INTERACTION OF PYRIDINE WITH PHOTOELECTRONS EMITTED AT THE SILVER AQUEOUS-SOLUTION INTERFACE

Pyridine added to a solution containing scavengers of photoelectrons e mitted from silver (N2O, CO2) causes a strong decrease in the measured photocurrent or even its complete suppression for concentrations of p yridine exceeding 0.1 M. Such behaviour, which remains in apparent con tradiction to the effect of deposited pyridine on photoemission from s ilver in vacuum, is due to the fact that pyridine itself acts as an ac ceptor of the emitted photoelectrons. As the anion radical formed unde rgoes reoxidation (back electron transfer) at the silver surface, this process leads to a decrease in the net photocurrent which is dependen t on the concentration ratio of the two competing accepters (i.e. pyri dine and N2O). The observation that pyridine (adsorbed on silver and i n solution) sustains a reversible electron transfer, along with the pr evious observation that photoemission from a roughened Ag electrode in to an aqueous solution extends to at least 650 nm, provides a possible interpretation of the surface-enhanced Raman spectroscopy effect for pyridine, which involves both electromagnetic and charge-transfer mech anisms. (C) 1998 Elsevier Science B.V.