Absolute cross sections for the K-shell photoionization of C-like nitrogen ions were measured by employing the ion-photon merged-beam technique at the SOLEIL synchrotron radiation facility in Saint-Aubin, France. Highresolution spectroscopy with E/∆E ≈ 7,000 was achieved with the photon energy from 388 to 430 eV scanned with a band pass of 300 meV, and the 399.4 to 402 eV range with 60 meV. Experimental results are compared with theoretical predictions made from the multi-configuration Dirac-Fock (MCDF) and R-matrix methods. The interplay between experiment and theory enabled the identification and characterization of the strong 1s → 2p resonances observed in the spectra.

Absolute cross sections for the K-shell photoionization of Be-like and Li-like atomic nitrogen ions were measured by employing the ion-photon mergedbeam 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 → 2p resonances features observed in the Kshell spectra of each ion and the region around 460 eV for the 1s → 3p resonance of the N 3+ ion yielding suitable agreement with experiment.