Spectroscopy of hydrogenlike and heliumlike argon

The x-ray transitions ($n=2\mathrm{}\to n=1\mathrm{}$) emitted by fast hydrogenlike and heliumlike argon ions have been studied. The absolute energy of the Lyman $\alpha$ lines of hydrogenlike ions has been measured and the value of the ($1s$) Lamb shift of argon evaluated for the first time. The ${}_{}{}^3{}_{}{}^{}P_{1,2}^{}{}_{}{}^{}$ and ${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$ transitions of heliumlike argon have also been studied at very high precision and their energies compared to multiconfiguration Dirac-Fock calculations. The energies of Lyman $\alpha$ lines are of 3323.2±0.5 eV ($\mathrm{Ly}{\alpha }_1$) and 3318.1±0.5 eV ($\mathrm{Ly}{\alpha }_2$), and those of $n=2\mathrm{}\to n=1\mathrm{}$ transitions for heliumlike argon are of 3123.6±0.25 eV (${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}$), 3126.4±0.4 eV (${}_{}{}^3{}_{}{}^{}P_2^{}{}_{}{}^{}$), and 3139.6±0.25 eV (${}_{}{}^1{}_{}{}^{}P_1^{}{}_{}{}^{}$).