Surface Science 206 (1988) 1-19 North-Holland, Amsterdam zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDC ADSORPTION AND REACTION OF CO, ON Ni{ 110): X-RAY PHOTOEMISSION, NEAR-EDGE X-RAY ABSORPTION FINE-STRUCTURE AND DIFFUSE LEED STUDIES G. ILLING, D. HESKETT *, E.W. PLUMMER *, H.-J. FREUND Lehrstuhl ftir Physikalische Chemie I, Ruhr-Universitiit Bochum, D-4630 Bochum, Fed Rep. of Germany J. SOMERS, Th. LINDNER, A.M. BRADSHAW Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4- 6, D-1000 Berlin 33, Germany U. BUSKOTTE, M. NEUMANN Fachbereich Physik, Universitiit Osnabriick, Barbarastrasse 7, D-4500 Osnabriick, Fed. Rep. of Germany U. STARKE, K. HEINZ institut ftir Angewandte Physik, Lehrstuhl ftir Festkiirperphysik der lJniversit& Erlangen-Niirnberg, Erwin-Rommel-Strasse I, D-8520 Erlangen, Fed. Rep. of Germany P.L. DE ANDRES * *, D. SALDIN and J.B. PENDRY The Blackett Laboratoty, Imperial College, London S W7 282, UK Received 31 March 1988; accepted for publication 21 July 1988 Using three different techniques - X-ray photoemission (XPS), near-edge X-ray absorption spectroscopy (NEXAFS) and diffuse LEED - we have studied the adsorption and reaction of CO, on Ni(ll0). In agreement with previous angle-resolved photoemission (ARUPS) and vibrational electron energy loss (EELS) data both a linear, physisorbed molecule and a bent, chemisorbed species CO,S- are found. An evaluation of the XPS line intensities shows that the stoichiometry of the chemisorbed species is 1 to 2 in carbon and oxygen. The polarisation dependence of the NEXAFS indicates that the physisorbed molecule lies with its axis parallel to the surface and that the molecular plane of the CO;- species is perpendicular to the surface. There is no clear preferential azimuthal orientation. This is in agreement with a diffuse LEED analysis where equal numbers of bent molecules adsorbed on atop sites and oriented along the (100) and (110) directions gave the best fit to the data. * Permanent address: Department of Physics, University of Pennsylvania, Philadelphia, PA 19104, USA. * * Permanent address: Instituto de Materiales, c/Serrano 144, E-28006 Madrid, Spain. 0039-6028/88/$03.50 0 Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)