X-ray absorption via Kα resonance complexes in oxygen ions

The Kα resonance complexes in oxygen ions OI-OVI 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 <sansserif>R</sansserif>-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 OI-OVI lie in the relatively narrow wavelength range 22-23.5 Å, 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.