DIRECT REACTION OF GAS-PHASE ATOMIC-HYDROGEN WITH CHEMISORBED HYDROGEN ON RU(001)

The adsorption of gas-phase atomic hydrogen on the Ru(001) surface results in a saturation coverage of 1.42 hydrogen adatoms per primitive surface unit cell, which may be compared with a saturation coverage of one hydrogen adatom per primitive surface unit cell in the case of dissociative chemisorption of molecular hydrogen. The observed saturation fractional coverage of 1.42 results from a steady-state balance of adsorption of gas-phase atomic hydrogen and reaction of gas-phase hydrogen with chemisorbed hydrogen adatoms, which produces molecular hydrogen that desorbs from the surface at a temperature at least 150 K below the temperature of recombinative desorption of two hydrogen adatoms. The cross section of this direct reaction of hydrogen was found to be remarkably large, approximately 40% of the cross section for chemisorption of the gas-phase atomic hydrogen. The reaction was found not to depend on surface temperature nor was there an observable kinetic isotope effect. © 1994 American Institute of Physics.