RAYLEIGH-BRILLOUIN SPECTROSCOPY OF GLOBULAR ALKANES

Rayleigh-Brillouin scattering has been studied as a function of temperature in a series of globular alkanes: 2,2-dimethylpropane, 2,3-dimethylbutane, and 3,3-diethylpentane. The calculated volume viscosities are larger than the shear viscosities for these liquids. The volume viscosities are analyzed in terms of a structural contribution with magnitude proportional to the shear viscosity and a contribution due to vibrational heat capacity relaxation. The vibrational relaxation times are long enough to make this contribution the largest source of hypersonic attenuation, but short enough that no measurable dispersion in the longitudinal sound velocity is observed. The calculated relaxation times are 22 ps for 2,2-dimethylpropane, 12 ps for 2,3-dimethylbutane, and 11 ps for 3,3-diethylpentane. © 1990 American Chemical Society.