Molecular beam studies of H2 and D2 dissociative chemisorption on Pt(111)

Abstract

Molecular beam techniques have been utilized to measure the dissociative chemisorption probability at zero surface coverage S0 for D2(H2) on Pt(111) as a function of initial energy Ei, angle of incidence θi, surface temperature Ts, isotopic mass and nozzle temperature Tn. S0 shows a large increase with translational energy, but no threshold in Ei, a peaking at θi=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.

The effect of corrugation on the quantum dynamics of dissociative and diffractive scattering of H2 from Pt(111)

“…[1][2][3][4][5][6][7][8] A vast amount of experimental studies of the H 2 ϩPt system is available in the literature. For the present work, experiments on the dynamics of reactive and inelastic scattering [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] are the most relevant. The H 2 ϩPt system has also received much theoretical attention.…”

“…This paradox arises from an apparent conflict between an experiment by Cowin et al 13 on rotationally inelastic and diffractive scattering of HD from Pt͑111͒ and an experiment by Luntz et al 18 on dissociative chemisorption of D 2 on Pt͑111͒.…”

“…In the experiment by Luntz et al, 18 the dissociative chemisorption probability at zero surface coverage, S 0 , was measured for D 2 on Pt͑111͒ as function of initial translational energy. Measurements were done for a polar angle of incidence i varying between 0°and 60°.…”

“…This result is in agreement with experiment. 18 The reaction probabilities computed for normal incidence show a small isotope effect. At larger E Z , the reaction probability curve for ϭ0 D 2 is shifted relative to that of ϭ0 H 2 to higher E Z by about 0.02 eV, which is approximately the difference in the computed dynamical barrier heights E 0 : E 0 ϭ0.206 eV for ϭ0 H 2 , and E 0 ϭ0.225 eV for ϭ0 D 2 .…”

Dynamic Deuterium Enrichment in Cometary Water via Eley–rideal Reactions

“…The ultimate proof for hydronium ion formation versus HDO + lies in the different exit energies (vide infra). Upon exposure of the Pt surface to 5×10 −8 Torr of D 2 gas, which adsorbs dissociatively on Pt (Luntz et al 1990), a 20 amu/e peak attributed to H 2 DO + is immediately observed, centered at ∼28 eV. The H 2 DO + peak intensity increases with the D 2 pressure and saturates at 1×10 −7 Torr.…”