LASER-INDUCED THERMAL DECAY OF SERS AS A PROBE OF SILVER SURFACE ACTIVE SITES IN ELECTROCHEMICAL SYSTEMS.

The activation parameters for the temperature dependent irreversible loss of surface enhanced Raman scattered (SERS) intensity from pyridine and chloride adsorbed at silver surfaces in an electrochemical environment have been determined. Accurate laser-induced surface temperatures must be known for these experiments and are calculated from the Stokes and anti-Stokes intensities of adsorbed pyridine. The laser-induced heating method is used successfully to promote a first order reaction at the electrode surface. It is found that the kinetic data follow Arrhenius behavior for both pyridine and chloride as shown in the figures. The activation energies are 13 kcal/mole and 26 kcal/mole for pyridine at two different types of sites on the silver surface. Similarly, values for coadsorbed chloride are determined from the Ag-Cl vibration and are found to be 13 kcal/mole and 25 kcal/mole. These values are consistent with a surface reaction that involves the discharge of a positively charged Ag adatom or cluster.