Photoionization and electron-ion recombination: The carbon sequence

We describe close-coupling calculations for photoionization and recombination using the R-matrix method. Photoionization of a large number of bound states of each atom or ion is considered, and cross sections are computed at a fine mesh of energies to delineate the extensive resonance structures. Photoionization of ground and excited configurations with n{≤}10 and l{≤}3 is considered. Partial photoionization cross sections into excited states of the residual ion are also obtained for the ground states of C⁰, N⁺, and O²⁺. An important type of autoionizing resonances due to the photoexcitation of the core ion is discussed. As the photoionization cross sections incorporate autoionization in detail, it is possible in principle to employ the Milne relation to obtain total, radiative plus dielectronic, recombination cross sections and rate coefficients. However, practical difficulties arise, and various approaches are described to overcome these. Comparison is made with the earlier results for photoionization cross sections and recombination coefficients. This work forms an extension of the Opacity Project.