Surface diffusion phenomena in gaseous diffusion, (3). Isotope effect on surface diffusion flow

We estimated the isotope effect on surface diffusion flow assuming that this flow originates in the hopping of adsorbed molecules, and obtained the conclusion that surface diffusion flow in monolayer adsorption has an isotope effect comparable to Kundsen flow. Based on this conclusion, and applying the new model for surface diffusion mechanism proposed previously, we analyzed isotope separation by gaseous diffusion in which Kundsen flow is accompanied by surface diffusion flow. In addition to the theoretical treatment, we made experiments on isotope separation under conditions of surface diffusion flow rate comparable to or a few times greater than that of Knudsen flow, and verified that the isotope effect on surface diffusion flow obeys the proposed theory. It was observed that the separation efficiency with the coverage (θ) around unity is much poorer than with low surface concentrations. (author)