Rayleigh-Brillouin scattering of carbon dioxide

The spectral line shape of spontaneous Rayleigh–Brillouin scattering in CO2 is studied in a range of pressures. The spectrum is influenced by the bulk viscosity ηb, which is a relaxation phenomenon involving the internal degrees of freedom of the molecule. The associated relaxation rates can be compared to the frequency shift of the scattered light, which demands precise measurements of the spectral line shape. We find ηb=(5.7±0.6)×10−6  kg m−1 s−1 for the range of pressures p=2–4 bar and for room temperature conditions.