Ab initio theoretical studies on U~(3+) and on the structure and spectroscopy of U~(3+) substitutional defects in Cs_2NaYCl_6, 5f~26 d~1 manifold

摘要

In this paper we present the results of spin-orbit relativistic ab initio model potential embedded cluster calculations of the 5f~26d~1 excited manifold of (UCl_6)~(3-) embedded in a reliable representation of the Cs_2NaYCl_6 elpasolite host. They are aimed at interpreting the 5f~3->5f~26d~1 absorption bands reported by Karbowiak et al. [J. Chem. Phys. 108, 10181 (1998).] An excellent agreement is found between the calculated energies of the absorption transitions from the ground state 5f~3 1GAMMA_(8u) (~4I_(9/2)) and the experimental data, which supports a detailed interpretation of the electronic nature of the adsorption spectrum in the energy region 14 000 -23 000 cm~(-1). In particular, the three unidentified electronic origins that had been experimentally detected are now assigned, and the observed bands are interpreted as having multiple electronic origins. From the structural point of view, the excited states of the 5f~26d~1 manifold are classified in two sets of main configuration 5f~26d(t_(2g))~1 and 5f~26d (e_g)~1 with bond distances R_e [5f~26d(t_2g)~1]