Impact site-dependent molecular anisotropy: NO scattering from Ru(0001)-(1x1)H

Oriented beams of NO molecules have been scattered from a Ru(0001)-(1×1)H surface. The interaction of NO with Ru-H is found to have both a strong orientation and lateral dependence. The angular distributions for N-end and O-end scattering are quite different, and demonstrate that in the chemisorbing region of the unit cell the N-end is strongly bonding, while the O-end is essentially repulsive. Above the so-called mirror reflection region the N-end and O-end interaction are equally repulsive. © 2004 Elsevier B.V. All rights reserved

The dynamics of the dissociative adsorption of methane on Pt(533)

The influence of well-defined steps on the dynamics of the dissociative chemisorption of methane on Pt(533) has been investigated using molecular beam techniques. The initial dissociative chemisorption probability S-0 has been determined as a function of incident energy E-i, angle of incidence theta(i), and surface temperature T-S. For incident kinetic energies in the range 26<E-i(meV)<1450, the initial dissociation probability of CH4 on the Pt(533) surface is higher than on Pt(111), for all surface temperatures investigated. This enhancement in dissociation is associated with the additional direct sticking mediated by the step sites, with no evidence for any additional indirect dynamical channel to dissociation induced by the step sites in the range of energies studied. The E-i dependence can be separated into the contributions of the (111) terraces and the (100) steps. The latter exhibits an effective activation barrier for dissociation approximate to300 meV lower than the (111) terraces. The angular dependence can also be interpreted as having two contributions, one associated with the (111) terraces, and the second associated with the steps. The angular dependence associated with the step sites is broader than the dependence expected for the (111) terraces, and has a maximum for incident trajectories with an angle between the angles corresponding to the normal directions of the (111) and (100) facets. An enhanced T-S dependence is also observed on the Pt(533) surface over Pt(111). This is also associated with the influence of the step sites, and results either from the lower barrier to dissociation, or more likely a more effective coupling of the energy from the surface into the reaction coordinate. (C) 2003 American Institute of Physics