Abstract
The rigorous Regge-pole method is used to investigate negative-ion formation in actinide atoms through electron elastic total cross sections (TCSs) calculation. The TCSs are found to be characterized generally by negative-ion formations, shape resonances and Ramsauer-Townsend(R-T) minima, and they exhibit both atomic and fullerene molecular behavior near the threshold. Additionally, a polarization-induced metastable cross section with a deep R-T minimum is identified near the threshold in the Am, Cm and Bk TCSs, which flips over to a shape resonance appearing very close to the threshold in the TCSs for Es, No and Lr. We attribute these new manifestations to size effects and orbital collapse significantly impacting the polarization interaction. From the TCSs unambiguous and reliable ground, metastable and excited states negative-ion binding energies (BEs) for Am−, Cm−, Bk−, Es−, No− and Lr− anions formed during the collisions are extracted and compared with existing electron affinities (EAs) of the atoms. The novelty of the Regge-pole approach is in the extraction of the negative-ion BEs from the TCSs. We conclude that the existing theoretical EAs of the actinide atoms and the recently measured EA of Th correspond to excited anionic BEs.
Highlights
The determination of unambiguous and reliable values of electron affinities (EAs) for complex electron-heavy systems such as lanthanide and actinide atoms, as well as fullerene molecules, is currently one of the most challenging problems in atomic and molecular physics and still plagues both experiments and theories alike
The focus of this paper is toward a fundamental understanding of negative-ion formation in low-energy electron scattering from the actinide atoms, Am, Cm, Bk, Es, No and Lr, through the calculation of electron elastic total cross sections (TCSs) using the rigorous Regge pole method
From the characteristic dramatically sharp resonances in the TCSs manifesting ground, metastable and excited-state negative-ion formation, we extract the binding energies (BEs) of the formed negative ions during the collisions
Summary
The determination of unambiguous and reliable values of electron affinities (EAs) for complex electron-heavy systems such as lanthanide and actinide atoms, as well as fullerene molecules, is currently one of the most challenging problems in atomic and molecular physics and still plagues both experiments and theories alike. A great motivation for this investigation is the remarkable agreement between the recent first ever EA measurement of the highly radioactive At atom [3] and various theoretical EAs [4]. In the context of the present investigation, the measured EA of the atomic At matched excellently with the Regge-pole-calculated binding energy (BE) of the ground state of the At− anion (see Table 1 for the comparison). Recently the EAs of Th and Hf were measured [5,6] For both atoms the measured and calculated EAs corresponded to the Regge-pole-calculated BEs of their anions in excited states [7,8] and not in their ground states
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