Quantum Corrections for the Second Gas‐Surface Virial Coefficient

The quantum corrections for the second gas–surface virial coefficient are derived and applied to the experimental data for H₂, D₂, CH₄, and CD₄ in the external field provided by a uniform graphite surface. These corrections cause quite sizable differences in the interaction energies and areas obtained for the hydrogen pair, but the differences are, of course, small in the case of the methanes. Quantum effects have been measured in dilute adsorption systems and found to be of considerable importance. Theoretically, Yaris and Sams have developed the second gas–surface virial coefficient $B_{\mathrm{AS}}$ from the Wigner–Kirkwood expansion to order ${\hslash }^4$ and examined three different models for the gas–surface interaction potential, using the data of Constabaris et al. Due to a misprint in the ${\hslash }^4$ term of Uhlenbeck and Beth, which has been carried through in the calculations of Yaris and Sams, we have recalculated the quantum corrected $B_{\mathrm{AS}}$ and fitted it to the data mentioned above.