The electronic spectra and magnetic circular dichroism of the uranyl ion

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Abstract
The MCD and absorption spectra of (Bu4N)UO2(NO3)3 have been measured over the range 18 000—33 000 cm-1 in a rigid polymer matrix at ∼10 K. A large number of sharp peaks are observed including structure in the high energy region previously referred to as the ‘structureless continuum’. It is shown that group theory places some rather strict limitations on the electronic states and the possible transitions between them, and we conclude that the most probable orbital ordering is e 1g < a 1g < a 2u < e 1u and that the low energy bands arise from transitions to the triplet states 3 E 1g and 3 E 2g . The higher energy band structure we assign as due to transitions to 3 E 1u . We show that second order spin-orbit interaction is necessary to account for the unsymmetric splitting of the triplets. Furthermore it is demonstrated that the symmetry D ∞h will not account for the intensity of absorption and MCD of the observed transitions and that the effective molecular symmetry is D 3.