Electronic spectroscopy of UO2 isolated in a solid Ar matrix

Dispersed fluorescence spectra have been recorded for UO2 isolated in a solid Ar matrix. Near UV excitation produced groups of emission bands in the 370-420 and 465-645 nm spectral regions. These bands originated from two energetically close upper levels and terminated on a range of low-lying electronic states. Comparisons with electronic structure calculations indicate that the ground and low-lying electronic states of UO2 are derived from the U(5f7s) configuration. The level of agreement between the observed and predicted electronic energies provides an impressive validation of the calculations. In previous studies of matrix isolated UO2, it had been suggested that the ground state in solid Ar is U(5f(2)) H-3. The present results do not appear to be consistent with this hypothesis.