Symmetry superposition studied by surface second-harmonic generation.

The components of a third-rank g' ' tensor have been split into contributions due to 1-fold, 2fold, 3-fold, and (x}-fold or isotropic rotation axes for a surface of C, symmetry. Theoretical analysis of the rotation patterns obtained by the surface second-harmonic (SH) generation indicates that a complete symmetry analysis cannot be performed without knowledge of the relevant distribution functions. Rotation axes of lower symmetry create via "overtones" or "harmonics" contributions apparent in the analysis of the rotation axes of higher symmetry. An experimental example is the observation of structural changes of Au(111) surfaces in an aqueous electrolytic environment. Potential-dependent buildup and removal of a Au(111)-(1X 23) surface could be monitored in situ