Inner-shell photoionization of OIII

A 25-state R-matrix calculation is performed to obtain photoionization cross-sections for transitions from the 1s²2s²2p^{2 3}P ground state of the OIII ion. Results are obtained for a range of photon energies, including those at which K-shell photoionization processes take place. We compare our results with those from previous calculations. Excellent agreement is obtained. We also consider resonances owing to transitions of a 1s electron excited into the 2p orbital and compare with a recent calculation.