COADSORPTION OF HYDROGEN AND POTASSIUM ON SILVER SINGLE-CRYSTAL SURFACES

Adsorption and coadsorption of H-2 (D-2) and potassium on the single c rystal silver surfaces (111) and (110) have been studied using TPD, an gle-resolved TPD, work function measurements and LEED. Atomic hydrogen was used to cover the silver surfaces, since a very high activation b arrier for molecular adsorption exists. From the Ag(111) surface hydro gen 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) i s characterized by two overlapping desorption peaks which are very sen sitive to small amounts of water coadsorption. Angular distributions o f the desorption probability following a cos(2.5)Theta and a cos(3.5)T heta function for Ag(111) and Ag(110) were observed, respectively. Upo n hydrogen saturation (0.65 ML) on Ag(111) the work function increases by 240 meV. Coadsorbed potassium shifts the desorption temperature fo r H-2 dramatically by 250 K to higher temperature on both surfaces. Si multaneous desorption of hydrogen and potassium on both silver surface s with a ratio of 1 K-atom to 4 H-2 molecules indicates a strong potas sium-hydrogen interaction in the coadsorbate.