VIBRATIONAL FREQUENCY-SHIFTS OF FLUID NITROGEN UP TO ULTRAHIGH TEMPERATURES AND PRESSURES

Vibrational frequency shift measurements in fluid nitrogen (over a temperature range of 77 K < T < 3521 K and a pressure range of 1 bar < P < 158 kbar) are used to test the predictions of a generalized perturbed hard sphere fluid theory. The experimental data include new Raman scattering measurements, up to near the freezing density of N2 at 295 K, as well as previous static and shocked high-pressure and temperature measurements. These are compared with the predictions of a theory which independently treats the effects of short range repulsive, long range attractive, and centrifugal forces. Repulsive solvation forces are modeled using the cavity distribution function of a reference hard sphere fluid. The temperature and density dependence of the reference fluid diameter is determined by fitting N2 equation of state data to an expression of Carnahan-Starling-van der Waals (CS-vdW) form. Attractive force perturbations are incorporated using a single temperature and density independent mean field parameter, and centrifugal forces are treated by interpolating low and high collision frequency expressions. The results are found to accurately reproduce both equation of state and frequency shift measurements over the entire temperature and pressure range of interest.