J. P. O’CONNELLAND J. M. PRAUSNITZ
632
Analytical Potential Models and the Properties of Noble Gases by J. P. O’Connell and J. M. Prausnitz College of Chemistry, University of California, Berkeley, California 3&20
(Received August 4, 1067)
Analytical expressions of the intermolecular potential function with two or more parameters are used to calculate the thermodynamic and transport properties of the heavy noble gases. Comparisons with data indicate that the Kihara potential is as good as any other model for predicting virial coefficients, viscosities, and diff usivities from a single set of parameters. However, the calculated coefficient for dispersion forces, the isotopic thermal diffusion factor, and the stable crystal structures of noble gases indicate that certain details of the potential may be inadequately described by all of the present expressions. In particular, over a wide temperature range, the thermal diffusion factor appears to be sensitive to the potential only in a narrow region of distance located somewhat to the right of the potential minimum; comparison with thermal diffusion data and analysis of crystal data suggest that in this region the slope of the potential should be greater than in present models.
Recently, there has been considerable reassessment of the present understanding of the form of the intermolecular potential function of the noble gases.’-12 The sensitivity to details of the potential has been established, at least in part, for several measurable macroscopic properties. Barker4 concluded that a significant test of a potential model is the degree towhich both second virial coefficient data and viscosity may be fitted simultaneously. However, Smith, Mason, and 1!tunnl3 and Munn and Smith6 indicate that the isotopic thermal diffusion factor is perhaps the only dilutegas property which is sufficiently sensitive to the form of the potential to distinguish between models in an experimentally accessible range of temperature. Furthermore, Alder and Paulson’” indicate that the crystal structures of the inert gases are extremely sensitive to small details of the two-body potential. In this paper we discuss our observations on the prediction of inert-gas properties from intermolecular potential functions. We place special emphasis on the Kihara potential with a spherical core r = m
r
