The electron affinity of the uranium atom

Abstract

The results of a combined experimental and computational study of the uranium atom are presented with the aim of determining its electron affinity. Experimentally, the electron affinity of uranium was measured via negative ion photoelectron spectroscopy of the uranium atomic anion, U−. Computationally, the electron affinities of both thorium and uranium were calculated by conducting relativistic coupled-cluster and multi-reference configuration interaction calculations. The experimentally determined value of the electron affinity of the uranium atom was determined to be 0.309 ± 0.025 eV. The computationally predicted electron affinity of uranium based on composite coupled cluster calculations and full four-component spin–orbit coupling was found to be 0.232 eV. Predominately due to a better convergence of the coupled cluster sequence for Th and Th−, the final calculated electron affinity of Th, 0.565 eV, was in much better agreement with the accurate experimental value of 0.608 eV. In both cases, the ground state of the anion corresponds to electron attachment to the 6d orbital.

Low-Energy Electron Elastic Total Cross Sections for the Large Actinide Atoms Cf, Fm and Md

“…Until very recently, there were no measured electron affinities (EAs) of the actinide atoms. A great achievement was the recent first time ever measurement of the EA of the highly radioactive At atom (Leimbach et al, 2020) as well as of the actinide atoms Th (Tang, et al, 2019) and U (Tang, Lu, Liu & Ning, 2021;Ciborowski et al, 2021). For the At atom the MCDHF-calculated value (Si & Froese Fischer, 2018) agrees excellently with the measured EA (Leimbach et al, 2020).…”

“…Previously, we investigated low-energy electron elastic TCSs using the rigorous Regge pole method and extracted the anionic BEs of the actinide atoms Th through Pa (Felfli & Msezane, 2019) and Am through Lr (Msezane & Felfli, 2021). And the anionic BEs were compared with the available calculated (O' Malley & Beck, 2009;Guo & Whitehead, 1989;Eliav, Kaldor, & Ishikawa, 1995;Borschevsky, et al, 2007) and the measured (Tang, et al, 2019;Tang, Lu, Liu & Ning, 2021;Ciborowski, et al, 2021) EAs. However, the TCSs for the large actinide atoms Cf, Fm and Md were never calculated.…”

“…Notably, close to the excited and metastable states anionic BEs, represented by the dramatically sharp resonances are SRs. Therefore, the delineation and identification of the dramatically sharp resonances are very important, particularly for those experimenters defining the EA as corresponding to the anionic BE of the least bound electron to the neutral atom (Tang, et al, 2019;Tang, Lu, Liu & Ning, 2021;Ciborowski, et al, 2021). However, if the EA is identified with the BE of the anionic ground state of the formed negative ion as in the cases of the Au, Pt and At atoms, there will be no ambiguity.…”

“…In the recent measurement of the EAs of the actinide atoms Th (Tang, et al, 2019) and U (Tang, Lu, Liu & Ning, 2021;Ciborowski, et al, 2021) the experimentalists claimed that their EAs corresponded to the BEs of the weakly bound electron to the neutral atoms. Importantly, the measured EAs of Th and U are close to the Regge pole-calculated BEs of their excited anionic states and not to their ground states (Msezane & Felfli, 2021).…”

Low-Energy Electron Elastic Collisions with Actinide Atoms Am, Cm, Bk, Es, No and Lr: Negative-Ion Formation

“…This renders obtaining unambiguous and reliable EAs for these systems very difficult, if not impossible. Indeed, many existing experimental and sophisticated theoretical EAs of the lanthanides and actinides are difficult to interpret, see for example [7][8][9][10]. A serious question then arises: Does the EA of complex heavy systems correspond to the BE of electron attachment in the ground, metastable or the excited state of the formed negative ion during the collision?…”