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O: Oberflächenphysik
O 24: Oberfl
ächenreaktionen (II)
O 24.11: Vortrag
Dienstag, 12. März 2002, 18:45–19:00, H44
Thermal and femtosecond laser-induced desorption of NO and NO+CO from PT(533) — •Ellen Backus, Michael Grecea, Heiner Scheld, Bernd Riedmüller, Mischa Bonn, and Aart Kleyn — Leiden Institute of Chemistry, Leiden University, Einsteinweg 55, 2333 CC Leiden
We use TDS, RAIRS and our new femtosecond laser system to unravel the desorption and reaction of CO and NO from a stepped Pt(533) surface. Our initial experiments are focused on the adsorption, dissociation and desorption behavior of NO. A minor fraction of NO molecules dissociated on the reactive steps followed by recombination of the nitrogen atoms to produce N2. As a sufficient number of free adsorption sites on the Pt surface are required for the kinetically hindered dissociation, saturation of produced N2 occurs at low coverages. Experiments with isotopically labelled NO show that also N2O is produced. In the femtosecond laser experiments the desorption reaction is ’switched on’ with an ultrashort light pulse. We investigate the kinetic energy distribution for laser-induced desorbing molecules. For desorbing NO molecules we find a very high translational temperature (about 2000 K) indicating an electron-mediated desorption. This is corroborated by the observation that the translational temperature depends very strongly on the laser fluence. Furthermore we will present measurements of the cross-sections for laser-induced desorption, and look for possible isotope effects and for laser-induced dissociation products.