Interpretation of the absorption spectrum of single crystal UCl4

Abstract

Temperature-dependent polarized absorption spectra of single crystal UCl4 have been investigated in the range 4000–25 000 Å. The spectra have been assigned and analyzed using the U4+ ion in a field of D2d point group symmetry as a model. An rms deviation of 91 cm−1 in the fit to 34 assigned levels was achieved using the following set of parameters: F2=172.6±1.8; F4=38.79±1.13; F6=2.565±0.101; ζ=1666±11; A 20〈 r2〉=−291.3± 82.6; A 40〈 r4〉=−378.4± 30.8; A 44〈 r4〉=−5940± 195; A 60〈 r6〉=−141.4± 30.3; A 64〈 r6〉=557.6± 184.6 (all units in cm−1). These optical data are interpreted to show that the ground state belongs to the Γ4 irreducible representation, with the first excited state being a Γ5 level at approximately 140 cm−1. The parameters are discussed in terms of the bonding characteristic of the coordinated complex ion.