RAMAN SPECTRAL STUDIES OF AQUEOUS ACIDIC PYRAZINE SOLUTIONS

Raman spectra of aqeous pyrazine have been investigated in acidic medi a: HCl from pH = 4 up to 11 M; HClO4 from 0.1 M to 12 M; H2SO4 form 0. 1 M to 18 M. From observation of the shifts of the bands from neutral solutions, it has been possible to identify bands uniquely characteris tic of unprotonated pyrazine and its two protonated forms. The diproto nated form was only observed for high concentrations of HClO4 and H2SO 4. From bandfitting of the spectral contours it has been possible to c onstruct the species distribution diagram and estimate the pK values. Raman bands of the three species have been identified and assigned. Th e results are used to explain an unassigned band at 1235 cm(-1), repor ted by several authors, in SERS from pyrazine on silver and gold elect rodes.