Abstract
One of the long standing debates in actinide chemistry is the level of localization and participation of the actinide 5f valence orbitals in covalent bonds across the actinide series. Here we illuminate the role of the 5f valence orbitals of uranium, neptunium and plutonium in chemical bonding using advanced spectroscopies: actinide M4,5 HR-XANES and 3d4f RIXS. Results reveal that the 5f orbitals are active in the chemical bonding for uranium and neptunium, shown by significant variations in the level of their localization evidenced in the spectra. In contrast, the 5f orbitals of plutonium appear localized and surprisingly insensitive to different bonding environments. We envisage that this report of using relative energy differences between the 5fδ/φ and 5fπ*/5fσ* orbitals as a qualitative measure of overlap-driven actinyl bond covalency will spark activity, and extend to numerous applications of RIXS and HR-XANES to gain new insights into the electronic structures of the actinide elements.
Highlights
One of the long standing debates in actinide chemistry is the level of localization and participation of the actinide 5f valence orbitals in covalent bonds across the actinide series
To answer the question if the An M4,5 absorption edge HR-XANES spectra are a good approximation of the ground state partial An 5f density of state, we have explicitly considered the role of multiplets in the Pu M4,5 absorption edge HR-XANES spectrum
We illustrate the unique utility that An 3d4f RIXS offers in characterizing actinide electronic structures; it allows direct determination and comparison of the level of 5f orbital localization and these orbitals’ participation in the chemical bonding for any type of materials, under static or dynamic conditions, not possible with other methods
Summary
One of the long standing debates in actinide chemistry is the level of localization and participation of the actinide 5f valence orbitals in covalent bonds across the actinide series. We envisage that this report of using relative energy differences between the 5fd/f and 5fp*/5fs* orbitals as a qualitative measure of overlap-driven actinyl bond covalency will spark activity, and extend to numerous applications of RIXS and HR-XANES to gain new insights into the electronic structures of the actinide elements. Marriage of advanced spectroscopy and theoretical modelling delivers mechanistic understanding of the electronic structure of An radioelements crucial to a number of applications. Those include the improved understanding of An interaction with the constituents of the geo and ecosphere on a molecular scale being highly relevant for the reliable assessment of their behaviour in the environment[5,6,7,8,9]. We are applying An M4,5 absorption edge high-energy resolution XANES (HR-XANES; XANES 1⁄4 X-ray absorption near edge structure) and 3d4f resonant inelastic X-ray scattering (3d4f RIXS)
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