The different initial interactions of benzotriazole (BTAH) with iron in both 0.5 M H2SO4 and simulated saline water (3.4% NaCl) have been investigated systematically by using a confocal microprobe Raman system, surface-enhanced Raman spectroscopy (SERS), and electrochemical potentiodynamic polarization curves. The SERS spectra of BTAH at the bare iron electrodes in both 0.5 M H2SO4 and simulated saline water have been obtained successfully for the first time. Electrochemical measurements show that the inhibition efficiency of BTAH is higher in saline water than that in acid solution, which is in accordance with the identification of the surface interaction on the basis of the SERS data. BTAH may be physisorbed onto the iron surface through its neutral molecule form or protonated BTAH2 + ions. While in saline water, the formation of the surface coordination compound characterized as Fe(II)-BTA may contribute to the outstanding spectral features. A cleavage of the NH bond is believed to occur while adsorption of BTAH onto iron proceeds. This more compact surface film results in a higher inhibition efficiency in comparison with that in an acid 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 the 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 intermediate 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.

Surface-enhanced Raman spectroscopy has been extended successfully to the study of a bare iron electrode (without any deposition of other noble metals) exposed to the neutral solution containing thiocyanate over a wide potential range from -1.8 to -0.4 V. The applied potential has a significant influence on the Raman frequency shift of SCN- as a result of the electrochemical Stark effect. Both N- and S-coordination modes were observed. Results show that at large negative potentials N-bound SCN- is favored, whereas at relatively positive potentials, S-bound thiocyanate predominates the iron surface. A sudden change in the d

Surface-enhanced Raman scattering (SERS) from the platinum electrode-acetonitrile interface in the presence of iodide, the lithium cation, water, and pyridine was analyzed as a function of applied potential. It was found that the typical Raman band of cyanide species by the dissociation of the solvent acetonitrile upon adsorption onto highly roughened platinum electrode surfaces was detectable for all of the systems that were studied. However, the onset potential of the dissociation reaction of acetontrile differed for the four systems. We assume that competitive adsorption may exist between each of the above four species and the solvent acetonitrile molecule, especially at the dissociation reaction-active sites of the Pt surface. This competitive adsorption therefore significantly inhibits the decomposition reaction of acetonitrile. The interactions of these adsorbates with Pt are assumed to weaken in the sequence pyridine > I-> water Li+ on the basis of the observations of different negative shifts of the onset potential of acetonitrile decomposition. For the system with water or iodide, double-band character for the CN band was also detected. It is assumed to be due to the existence of two types of adsorbed ion pairs at the Pt surface: CN-…CH3CN and CN-…Li+/Na+.

Surface-enhanced Raman scattering (SERS) spectrum of imidazole adsorbed at a silver electrode in nonaqueous acetonitrile solution has been investigated as a function of applied potential. The electrolyte is 0.1M LiClO4. Results show that imidazole adsorbs on silver as a neutral molecule via the pyridine nitrogen atom. Coadsorption of perchlorate anion with imidazole, possibly by forming intermolecular hydrogen bonding, is also suggested by the enhancement of the ClO4-band at 933 cm-1. An edge-on orientation of imidazole at more positive potentials is proposed by the observation of the increase in frequency of the ring breathing modes, along with the enhancement of most of the in-plane modes of imidazole. When the potential is made more negative, particularly near -0.5V, the imidazole ring may change from vertical to be slightly inclined to the silver surface at an intermediate angle from the surface normal. At the same time, a slight rotation of the imidazole ring plane may occur, evidenced by the observation of the changes in relative intensity of