https://doi.org/10.1140/epjd/s10053-024-00910-x
Regular Article - Atomic Physics
High-precision,reference-free measurements of 
transitions in boron-like sulfur and argon
1
Laboratoire Kastler-Brossel, Sorbonne Université, Collège de France, CNRS, École Normale Supérieure, 4 place Jussieu, 75005, Paris, France
2
Institut des NanoSciences de Paris, Sorbonne Université, CNRS, 4 place Jussieu, 75005, Paris, France
3
Laboratório de Instrumentação Engenharia Biomédica e Física da Radiação, Facultade CÎencas e Tecnologia, Universidade Nova de Lisboa, 2829-516, Caparica, Portugal
Received:
21
May
2024
Accepted:
23
August
2024
Published online:
13
September
2024
We have measured several transition energies in core-excited boron-like ions of sulfur and argon. The measurements are reference-free, with an accuracy of a few parts per million. The x-rays were produced by the plasma of an electron cyclotron resonance ion source and measured with a double-crystal x-ray spectrometer. The precision obtained for the measured 
lines is 
for sulfur and 
for argon. The line energies are compared to relativistic atomic structure calculations performed with the mdfgme multi-configuration Dirac–Fock code. This comparison is used for line identification and tests the theoretical methods, which are in agreement with the experimental data up to 
. The theoretical calculations have been extended to B, 
, 
, 
and 
, which were the only B-like ions where such transitions were measured up to now.
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© The Author(s), under exclusive licence to EDP Sciences, SIF and Springer-Verlag GmbH Germany, part of Springer Nature 2024. Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.
