X-ray absorption LIII and MV edges of hexavalent lower actinides

X-ray absorption spectroscopy is used to probe the electronic and structural features of the actinides. To better understand the effect of the effective charge and polyhedron on the edge structure, we discuss the L-m and M-v edges in AnO(2)(NO3)(2)(TBP)(2) (where the actinide is shortly linked to the 'yl' oxygens) and in the perovskite Ba(2)ZnAnO(6) (where the hexavalent actinide is in the cubic structure as An(6+)), An = U, Np, Pu. Using FEFF8 simulations, both features and position of the L-m and M-v edges are explained within a crystal field splitting of the orbitals picture and a multiple scattering picture. (C) 2000 Academic des sciences / Editions scientifiques et medicales Elsevier SAS.