Coadsorption of hydrogen and potassium on silver single crystal surfaces

Adsorption and coadsorption of H-2 (D-2) and potassium on the single crystal silver surfaces (111) and (110) have been studied using TPD, angle-resolved TPD, work function measurements and LEED. Atomic hydrogen was used to cover the silver surfaces, since a very high activation barrier for molecular adsorption exists. From the Ag(111) surface hydrogen desorbs in a single peak with a close to second order reaction and a desorption energy of 7 kcal/mol. Hydrogen desorption from Ag(110) is characterized by two overlapping desorption peaks which are very sensitive to small amounts of water coadsorption. Angular distributions of the desorption probability following a cos(2.5)Theta and a cos(3.5)Theta function for Ag(111) and Ag(110) were observed, respectively. Upon hydrogen saturation (0.65 ML) on Ag(111) the work function increases by 240 meV. Coadsorbed potassium shifts the desorption temperature for H-2 dramatically by 250 K to higher temperature on both surfaces. Simultaneous desorption of hydrogen and potassium on both silver surfaces with a ratio of 1 K-atom to 4 H-2 molecules indicates a strong potassium-hydrogen interaction in the coadsorbate.