Rayleigh–Brillouin light scattering spectroscopy of nitrous oxide (N2O)

Highlights: • High signal-to-noise Rayleigh–Brillouin scattering data in N₂O gas. • Good agreement with Tenti model in kinetic regime. • Good agreement with hydrodynamic model at high pressures. • Determination of bulk viscosity for N₂O gas. High signal-to-noise and high-resolution light scattering spectra are measured for nitrous oxide (N₂O) gas at an incident wavelength of 403.00 nm, at 90° scattering, at room temperature and at gas pressures in the range $0.5-4$ bar. The resulting Rayleigh–Brillouin light scattering spectra are compared to a number of models describing in an approximate manner the collisional dynamics and energy transfer in this gaseous medium of this polyatomic molecular species. The Tenti-S6 model, based on macroscopic gas transport coefficients, reproduces the scattering profiles in the entire pressure range at less than 2% deviation at a similar level as does the alternative kinetic Grad's 6-moment model, which is based on the internal collisional relaxation as a decisive parameter. A hydrodynamic model fails to reproduce experimental spectra for the low pressures of 0.5-1 bar, but yields very good agreement ( < 1%) in the pressure range $2-4$ bar. While these three models have a different physical basis the internal molecular relaxation derived can for all three be described in terms of a bulk viscosity of ${\eta }_b\sim (6\pm 2)\times {10}^{-5}$ Pa · s. A 'rough-sphere' model, previously shown to be effective to describe light scattering in SF₆ gas, is not found to be suitable, likely in view of the non-sphericity and asymmetry of the N-N-O structured linear polyatomic molecule.