Acetate adsorption at g-old electrodes is studied in perchloric acid Solutions by cyclic voltammetry and in-situ infrared spectroscopy. External reflection measurements, performed with gold single crystal electrodes, are combined with Surface Enhanced Infrared Reflection Absorption Spectroscopy experiments under attenuated total reflection conditions (ATR-SEIRAS) carried Out with sputtered gold thin-film electrodes. Theoretical harmonic IR frequencies of acetate species adsorbed with different geometries oil Au clusters with (1 1 1), (100) and (1 10) orientations have been obtained from B3LYP/LANL2DZ, 6-31 +G* calculations. The theoretical and experimental results confirm that. irrespective of the surface crystallographic orientation, bonding of acetate to the surface involves the two oxygen atoms ofthe carboxylate group, with the OCO plane perpendicular to the metal Surface. DFT calculations reveal also that the total charge ofthe metal cluster-acetate supemolecule has small effect on the vibrational frequencies of adsorbed acetate species. Both the external and the internal reflection measurements show the co-adsorption of acetate and perchlorate anions. Step-scan measurements carried Out with the gold thin-film electrodes have allowed the monitoring ofthe time-dependent behaviour of perchlorate, acetate and water bands in potential step experiments. Acetate adsorption Under those conditions is shown to involve perchlorate desorption and to follow a Langmuir-type kinetics. The step-scan spectra also show the rise and decay of transient water structures with parallel time-dependent shifts of the background intensity in the infrared spectra. (c) 2007 Elsevier Ltd. All rights reserved.