Kinetic theory for a mobile adsorbed gas

Publisher Website
Google Scholar
Abstract
The equations of motion for a classical adsorbed gas on a single crystal surface, in which the kinetic energy of the adsorbate is large compared with the potential barrier between sites, are derived. If the corrugation of the surface is sufficiently small, an isolated adsorbate will translate in a ballistic motion parallel to the surface for a distance that is much larger than its diameter before transferring a significant fraction of its parallel momentum to the lattice. A kinetic theory that includes effects of adsorbate–adsorbate collisions as well as the adsorbate–lattice coupling is derived. If the only role of the substrate was to confine the adsorbed species to a thin layer, then the equations of motion would be those for a two-dimensional gas. However, the transfer of momentum and energy between the adsorbate and the lattice affects the form of the transport equations and is essential to obtain Fick’s law for diffusion due to adsorbate concentration gradients.