Calculation of the Vapor-Pressure Ratio of the Isotopes of Solid Ne and Ar

The improved self‐consistent phonon theory of Goldman, Horton, and Klein for the Helmholtz energy of anharmonic crystal is used to calculate the vapor‐pressure ratios of the common isotopes of Ne and Ar. For both substances, a Mie–Lennard‐Jones $\text{(m\hspace{0.17em}−\hspace{0.17em}6)}$ nearest‐neighbor potential $\text{(m\hspace{0.17em}=\hspace{0.17em}12}\mathrm{and}\text{13)}$ with parameters chosen to fit the zero‐temperature latent heat and molar volume is found to give reasonable agreement with experiment.