Rayleigh-Brillouin light scattering studies of NC(CH₂)_nCN liquids

Abstract

Polarized and depolarized Rayleigh-Brillouin light scattering spectra of n-alkanedinitriles NC(CH₂) _n CN (n=1-6) were studied as a function of temperature. The hypersonic velocity and volume viscosity have been determined from the frequency shift and linewidth of the Brillouin spectrum. For all dinitriles studied, the sound attenuations over one sound wavelength are found to be small and to decrease with increasing temperature. Rayleigh relaxation times are obtained from the depolarized Rayleigh spectra. Using the modified Stokes-Einstein-Debye equation, the effective hydrodynamic volumes for reorientation of all dinitriles are determined. The plot of the Rayleigh relaxation times with respect to ηT ^-1 shows a non-vanishing intercept. Activation energies extracted from the Rayleigh relaxation times have been compared with those obtained from other methods and good agreements have been found. The even-odd effects are found on the volume viscosity and the reorientational activation energy for these liquids.