The Visible and Near-Infrared Absorption Spectra of Some Trivalent Actinide and Lanthanide Elements in DClO₄ and in Molten Nitrate Salts

Abstract

Molten salts constitute an important class of solvents for the study of the chemistry of the actinide and lanthanide elements, particularly the intensely radioactive transuranium elements where the stability of certain of these systems to radiation decomposition is important. One tool useful in this type of study is the observation of absorption spectra. In the present investigation we report observations of absorption spectra of trivalent actinide and lanthanide ions in LiNO₃-KNO₃ eutectic at 150°C in the region between 0.36 and 2.5 μ. Transitions to low-lying excited states have been observed in crystals of both actinide and lanthanide elements in the near-infrared region (1.3–2.5μ) and thus would be predicted to be observable in solution. However, the existence of intense solvent absorption bands in aqueous solution above 1.3 μ constitutes a severe limitation on the use of that medium. In the nitrate eutectic there are essentially no interfering solvent absorption bands between 1.3 and 2.5 μ. It is also possible to observe portions of this region in deuterated solvents, and thus we are able to compare over an extended range the effects of different ligand fields on 4f and 5f electrons. The bands observed in the near-infrared region should prove to be of analytical importance since the extinction coefficients appear to be comparable to many of the more intense bands in the visible region.

Based on work performed under the auspices of the U.S. Atomic Energy Commission.