Studies of depolarized and polarized Rayleigh–Brillouin spectra of a supercooled liquid: Salol

Abstract

An extensive interferometric study of polarized and depolarized Rayleigh–Brillouin spectra of neat salol was carried out as a function of temperature and scattering angles. Considerable dispersion is observed in the isotropic spectrum, as manifested by the nonlinear temperature dependence in the longitudinal hypersonic frequency and a maximum in the linewidth. The relaxation behavior of the longitudinal hypersonic frequency is shown to be due to the bulk viscosity. Upon decreasing the sample temperature, the shear wave spectrum changes from diffusive to oscillatory behavior. In the oscillatory region, the shear wave frequency decreases linearly with increasing temperature and extrapolates to a vanishingly small value at the temperature at which the longitudinal acoustic wave linewidth is maximum. Curve fitting the VH spectrum to theory shows that the shear frequency is proportional to q; the shear wave linewidth and the rotation–translation coupling parameter to q2. These results are consistent with a linear viscoelastic theory, or the microscopic displacement density theory (taking in the small q limit) previously developed.