Light scattering in binary gas mixtures : evidence of fast and slow sound modes

Luo, Hongda (1990) Light scattering in binary gas mixtures : evidence of fast and slow sound modes. Masters thesis, Memorial University of Newfoundland.

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Abstract

In this thesis Brillouin scattering data are presented for three different binary gas mixtures composed of species with widely different masses, i.e. Ar + H₂(mAr/mH₂ ≃20), SF₆ + CH₄ (mSF₆/mCH₄ ≃ 9), and SF₆ + H₂(mSF₆/mH₂ ≃73). Under the experimental conditions predicted by the theory a fast sound mode contribution to the light scattering spectra of Ar + H₂ mixtures has been detected. Unlike the ordinary sound mode the fast sound mode propagates only in the light component with a velocity higher than that obtained using hydrodynamic theory. However, the attempts to observe the same effect in mixtures of SF₆ + CH₄ under similar conditions were unsuccessful. An analogous slow sound mode contribution to the spectra of SF₆ + H₂ mixtures has been clearly identified and it was found this mode was, in general, much easier to detect. -- A new parameter called the effective mean free path was also introduced in order to obtain a more consistent characterization of the dynamical behavior in binary mixtures with disparate masses.

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