Spin-orbit coupling, actinides

As the actinides are a Second f series it is natural to expect similarities with the lanthanides in their magnetic and spectroscopic properties. However, while previous treatments of the lanthanides (p. 1242) provide a useful starting point in discussing the actinides, important differences are to be noted. Spin-orbit coupling is again strong (2000-4000 cm ) but, because of the greater exposure of the 5f... 

In actinides, the J terms are closer in eneigy and more heavily admixed by spin-orbit coupling. 

More recently, the CASSCF/CASPT2 method with spin-orbit coupling has been applied to a number of problems in actinide chemistry. Some recent examples are the electronic spectrum of U02 [38], the electronic structure of PhUUPh [62], the diactinides Ac2, Th2, Pa2, and U2 [36, 37], etc. Some of this work has recently been reviewed [63]. 

A comparable temperature dependence of resistivity was obtained for a mixed phase sample of Cel2. The formation of apparently metallic phases for only the iodides of five lanthanide and actinide elements is considered in terms of the stoichiometry, the electronic structure of the cation, the possible nature of the band, and the role of the anion. In contrast, the intermediate Lai2.1,2 phase exhibits semiconduction. Its magnetic data between 80° and 300° K. can be best accounted for if the reduced component is considered to be La ", [Xe]5d with a ground term, a spin-orbit coupling constant A — 050 cm. and only small covalency and asymmetry parameters. 

We have examined the effects of spin-orbit coupling on the geometry structures and vibrational frequencies of U(C7H7)2 and found them to be negligible (<1%) for the/ actinide system. J Li, BE Bursten. To be submitted. 

The present method to study heavy element compounds in new and our experience is so far limited to atoms and some small molecules. It has the virtue that we can now use the machinery of CASSCF/CASPT2 for the entire periodic system. The method has been tested for all alkaline, alkaline earth, main group, transition metal atoms and in addition for some of the lanthanides and actinides. The results are promising. One example It has recently been possible to assign the electronic spectrum of the UO2 molecule (more than 150 electronic levels were computed) [33]. A drawback is that for the heaviest elements one has to include a large number of electronic states in order to fully account for the effects of spin-orbit coupling. 

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