The Rayleigh-Brillouin Light Scattering Spectrum of Dense Argon Gas Between 70 and 260 MPa at T = 298 K: the Sound Velocity and the Specific Heats Ratio γ

Measurements of the Rayleigh–Brillouin spectrum in dense argon gas at T = 298 K and pressures between 70 and 260 MPa are reported. No dispersion in the sound velocity was found up to frequencies of the order of 4 GHz, and low and high frequency measurements agree within 0.5%. This permits the use of hypersonic velocity for deriving thermodynamic quantities for this system. From our measurements we have derived the density behavior of the specific heats ratio γ. Moreover, in absence of dispersion, we have shown that Brillouin scattering gives the sole possibility of measuring both the very low and high sound velocities in fluids, at the same time, therefore giving the direct possibility of checking either the absence or presence of dispersion.