Ab initio theoretical studies on U3+ and on the structure and spectroscopy of U3+ substitutional defects in Cs2NaYCl6, 5f 26d1 manifold

In this paper we present the results of spin-orbit relativistic ab initio model potential embedded cluster calculations of the 5f(2)6d(1) excited manifold of (UCl6)(3-) embedded in a reliable representation of the Cs2NaYCl6 elpasolite host. They are aimed at interpreting the 5f(3)-->5f(2)6d(1) absorption bands reported by Karbowiak [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) 1 Gamma(8u)(I-4(9/2)) and the experimental data, which supports a detailed interpretation of the electronic nature of the absorption 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(2)6d(1) manifold are classified in two sets of main configuration 5f(2)6d(t(2g))(1) and 5f(2)6d(e(g))(1) with bond distances R-e [5f(2)6d(t(2g))(1)]<R-e[5f(3)]<R-e[5f(2)6d(e(g))(1)]. The energies of the 5f(2)6d(1) manifold of free U3+ have also been calculated; experimental data on them are not available in the literature to the best of our knowledge. These results contribute to show that wave function based ab initio methods can provide useful structural and spectroscopic information, complementary to the experimental data, in studies on actinide ion impurities doping ionic hosts, where large manifolds of 5d(n-1)6d(1) excited states are involved. (C) 2003 American Institute of Physics.