COMPARISON OF CHARGE-TRANSFER ENHANCEMENT IN THE SURFACE ENHANCED RAMAN-SCATTERING OF PYRIDINE ON COPPER AND SILVER ELECTRODES

The object of the experiments described here is to compare the charge transfer (CT) excitation of surface enhanced Raman scattering (SERS) from pyridine adsorbed on Cu and Ag electrodes. The CT excitation is probed by varying both the applied potential and the excitation energy. SERS intensity-potential profiles of pyridine on Cu electrodes using excitation wavelengths of 620, 720, and 1064 nm and on Ag electrodes using excitation wavelengths of 580, 620, and 720 nm are presented. The maximum intensities displayed in these profiles for the two metals occur at similar applied potentials. However, these profiles differ from those predicted on the basis of the potential-dependent adsorption behavior of pyridine on Cu and Ag electrodes. These results are discussed in term of the energetics of the CT bands for pyridine on Cu and Ag electrodes. The energy position and width of the CT band can be determined from the SERS intensity-potential profiles. Although the CT bands are energetically similar for both electrodes, the energy width of the Ag CT band is ca. 65% less than the energy width of the Cu CT band suggesting that the CT sites on Cu are energetically more heterogeneous that those on Ag.