On the Intermolecular Potential of Helium

Experimental values of the second virial coefficient from 0°C to 1200°C (see preceding paper) were used to test various intermolecular potential functions for helium. A Lennard Jones potential, E(r)=λr−n−μr−m,with m=6 and with n either 9 or 12 could not be made to fit the experimental data over the entire temperature range. The coefficients λ and μ derived from the data showed a marked temperature dependence. The theoretically calculated potentials of Slater and Kirkwood and of Margenau were found to give values of the second virial which were approximately 8.5 percent and 27 percent lower, respectively, than the experimental values. A potential function with exponential repulsion, which gives a more satisfactory fit with the experimental data, was derived empirically. A semi-empirical expression given by Keyes (reference 17) for B as a function of temperature was also compared.