Spectroscopy of lanthanide and actinide impurities

In lanthanide and actinide ions the dense manifold of excited states of the partially filled nf and nf n + )d configurations is responsible for the interesting spectroscopic and optical properties. In lanthanides, the electrons in 

In a recent series of articles [179-181], Seijo and Barandiaran have investigated the spectroscopy of several actinide impurities (Pa - -, and in crystal environments. In particular, they discuss the relative position of the 5 and 5/ 6i/ manifolds (see also chapter 7 of this book). All calculations use relativistic large-core AIMPs on the actinide centres and on the chlorine ligands. The transferability of these frozen core potentials from the neutral / elements to their cation has been discussed in Ref [182]. The crystal environment is described by the AIMP embedding cluster method. Electron and spin-orbit interactions are treated simultaneously by the three-step spin-fi e-state-shifted method detailed in section 2.2.5, using either MRCI or CASSCF/MS-CASPT2 methods in the spin-fi ee step. The active space includes the 5/ and 6d orbitals of the actinide centre, as well as the Is orbitals in order to avoid the prob- 

The comparison of the calculated spectra of the free ions and the ones in the crystal is not straightforward. Indeed, in the crystal, the presence of the first coordination shell increases the number of electrons and basis functions in the calculations, resulting in a blow-up of the Cl expansion, mainly due to the generated doubly-excited configurations. One should bare in mind that this increase is about six time as fast in double group symmetries as in the non-relativistic symmetry. In a non effective Hamiltonian method, the only way to keep the size of the DGCI matrix to an affordable size of few million configurations, is to cut down the number of correlated electrons. This may essentially deteriorate the quality of electron correlation as the contributions of the spin-orbit interaction 

Calculated adiabatic excitation energies Ai and experimental values in cm taken from Refs. [155,185] for the free uranyl and neptunyl ions and impurities in CS2UO2CI4 crystal. 

State A free Uranyl ion A impur. Exp. State Neptunyl ion impur. Exp. 

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