2017MNRAS.465.4690M

Absolute cross-sections for the K-shell photoionization of Be-like (O^4 +^) and Li-like (O^5 +^) atomic oxygen ions were measured for the first time (in their respective 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/ΔE ≃ 3200 (≃170 meV, full width at half-maximum) was achieved with photon energy from 550 to 670 eV. Rich resonance structure observed in the experimental spectra is analysed using the R-matrix with pseudo-states (RMPS) method.
Result. are also compared with the screening constant by unit nuclear charge (SCUNC) calculations. We characterize and identify the strong 1s - 2p resonances for both ions and the weaker 1s - np resonances (n >= 3) observed in the K-shell spectra of O^4 +^.