Dispersion Relation of a Rarefied Polyatomic Gas with Molecular Relaxation Processes Based on Extended Thermodynamics

We study theoretically the dispersion relation of a rarefied polyatomic gas with molecular rotational- and vibrational-relaxation processes basing on extended thermodynamics with 15 fields. We study, in particular, its temperature dependence in the cases where the rotational and vibrational modes may or may not be excited. It is shown that the curve of the attenuation per wavelength with respect to the frequency has up to three peaks depending on the temperature and on the relaxation times. The peak in a low frequency region is predicted in detail because its experimental measurement is relatively easy.