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(1 H ,3 H )‐pyrimidinetrione‐5‐oxime, H 3 V] and sodium violurate (NaH 2 V) 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 H 3 V, H 2 V − and HV 2− (violurate dianion). The surface‐enhanced Raman (SER) spectra of the H 2 V − 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 H 2 V − 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 ( NO − ) being reduced to form an NH 2 group. The SER spectra of this new species are enhanced for potentials more negative than −0.7 V.