HIGH-PRESSURE BRILLOUIN-SCATTERING STUDY OF DENSE ARGON AND NITROGEN

We have measured the Brillouin shift as a function of hydrostatic pres sure in dense argon and nitrogen at different constant temperatures. W e show that for argon there is a linear relation between the index of refraction and the reduced density. A comparison of the sound velociti es determined ultrasonically and from our Brillouin data shows a negat ive velocity dispersion. This is in agreement with theoretical predict ions and measurements of the temperature dependence of the sound veloc ity along the vapor-pressure equilibrium curve using Brillouin scatter ing. The fact that the negative velocity dispersion increase with pres sure at constant temperature is smaller at lower temperatures is, howe ver, puzzling and cannot be explained within the framework of the abov e-mentioned theoretical model. (C) 1996 American Institute of Physics.