SERS STUDIES OF MONOPROTONATED PYRAZINE (PYRAZINIUM) CATIONS ADSORBEDONTO POSITIVELY CHARGED SILVER ELECTRODES

The surface-enhanced Raman scattering (SERS) spectra of monoprotonated pyrazine cations adsorbed on silver electrodes have been measured. Th e molecular orientation of the pyrazinium cation is dependent on the e lectrode potential. At potentials more positive than -170 mV the monop rotonated pyrazine is adsorbed end-on. However, the spectral features suggest a flat orientation as the potential becomes more negative than -300 mV. Monoprotonated pyrazine cations with both orientations can c oexist at potentials between these limits. The adsorption of the posit ive ion to a positively charged electrode is mediated by specifically adsorbed bromide ions.