Observation of a Frequency-Dependent Thermal Conductivity in a Polyatomic Gas

A frequency-dependent thermal conductivity, associated with the thermal relaxation of the vibrational degrees of freedom in a polyatomic gas, has been observed in a study of the density fluctuation spectrum of dilute S${\mathrm{F}}_6$. Spectra calculated from the two-temperature hydrodynamic theory of Morse, Sugawara, and Yip, which explicitly accounts for a frequency dependent thermal conductivity, are shown to agree well with the measured spectra.