Untersuchung der Adsorption von Sauerstoff und Kohlendioxid auf Metalloberflaechen

The adsorption of oxygen on Rh(111) and of carbon dioxide also on Rh(111) and on Ni(110) was investigated with high resolution helium atom scattering, photoelectron spectroscopy and for the first system also with sticking coefficient measurements. Moreover, structural determinations of the rather complex superstructure of the oxygen covered Cu(100) and Al(111) surfaces were performed. The combination and simultaneous use of the above mentioned methods yield a detailed description of the oxygen rhodium potential energy surface. The adsorption process exhibits, at surface temperatures between 100 K and 300 K for low energies of the oxygen molecules (<100 MeV), a precursor mediated behaviour. For intermediate energies, between 100 MeV and 200 MeV, the observed behaviour changes from direct dissociative chemisorption at low surface coverage to a precursor mediated process at higher coverages. Finally, at high energies (>200 MeV), a direct dissociative chemisorption behaviour occurs. It was shown that in a one-dimensional picture the potential energy surface was build up by three adsorption states, where the energy barriers turn out to be carrier distributions, for which most of the minima and maxima could be determined. Moreover, the adsorption behaviour of the oxygen depends upon the incident angle of the molecules and the existing coverage on the surface. An additional detailed investigation of the low temperature adsorption (40 K) led to the result that, because of the high reactivity of the Rh(111) surface to oxygen, all molecules dissociatively chemisorb at such low surface temperatures in the submonolayer range. Oxygen molecules only physisorb on a surface precovered with oxygen. For the analysis of the inelastic helium atom scattering data lattice dynamic calculations using the slab model were performed. This yields a good agreement with the measured data for the different superstructure models. It was shown for the adsorption of CO_2 on the metal surfaces that it is, in principle, possible to investigate a change in the nature of the chemical bond for an adsorbed molecule with inelastic helium atom scattering. In this case the transformation from CO_2 to CO_2"- was observed directly. The elastic helium atom scattering data for the structural determination of the oxygen covered Cu(100) and Al(111) surfaces were numerically simulated using the two-dimensional Eikonal approximation. This method produced distinct information about the domain and island distributions on the surfaces and about the structure within these domains and islands. (orig.)351 refs.Available from TIB Hannover: RA 1396(1995,3) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman