The Cd-2(2+) in molten metal halides and at electrode interfaces

The structural properties of the cadmium species formed by dissolution of c admium metal in molten cadmium halides (CdX2: X = Cl, Br, I) and in molten mixtures of cadmium chloride with alkali chlorides have been investigated b y Raman spectroscopy. The data indicate that in these ionic solvents the pr edominant species present is the solvated Cd-2(2+) subvalent cation. With i ncreasing ionic strength of the counter anion the frequency of the diatomic cation shifts from 158 cm(-1) for the chloride melt to 183 cm(-1) for the iodide melt. Due to the overlap of the electronic absorption edge of the Cd -2(2+) with the laser lines used to excite the spectra the Raman band inten sities of the solute species are preresonance enhanced. The dissolution of cadmium metal in the cadmium chloride-alkali chloride mixtures increases wi th temperature and depends on the stability of the CdCl42- species formed i n these melts. The looser the CdCl42- association the higher the solubility and the stability of the Cd-2(2+) species. Raman spectroelectrochemical me thods have been applied for studying amorphous carbon electrode surfaces du ring electrolysis of CdCl2 in LiCl-KCl eutectic. A new Raman band measured at similar to 158 cm(-1) during electrolysis was attributed to the subvalen t Cd-2(2+) species. It seems that these species are formed in the vicinity of the electrode by a homogeneous electrochemical reaction.