Strong electron correlation in UO2−: A photoelectron spectroscopy and relativistic quantum chemistry study

Abstract

The electronic structures of actinide systems are extremely complicated and pose considerable challenges both experimentally and theoretically because of significant electron correlation and relativistic effects. Here we report an investigation of the electronic structure and chemical bonding of uranium dioxides, UO2(-) and UO2, using photoelectron spectroscopy and relativistic quantum chemistry. The electron affinity of UO2 is measured to be 1.159(20) eV. Intense detachment bands are observed from the UO2(-) low-lying (7sσg)(2)(5fϕu)(1) orbitals and the more deeply bound O2p-based molecular orbitals which are separated by a large energy gap from the U-based orbitals. Surprisingly, numerous weak photodetachment transitions are observed in the gap region due to extensive two-electron transitions, suggesting strong electron correlations among the (7sσg)(2)(5fϕu)(1) electrons in UO2(-) and the (7sσg)(1)(5fϕu)(1) electrons in UO2. These observations are interpreted using multi-reference ab initio calculations with inclusion of spin-orbit coupling. The strong electron correlations and spin-orbit couplings generate orders-of-magnitude more detachment transitions from UO2(-) than expected on the basis of the Koopmans' theorem. The current experimental data on UO2(-) provide a long-sought opportunity to arbitrating various relativistic quantum chemistry methods aimed at handling systems with strong electron correlations.

Collision‐induced dissociation of uranyl‐methoxide and uranyl‐ethoxide cations: Formation of UO 2 H + and uranyl‐alkyl product ions

“…The transfer of uranium as monopositive pentavalent U V O 2 + , from solution to the gas phase using electrospray ionization (ESI), was first reported in 1992 . Thereafter, advances in the fundamental understanding of uranyl coordination chemistry have been achieved by using ESI, including the generation of a wide range of singly and doubly charged complexes that contain actinyl cations …”

“…[15] Thereafter, advances in the fundamental understanding of uranyl coordination chemistry have been achieved by using ESI, including the generation of a wide range of singly and doubly charged complexes that contain actinyl cations. [16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] In an earlier study, ESI and multiple-stage tandem mass spectrometry (MS n ) were used to characterize the dissociation pathways for uranyl nitrate or hydroxide cations coordinated by water or alcohol ligands. [36] In general, collision-induced dissociation (CID) of the uranyl complexes resulted in the elimination of coordinating water and alcohol ligands.…”

Gas Phase Reactions of Ions Derived from Anionic Uranyl Formate and Uranyl Acetate Complexes

“…Electrospray ionization (ESI) provides easy access to a wide range of gasphase complexes containing uranium in high oxidation states (+5 and +6) for studies of intrinsic structure and reactivity (i.e., outside of the influence of solvent or other condensed phase effects) in a species specific fashion. For example, the transfer of uranium as mono-positive, pentavalent U V O 2 + from solution to the gas phase using ESI was first reported in 1992 [5] and since then, advances in the fundamental understanding of uranyl coordination chemistry have been made using the ionization method [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21]. Most importantly, ESI has been used to generate gas-phase, doubly charged complexes containing UO 2…”

PrB7−: A Praseodymium‐Doped Boron Cluster with a PrII Center Coordinated by a Doubly Aromatic Planar η7‐B73− Ligand

“…Then ext band Ai sd erived from electron detachment from ad eeper boron-based bonding 4e 1 orbital (HOMO), rather than the next two SOMOÀ1(6a 1 )and SOMOÀ2(1b 1 ) of Pr 4f character.T his breakdown of the Koopmans theorem is common in strongly correlated f-element systems. [33,35] Themore contracted Pr 4f orbitals are significantly stabilized upon electron detachment, so that the (4e 1 ) 3 (4f) 2 -(6s) 1 configuration becomes energetically more favorable than (4e 1 ) 4 (4f) 1 (6s) 1 in neutral PrB 7 .T his trend of f-orbitals being increasingly more stabilized upon electron ionization is also observed in other 4f and 5f systems. [36] Thee lectron detachment from the 4e 1 HOMO orbital leads to two final states, 5 E 2 (VDE:2 .96 eV) and 3 E 2 (VDE:3 .11 eV).…”

“…[32] TheP r4f 2 6s 1 configuration in PrB 7 À is reminiscent of the U5f 2 7s 1 configuration in UO 2 À . [33] Thepreference of occupying the n sorbitals rather than the (nÀ2)f orbitals in Figure 1. The photoelectron spectrum of PrB 7 À at 193 nm (6.424 eV).…”