HYDROGEN ADSORPTION ON ALKALI-METAL SURFACES - WETTING, PREWETTING AND TRIPLE-POINT WETTING

We report the results of a quartz microbalance study of the multilayer adsorption of H-2 and D-2 on sodium and on rubidium. On sodium H-2 and D-2 display, the well known phenomenon of triple-point wetting. Interestingly low temperature adsorption isotherms of H-2 on the evaporated Na surface show sharp layering transitions. On rubidium a weaker substrate H-2 and D2 undergo a wetting transition in the liquid phase followed by sharp prewetting transitions away from liquid-vapor coexistence. The prewetting phase diagram of H-2 on Rb has been quantitatively mapped out.