# The absolute PI cross sections (panels (a), (c) and (e)) from the DARC calculations, and resonance strengths (panels (b), (d) and (f)) from MCDF calculations, as functions of the photon energy (eV) for the Fe^{16+} (top), Kr^{26+} (middle) and Xe^{44+} (bottom) ions

**Figure 2.** The absolute PI cross sections (panels (a), (c) and (e)) from the DARC calculations, and resonance strengths (panels (b), (d) and (f)) from MCDF calculations, as functions of the photon energy (eV) for the Fe^{16+} (top), Kr^{26+} (middle) and Xe^{44+} (bottom) ions. The photon energies from DARC have been shifted 5.1, 6.7 and 10.85 eV towards the lower energy for Fe^{16+}, Kr^{26+} and Xe^{44+}, respectively, to match the MCDF calculations. The vertical dotted lines mark the 2s*n*p resonances series obtained by DARC; the vertical lines in panel (b), (d) and (f) give the resonance strength on the resonant positions for 2s*n*p ^{3}P_{1} (solid diamonds) and ^{1}P_{1} (6 ≤ *n* ≤ 13) (hollow diamonds) states of Fe^{16+}, Kr^{26+} and Xe^{44+}. The dashed lines show the ionization threshold of 2p_{1/2}, 2p_{3/2} and 2s_{1/2} states for 2s^{2}2p^{6}.

**Abstract**

Photoionization (PI) cross sections of the ground state 1s^{2} 2s^{2} 2p^{6}^{1} S_{0} of Ne-like Ar^{8+}, Fe^{16+}, Kr^{26+} and Xe^{44+} ions are calculated by using the Dirac atomic *R*-matrix code based on a fully relativistic *R*-matrix method. To analyze the detailed resonant structure, systematical calculations based on the multiconfiguration Dirac–Fock method are performed for the dominant 2s → *n*p resonant transitions, and the resonant energies, strengths and total natural widths are presented. The resonant structures and characteristics of the PI cross sections and resonance strengths along the Ne-like sequence are discussed with emphasis on the influence of relativistic effects. For the Ar^{8+} ion, good agreement is found between the present results and available theoretical calculations and experimental data.