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31st International Conference on Photonic, Electronic and Atomic Collisions, ICPEAC XXXI, Deauville, France, 23 Jul 2019 - 30 Jul 2019; Journal of physics / Conference series 1412, 152011 (2020). doi:10.1088/1742-6596/1412/15/152011, Published by IOP Publ., Bristol

Absolute cross sections for the {\it K}-shell photoionisation of Be-like (O$^{4+}$) and Li-like (O$^{5+}$) atomic oxygen ions were measured for the first time (in their respective {\it K}-shell regions) by employing the ion-photon merged-beam technique at the SOLEIL synchrotron-radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/$\Delta$E $\approx$ 3200 ($\approx$ 170 meV, FWHM)was achieved with photon energy from 550 eV up to 670 eV. Rich resonance structure observed in the experimental spectra is analysed using the R-matrix with pseudo-states (RMPS) method. Results are also compared with the screening constant by unit nuclear charge (SCUNC) calculations. We characterise and identify the strong $\rm 1s \rightarrow 2p$ resonances for both ions and the weaker $\rm 1s \rightarrow np$ resonances ($ n \ge 3$) observed in the {\it K}-shell spectra of O$^{4+}$., Comment: 6 figures, 7 Tables, accepted for publication in MNRAS

Absolute cross sections for the single and double K-shell photoionization of carbon like O2+ and nitrogen like O+ ions were measured in the 526–620-eV photon energy range by employing the ion-photon merged-beam technique at the SOLEIL synchrotron radiation facility. High-resolution spectroscopy up to E/ Delta(E) ≈ 5300 was achieved. Rich resonance structures observed in the experimental spectra are analyzed and identified with the aid of R-matrix and multiconfiguration Dirac-Fock (MCDF) methods. For these two atomic oxygen ions of particular astrophysical interest we characterized the strong 1s → 2p and the weaker 1s → np (n > 2) resonances observed. A detailed comparison of the energies of the 1s → 2p resonances in the first members of the oxygen isonuclear sequence measured by synchrotron based experiments and the Chandra and XMM-Newton x-ray satellites is presented. M.F.G.acknowledges funding from the Scientific Research Support Fund, Jordan, under Contract No. as/2/02/2010. I.Q.A. acknowledges financial support from the SESAME – Lounsbery Foundation for a training fellowship. B.M.M. acknowledges support from the U.S. National Science Foundation through a grant to ITAMP at the Harvard-Smithsonian Center for Astrophysics, the RTRA network Triangle de la Physique, and a visiting research fellowship (VRF) from Queen’s University Belfast.

Measurements of absolute cross sections for the {\it K}-shell photoionization of B-like atomic nitrogen ions were carried out utilizing the ion-photon merged-beam technique at the SOLEIL synchrotron radiation facility in Saint-Aubin, France. High-resolution spectroscopy with E/$\Delta$E $\approx$ 13,500 was the maximum resolution achieved. We have investigated two photon energy regions: 404 eV -- 409 eV and 439 eV -- 442 eV. Resonance peaks found in the experimental measured cross sections are compared with theoretical estimates from the multi-configuration Dirac - Fock, R-matrix and empirical methods, allowing identification of the strong 1s $\rightarrow$ 2p and the weaker 1s $\rightarrow$ 3p resonances in the observed {\it K}-shell spectra of this B-like nitrogen ion., Comment: 16 pages, 3 figures, 2 tables: Accepted for publication in J. Phys. B: At. Mol. & Opt. Phys. arXiv admin note: substantial text overlap with arXiv:1308.6795

Absolute cross sections for the {\it K}-shell photoionization of Be-like and Li-like atomic nitrogen ions were measured by employing the ion-photon merged-beam technique at the SOLEIL synchrotron radiation facility in Saint-Aubin, France. High-resolution spectroscopy at nominal resolutions of 38 meV, 56 meV, 111 meV, 133 meV FWHM for Be-like and 125 meV FWHM for Li-like atomic nitrogen ions was achieved for the photon energies ranging from 410 eV up to 460 eV. The experimental measurements are compared with theoretical estimates from the multi-configuration Dirac-Fock (MCDF), R-matrix and an empirical method. The interplay between experiment and theory enabled the identification and characterisation of the strong 1s $\rightarrow$ 2p resonances features observed in the {\it K}-shell spectra of each ion and the region around 460 eV for the 1s $\rightarrow$ 3p resonance of the N$^{3+}$ ion yielding suitable agreement with experiment., 22 pages, 5 figures, 3 Tables. J. Phys. B: At. Mol.Opt. Phys. (2013) in press