Surface Enhanced Raman Spectroscopy - Vibrational Spectroscopy of Adsorbates at the Metal-Electrolyte Interface

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Abstract
Surface enhanced Raman spectroscopy has been used to study the adsorption of pyridine and cyanide on Cu, Ag, and Au electrodes. The Raman spectra for pyridine on these three substrates closely resembled each other, and the Raman peaks exhibited small shifts from the corresponding peaks in an aqueous pyridine solution. The low frequency vibrational modes in the region 200–250 cm−1 are attributed to the metal-pyridine stretches, namely, v[Cu-N(pyridine)] = 241 cm−1, v[Ag-N(pyridine)] = 237 cm−1, and v[Au-N(pyridine)] = 232 cm−1. The energies of the metal-pyridine stretches were quite insensitive to the kind of substrate the molecule was on. We report also the surface enhanced Raman scattering from cyanide adsorbed on Au. The CN stretching frequency was at 2109 cm−1, which was attributed to that of the adsorbed Au(CN)− 2 complex. In addition, three low frequency modes were observed at 88, 228, and 325 cm−1. Cyanide adsorption on Cu and Ag electrodes was also investigated. For the Cu/cyanide system, Raman shifts at 175, 312, 434, and 2089 cm−1 were observed. They are due to the presence of the complex ions, Cu(CN)2- 3 and Cu(CN)3- 4. For the Ag/cyanide system, Raman shifts at 143, 218, 303, and 2104 cm−1 were observed. They are due to the presence of Ag(CN)2- 3 complex.

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