The Intermolecular Potentials of Helium and Hydrogen

Abstract

The parameters for helium and hydrogen of the ``exp‐six'' potential, $$\mathrm{[open\; phi](r)=}\frac{\epsilon }{\text{1−6/α}}\left[\frac{6}{\alpha }{e}^{{\text{α(1−r/r}}_m)}-{\left(\frac{r_m}{r}\right)}^6\right],$$ have been calculated by use of experimental values of the second virial coefficients and viscosity coefficients. Because of the uncertainty of the quantum corrections, no low temperature data were used in determining the parameters. The exp‐six potential is able to reproduce both the second virial and the viscosity coefficients within experimental error, and is thus an improvement over the simpler Lennard‐Jones (12‐6) potential. In addition, other transport properties are accurately predicted. A combination rule is suggested for calculation of the exp‐six potential between two unlike molecules from the potentials between two pairs of like molecules, and is used to calculate a number of properties of helium‐hydrogen mixtures with satisfactory results.