Mossbauer spectroscopy of neptunyl species

Systematics of hyperfine parameters from Np-237 Mossbauer resonance data of compounds with Np in a high formal charge state (Np6+, Np7+) are discussed with respect to electronic structure properties. In neptunyl(VI) species, we find a linear correlation between the isomer shift and the strength of quadrupole interaction. Both scale linearly with the actinide-oxygen bond length, stressing the central role of this parameter. Some Compounds show paramagnetic relaxation spectra which makes their analysis difficult. The hyperfine interactions are often not rotational symmetric indicating a deviation from the simple linear O-Np-O configuration. Mossbauer spectra of NpO3 center dot 2H(2)O reveal that this compound should be described as a neptunyl. A comparison or hyperfine parameter systematics indicates that the Np valence electron properties in Np(VII) species are basically similar to those in Np(VI) neptunyls. (c) 2004 Elsevier Inc. All rights reserved.