INFRARED ATTENUATED TOTAL REFLECTION SPECTROSCOPY AT THE METAL ELECTROLYTE INTERFACE

The Kretschmann configuration for exciting surface plasmon polaritons by attenuated total reflection has been employed to study the electrode potential dependence of the reflectance in the infrared spectral range (2800-1) of a thin Au(111) film in contact with 1 N sulphuric acid in isotopic mixtures of H2O and D2O. It is shown that increased sensitivity due to the polariton resonance can only be ibtained if the absorption coeficcient of the solution is fairly low. The contributions to the differential reflectance signal Δ RR from electron density variations in the metal surface, changes in the refractive index of the Helmholtz layer and alterations of the vibrational properties of solvent molecules as a function of electrode potential have been analysed. The results of model calculations are compared to the experimental data and the dominant contributions to ΔRR are identified. The possibility of obtaining information on the vibrational properties of the interfacial region with this new experimental method is discussed.