FAST AND SLOW SOUND IN THE 2-TEMPERATURE MODEL

The dispersion relation for disparate mass gas mixtures is derived fro m a simplified two-temperature model. It is shown that the hydrodynami c sound mode (kl-->0) goes over continuously into either a fast or a s low propagating sound mode (kl--> infinity), depending on the composit ion. The composition that demarcates the composition regions where the continuation of the hydrodynamic sound mode is a fast or slow propaga ting mode is called the critical composition. The existence of such a critical composition is confirmed experimentally by new Rayleigh-Brill ouin experiments on H-2 + Xe mixtures.