IUVSTA 15th International Vacuum Congress (IVC-15), AVS 48th International Symposium (AVS-48), 11th International Conference on Solid Surfaces (ICSS-11)
    Surface Science Thursday Sessions
       Session SS3-ThP

Paper SS3-ThP11
Adsorption of Cyclopentene and Cyclohexene on Ordered Sn/Pt(111) Surface Alloys

Thursday, November 1, 2001, 5:30 pm, Room 134/135

Session: Surface Reactions Poster Session
Presenter: J. Breitbach, University of Bonn, Germany
Authors: J. Breitbach, University of Bonn, Germany
D. Franke, University of Bonn, Germany
G. Hamm, University of Bonn, Germany
F. Jaeger, University of Bonn, Germany
C. Becker, University of Bonn, Germany
K. Wandelt, University of Bonn, Germany
Correspondent: Click to Email
The adsorption of cyclopentene (C@sub 5@H@sub 8@) and cyclohexene (C@sub 6@H@sub 10@) on Pt(111) and two Sn/Pt(111) surface alloys has been investigated using HREELS, UPS, LEED and TPD. The two ordered Sn/Pt(111) alloys were prepared by annealing a Sn film deposited onto Pt(111). Depending on the temperature of annealing the surface exhibited a (2x2) or (@sr@3x@sr@3)R30° LEED pattern corresponding to a surface composition of Pt@sub 3@Sn and Pt@sub 2@Sn, respectively.@footnote 1@ At temperatures below 250K C@sub 5@H@sub 8@ and C@sub 6@H@sub 10@ adsorb intact on the pure Pt(111) surface. The di-@sigma@-bonding of the molecules is signified by the absence of the olefinic CH-stretching mode that is identified for the undisturbed molecules in the multilayer. Upon heating part of the C@sub 5@H@sub 8@ and C@sub 6@H@sub 10@ desorb and the remaining amounts are converted to C@sub 5@H@sub 5@ and C@sub 6@H@sub 6@, respectively. On the alloy surfaces the decomposition of C@sub 5@H@sub 8@ and C@sub 6@H@sub 10@ is completely suppressed. As the Sn concentration is increased, there is a marked decrease in the C@sub 5@H@sub 8@ desorption temperature from 278K on Pt(111) to 243K on the (2x2) alloy and to 192K on the (@sr@3x@sr@3)R30° alloy. This behaviour is in close analogy to the behaviour of ethylene on Sn/Pt(111)@footnote 2@ and hints to similar adsorption geometries of cyclopentene and ethylene on the pure Pt(111) surface. The adsorption of C@sub 6@H@sub 10@ is more dramatically influenced by alloying: On the (2x2) surface C@sub 6@H@sub 10@ is still di-@sigma@ bonded, while on the (@sr@3x@sr@3)R30° surface C@sub 6@H@sub 10@ is physisorbed. It can be concluded that C@sub 6@H@sub 10@ adsorbs on Pt-threefold hollow sites on Pt(111), which are not present on the (@sr@3x@sr@3)R30° surface. @FootnoteText@ @footnote 1@ M.T. Paffett, R.G. Windham Surf. Sci. 208 (1989) 34 @footnote 2@ Y.-L. Tsai, C. Xu and B.E. Koel Surf. Sci. 385 (1997) 37.