AVS 52nd International Symposium
    Surface Science Tuesday Sessions
       Session SS1-TuM

Paper SS1-TuM10
Vibrational and Photoelectron Spectroscopy of Formic Acid and Water Coadsorbed on Au(111) Surfaces: Chemical Interaction and Compound Formation

Tuesday, November 1, 2005, 11:20 am, Room 202

Session: Vibrational Spectroscopy of Surfaces
Presenter: G. Pirug, Forschungszentrum Jülich GmbH, Germany
Authors: G. Pirug, Forschungszentrum Jülich GmbH, Germany
M. Kazempoor, Forschungszentrum Jülich GmbH, Germany
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The coadsorption of formic acid (HCOOH) and water (H@sub 2@O) has been studied on Au(111) single crystal surfaces by means of vibrational spectroscopy (HREELS) and photoelectron spectroscopy (XPS) in the temperature range between 90 K and 200 K. Formic acid adsorbs at 90 K molecularly with vibrational modes characteristic for solid formic acid. Annealing results in a complete desorption at 190 K. Upon sequential adsorption of formic acid and water at 90 K no significant chemical interaction can be deduced from the vibrational signatures and the core level photoelectron binding energies. Independent of the sequence of exposure coadsorption or layered growth without intermixing is observed in the monolayer and the multilayer regime, respectively. Heating of the coadsorbed layer to about 140 K results in the formation of a new surface complex with characteristic vibrational losses at 190, 590 and 1000 cm @super -1@. Based on these frequencies and supported by the corresponding stoichiometries as deduced from XPS possible compounds will be discussed. Upon further annealing this complex decomposes leaving only molecularly adsorbed formic acid on the surface at 160 K. These results will be discussed in the light of recent findings for the electrochemical oxidation of formic acid on Au surfaces.