High-precision measurements of $n=2\to n=1$ transition energies and level widths in He- and Be-like Argon Ions

TL;DR

This study achieved highly precise, reference-free measurements of specific transition energies and widths in He- and Be-like argon ions, validating theoretical models and providing new experimental benchmarks.

Contribution

First reference-free measurements of key transition energies and widths in He- and Be-like argon ions, with high accuracy and comparison to advanced theoretical calculations.

Findings

Transition energies measured with better than 3 parts in 10^6 accuracy.

Results agree with recent theoretical calculations within uncertainties.

Width measurements test radiative decay and Auger processes in highly-charged ions.

Abstract

We performed a reference-free measurement of the transition energies of the $1s 2p\,^1P\_1\to 1s^2 \,^1S\_0$ line in He-like argon, and of the $1s 2s^2 2p\,^1P\_1\to 1s^2 2s^2\,^1S\_0$ line in Be-like argon ions. The highly-charged ions were produced in the plasma of an Electron-Cyclotron Resonance Ion Source. Both energy measurements were performed with an accuracy better than 3 parts in $10^6$, using a double flat-crystal spectrometer, without reference to any theoretical or experimental energy. The $1s 2s^2 2p\,^1P\_1\to 1s^2 2s^2\,^1S\_0$ transition measurement is the first reference-free measurement for this core-excited transition. The $1s 2p\,^1P\_1\to 1s^2 \,^1S\_0$ transition measurement confirms recent measurement performed at the Heidelberg Electron-Beam Ion Trap (EBIT). The width measurement in the He-like transition provides test of a purely radiative decay calculations. In the case of the Be-like argon transition, the width results from the sum of a radiative channel and three main Auger channels. We also performed Multiconfiguration Dirac-Fock (MCDF) calculations of transition energies and rates and have done an extensive comparison with theory and other experimental data. For both measurements reported here, we find agreement with the most recent theoretical calculations within the combined theoretical and experimental uncertainties.