Surface-enhanced Raman spectroscopy electrolyte solutions

Interfacial water molecules play important roles in many physical, chemical and biological processes. A molecular-level understanding of the structural arrangement of water molecules at electrode/electrolyte solution interfaces is one of the most important issues in electrochemistry. The presence of oriented water molecules, induced by interactions between water dipoles and electrode and by the strong electric field within the double layer has been proposed [39-41]. It has also been proposed that water molecules are present at electrode surfaces in the form of clusters [42, 43]. Despite the numerous studies on the structure of water at metal electrode surfaces using various techniques such as surface enhanced Raman spectroscopy [44, 45], surface infrared spectroscopy [46, 47[, surface enhanced infrared spectroscopy [7, 8] and X-ray diffraction [48, 49[, the exact nature of the structure of water at an electrode/solution interface is still not fully understood. 

Beyond intramolecular modes of species present in the electrolyte solution or interacting with an electrode surface, modes caused by adsorptive interaction between the adsorbed species and the electrode surface can be studied (e.g. the silver-halide stretching mode with surface enhanced Raman spectroscopy (SERS) for details. 

Surface-enhanced Raman scattering is a surface phenomenon and only molecules close to the substrate surface show enhanced Raman spectra. In a mixture there will be competition for surface sites. If one species is more highly attracted to the surface than another the latter will not show a SERS spectrum. For this reason, we can use SERS spectroscopy for identifying and quantifying the individual adsorb compound in the first monolayer of mixtures of CPC and PNP. The ex situ surface roughening procedure is carried out in a 0.1 M KCl electrolyte solution in the absence of other molecules and the binary mixture of CPC/PNP is then added to the op-toelectrochemical cell. The detailed analysis of the system containing mixtures of CPC and PNP can be summarized as follow ... 

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