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

Abstract

The rigorous Regge pole method has been used to investigate negative-ion formation in the large actinide atoms Cf, Fm and Md through the elastic total cross sections (TCSs) calculation in the electron impact energy range 0.0 ≤ E ≤ 10.0eV. Ground, metastable and excited negative-ion formation as well as shape resonances (SRs) and Ramsauer-Townsend (R-T) minima are found to characterize generally the TCSs which also exhibit fullerene molecular behavior near threshold through the TCSs of the highest excited states, while maintaining atomic character through the ground state TCSs. Additionally, a polarization-induced metastable TCS with a pronounced SR appears for the first time very close to threshold in the Cf TCSs, having flipped over from a deep R-T minimum near threshold in the Bk TCSs. This behavior manifests the impact of the size effect and the 6d-orbital collapse as well as demonstrates the sensitivity of the R-T minima and the SRs to the electronic structure of these atoms, thereby permitting their first ever use as novel confirmation of Cf as a transitional element in the actinide series. Rigorous and unambiguous ground, metastable and excited anionic states BEs extracted from the TCSs are compared with the existing electron affinities.

Recent Progress in Low-Energy Electron Elastic-Collisions with Multi-Electron Atoms and Fullerene Molecules

“…There are no measured EAs for the actinide atoms beyond U to compare our BEs with. However, theoretical EAs are available [36,76,78,79] and these have been compared with our data for the actinide atoms [54,77,80], see also Table 3.5. For atomic Lr the EA values of 0.310 eV [78] and 0.295eV [36] are very close to the Regge pole BE of the highest excited state, namely 0.321eV.…”

“…Hitherto fore, they were scattered all over the literature. Importantly, the recent data from [80] are crucial for understanding Section 3.7. Table 3.5: Negative ion binding energies (BEs) in eV and energy positions of ground-state Ramsauer-Townsend (R-T) minima, in eV obtained from the TCSs for the actinide atoms from Pu through Lr.…”

“…The second 6d-orbital collapse occurs in the transition Cm[Rn]7s 2 5f 7 6d to Bk[Rn]7s 2 5f 9 . To facilitate the discussion we have included for convenience Table 3.7; the data have been taken from [54,77,80]. Table 3.7 shows that the ground state anionic BE increased significantly from 3.32eV in Cm to 3.55eV in Bk, thereby widening the energy space for the flip over to take place.…”

“…Negative-ion binding energies (BEs), in eV extracted from the TCSs for the actinide atoms Np through Fm are taken from[54,77,80]. GRS, MS-n and EX-n (n=1, 2) represent respectively ground, metastable and excited anionic states.…”