Double photoexcitation involving2pand4felectrons inL3-edge x-ray absor

Abstract

The L 3 -edge x-ray absorption spectrum of Pa͑V͒ fluoride in aqueous solution show clear evidence for the double photoexcitation involving 2p and 4f electrons. A comparison with the ͓2p4f͔ double-electron excitations observed in the L 3 -edge x-ray absorption spectra of other actinides ͑thorium, uranium, neptunium, plutonium, and americium͒ indicates a monotonic increase in the excitation energy. The sharp edgelike structure of the multielectron excitation reveals the origin of a shake-up channel.

Ab Initio X-ray Absorption Spectroscopy Study of the Solvation Structure of Th(IV), U(IV), and Np(IV) in Aqueous Solution

“…In the case of EXAFS the coordination number is directly proportional to the amplitude reduction factor, S 0 2 , and also strongly correlated to the Debye−Waller factor. As a consequence, EXAFS always suffers from relatively large errors when determining the coordination numbers, ranging from 10% to 25%. , In addition, several works have pointed out the existence of double-electron excitations in the L 3 -edge X-ray absorption spectra of actinides which may affect the structural determination by EXAFS. , This problem has been largely discussed in the case of the absorption at the L-edges of the lanthanides , or at the K-edge of their isoelectronic yttrium atom …”

First structural characterization of Pa(iv) in aqueous solution and quantum chemical investigations of the tetravalent actinides up to Bk(iv): the evidence of a curium break

“…This is the first reported XANES spectrum of aqueous Pa(IV). The white line position of Pa(IV) (16 737.3 eV) is about 4 eV lower in energy than that of Pa(V) (16 741.5 eV) 10 (Table S1 †). The corresponding differences for tetra and pentavalent uranium, neptunium, and plutonium are smaller or even reversed owing to their pentavalent ions present as dioxo actinyl ions in aqueous media, while Pa(V) occurs as a monooxo protactinium cation.…”

EXAFS Study of the Speciation of Protactinium(V) in Aqueous Hydrofluoric Acid Solutions

“…17−19 In the absence of a standard to determine the value of S 0 2 and in order to minimize the uncertainty in the determination of the coordination number, the overall amplitude factor was fixed at 1.0 or 0.9 for all fits. While 1.0 is the theoretical value of S 0 2 , 0.9 is often chosen in the literature as a more suitable value when trying to fit the coordination number N. 12,20,21 The results of the EXAFS fits are summarized in Tables 1 (single-shell model) and 2 (split-shell model with one longer Pa−O distance). Experimental and best-fit EXAFS spectra are shown in Figures 2 and 3 in both k and R space.…”

“…In another study, Hennig et al found that introducing a split-shell model with a longer Pa−F/O distance is necessary to properly fit the data at 0.5 M HF, suggesting the presence of one or two water molecules in the coordination sphere of protactinium under these conditions. 12 Additional experiments are therefore necessary to resolve the ambiguity regarding the coordination environment of protactinium(V) fluoro complexes in aqueous solutions. Following these observations, we present our study of the coordination of protactinium(V) in aqueous HF solutions ranging from 0.5 to 27 M HF using EXAFS.…”