RAMAN LIGHT-SCATTERING FROM SUPRACRITICAL BINARY-FLUID MIXTURES - CH4CF4/

A supracritical fluid mixture of CH4/CF4 (1:9 mole ratio) has been stu died at 323 K at densities between 3.0 and 19.1 mol -l (m/l) by inelas tic (Raman) light scattering originating from the v(1) totally symmetr ic stretching mode of methane. Furthermore, a Raman depolarization rat io study of the integrated intensities of the v(1) mode was also carri ed out as a function of density. A model is proposed to aid in the und erstanding of the intensity-density behavior in terms of both allowed and interaction-induced (ii) contributions to the overall observed sig nal. The model makes use of one, two, and three body light scattering via both the dipole polarizability, the dipole-quadrupole polarizabili ty, and also takes into account various partner combinations in the mu ltibody light scattering. Whereas, the model generally predicts correc t I-vh behavior, (here I is the Raman intensity and the subscripts ref er to the vertical polarization direction of the laser (v) and the dir ection of the analyzer either v or h (horizontal)), it is shown that t he 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. ( C) 1996 American Institute of Physics.