BIMODAL ANGULAR AND VELOCITY DISTRIBUTIONS OFCO2DESORBING AFTER OXIDATION OF CO ONPt(111)

E. Poehlmann, M. Schmitt, H. Hoinkes and H. Wilsch
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E. Poehlmann: Physikalisches Institut der Universität Erlangen-Nürnberg, Erwin-Rommel-Str. 1, D-91058 Erlangen, Germany
M. Schmitt: Physikalisches Institut der Universität Erlangen-Nürnberg, Erwin-Rommel-Str. 1, D-91058 Erlangen, Germany
H. Hoinkes: Physikalisches Institut der Universität Erlangen-Nürnberg, Erwin-Rommel-Str. 1, D-91058 Erlangen, Germany
H. Wilsch: Physikalisches Institut der Universität Erlangen-Nürnberg, Erwin-Rommel-Str. 1, D-91058 Erlangen, Germany

Surface Review and Letters (SRL), 1995, vol. 02, issue 06, 741-758

Abstract: Time-of-flight (TOF) distributions ofCO2molecules desorbing after the oxidation of CO onPt(111)were investigated at various desorption angles ϑ for surface temperaturesTsin the range 550–800 K. ThePt(111)surface was exposed to a continuous flow ofO2from a doser and to a chopped CO nozzle beam. Surface residence-time effects proved to be unimportant or were elucidated. Bimodal TOF distributions composed of two parts were obtained: molecules with a Maxwellian velocity distribution corresponding toTsappeared in a cosine-shaped angular distribution and molecules with appreciably higher kinetic energies (mean kinetic energy normal to the surface ⊥≈9kTs) were observed in a narrow angular distribution proportional tocos8ϑ. The partition of the total desorbingCO2flux to these two channels depended onTsand ϑ and the total oxygen dosed0accumulated during an experiment. With increasingd0the Maxwellian component markedly increased at the expense of the fast component. The observed trends suggest almost only fast desorption from cleanPt(111). We therefore assume Maxwellian desorption to occur mainly from surface sites gradually produced under the influence of oxygen.

Date: 1995
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DOI: 10.1142/S0218625X95000674

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