Luminescence spectra of the uranyl ion in two geometrically similar coordination environments. Uranyl nitrate hexahydrate and di-.mu.-aquo-bis[dioxobis(nitrato)uranium(VI)] diimidazole
The luminescence spectra of the uranyl ion have been obtained at room and liquid nitrogen temperatures in the crystal hosts of uranyl nitrate hexahydrate (UNH) and di~~-aquo-bis(dioxodinitratouranium(VI)) di-imidazole (UNI). In both coordination spheres, the uranyl ion lies at the center of similar, distorted coordination hexagons consisting of two bidentate nitrate groups and two water molecules; the only difference in the coordination geometries is that the water molecules are terminal in the UNH complex and bridging in the UNI complex. The uranium-uranium "bond" distance in the UNI complex is 3.93 A. At room temperature, the emission spectra of the two compounds are essentially identical, but significant differences appear upon cooling to 77°K. Vibronic structure is observed in the crystal of the UNI complex b4t not in the crystal of uranyl nitrate hexahydrate; this implies that the geom~try of the uranyl ion in the two excited states is somewhat different. An energy level sequence is presented in which the various emission lines arise from a slightly split excited state (splitting approximately 80-85 cm-1) to several vibrational levels of the ground electronic manifold. The energy spacing of the ground vibrational levels (approximately 860 cm-1) was found to vary when changing crystal systems.
- Research Organization:
- Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
- Sponsoring Organization:
- Earth Sciences Division
- DOE Contract Number:
- DE-AC02-05CH11231
- OSTI ID:
- 1064008
- Report Number(s):
- LBL-10542
- Journal Information:
- Journal of Physical Chemistry, Vol. 84, Issue 20; ISSN 0022-3654
- Country of Publication:
- United States
- Language:
- English
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