X-ray absorption via Kα resonance complexes in oxygen ions

The Kα resonance complexes in oxygen ions O I O VI are theoretically computed and resonance oscillator strengths and wavelengths are presented. The highly resolved photoionization cross sections, with relativistic fine structure, are computed in the coupled channel approximation using the Breit-Pauli R-matrix method. A number of strong Kα resonances are found to be appreciable, with resonance oscillator strengths fr > 0.1. The Kα resonance wavelengths of O I-O-VI lie in a relatively narrow wavelength range 22−23.5Å, and the X-ray opacity in this region should therefore be significantly affected by K → L transitions in oxygen. The results should be useful in the interpretation of soft X-ray spectra observed from Chandra and XMM-Newton .