First ionization potential of the heaviest actinide lawrencium, element 103

¹ Japan Atomic Energy Agency, Tokai, Ibaraki 319-1195, Japan
² The Van Swinderen Institute for Particle Physics and Gravity, University of Groningen, 9700 AB Groningen, The Netherlands
³ ISOLDE, CERN, CH-1211 Geneva 23, Switzerland
⁴ Graduate School of Science and Engineering, Ibaraki University, Mito, Ibaraki 310-8512, Japan
⁵ Helmholtz-Institut Mainz, 55099 Mainz, Germany
⁶ GSI Helmholtzzentrum für Schwerionenforschung, 64291 Darmstadt, Germany
⁷ Institut für Kernchemie, Johannes Gutenberg-Universität Mainz, 55099 Mainz, Germany
⁸ School of Chemistry, Tel Aviv University, 69978 Tel Aviv, Israel
⁹ Nishina Center for Accelerator-Based Science, RIKEN, 2-1 Hirosawa, Wako, Saitama 351-0198, Japan
¹⁰ Graduate School of Science, Hiroshima University, Kagamiyama, Higashi-Hiroshima 739-8526, Japan
¹¹ Institute of Science and Technology, Niigata University, Niigata 910-2181, Japan

^a Corresponding author:e-mail: sato.tetsuya@jaea.go.jp

Published online: 1 December 2016

Abstract

The first ionization potential (IP₁) of element 103, lawrencium (Lr), has been successfully determined for the first time by using a newly developed method based on a surface ionization process. The measured IP₁ value is 4.963^0.08_0.07 eV. This value is the smallest among those of actinide elements and is in excellent agreement with the value of 4.963(15) eV predicted by state-of-the-art relativistic calculations also performed in this work. Our results strongly support that the Lr atom has an electronic configuration of [Rn]7s²5f¹⁴7p¹_1/2, which is influenced by strong relativistic effects. The present work provides a reliable benchmark for theoretical calculations and also opens the way for studies on atomic properties of heavy elements with atomic number Z > 100. Moreover, the present achievement has triggered a controversy on the position of lutetium (Lu) and Lr in the Periodic Table of Elements.