The electronic spectra of alkali metal uranates and band assignments: an analysis of their diffuse reflectance spectra

The diffuse reflectance spectra of alkali metal (Li, Na, K, Rb and Cs) mono- and diuranates, as well as several additional lithium polyuranates(VI), have been measured at 25 and -196 degreesC, and up to 500 degreesC for the potassium uranates. The spectra of the mono- and diuranates of caesium and sodium were similar as were the spectra of the uranates of rubidium and potassium, because of identical site symmetries. Spectra recorded at -196 degreesC exhibited enough features to enable their resolution into individual overlapping bands. Existing theoretical models of the uranate spectra have been critically examined. The recorded spectra were analysed using the MO diagram for the octahedral UO66- moiety. The spectra were interpreted in terms of the various expected uranate ion site symmetries and the results obtained for all the alkali metal mono- and diuranates are reported here.