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

Paper SS3-FrM7
The Local Adsorption Structure of CH@sub 3@- on Cu(111)

Friday, November 2, 2001, 10:20 am, Room 122

Session: Clean and Adsorbed Surfaces
Presenter: J. Robinson, University of Warwick, UK
Authors: M. Pascal, University of Huddersfield, UK
C.L.A. Lamont, University of Huddersfield, UK
J. Robinson, University of Warwick, UK
R.L. Toomes, University of Warwick, UK
J.-H. Kang, University of Warwick, UK
D.P. Woodruff, University of Warwick, UK
L. Constant, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Germany
S. Bao, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Germany
M. Kittel, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Germany
J.-T. Hoeft, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Germany
M. Polcik, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Germany
Correspondent: Click to Email
Methyl is an important intermediate in many surface reactions, but there is a dearth of information on its local adsorption geometry. We present the results of both experimental and theoretical studies of the structure of CH@sub 3@- on Cu(111). The experiments were based on C 1s scanned-energy mode photoelectron diffraction (PhD) from a surface formed either by exposure to CH@sub 3@- ions from a Bent-type azomethane (CH@sub 3@-N-N-CH@sub 3@) cracking source, or from surface dissociation of methyl iodide (CH@sub 3@I) on the surface. The coadsorbed I , which occupies the fcc hollow sites (directly above a third layer Cu atom) appears to have little effect on the geometry of the methyl which also occupies an fcc hollow site but shows a marginally (0.04±0.03 Å) smaller layer spacing relative to the substrate in the presence of the coadsorbate. In the pure methyl layer the C-Cu outermost layer spacing is 1.66±0.02Å. Density-functional theory results (using the CASTEP code in GGA with ultrasoft pseudopotentials) reproduce the preference for hollow site adsorption (albeit with a very small preference for the hcp hollow) but also reveal a strong preference for an azimuthal orientation in which the C-H bonds are oriented along the Cu-Cu close packed directions, placing the H atoms closer to near-neighbour Cu atoms.