K-SHELL PHOTOABSORPTION STUDIES OF THE CARBON ISONUCLEAR SEQUENCE

K-shell photoabsorption cross sections for the isonuclear C I-C IV ions have been computed using the R-matrix method. Above the K-shell threshold, the present results are in good agreement with the independent-particle results of Reilman and Manson. Below threshold, we also compute the strong 1s → np absorption resonances with the inclusion of important spectator Auger broadening effects. For the lowest 1s → 2p, 3p resonances, comparisons to available C II, C III, and C IV experimental results show good agreement in general for the resonance strengths and positions. Our results also provide detailed information on the C I K-shell photoabsorption cross section including the strong resonance features, since very limited laboratory experimental data exist. The resultant R-matrix cross sections are then used to model the Chandra X-ray absorption spectrum of the blazar Mkn 421.