Speaker
Description
Chemical studies of the heaviest elements provide crucial and challenging opportunities not only to advance our understanding of properties of matter at the limits of existence but also those to elucidate the influence of relativistic effects on atomic electrons and to architect the periodic table of the elements at the farthest reach [1,2]. The influence of relativistic effects on electronic orbitals has, so far, indirectly inferred through a comparison of chemical properties of the heaviest elements with those of their lighter homologues and those predicted by theoretical calculations. The first ionization energy (IP$_{1}$) is one of the most sensitive atomic properties which reflect the outermost electron configuration. Thus, accurate IP$_{1}$ values of the heaviest elements allows us to give significant information on valence electronic configuration affected by relativistic effects.
The ground-state electronic configuration of element 103, lawrencium (Lr), is predicted to be [Rn]5f$^{14}$7s$^{2}$7p$_{1/2}$ which is different from that of the lanthanide homologue Lu, [Xe]4f$^{14}$6s$^{2}$5d, because the 7p$_{1/2}$ orbital is expected to be stabilized below the 6d orbital by strong relativistic effects [3]. Lr is expected to be the first element where relativistic effects would directly change the electronic ground-state configuration with respect to the normal prediction of the periodic table.
In the previous paper [4], we reported the determination of IP$_{1}$ of Lr by using a novel technique based on a surface ionization process coupled to an on-line mass separation technique. Our experimental IP$_{1}$ is in excellent agreement with theoretical calculations. This good agreement with predictions obtained using relativistic calculations, which favour a 7s$^{2}$7p$_{1/2}$ configuration in the Lr atom, supports this ground-state configuration.
In the next stage, we plan to directly determine the ground-state configuration of Lr by applying the Stern-Gerlach technique of magnetic deflection of atomic beams. Here, a well-collimated atomic beam passes through an inhomogeneous magnetic field that splits the beam into (2$J$ + 1) components; $J$ is the total electronic angular momentum of the atom. From the number of beam split components, the ground-state configuration of the Lr atom can be determined unambiguously. We have just started the development of an apparatus for effective extraction of the atomic Lr beam by exploiting a small cavity type atomic beam source that can be heated by electron bombardment. In the contribution, we present the status and achievement, and future prospect of this program.
References
[1] A. Türler, V. Pershina, Chem. Rev. 2013, 113,1237-1312.
[2] The Chemistry of Superheavy Elements, 2nd ed.; Schädel, M., Shaughnessy, D., Eds.; Springer: Heidelberg, 2013.
[3] J.-P. Desclaux, B. Fricke, J. Phys. 1980, 41,943-946.
[4] T. K. Sato et al. Nature 2015, 520, 209-211.
