Abstract: Enhanced sensitivity for electron affinity measurements of rare elements
The electron affinity (EA) reflects the energy released when an electron is attached to a neutral atom and encodes key information about atomic structure, electron correlation effects and chemical reactivity. However, conventional techniques for EA determination lack the experimental sensitivity to probe very scarce samples. Consequently, the EA of the heaviest elements of the periodic table remain experimentally unexplored despite their fundamental importance to benchmark atomic many-body calculations with implications across atomic and nuclear physics, quantum chemistry and radiopharmaceutical research [1,2].
We have developed a novel technique to determine EAs through Laser Photodetachment Threshold Spectroscopy, performed in an electrostatic ion beam trap, a so-called MR-ToF device [3]. Our method increases the sample’s exposure to laser photons and, thus, enhances the experimental sensitivity by three orders of magnitude. Moreover, the additional exposure time allows the use of lower-power continuous-wave narrow-band lasers that reduce uncertainties associated with broadening effects induced by the laser bandwidth. By applying this technique, we measured the EA of 35Cl to be 3.612720(44) eV, achieving state-of-the-art precision while employing five orders of magnitude fewer anions. This unprecedented sensitivity paves the way for systematic EA measurements across isotopic chains - including isotope shifts and hyperfine splittings - and ultimately for the first direct determination of electron affinities in superheavy elements. In this contribution, I will introduce our novel method, present our experimental results and give an outlook to future possibilities of measurements of electron affinities of rare elements, an essential atomic property that is thus far unknown across approximately one-third of the periodic table.
References: [1] D. Leimbach et al., Nat. Commun. 11, 3824 (2020). [2] C. Ning, Y. Lu., J. Phys. Chem. Ref. Data 51, 021502 (2022). [3] F. M. Maier, E. Leistenschneider et al., Nat. Commun. 16, 9576 (2025).