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Local adsorption sites and bondlength changes in Ni/H/CO and Ni/CO

DOI: 10.1016/S0039-6028(03)00885-9 DOI Help

Authors: J. T. Hoeft (Fritz-Haber-Institut der Max-Planck-Gesellschaft) , M. Polcik (Fritz-Haber-Institut der Max-Planck-Gesellschaft) , D. I. Sayago , M. Kittel (Fritz-Haber-Institut der Max-Planck-Gesellschaft) , R. Terborg (Fritz-Haber-Institut der Max-Planck-Gesellschaft) , R. L. Toomes (Department of Physics, University of Warwick) , J. Robinson (Department of Physics, University of Warwick) , D. P. Woodruff (Department of Physics, University of Warwick) , M. Pascal (Department of Chemical and Biological Sciences, Centre for Applied Catalysis, University of Huddersfield) , G. Nisbet (Diamond Light Source) , C. L. A. Lamont (Department of Chemical and Biological Sciences, Centre for Applied Catalysis, University of Huddersfield)
Co-authored by industrial partner: No

Type: Journal Paper
Journal: Surface Science , VOL 540 , PAGES 441 - 456

State: Published (Approved)
Published: August 2003

Abstract: The local adsorption geometry of CO adsorbed in different states on Ni(1 0 0) and on Ni(1 0 0) precovered with atomic hydrogen has been determined by C 1s (and O 1s) scanned-energy mode photoelectron diffraction, using the photoelectron binding energy changes to characterise the different states. The results confirm previous spectroscopic assignments of local atop and bridge sites both with and without coadsorbed hydrogen. The measured Ni–C bondlengths for the Ni(1 0 0)/CO states show an increase of 0.16 ± 0.04 Å in going from atop to bridge sites, while comparison with similar results for Ni(1 1 1)/CO for threefold coordinated adsorption sites show a further lengthening of the bond by 0.05 ± 0.04 Å. These changes in the Ni–CO chemisorption bondlength with bond order (for approximately constant adsorption energy) are consistent with the standard Pauling rules. However, comparison of CO adsorbed in the atop geometry with and without coadsorbed hydrogen shows that the coadsorption increases the Ni–C bondlength by only 0.06 ± 0.04 Å, despite the decrease in adsorption energy of a factor of 2 or more. This result is also reproduced by density functional theory slab calculations. The results of both the experiments and the density functional theory calculations show that CO adsorption onto the Ni(1 0 0)/H surface is accompanied by significant structural modification; the low desorption energy may then be attributed to the energy cost of this restructuring rather than weak local bonding.

Journal Keywords: Density functional calculations; Photoelectron diffraction; Chemisorption; Surface structure, morphology, roughness, and topography; Nickel; Carbon monoxide; Hydrogen atom; Low index single crystal surfaces

Subject Areas: Physics, Chemistry, Materials

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