On the electronic configuration in Pu
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0986-OO01-03
On the electronic configuration in Pu J G Tobin1, P Soderlind1, A Landa1, K T Moore1, A J Schwartz1, B W Chung1, M A Wall1, J M Wills2, R G Haire3, and A L Kutepov4 1 LLNL, Livermore, CA, 94550 2 LANL, Los Alamos, NM, 87545 3 ORNL, Oak Ridge, TN, 94550 4 VNIITF, Snezhinsk, Russian Federation Abstract Synchrotron-radiation-based x-ray absorption, electron energy-loss spectroscopy, and densityfunctional calculations have been used to study the electron configuration in Pu. These methods suggest a 5f n configuration for Pu of 5 ≤ n < 6, with n ≠ 6. X-ray Absorption and Electron Energy Loss Spectroscopy The data from x-ray absorption (XAS) and electron energy loss spectroscopy (EELS) indicate that the number of 5f electrons, n, involved in bonding of Pu must be at least as great as 5 and less than 6. The equivalence of the XAS and high-energy EELS measurements for assessing the electronic states has already been demonstrated for Ce and Pu, as well as for other actinides [15]. The argument against n = 6 will now be discussed in a step-wise fashion. I. The relative diminishment of the Pu 4d3/2 peaks indicates strong relativistic effects in the Pu 5f states, i.e., a jj-coupling or jj-skewed intermediate coupling scheme. As can be seen in Figure 1, the intensity of the 4d3/2 peak of Pu is significantly reduced versus that for U [6]. This large reduction is driven by the electric dipole selection rule that forbids the transition from a pure d3/2 peak into a pure f7/2 peak. This reduction also implies that the Pu 5f states must be split into two lobes, the lower (mainly occupied) lobe being principally pure 5/2 character and the upper (unoccupied) lobe being principally pure 7/2 character. This picture is shown schematically in Figure 2. This result is independent of any particular theoretical model for spin-orbit splitting or the calculation of x-ray absorption cross section and thus does not depend upon the details of the branching ratio analysis presented previously [1,4]. II. Coupled with the result in I above, the absence of a pre-peak in the Pu 5d XAS and EELS indicates that n must be at least 5. As shown in Figure 3, there is a pre-peak in the EELS 5d to 5f transition for Th and U, but not for Pu. Similar results (Figure 4) have been obtained for 5d XAS. [2]. The pre-peak structure in the 4d XAS of the rare earths was explained many years ago by Dehmer et al. [7]: it is driven by the combination of angular momentum coupling between the 4d and 4f states and the dependence of the Coulombic energy term upon the coupling details. The spectroscopic transition for the rare earths can be summarized as follows. 4d104f n+ hν 4d 94f
n+1
Eq A
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When n = 14, there is no transition. When n = 13, there is a single main peak, without any prepeaks [2]. This is because
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