High-precision measurements of n=2→n=1 transition energies and level widths in He-and Be-like argon ions

This research was supported in part by Projects No. PEstOE/FIS/UI0303/2011 and No. PTDC/FIS/117606/2010, and by research center Grant No. UID/FIS/04559/2013 (LIB-Phys), from FCT/MCTES/PIDDAC, Portugal. We acknowledge partial support from NIST (P.I.), from PESSOA Huber Curien Program No. 38028UD, and PAUILF Program No. 2017-C08. P.A., J.M., and M.G. acknowledge support from FCT under Contracts No. SFRH/BPD/92329/2013, No. SFRH/BD/52332/2013, and No. SFRH/BPD/92455/2013, respectively. Laboratoire Kastler Brossel (LKB) is "Unite Mixte de Recherche de Sorbonne Universite, de ENS-PSL Research University, du College de France et du CNRS No. 8552." P.I. is a member of the Allianz Program of the Helmholtz Association, Contract No. EMMI HA-216 "Extremes of Density and Temperature: Cosmic Matter in the Laboratory." The SIMPA ECRIS has been financed by grants from CNRS, MESR, and University Pierre and Marie Curie (now Sorbonne Universite). The experiment has been supported by BNM Grant No. 0130002 and ANR Grant No. ANR-06-BLAN-0223. We wish to thank Jean-Paul Desclaux for his help improving the MCDFGME code, and Dr. Martino Trassinelli (INSP) for valuable discussions and his help during early stages of the experiment. We performed a reference-free measurement of the transition energies of the 1s2p1P1→1s21S0 line in He-like argon, and of the 1s2s22p1P1→1s22s21S0 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 106, using a double flat-crystal spectrometer, without reference to any theoretical or experimental energy. The 1s2s22p1P1→1s22s21S0 transition measurement is the first reference-free measurement for this core-excited transition. The 1s2p1P1→1s21S0 transition measurement confirms recent measurement performed at the Heidelberg electron-beam ion trap. The width measurement in the He-like transition provides test of a purely radiative decay calculation. 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 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. publishersversion published