The origin of intense Raman spectra from pyridine at silver electrode surfaces: The role of surface carbon

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Abstract
Intense Raman spectra from pyridine at polished silver electrode surfaces, subjected to a single anodic cycle, appear to be associated with pyridine adsorption in graphitic carbon overlayers on the silver surface. This interpretation is based on the absence of pyridine line enhancement for ‘clean’ (or carbon‐free) systems and the simultaneous appearance of intense pyridine and carbon spectra for the systems subjected to a single anodic cycle. Features arising from surface carbon are evident in spectra reported by earlier authors. The evidence for the presence of carbon is based firstly on the conversion of the species in question to hydrocarbons at reducing potentials and secondly on similarities in the spectra of the systems: Ag/0.1 M KCl, Ag/0.1 M KF and Ag/0.1 M KCl, pyridine, in the region of the D and G modes of graphite (1200–1700 cm−1). Similar intensity–potential curves for the pyridine line at 1008 cm−1 and the carbon band at 1595 cm−1 indicate a surface association between these two species. The stability of the pyridine species generating the 1008 cm−1 line on a dry electrode surface favours intercalation (internal adsorption) rather than external physical electrosorption on carbon. The line at 1025 cm−1 is assigned to a silver(I) pyridine complex.