| Stimulated gain spectroscopy (SGS) is shown to be an excellent tool for the investigation of low frequency dynamics of molecular liquids, with sufficient resolution and signal-to-noise ratio to reflect intermolecular interactions. In the first of two experiments, CCl4 is selected for its isotropic polarizability which ensures that depolarized scattering is due to intermolecular interactions and thus provides a good test of various models for collision-induced (CI) anisotropy based on different power dependences of the interaction distance, r. The depolarized spectrum for CCl4 was decomposed phenomenologically into two modeled components representing diffusive relaxation and collision-induced scattering. Of several distinct models based on different sources for the induced anisotropy, results show a model based on a collision-induced electronic repulsive force with a r−9 dependence provides the best fit to the CCl4 spectrum.; In a second experiment, high pressure is incorporated into the SGS experiment and benzene spectra at atmospheric pressure and at 350 bars are analyzed using a curve-fitting model comprised of a low frequency diffusive reorientational term, a high frequency librational term, and an intermediate frequency term which results from translational and rotational collisions. The 3% increase in liquid density results in a 17% decrease in the rate of reorientational diffusion and a librational component with a 12% higher center frequency and a 31% reduction in inhomogeneous broadening. The intermediate frequency term exhibits the strongest pressure sensitivity, resulting in a broader, higher intensity component with a 32% higher characteristic frequency. |
