Negative Ion Formation in Low-Energy Electron Collisions with the Actinide Atoms Th, Pa, U, Np and Pu

Abstract

Here we investigate ground and metastable negative ion formation in low-energy electron collisions with the actinide atoms Th, Pa, U, Np and Pu through the elastic total cross sections (TCSs) calculations. For these atoms, the presence of two or more open d-and f-subshell electrons presents a formidable computational task for conventional theoretical methods, making it difficult to interpret the calculated results. Our robust Regge pole methodology which embeds the crucial electron correlations and the vital core-polarization interaction is used for the calculations. These are the major physical effects mostly responsible for stable negative ion formation in low-energy electron scattering from complex heavy systems. We find that the TCSs are characterized generally by Ramsauer-Townsend minima, shape resonances and dramatically sharp resonances manifesting ground and metastable negative ion formation during the collisions. The extracted from the ground states TCSs anionic binding energies (BEs) are found to be 3.09eV, 2.98eV, 3.03eV, 3.06eV and 3.25eV for Th, Pa, U, Np and Pu, respectively. Interestingly, an additional polarization-induced metastable TCS with anionic BE value of 1.22eV is generated in Pu due to the size effect. We also found that our excited states anionic BEs for several of these atoms compare well with the existing theoretical electron affinities including those calculated using the relativistic configuration-interaction method. We conclude that the existing theoretical calculations tend to identify incorrectly the BEs of the resultant excited anionic states with the electron affinities of the investigated actinide atoms; this demonstrates the great need for experimental verification and unambiguous determination of their electron affinities.

Negative Ion Binding Energies in Complex Heavy Systems

“…In the lanthanide and actinide atoms, in particular the presence of two or more open d-and f-subshell electrons presents formidable computational complexity when using conventional theoretical methods to calculate electron affinities (EAs) of complex heavy systems. Thus, recent years have witnessed the proliferation in the published literature of incorrect experimental and theoretical EAs for the lanthanide [2] and actinide [3] atoms as well as for atomic Nb. For the complex atoms such as Nb experiments have concentrated efforts mainly on the accuracy rather than on the reliability of the existing EAs.…”

“…(5) Very recently, electron scattering TCSs for the very complicated actinide atoms Th, Pa, U, Np and Pu were calculated [3]. It was concluded that the existing theoretical calculations tend to identify incorrectly the BEs of the resultant excited anionic states with the EAs of the investigated actinide atoms; this suggests a need for an unambiguous definition and determination of the EAs.…”

Doubly-Charged Negative Ions as Novel Tunable Catalysts: Graphene and Fullerene Molecules Versus Atomic Metals

“…In Figure 1 , the standard elastic TCSs for the Au and C 60 systems taken from [ 32 ] are displayed. They reveal the important characteristic negative ion BEs, R–T minima and shape resonances.…”

“…Generally, calculated low-energy electron elastic TCSs are characterized by dramatically sharp resonances that manifest ground, metastable and excited negative ion formation, with the ground state binding energies (BEs) yielding the important EAs that are theoretically challenging to calculate for complex heavy systems. In Figure 1, the standard elastic TCSs for the Au and C 60 systems taken from [32] are displayed. They reveal the important characteristic negative ion BEs, R-T minima and shape resonances.…”

Doubly-charged Negative Ions as Novel Tunable Catalysts: Graphene and Fullerene Molecules Versus Atomic Metals

“…In Fig. 1 the standard elastic TCSs for the Au and C 60 systems taken from [32], are displayed. They reveal the important characteristic negative ion BEs, R-T minima and shape resonances.…”