The adsorption of water on the stepped Pt(533) surface has been investigated using temperature-programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). Both the TPD spectra and the RAIRS results reveal two submonolayer states and one multilayer phase. In the submonolayer regime, water first adsorbs on the Pt(100)-step edges of the surface. The water molecules at these steps induce a supplementary stabilization of the water that subsequently adsorbs onto the four atoms wide (111) terraces. In contrast, the multilayer TPD feature is not affected by the stepped nature of the substrate and is very similar to water desorption from, for example, the flat Pt(111) surface. RAIRS data indicate strong hydrogen-bonding interactions between water molecules adsorbed on the steps already at very low coverages (≤0.13 ML). This is in agreement with DFT calculations that demonstrate that the water−water interaction is sufficiently strong that water molecular chains could be formed along the step edges at very low coverage. Both the RAIRS data and the DFT calculations support intact H2O adsorption on Pt(533).

The scattering of Ar atoms on a Ru (0001) surface has been studied by applying supersonic molecular beam techniques. Variation of the incidence energy (E i ) results in a rich variety of angular and energy distributions. At a low energy, clear zero-order diffraction has been identified. At higher energies (5 1 eV), argon scattering of Ru (0001), however, seems to be dominated by a totally different mechanism, which appears to be almost quantitatively reproduced by the washboard model, developed by Tully (J. C. Tully, J. Chem. Phys., 1990, 92, 680, ref. 1). This is surprising since his comparison of the washboard model to a reference of classical trajectory calculations for the Ar=Pt ( 111) system showed essential deviations. Our attempt to reproduce the experimental Ar=Ru (0001) data by similar simulations was unsuccessful, most likely due to shortcomings in the description of the solid state.

Dissociative chemisorption of CH 4 on a cesiated Pt(111) surface studied by supersonic molecular beam scattering techniquesThe influence of well-defined steps on the dynamics of the dissociative chemisorption of methane on Pt͑533͒ 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 i , and surface temperature T S . For incident kinetic energies in the range 26 ϽE i (meV)Ͻ1450, the initial dissociation probability of CH 4 on the Pt͑533͒ surface is higher than on Pt͑111͒, 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 ͑111͒ terraces and the ͑100͒ steps. The latter exhibits an effective activation barrier for dissociation Ϸ300 meV lower than the ͑111͒ terraces. The angular dependence can also be interpreted as having two contributions, one associated with the ͑111͒ terraces, and the second associated with the steps. The angular dependence associated with the step sites is broader than the dependence expected for the ͑111͒ terraces, and has a maximum for incident trajectories with an angle between the angles corresponding to the normal directions of the ͑111͒ and ͑100͒ facets. An enhanced T S dependence is also observed on the Pt͑533͒ surface over Pt͑111͒. 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.

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