Dynamics of relaxation processes in liquids: Analysis of oscillation and orientation spectra

Based on the spectra of molecular (Rayleigh) scattering of light, we investigate relaxation dynamics in the molecules of para-, meta-, and ortho-xylenes which are confined in a container and heated from room through critical temperature Tc. We experimentally elucidate the successive transitions from hindered to absolutely-free rotations at temperatures up to a pre-critical temperature T*(< Tc) and then from individual to collective motions (macroscopic vibrations) of the molecules at higher temperatures above T⁎ up to Tc. Close to Tc, the inner field anisotropy is the same along three axes of inertia of the ellipsoid, and the depolarization degree is universal and independent of the specific nature of xylene isomers. A marked deviation from the Rayleigh's theory is also found in the spectral intensity of scattering light.