The nature and the orientation of molecules adsorbed on certain rough metallic surfaces can be readily determined by surface-enhanced Raman scattering (SERS). This surface-enhancement phenomenon, allied to basic characteristics of Raman scattering, suggests that the SERS effect is potentially a powerful tool for the investigation of electrochemical problems. However, the magnitude of the enhancement depends on several factors, such as electrode potential, laser wavelength, surface coverage and morphology. The objective of this thesis was to extend the knowledge of the influence of these factors on the overall SERS. Pyrazine (pz) was chosen as the probe molecule. Pz has a molecular centre of inversion which makes this molecule a good model for molecular orientation studies.

A Raman study of pz and its protonated forms in solution was performed in order to better understand the pz vibrational spectrum. All bands for pz and its protonated forms were assigned using the correlation table technique and ab initio calculations. The pKₐ values for both the first and the second protonation of pz were also estimated, and were in good agreement with previous measurements. SERS spectra of pyrazine adsorbed on a polycrystalline silver electrode were obtained. The SERS selection rules indicated that pz adsorps end-on, using one of its nitrogen electron lone pairs. It was observed that pz is electrochemically reduced at potentials more negative than -900 mV. The reduction process was investigated using SERS and electrochemical techniques. The observation of bands, arising from reduction products of pz, at positive potentials explained most of the controversial results for the SERS spectrum of pz, previously reported in the literature. The SERS spectra of pyrazinium (pzH⁺) adsorbed on a polycrystalline silver electrode indicated that the orientation of the adsorbed cation depends on the applied potential.

SERS spectra of pyrazine adsorbed on "smooth" and rough polycrystalline gold electrodes were also obtained. The roughness factors of a number of gold surfaces, prepared by varying the number of applied oxidation-reduction cycles (ORCs), were monitored by atomic-force microscopy (AFM). The surface-enhancement was correlated to the surface morphology. The results indicated that an optimum SERS signal was generated from a surface containing features of approximately 100 nm-size. The SERS intensity was also correlated to surface concentration data, obtained independently by electrochemical methods. A novel procedure to determine the SERS intensity from a "smooth" surface was developed, and a linear relationship between SERS intensities and the surface concentration data was observed. Finally, the SERS spectra from pz adsorbed on a Au(210) single-crystal electrode was obtained;​ this is the first report of a SERS spectrum from this "unroughened" surface. The correlation between the SERS intensities and the surface coverage was also investigated for Au(210).