ABSTRACTION OF H ADSORBED ON PT(111) SURFACES WITH GASEOUS D ATOMS - ISOTOPE AND FLUX EFFECTS

Abstraction of H adsorbed on Pt(111) surfaces by gaseous D atoms was s tudied with direct product detection as a function of coverage and ato m flux at a substrate temperature of 85 K. The reaction products are H D and the homonuclear surface species H-2. The product reaction kineti cs is very similar to that of the alternate isotope combination, H --> D-ad, reported earlier. The reaction kinetics is not in accordance wi th the operation of an Eley-Rideal mechanism but is better described b y a hot atom scheme. With both isotope combinations the kinetics is in dependent of the atom flux. The reaction yield of the homonuclear spec ies scales with the square of the species' initial coverage, in accord ance with a second-order process as origin of these products. Isotope effects were not observed in the yields, but were apparent in abstract ion cross-sections. (C) 1998 Elsevier Science B.V. All rights reserved .