The Rayleigh – Brillouin Spectrum of Normal and Parahydrogen: A Test of Model Solutions of the Wang–Chang Uhlenbeck Equation

This paper reports the observation at high resolution of the Rayleigh–Brillouin spectrum of normal and parahydrogen at room temperature. The spectra are compared with a number of kinetic model calculations based on the Wang–Chang Uhlenbeck equation. It is concluded that n-H2 behaves effectively as a system characterized by a single relaxation time for the internal degrees of freedom and that the S6 model of Tenti et al. gives a very good description of the Rayleigh–Brillouin spectrum of a molecular gas at low and medium densities. At higher densities the models fail because the Wang–Chang Uhlenbeck equation is no longer valid.