ELECTROREFLECTANCE STUDY ON THE CHARGE-TRANSFER TRANSITION AT SILVER-ELECTROLYTE INTERFACES

Electroreflectance (ER) spectra at silver-electrolyte interfaces have been measured in order to study the charge-transfer (CT) transition ef fect. On the silver surface with pyridine or piperidine adsorbates, an anomalous absorption band is observed near 2 eV in the ER spectra whe n adsorbed molecules make direct contact with the silver surface. This newly observed absorption band is associated with the CT transition, which is analogous to earlier results in ultra-high vacuum systems. Th e energy of the CT transition depends predominantly on the potential o f the silver electrode and is attributed to the Stark shift induced by the potential. In addition to the ER data, the surface-enhanced secon d-harmonic generation (SESHG) results indicate that the potential depe ndence of the SESHG intensity originates from the CT state excitation through the potential-tuned resonance process.