Velocity and Attenuation of Hypersonic Waves in Liquid Nitrogen

High‐resolution thermal Brillouin scattering techniques have been used to measure the velocity and damping of sound in liquid nitrogen in the 3–5 GHz range. The measurements were carried out along the saturated vapor line from the triple point to the normal boiling point. No deviation from previous ultrasonic values of velocity or the classical ${\nu }^2$ attenuation is observed at these frequencies. Thus acoustic dispersion due to the 2 GHz relaxation frequency of the internal molecular vibration is completely negligible.