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: $$\begin{array}{ccc}{\mathrm{Rb}}^{+}:& {\tau }_3{\text{=(0.8±0.3)×10}}^{\text{−13}}\exp \text{[(26 400±350)/T]}\sec ,& {\text{1000<T<1250}}^{\circ }\mathrm{K};\\ {\mathrm{K}}^{+}:& {\tau }_3{\text{=(1.0±0.3)×10}}^{\text{−13}}\exp \text{[(27 000±350)/T]}\sec ,& {\text{1050<T<1260}}^{\circ }\mathrm{K};\\ {\mathrm{Na}}^{+}:& {\tau }_3{\text{=(0.2±0.1)×10}}^{\text{−13}}\exp \text{[(31 900±300)/T]}\sec ,& {\text{1160<T<1400}}^{\circ }\mathrm{K}.\end{array}$$ The interaction of the alkali ion with the metal surface was described by a one‐dimensional potential function of the form $${\mathrm{V(x)=l}}_{+}\left[\text{1+}\frac{1}{\text{n−1}}{\left(\frac{r_e}{x}\right)}^n-\frac{n}{\text{n−1}}\left(\frac{r_e}{x}\right)\right],$$ 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 r_i as the distance of closest approach to the surface for an ion with energy l₊, the parameters n and r_e were calculated for each alkali ion. It was found that the values of n increase and those of (r_e—r_i) decrease as the atomic number of the alkali ion increases.