Berlin 2008 – scientific programme

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O: Fachverband Oberflächenphysik

O 55: Poster Session III - MA 141/144 (Methods: Atomic and Electronic Structure; Particles and Clusters; Heterogeneous Catalysis; Semiconductor Substrates: Epitaxy and Growth+Adsorption+Clean Surfaces+Solid-Liquid Interfaces; Oxides and Insulators: Solid-Liquid Interfaces+Epitaxy and Growth; Phase Transitions; Metal Substrates: Adsorption of Inorganic Molecules+Epitaxy and Growth; Surface Chemical Reactions; Bimetallic Nanosystems: Tuning Physical and Chemical Properties; Oxides and insulators: Adsorption; Organic, polymeric, biomolecular films; etc.)

O 55.68: Poster

Wednesday, February 27, 2008, 18:30–19:30, Poster F

The structure of the first layer of acetylene adsorbed on NaCl(100) — Aldo Cartagena, •Jochen Vogt, and Helmut Weiss — Chemisches Institut der Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg

Acetylene adsorbed on NaCl(100) is considered as a model system of physisorption under the conditions of a moderate lattice mismatch and, moreover, the formation of hydrogen bonds between neighboring molecules. Hydrogen bonds are known to cause red-shifts of the IR-active C–H stretch modes of the molecules. In low-energy electron diffraction experiments, a (3√2×√2)R45^∘ symmetry of the first layer of acetylene is observed at 75 K, in agreement with a previous study [1]. Under the same conditions, polarization infrared spectroscopy reveals a splitting of the asymmetric stretch mode in three absorptions at 3227.3, 3230.5, and 3248.7 cm⁻¹, respectively, also in agreement with a previous study [2]. We use potential calculations to determine the structure of the adlayer and vibrational exciton theory guided by ab initio calculations to give a new assignment of the observed IR transitions to molecules on inequivalent sites, the latter being interlinked by different numbers of hydrogen bonds.

[1] A. Glebov et al., Phys. Rev. B 106 (1997) 6499

[2] S. K. Dunn et al., J. Phys. Chem. 96 (1992) 5284