Adsorption of Xenon and Hydrogen Atoms and their Interaction on Silver Films

Abstract

The adsorption of xenon, hydrogen, and mixtures of xenon and hydrogen on silver films at 77 K has been investigated by measurement of surface potentials by the diode method. Average surface potentials of xenon and hydrogen at maximum coverage were found to be 0.47 V and —0.32 V respectively, in agreement with previous investigations. Hydrogen was adsorbed only when atomized and at a rate which decreased with coverage. When xenon and hydrogen atoms were adsorbed together on silver, considerable interaction between them was indicated. Under certain conditions, addition of xenon to hydrogen adsorbed on a silver surface resulted in desorption of hydrogen. This desorption does not involve simple displace ment of hydrogen as has been observed in other systems. Addition of xenon appears to “ activate ” a certain number of surface hydrogen atoms in such a way that the probability of their reacting with gas phase hydrogen atoms is increased. A quantitative model which accounts for the variation in hydrogen pressure with time during the desorption process has been set up.