**Figure 1.** Comparison of PI cross sections between the present results and the available theoretical and experimental data for Ar^{8+}. (a) Our results from DARC; (b) the convoluted results of DARC (black line), our MCDF results (blue vertical lines with circles), and those calculated by Simon *et al* (red vertical lines with diamonds) using a Gaussian profile of FWHM = 800 meV, and the results from TOPbase [2] (magenta dotted line) convoluted with FWHM = 300 meV; (c) overview of experimental PI spectrum of the Ar^{8+} ion [21].

**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.