbon dioxide when approaching the critical temperature along the critical isochore is presented. The study of the depolarized Raman scattering was carried out on the Fermi diad ν₁, 2ν₂ and was supplemented by a study of the polarized Raman scattering. Contributions to the different physical mechanisms which can give rise to the depolarized spectra are carefully analyzed. We have shown that the orientational dynamics of CO₂ molecules are unchanged by critical slowing down of the diffuse hydrodynamical mode associated to fluctuations of the order parameter in the range 0.01 °C<T–T_c<10 °C. Moreover we found that the frequency variation of the polarized Fermi diad can be well described using only density terms. The variation of the spectral intensities of the different polarized and depolarized bands is well explained in terms of only turbidity and multiple scattering phenomena owing to the intensive quasielastic polarized Rayleigh scattering.