Formation of weakly bound, ordered adlayers of CO on rutile TiO2(110): A combined experimental and theoretical study

Martin Kunat1, Franziska Traeger1, David Silber1, Henshan Qiu1, Yuemin Wang1, Andre C. van Veen2, Christoph Wöll1, Piotr M. Kowalski3,, Bernd Meyer3,4, Christof Hättig3, Dominik Marx3,
1Lehrstuhl für Physikalische Chemie I, Ruhr-Universität Bochum, 44780 Bochum, Germany
2Lehrstuhl für Technische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany
3Lehrstuhl für Theoretische Chemie, Ruhr-Universität Bochum, 44780 Bochum, Germany
4Interdisziplinäres Zentrum für Molekulare Materialien (ICMM) and Computer-Chemie-Centrum (CCC), Universität Erlangen-Nürnberg, 91052 Erlangen, Germany

J. Chem. Phys., 130, 144703 (2009).
(Received 11 December 2008; accepted 23 February 2009; published online 9 April 2009)

The adsorption of CO on the rutile TiO2(110) surface was investigated using He atom scattering (HAS), high resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS), and different types of ab initio electronic structure calculations. The experimental and theoretical results allow to put forward a consistent picture for this rather complicated adsorbate system. At 70 K a (2x1) adlayer with a glide symmetry plane is formed, containing two molecules per unit cell which are tilted in alternate directions by about 20 degrees relative to the surface normal. For this high density phase, the theoretical calculations reveal a substantial repulsion between CO molecules on neighboring lattice sites, in accord with the results of a detailed analysis of the experimental TDS data. The CO binding energy depends strongly on coverage and varies between 0.20 eV for the saturated monolayer and 0.36 eV for isolated molecules. The CO-CO repulsion leads to the desorption of about half of the CO molecules above 70 K and the formation of low density phases. HAS gave no indication of ordered adlayers at these lower coverages. For the internal stretching vibration of the CO molecules a value of 273 meV was determined by HREELS, in very good agreement with the theoretical calculations.

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