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.
Highlights
One of the most challenging problems in atomic and molecular physics, when exploring negative ion formation in complex heavy atoms and fullerene molecules and to date still continues to plague both experiments and theory, is the determination of accurate and reliable values for the important electron affinity (EA) of the atoms and molecules involved
For a better understanding and appreciation of the physics involved in the calculations of the total cross sections (TCSs) for the actinide atoms presented for the first time in Figure 2 through 6, we first present in Figure 1 left and right panels our results for the structurally complicated Au atom and the C60 fullerene molecule, respectively
We found that the TCSs for these actinide atoms are characterized by ground, metastable and excited negative ion formation
Summary
One of the most challenging problems in atomic and molecular physics, when exploring negative ion formation in complex heavy atoms and fullerene molecules and to date still continues to plague both experiments and theory, is the determination of accurate and reliable values for the important electron affinity (EA) of the atoms and molecules involved. In the lanthanide and actinide atoms the presence of two or more open d- and f- subshell electrons results in enormous numbers of complicated and diverse electron configurations that characterize low-energy electron interactions in these systems. These present formidable computational complexity when using conventional theoretical methods that renders obtaining accurate and reliable EAs very difficult, if not impossible. The published literature abounds in incorrect EAs for the lanthanide and actinide atoms These reflect the difficulties in the theoretical understanding of the fundamental mechanism responsible for low-energy electron attachment in these systems leading to stable negative ion formation. To our knowledge no such experimental determination of the EAs of the actinide atoms has been reported
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