Dresden 2009 – scientific programme
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O: Fachverband Oberflächenphysik
O 17: Oxides and insulators III
O 17.7: Talk
Tuesday, March 24, 2009, 12:00–12:15, SCH A01
Structure of CO2 adsorbed on the KCl(100) single crystal surface — •Jochen Vogt, Milica Hadnadiev, and Helmut Weiss — Chemisches Institut der Otto-von-Guericke-Universität Magdeburg, Universitätsplatz 2, 39106 Magdeburg, Germany
Self-organization phenomena in two dimensions are a hallmark of systems with weak molecule-surface interaction in gas adsorption. On insulator single crystal surfaces, such systems can be ideally studied experimentally, e. g. by means of polarization infrared spectroscopy (PIRS) and low-energy electron diffraction (LEED). On the KCl(100) surface at a temperature of 80 K, the first layer of carbon dioxide grows in three different phases: firstly a lattice-gas, secondly a disordered phase at submonolayer coverage, which thirdly undergoes a phase-transition to a highly ordered (6√2×√2)R45∘ structure, if the CO2 partial pressure exceeds a critical temperature-dependent value. So far, not much was known about the structure of the 237 Å2 unit cell of the high-order phase which in absolute terms offers place for up to 14 inequivalent CO2 molecules. Total energy minimizations and Monte Carlo Simulations based on pair-potentials favor a structure containing 12 inequivalent molecules. Using a vibrational exciton approach, simulated infrared spectra based on this structure are in very satisfactory agreement with experimental IR spectra. According to theory, 10 molecules are stabilized on the surface due to a predominant molecule-molecule interaction, while only two molecules are "pinned" onto the surface at sites with favorable molecule-surface interaction. This might explain the rapid aging of the structure observed in the experiments.