SERS STUDY OF THE ELECTROCHEMICAL REDUCTION OF PYRAZINE ON A SILVER ELECTRODE

The electrochemical reduction of pyrazine (pz) on a silver electrode f rom a 1.0 M KBr solution has been investigated by surface enhanced Ram an scattering (SERS). New bands from products of reduced pyrazine were observed at potentials more negative than -900 mV (vs. SCE). The main product is believed to be the 1,4-dihydropyrazine cation (DHPz(+)). T he reduction is not completly reversible. It is clear from the observe d spectroscopic and electrochemical data that some of the DHPz(+) was not re-oxidized when the potential scan was switched to positive value s. This DHPz(+) (or one of its derivatives with similar structure) rem ained trapped on the electrode surface even at potentials more positiv e than the point of zero charge (pzc) of silver in this medium. It is proposed that the cation binds to adsorbed halide at potentials more p ositive than the pzc. The presence of reduced pyrazine products at pot entials more positive than the pzc can lead to misinterpretations of t he SER spectrum of pyrazine.