Dithizone adsorption at metal electrodes. 2. Raman spectroelectrochemical investigation of effect of applied potential at a silver electrode

The technique of laser Raman spectroelectrochemistry has been applied to the study of the adsorption of the diphenylthiocarbazone (dithizone) anion and its redox forms at a silver electrode in aqueous alkaline media. Raman spectra of the adsorbed forms of the dithizone moiety obtained at 100-mV intervals from -1.20 to +1.00 V (vs. Ag/AgCl) are presented. Comparison of these surface spectra with spectra obtained for authentic samples of the anion, silver(I) dithizonate, and the two oxidation products (tetrazolium and disulfide compounds) confirm the identity of the surface species at the various applied potentials. The anion, which adsorbs at potentials positive to the potential of zero charge (pzc), is oxidized to the disulfide at potentials greater than 0.00 V, and this disulfide is the predominant species found on the surface in the potential range 0.10-1.00 V. Comparison of vibrational frequencies as a function of applied potential for adsorbed dithizone with authentic silver(I) dithizonate shows that the bonding of Ag to N and S is similar in the two cases. Orientation of surface dithizone can be described approximately.