A STUDY OF THE INFLUENCE OF HALIDE ADSORPTION ON A RECONSTRUCTED AU(111) ELECTRODE BY 2ND HARMONIC-GENERATION

Optical second harmonic generation (SHG) rotational anisotropy measurements were employed to study the influence of specifically adsorbed anions on the reconstructed Au(111)-(1 x 23) surface. Azimuthal rotation of the gold electrode at different potentials yields for the unreconstructed Au(111)-(1 x 1) surface the well-known three-fold symmetry pattern, while for the reconstructed Au(111)-(1 x 23) an additional one-fold symmetry pattern is observed, which leads to an assignment of C(s)-symmetry for this surface. Due to the observation of this symmetry change C(s) <--> C3v it is possible to monitor in situ the reversible transition between Au(111)-(1 x 23) and Au(111)-(1 x 1). While in perclorate solution the phase transition occurs over a wide potential region, in halide containing solution the same phase transition is restricted to the sharp potential region typical for the halide adsorption.