Journal of Chemical Physics, Vol.105, No.17, 7285-7293, 1996
Raman Light-Scattering from Supracritical Binary-Fluid Mixtures - CH4/CF4
A supracritical fluid mixture of CH4/CF4 (1:9 mole ratio) has been studied at 323 K at densities between 3.0 and 19.1 mol -l (m/l) by inelastic (Raman) light scattering originating from the v(1) totally symmetric stretching mode of methane. Furthermore, a Raman depolarization ratio study of the integrated intensities of the v(1) mode was also carried out as a function of density. A model is proposed to aid in the understanding of the intensity-density behavior in terms of both allowed and interaction-induced (ii) contributions to the overall observed signal. The model makes use of one, two, and three body light scattering via both the dipole polarizability, the dipole-quadrupole polarizability, and also takes into account various partner combinations in the multibody light scattering. Whereas, the model generally predicts correct I-vh behavior, (here I is the Raman intensity and the subscripts refer to the vertical polarization direction of the laser (v) and the direction of the analyzer either v or h (horizontal)), it is shown that the standard assumption of the no V-R coupling is violated, leading to a different mechanism for I-iso Raman light scattering. This leads to extensive three-body ii I-iso signal cancellation, but none from the I-vh spectrum. The model adequately explains these concepts through the usual interaction induced processes as well as a unique cross term.