Surface-enhanced Raman scattering spectra of thiourea adsorbed at an iron electrode in NaClO4 solution

Surface-enhanced Raman scattering (SERS) spectra of thiourea at an electrochemically activated iron electrode have been investigated as a function of applied potential. The marked downshift of the CS stretching and upshift of the NCN symmetric stretching by comparison of the SERS with the normal Raman spectrum of thiourea are clearly observed and interpreted by coordination of thiourea with tire iron surface through sulfur atom. The appearance of the low-frequency mode at ca. 283 cm(-1) assigned to the Fe-S vibration supports the assumption of S-coordination of thiourea. The orientation of thiourea molecules is assumed to be slightly inclined to the iron surface at an inter-mediate angle due to the observation of the SCNN out-of-plane bending band. Potential dependence of the SERS spectra shows that thiourea may interact more strongly with the iron surface at relatively positive potentials. Coadsorption of the supporting electrolyte anion ClO4- with thiourea has also been confirmed by the SERS spectra.