Publication costs assisted by the National Bureau of StandardsThe m-6-8 model potential function is applied to the gases argon, krypton, xenon, nitrogen, methane, and carbon dioxide and to the properties viscosity coefficient, self-diffusion coefficient, thermal conductivity coefficient, virial coefficient, and the isotopic thermal diffusion factor. The potential is shown to have a considerable advantage over previous simple analytic models in that it can satisfy two criteria: (a) it can be used to correlate a given property for all the gases studied over a wide temperature range with a single set of parameters, and (b) it can be used to correlate both transport and equilibrium properties for the monatomic gases with a single set of parameters. Reasons for the failure of polyatomic gases to satisfy (b) are suggested. A brief discussion on the relation of the potential to theory is given. (1) Work carried out at the National Bureau of Standards under the partial sponsorship of the Office of Standard Reference Data (for H. J. M. Hanley) and (for M. Klein), supported, in part, by the Air Force Command, Arnold Engineering Development Center, Tullahoma, Tenn. Delivery Order Number (40-600) 66-938 Program Element 61445014 AF Project 8951.(2) M. Klein and H. J. M. Hanley, J. Chem. Phys., 53, 4722 (1970).

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Tables of co lli sion int egra ls ~,re prese nted for th e (m, 6) pote ntia l function for 87 redu ced temperatures fo,: eac h of 10 va lu es uf 111. I he exponents 111 used were III = 9. 12, 15, 18, 21,24,30,40,50, a nd 75.Co mpan so ns are made wIth five other calc ul at. ion s for the case 111 = 12. The accu racy of th e ca lc ulation a ll pea rs to be a t leas t seve ra l parts in 10,000.

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The equation of state for hard spheres as predicted by the chain, watermelon, convolution-hypernetted chain (CHNC), Percus-Yevick, and two new approximations to the pair correlation function are compared with each other and with a reference isotherm. The equations of state of the chain and watermelon approximations have been found to be only slight improvements over the linear correction to the ideal gas law. The Percus-Yevick theory has been found to be an improvement over the CHNC approximation for hard spheres in agreement with the results of Hoover and Poirier for hard cubes and of Broyles for several densities of the Lennard-Jones (12,6) gas. The new approximations are designated n = 1 and n = 2. They make use of the solutions to the CHNC integral equation but do not include all the diagrams for the pressure. The approximation n = 2 was found to yield an equation of state in excellent quantitative agreement with the reference isotherm for densities up to 0.707 times the close packed density. Both the nearest and next nearest neighbors were computed as a function of density in each approximation. Only the CHNC and Percus-Yevick results extrapolate to the proper value at the density of close packing. Both of these approximations, furthermore, indicate the existence of a singularity at densities less than or equal to that of close packing. The approximations considered seem to form part of a uniform approach to the reference isotherm. At the same time, the representations of the known virial coefficients associated with each do not approach the correct virial coefficients in a uniform fashion. Therefore, an understanding of this sequence of approximations cannot be had from the usual examination of virial coefficients.