High-precision, reference-free measurements of 2p $\rightarrow$ 1s transitions in boron-like sulfur and argon

TL;DR

This paper reports highly precise, reference-free measurements of 2p to 1s transition energies in boron-like sulfur and argon ions, comparing results with advanced theoretical calculations to test atomic models.

Contribution

It provides the first high-precision, reference-free measurements of these transitions in sulfur and argon, and extends theoretical calculations to other B-like ions for comparison.

Findings

Measured transition energies with 2-4 ppm accuracy.

Achieved agreement between experiment and theory within 15 meV.

Extended theoretical calculations to additional B-like ions.

Abstract

We have measured several 2p $\rightarrow$ 1s 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 a an electron-cyclotron resonance ion source and were measured by a double-crystal x-ray spectrometer. The precision obtained for the measured 1s2s22p2 J -- 1s2 2s2 2p J ' lines is $\approx$4 ppm for sulfur and $\approx$2 ppm 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 test the theoretical methods, which reach an agreement with experimental data up to 15 meV. The theoretical calculations have been extended to C+, Si9+, Cr19+ and Fe21+, which were the only B-like ions where such transitions were measured up to now.