Optical spectrum and crystal-field analysis of uranium trifluoride

The first low temperature absorption spectrum and crystal-field analysis of uranium trifluoride are presented. The measurements have been performed on a polycrystalline sample in the 4000-30,000 cm−1 range at 4.2 K. One may notice the largest crystal-field splitting of SLJ multiplets among all so far reported data for uranium(III) as well as in polycrystalline samples and U3+ doped single crystals. In the presented analysis 94 experimental crystal-field levels, observed in 0-24,116 cm−1 energy range, have been identified and fitted to a semiempirical Hamiltonian representing the combined atomic and crystal-field interactions at the C2 site symmetry. In order to exclude a possible influence of inaccuracy in the description of the free-ion multiplets on crystal-field parameters a number of additional freely varied parameters associated with the centroids of the free-ion multiplets were introduced. In the final step of the fitting procedure eight free-ion and 14 CF parameters were freely varied giving B02=-833(45), ReB22=272(36), B04=1817(89), ReB24=186(106), ImB24=776(82), ReB44=523(104), ImB44=+1460(58), B06=1081(105), ReB26=-841(89), ImB26=-2459(74), ReB46=-665(88), ImB46=-1024(74), ReB66=1416(56), ImB66=-1682(93) and r.m.s. = 24 cm−1. The performed calculation procedure enabled the determination of good starting values, reliable crystal-field parameters and a small r.m.s. deviation.