Physical adsorption of simple gases on the (111) face of sulfur; a model for the adsorption by heterogeneous surfaces, including lateral interactions

As revealed by previous ab initio calculations, the surface of the (111) face of rhombic sulfur is characterized by heterogeneous but low adsorption energies. This implies relatively important contributions from lateral interactions in the adsorption mechanism. A theoretical model is presented for this case, also taking into account the random distribution of the sites. One assumes a local Fowler-Guggenheim isotherm and that the adsorption energies have a skew-Gaussian distribution with a non-zero minimum value. The resulting isotherm is tested in a satisfactory way with the data obtained for nitrogen, argon, methane and neopentane adsorption in the submonolayer region.