INTERACTION 2ND ACOUSTIC VIRIAL-COEFFICIENTS OF (N-2 + AR) BETWEEN 90-K AND 373-K

The speed of sound in an equimolar mixture of nitrogen and argon has been measured in the temperature range 90 to 373 K and in the density range 10 to 200 mol/m3 using a spherical resonator. Values of the mixture second acoustic virial coefficient have been determined from the results with an estimated imprecision of no worse than 0.13 cm3/mol. This estimation of imprecision includes all known sources of systematic and random errors at the level of one standard deviation. By combining the results with information calculated from the second acoustic virial coefficients of the pure components, we have derived from the mixture results an interaction second acoustic virial coefficient with an estimated imprecision no worse than 0.25 cm3/mol. The results are compared with values calculated from several recent intermolecular potential-energy functions for the nitrogen-argon stystem. None of the functions proved able to predict the acoustic virial coefficients to within the high precision of the present measurements. Ordinary (p, V, T) interaction second virial coefficients have been calculated from the measurements and the results are believed to be of superior accuracy to directly measured values at low temperatures.