RAMAN AND SURFACE-ENHANCED RAMAN-SCATTERING OF VIOLURIC ACID AND VIOLURATE ION ADSORBED ON A SILVER ELECTRODE

The Raman spectra of violuric acid [2,4,6(H-1,H-3)-pyrimidinetrione-5-oxime, H3V] and sodium violurate (NaH2V) were investigated as solids and in aqueous solution at different pH. A tentative vibrational assignment is presented. From the Raman spectra obtained in solution it was possible to identify some characteristic Raman shifts for H3V, H2V- and HV2- (violurate dianion). The surface-enhanced Raman (SER) spectra of the H2V- ion adsorbed on a silver electrode in borate buffer solution (pH 8.4) was also investigated. For potentials less negative than -0.5 V the H2V- anion adsorbs with the nitrogen atom of the oxime group and the oxygen atom of a neighbouring carbonyl group towards the surface. For potentials more negative the surface species undergoes reduction, with the oximate group (= N-O-) being reduced to form an NH2 group. The SER spectra of this new species are enhanced for potentials more negative than -0.7 V.