Kinetics of Desorption. III. Rb+, K+, and Na+ on Rhenium

The mean adsorption lifetimes (τ3) of Rb+, K+, and Na+ ions on a clean polycrystalline rhenium surface have been measured in the millisecond region as a function of temperature under conditions of very low surface coverage. The results of these measurements are given by: Rb+:τ3=(0.8±0.3)×10−13exp[(26 400±350)/T]sec,1000<T<1250∘K;K+:τ3=(1.0±0.3)×10−13exp[(27 000±350)/T]sec,1050<T<1260∘K;Na+:τ3=(0.2±0.1)×10−13exp[(31 900±300)/T]sec,1160<T<1400∘K. The interaction of the alkali ion with the metal surface was described by a one-dimensional potential function of the form V(x)=l+[1+1n−1(rex)n−nn−1(rex)],where x is the perpendicular distance of the adsorbed ion from the surface and l+ is the observed desorption energy. By choosing the Pauling ionic radius ri as the distance of closest approach to the surface for an ion with energy l+, the parameters n and re were calculated for each alkali ion. It was found that the values of n increase and those of (re—ri) decrease as the atomic number of the alkali ion increases.