Rayleigh-Brillouin scattering of carbon dioxide

TL;DR

This study measures the spectral lineshape of Rayleigh-Brillouin scattering in CO2 to determine its bulk viscosity, revealing how molecular internal degrees of freedom influence the scattering spectrum at various pressures.

Contribution

The paper provides the first precise measurement of CO2's bulk viscosity through spectral lineshape analysis of Rayleigh-Brillouin scattering under different pressures.

Findings

Bulk viscosity of CO2 is approximately 5.7 x 10^{-6} kg/(ms).

Spectral lineshape is influenced by internal molecular relaxation processes.

Results are consistent across pressures of 2-4 bar at room temperature.

Abstract

The spectral lineshape of spontaneous Rayleigh-Brillouin scattering in CO2 is studied in a range of pressures. The spectrum is influenced by the bulk viscosity, 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 lineshape. We find the value of the bulk viscosity around 5.7 X 10^{-6} kg/(ms) for the range of pressures p= 2-4 bar and for conditions of room temperature.