Chemisorption of atomic hydrogen on clean and Cl-covered Ag(111)

The chenaisorption of atomic hydrogen and deuterium on clean and Cl-covered Ag(111) has been studied using temperature programmed desorption (TPD), work function change (δφ) measurements and ultra-violet photoelectron spectroscopy (UPS). The desorption of molecular hydrogen and deuterium follows a fractional-order kinetic description with an activation energy of 5.5 kcal/mol (H₂) and 6.4 kcal/mol (D₂). Based on these results and the absence of dissociative chemisorption at 100 K, an upper limit for the Ag-D(H) bond of 53. (52) kcal mol^-1 is derived. UPS reveals an H(1s)-derived bonding state at about 7.3 eV below the Fermi level. There are no significant changes in the shape of the Ag d-band, consistent with its, at most, very weak involvement in the D-Ag bond. Saturation exposure of the clean Ag(111) surface to atomic D results in a Δφ of -0.17 eV. Surface Cl alters the bonding and reduces the saturation coverage of D, results that are interpreted in terms of each Cl controlling a large number of D(a) adsorption sites and leading to widely varying local surface coverages.