AgCl–Ag cluster enhanced optical second harmonic generation from an electrode surface

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Abstract
Evidence is given for the presence of AgCl–Ag cluster complexes on a silverelectrodesurface. The complexes are formed during electrochemical cycling of the electrode in a KCl electrolyte. These cluster complexes provide a resonance enhancement for surface optical second harmonic generation from the electrode during electrochemical reduction of adsorbed AgCl oxidation product. The complexes possess a strong electronic resonance in the visible wavelength region and may be related to species in the silver halide photographic process. Recent surface enhanced Raman scattering studies of this surface have demonstrated a resonance enhancement from similar cluster structures. Previous second harmonic studies on this system have not identified any resonance enhancement from surface complexes. The studies of this paper address the question of resonance enhancement from surface sites or clusters and their contribution to second harmonic generation from these interfaces. In addition, multiphoton induced luminescence studies of the surface clusters are presented. These studies indicate that the silver clusters associated with the AgCl–Ag cluster complex formation are six atoms in size or less. Second harmonic generation and cluster luminescence are also used to follow and elucidate molecular level events at the electrodesurface during oxidation and reduction in the electrochemical cycling experiments.

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