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

The vibrational spectrum of carbon monoxide at the Pt/acetonitrile interface as a function of applied potential has been investigated using the surface-enhancedRamanspectroscopy technique. The electrolyte is 0.1 M LiClO4. The bands observed at ca. 506 and 2055 cm-1 are attributed to the platinum-CO (Pt-C) and intramolecular C-O (C-O) stretching vibrations, respectively, suggesting linearly adsorbed CO on platinum. The (Pt-C) band has an experimental Stark tuning rate of-4 cm-1/V, while the slope of (C-O) band frequency versus potential approaches zero before the onset of electro-oxidation ofCOads, possibly resulting from low surface coverage ofCOon platinum. The roughened Pt electrode surface has a high electrocatalytic activity, on whichCOelectro-oxidation occurs at ca.-0.7V(vs Ag/Ag+). The main product ofCOads oxidation is confirmed to be carbonate due to the existence of trace water in the double-layer region as a source of oxygen for the reaction. It has also been found that the solvent acetonitrile can exert a chemisorbed decomposition reaction on the roughened Pt surface, while the adsorption of CO can significantly inhibit this reaction.

Surface-enhanced Raman scattering (SERS) spectra of pyridine adsorbed onto bare platinum and nickel electrodes in nonaqueous solutions are reported in this Letter. There are similarities and differences between the SERS from aqueous and nonaqueous solutions. The surface enhancement factor for platinum in acetonitrile solution has been calculated to decrease by a factor of ca. 10 compared with that in the aqueous media. The double-band character for the ring breathing mode is observed at 1009 and 1019cm-1. Two adsorption modes of pyridine on the platinum surface were assumed. Part of the pyridine molecules may be chemisorbed onto the surface, with the ring plane oriented vertical to the surface; other pyridine molecules may co-adsorb with lithium cations onto the surface.

Surface-enhanced Raman scattering from a silver electrode in solution of 0.1 M LiClO4 in acetonitrile has been analyzed as a function of applied potential. Three m (O-H) bands associated with the interfacial water and two m (O-H) bands associated with the OH ion species were observed depending on the electrode potential. The band at 3487cm 1 is favored at relatively positive potentials and assigned to H2O molecules interacting with the electrode surface via the oxygen atoms. Another band at 3586cm 1 appears in a wider potential region and is assigned to the H2O molecules with one or both of the hydrogen atoms facing the electrode surface. Additionally, evidence for the possible surface ion pair, Li

The vibrational spectrum of carbon monoxide, exerted by dissociation of formic aid, has been investigated at the platinum electrode as a function of applied potential by using the surface-enhanced Raman spectroscopy (SERS) technique. The electrolyte is 0.1M LiClO4. Two typical SERS features observed at 475-490 and 2055-2080 cm-1 are attributed to the platinum-CO (Pt-C) and intramolecular C-O (C-O) stretching vibration, respectively, indicating linearly adsorbed CO on platinum. Comparisons of the present data with previous studies in aqueous solutions show that solution components, particularly the dielectric in the inner double layer, may significantly influence the interaction of CO with platinum, especially the CO intramolecular mode. Electrooxidation of CO was observed to occur at potentials more positive than 0.6 V, being slightly negative relative to previous studies for CO on smooth platinum, suggestive of a higher electrocatalytic activity for the present highly roughened platinum surface. At positive and moderately negative potentials (-0.2 to 0.6 V), the Pt-C and CO intramolecular bands exhibit opposite frequency changes with decreasing potential, with Stark tuning rate being -6 and 24 cm-1/V, respectively. At more negative potentials, both

Using confocal Raman microscopy, potential dependent surface-enhanced Raman spectra (SERS) of pyridine adsorbed on a bare zinc (Zn) bulk electrode were observed for the first time, and the adsorption behavior of pyridine on zinc was discussed. An electrochemical oxidation-reduction method was employed to roughen Zn electrodes for creating SERS. Related SEM measurement was performed to obtain the morphological information of the roughened electrode for understanding the SERS mechanism on it. An enhancement factor of around two orders of magnitude for pyridine adsorbed on a roughened Zn electrode was estimated.