Assessment of the Second-Ionization Potential of Lawrencium: Investigating the End of the Actinide Series with a One-Atom-at-a-Time Gas-Phase Ion Chemistry Technique

Abstract

Experiments were performed at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron facility to investigate the electron-transfer reduction reaction of dipositive Lr (Z = 103) with O 2 gas. Ions of 255 Lr were produced in the fusion−evaporation reaction 209 Bi( 48 Ca,2n) 255 Lr and were studied with a novel gas-phase ion chemistry technique. The produced 255 Lr 2+ ions were trapped and O 2 gas was introduced, such that the charge-exchange reaction to reduce 255 Lr 2+ to 255 Lr 1+ was observed and the reaction rate constant was determined to be k = 1.5(7) × 10 −10 cm 3 /mol/s. The observation that this reaction proceeds establishes the lower limit on the second ionization potential of Lr to be 13.3(3) eV. This gives further support that the actinide series terminates with Lr. Additionally, this result can be used to better interpret the situation concerning the placement of Lu and Lr on the periodic table within the current framework of the actinide hypothesis. The success of this experimental approach now identifies unique opportunities for future gas-phase reaction studies on actinide and super heavy elements.

Multireference Wavefunction-Based Investigation of the Ground and Excited States of LrF and LrO

“…18−20 In 2021, the second ionization potential for atomic lawrencium was measured with a one-atom-at-a-time technique, and found to be 13.3(3) eV. 21 The particularly complicated electronic structure of actinides is due to their open-shell s, d, p, and f orbitals, resulting in multiple near-degenerate electronic states. The prevalence of close, low-lying states on actinide complexes results in numerous challenges in terms of accounting for and resolving states, converging energies, and computational affordability (memory and processors required).…”

“…provided the first ionization potential for the lawrencium atom, determined to be 4.96 –0.07 +0.08 eV . It was noted in this study that measurements on transactinide elements are hampered by the difficulty in obtaining them at more than one-atom-at-a-time quantitities. − In 2021, the second ionization potential for atomic lawrencium was measured with a one-atom-at-a-time technique, and found to be 13.3(3) eV …”

“… 18 − 20 In 2021, the second ionization potential for atomic lawrencium was measured with a one-atom-at-a-time technique, and found to be 13.3(3) eV. 21 …”