Raman potential-depending

Zhang Y, Edens G and Weaver M J 1991 Potential-dependent surfaoe Raman speotrosoopy of Buokminsterfullerene films on gold vibrational oharaoteristios of anionio versus neutral Cgg J. Am. Chem. Soc. 113 9395-7... 

The application of surface-enhanced Raman spectroscopy (SERS) for monitoring redox and other processes at metal-solution interfaces is illustrated by means of some recent results obtained in our laboratory. The detection of adsorbed species present at outer- as well as inner-sphere reaction sites is noted. The influence of surface interaction effects on the SER spectra of adsorbed redox couples is discussed with a view towards utilizing the frequency-potential dependence of oxidation-state sensitive vibrational modes as a criterion of reactant-surface electronic coupling effects. Illustrative data are presented for Ru(NH3)63+/2+ adsorbed electrostatically to chloride-coated silver, and Fe(CN)63 /" bound to gold electrodes the latter couple appears to be valence delocalized under some conditions. The use of coupled SERS-rotating disk voltammetry measurements to examine the kinetics and mechanisms of irreversible and multistep electrochemical reactions is also discussed. Examples given are the outer- and inner-sphere one-electron reductions of Co(III) and Cr(III) complexes at silver, and the oxidation of carbon monoxide and iodide at gold electrodes. 

A plot of the potential-dependence of the Raman intensities of a Ru binuclear p-oxo water oxidation catalyst showed evidence for one-, two-, and four-electron oxidized species. Oxygen isotopic labeling was used to characterize the catalytically active fully oxidized state.91... 

Corio, P., and Temperini, M. (2003) Surface enhanced Raman spectroscopy smdy of the potential dependence of thymine on silver electrodes. Journal of Solid State Electrochemistry, 7, 576-581. 

Vidugiris, G.J.A., Gudavicius, A.V., Razumas, V.J., and Kulys, J.J. (1989) Structure-potential dependence of adsorbed enzymes and amino adds revealed by the surface enhanced Raman effect European Biophysis Journal, 17, 19-23. 

Billmann and Otto have shown that the potential dependence of SERS depends also on the presence of other constituents beside the Raman scattering molecule. Thus, pyridine produced a lower signal at -0.8 V than at -1.0 V in the presence of cyanide, while in its absence the inverse was seen. Similarly, the cyanide signal (at 2113 cm ) was higher at -0.8 V than at -1.0 V in the presence of pyridine, and vice versa in its absence. This behavior can perhaps be understood on the basis of competition of the two species over the available surface. The cyanide is more strongly adsorbed at the less cathodic potentials. 

Since colloidal particles of silver and gold also give large SERS effects, it is useful to consider these as disconnected microelectrodes. Controlled variations in the potential at the interface between silver sol particles and electrolyte solution have been achieved by adding the Eu3+/Eu2+ redox system and varying the concentration ratio [22]. From measurements of SER spectra of pyridine adsorbed on the silver sol, the potential-dependent effects have been found to be identical with those given by bulk silver electrodes. These experiments also demonstrated that the intensity ratio of the pyridine Raman bands at ca. 1010 and 1040 cm-1 may be used as a simple but effective measure of sin-face potential for colloidal metals. 

P. Corio, P.S. Santos, V.W. Brar, G.G. Samsonidze, S.G. Chou, and M.S. Dresselhaus, Potential dependent surface Raman spectroscopy of single wall carbon nanotube films on platinum electrodes, Chem. Phys. Lett., 370, 675-682 (2003). 

The tremendous advances that have occurred in the spectroscopic analysis of the electrode/electrolyte interface have begun to provide a fundamental understanding of the elementary processes and the influence of process conditions. Surface-sensitive spectroscopic and microscopic analyses such as surface-enhanced Raman scattering (SERS) [1], potential-difference infrared spectroscopy (PDIRS) [2], surface-enhanced infrared spectroscopy (SEIRS) [3], sum frequency generation (SFG) [4], and scanning tunneling microscopy (STM) [5,6] have enabled the direct observation of potential-dependent changes in molecular structure [2,7] chemisorption [8,9], reactivity [10], and surface reconstruction [11]. 

Coadsorption of Thiourea and Thiocyanide Raman spectroscopy, not only identifies the orientation of a single species bonding to the electrode, but also reflects the interaction of the different adsorbed species at the electrode the coadsorption behavior. By carefully analyzing the potential-dependent band features including frequency, intensity, width, and shapes, one can classify the electrochemical coadsorption into two types parallel (competitive) and induced coadsorption. Furthermore, with precise control of the experimental conditions, one is able to see the transition of the type of coadsorption. 

The adsorption of NAD+ on Au has been further studied during recent years using fourier transform surface-enhanced Raman scattering (FT-SERS) [113-115]. The surface-enhanced Raman scattering (SERS) of NAD+ shows a strong potential dependence in the non-Faradaic regions. Either the adenine or the nicotinamide... 

Raman intensities are a function of the change in polarizability of a molecule. The polarizability, however, is a second derivative of the potential energy with respect to an external electric field which makes the Raman intensity dependent on a third-order derivative of the potential energy. For this reason, it is imperative to use an accurate analytical description of the polarizability to obtain a reasonable prediction of Raman intensity for a given vibrational frequency. Frisch et al. (1986) have derived the following expression for the polarizability derivative with respect to movement of atomic coordinates, x. 

Figure 8.6 Schematic of adsorption mode of benzotriazole on an iron electrode in sulfuric acid at potentials, (a) Positive to potential of zero charge (PZC) (b) PZC (c) Negative to PZC (d) Normal Raman spectrum of the Fe(ll) BTA complex and potential-dependent surface Raman spectra of BTAH on an iron electrode in saline water.

Figure 10.4 Electrode potential-dependent Raman spectra of hydrogen adsorption at a roughened polycrystalline platinum electrode surface. Reprinted from Ref [27] with permission from Elsevier.

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