1,10-phenanthroline adsorption on iron electrode monitored by surface-enhanced Raman scattering (SERS). Comparison to SERS of phen and its transition metal complex on silver electrode

The SER spectra of 1,10-phenanthroline (phen) adsorbed on Fe electrode in chloride medium as a function of applied potentials at 632.8 and 514.5 nm excitation wavelengths are presented. SERS spectra of phen on Co and Ni electrodes at 632.8 ran are also shown. The SER signatures of the surface complex indicate its similarity with the chemically prepared [M(phen)(3)](2+), where M = Fe2+, Co2+, or Ni2+. The same changes in relative intensities of the bands with applied potential are observed for phen on transition metals and for [M(phen)(3)](2+) on silver electrodes. These spectral changes at 632.8 nm excitation radiation resemble the spectral changes in the resonance Raman spectra of [M(phen)(3)]Cl-2 at different excitation laser lines. At the potential of maximum intensity, the strongest band in phen on Ag SER spectrum is ca. 70 times higher than that in phen on Fe, while the phen on Fe SER excitation profile is ca. 5 times higher than that of phen on Ag. At 632.8 nm radiation, the band at 557 cm(-1) for phen on Fe shows the highest profile in SER excitation profiles, while for phen on Ag the most enhanced band is at 1578 cm(-1). These results indicate that the CT excited states in phen on Fe and phen on Ag are different and that the SER CT mechanism in phen on Fe is more effective. The magnitude and dissimilarities in the [Fe(phen)(3)]Cl-2 resonance Raman profiles as compared to the SER excitation profiles of [Fe(phen)(3)](2+) on Ag emphasize the different origins of the two enhancement processes.