Crystal-field excitations in uranium dioxide

The energy levels of the configuration f² in an eight-fold cubic crystal field (CF) have been calculated, and the results are used to explain the experimental spectrum of UO₂. The fourth-order CF potential turns out to be much smaller than usually assumed for this compound. This has an effect of reducing the J-mixing in the wavefunctions, particularly in the case of the ground state wavefunction. In spite of the strength of the CF, the ground state l³H₄T₂> is found to be modified only slightly by the J-mixing effect; it consists of 89.4% ³He₄, and the remaining eleven components make up the rest. Very good correlation is obtained between the experimental and simulated energy-level schemes. The predominance of ³H₄ in the ground state consequently increases the value of the calculated effective magnetic moment. The results are compared with our previous predictions about the system, and relevant conclusions drawn in the light of experimental data now available. © 1998 Elsevier Science B.V.