MOLECULAR-BEAM STUDIES OF H-2 AND D-2 DISSOCIATIVE CHEMISORPTION ON PT(111)

Molecular beam techniques have been utilized to measure the dissociative chemisorption probability at zero surface coverage S0 for D 2(H2) on Pt (111) as a function of initial energy E i, angle of incidence θi, surface temperature T s, isotopic mass and nozzle temperature Tn. S0 shows a large increase with translational energy, but no threshold in E i, a peaking at ωi, = 0° and an independence with Ts, isotope and Tn. These results are interpreted in terms of direct dissociative chemisorption on the Pt ( 111 ) terraces. The dynamical picture that emerges is that although there is no significant barrier to dissociation along the minimum energy path, barriers do exist along nonoptimal reactive trajectories. Thus, the "translational activation" and other dynamical observations are intimately related to the multidimensional aspects of the dissociative potential energy surface. Some aspects of the dissociative chemisorption, however, still seem somewhat surprising within this general description. © 1990 American Institute of Physics.