Dresden 2009 – wissenschaftliches Programm

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O: Fachverband Oberflächenphysik

O 39: Metal substrates: Solid-liquid interfaces

O 39.7: Vortrag

Mittwoch, 25. März 2009, 16:30–16:45, SCH A315

Dependency of the Vibrational Stark-Effect on the preadsorbed Anion-Species on a Cu(100) Electrode Surface — •Melanie Röefzaad, Duc Than Pham, Peter Broekmann, and Klaus Wandelt — Institute for Physical and Theoretical Chemistry, University of Bonn

Fourier transform infrared reflection absorption spectroscopy (FT IRRAS), combined with electrochemical STM, has been used to monitor the vibrational frequency shifting as a function of the electrode potential and the pre-adsorbed anion-species. As probe-molecule served the redoxactive 1,1′-diphenyl-4,4′-bipyridinium (DPV). Halogenide anions are pre-covering the electrode surface by specific adsorption in a wide potential range.^[1] These highly ordered anion-layers are able to serve as a template for the adsorption of DPV. EC-STM studies revealed no structural changes in the adsorbed monolayer while changing the anion or the potential. Excluding changes in IRRA-spectra through reorientation, shifts induced by changing the applied potential are nicely visible. The expected effect was missing in the case of pre-adsorbed Cl⁻ and Br⁻. Only with I⁻ significant changes in the IRRA-spectra could be observed. Specific bands show a clear shift to higher frequencies. Those shifts indicate a strengthening of the bonds between the adsorbed molecules formed through charge-transfer-complexation. This gives a clue to a higher electrostatic effect on the organic adlayer with pre-adsorbed iodide due to its reduced partial charge and as a consequence, a more covalent bonding to the copper surface.

^[1] Broekmann et al., Surf. Sci. 517 (2002) 123