THE ABSORPTION SPECTRUM OF THE URANYL ION IN PERCHLORATE MEDIA-MATHEMATICAL RESOLUTION OF THE OVERLAPPING BAND STRUCTURE AND STUDIES OF THE ENVIRONMENTAL EFFECTS.
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Date
1965
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Ohio State University
Abstract
The complicated absorption spectrum that is observed for the $UO^{++}_{\ 2}$ ion between 3300 and 5000 {\AA} arises from one or more vibrationally perturbed electronic transitions; some fourteen transitions are observed in this wavelength interval. Each band overlaps the adjacent bands on both the high- and low-frequency side of the band center, and results in the rather ill-defined (in some areas) summed spectrum that is observed. This overlapping coupled with the fact that the individual transitions react in different ways to changes with respect to temperature or solution parameters, complicates interpretation of the spectra, and related spectral studies. With this overlapping, it was heretofore difficult, if not impossible, to obtain the parameters (position, intensity, and half-band width) of any single absorption band or transition, with any reasonable certainty. Computer techniques developed for the mathematical resolution of complex overlapping spectra have recently been greatly improved and have been applied to a study of the fundamental parameters of the absorption spectra of $UO^{++}_{\ 2}$ ion and related systems. Studies of the most appropriate mathematical functions for representing the shapes of various types of spectral bands, of the factors that contribute to the broadening of the ``lines'' into bands in the condensed systems that liquids represent, and of spectral band structure, will be briefly reviewed. The present results show that some prior inferences concerning the $UO^{++}_{\ 2}$ band intensities (and half-band widths) are probably in error. The intensities obtained from our recent results from the resolution of the spectrum are interpreted with respect to some theoretical models recently proposed for the electronic-vibronic level structure. Proposals for the mirror-symmetric imaging of the fluorescence emission band spectrum of $UO^{++}_{\ 2}$ with respect to the absorption spectrum are discussed with regard to our recent measurements of the intensities, and to the intensity distribution in the fluorescence emission spectrum of $UO^{++}_{\ 2}$ in perchlorate media. Studies have been made of the effects of complexing ions, hydrolysis, ionic strength, uranyl ion concentration, and of temperature $(25-95^{\circ}C)$ on the $UO^{++}_{\ 2}$ spectra in perchlorate media. Work in perchlorate is not only of basic interest, but also serves as reference data for spectral studies of $UO^{++}_{\ 2}$ in other ionic complexing systems, and may be of help in a further analysis of the $UO^{++}_{\ 2}$ spectrum. The spectra of the uncomplexed $UO^{++}_{\ 2}$ ion have been considered in a study of the effects on the spectra of the progressive complexation of $UO^{++}_{\ 2}$ by $NO^{-}_{3}$, as a function of several experimental parameters. Even under conditions where hydrolysis effects are non-existent, changes are observed, for example, in all three parameters of each band with all experimental parameters invariant except temperature. Changes in the individual band parameters are the result of the effects of complex ion formation on the spectral bands which represent the electronic and vibronic parameters of the parent ion. These changes may be very dramatic.
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Author Institution: Oak Ridge National Laboratory