Interaction of alkanes with graphite

Abstract

The energies of interaction of the molecules CH₄, C₂H₆, C₃H₈, n-C₄H₁₀, n-C₅H₁₂ and n-C₆H₁₄ with the surface of graphite lattice have been calculated employing a Monte Carlo method. The present calculations are based on the assumption that the interaction energy is expressible as a sum of the pair interactions between carbon atoms of the graphite lattice and those constituting the adsorbate molecule. The CC, CH, and HH atom pair interactions are expressed in terms of the Buckingham potential function. The computation includes calculation of the molecule/surface second virial coefficients at various temperatures. This led to a theoretical determination of isosteric heats of adsorption in the limit of zero coverage, which agree reasonably well with corresponding experimental values. The calculated molecule/surface potential energy functions for n-C₄H₁₀, n-C₅H₁₂ and n-C₆H₁₄ are found to be unusual in that their attractive regions contain conspicuously flatter portions in the molecule-surface distance range 5–8 Å.