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 f r > 0.1. The Kα resonance wavelengths of O I‐O VI lie in the relatively narrow wavelength range 22‐23.5 ˚ A, 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