Brillouin Spectra of Ethyl Ether and Carbon Disulfide

Brillouin spectra of ethyl ether and carbon disulfide (at 20.0°C) were investigated for scattering angles of 20°–145°. A single‐mode laser was used for excitation; scattered light was collected in a solid angle of 1.5×10⁻⁴ sr; and the total instrumental width was ∼100 Mc/sec. Linewidths of 10±5 to 215±10 Mc/sec were measured and velocities determined to an accuracy of ±0.5%. In ethyl ether the phonon velocity and attenuation were constant in the frequency range 0.8–4.1 Gc/sec, and the values agreed with acoustic measurements at 100 Mc/sec. In ${\mathrm{CS}}_2$ a considerable decrease in attenuation was observed in the range 1.7–6.1 Gc/sec, with the value at high frequency approaching the classical attenuation attributed to shear viscosity. This variation in attenuation is in good agreement with the theory of a single relaxation time for the total vibrational specific heat, as established by acoustic measurements in the frequency range 2–200 Mc/sec.