Near-Visible Absorption Spectra of the CsUO2(NO3) Crystal

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Abstract
The near‐visible absorption spectrum of a single‐domain crystal of cesium uranyl nitrate at a temperature of 20°K is interpreted. Selection rules are given for a trigonally coordinated uranyl complex in a crystal having two molecules per unit cell. Lower lying levels, whose excitation gives rise to the fluorescent and magnetic series, are assigned as the A2 and E species of the D3 point group. Given these assignments, absorption between levels exhibiting the strongest fluorescence occurs only by allowed quadrupole transitions; a vibronic interaction is suggested to account for the radiative decay rates. Certain higher levels are assigned alternately, in pairs, to the A2g and A2u species of the D3d point group as a consequence of the intermolecular interaction in the unit cell. Estimates of the strengths of the various interactions considered are required and, as a first step, the singlet—triplet intervals for two uranyl models are calculated and found to be comparable with, or less than, the spin—orbit splitting.

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