Autoionization phenomena in dense photoionized plasmas

Elementary electron-ion collisional and spontaneous radiative transitions involving autoionizing resonances play important roles in atomic ionization, recombination, and radiative-emission processes in high-temperature astrophysical and laboratory plasmas. When electron-ion collisions are dominant, the ionization structure is usually determined by the steady-state (or dynamical) balance between electron-impact ionization (including autoionization following inner-shell-electron excitation) and radiative recombination combined with dielectronic recombination. The atomic radiative-emission spectrum tends to be dominated by the electron-impact excitation of ordinary spectral lines together with dielectronic satellite lines. In photoionized plasmas, a much higher degree of ionization can be established at a lower electron temperature, particularly as a result of multiple ionization due to Auger transitions following K inner-shell-electron photo-ionization. Radiative and dielectronic recombination can occur predominantly via transitions that are usually not considered to be important, and the unified quantum-mechanical description of the combined electron-ion photo-recombination process may be necessary. The satellite-line emission produced by the radiative decay of multiple-vacancy states can be more prominent, relative to the characteristic-line emission from the decay of single-vacancy states. We have developed a multiple-vacancy-state model for single and multiple ionization, together with characteristic-line and satellite-line emission, resulting from the cascade decay (by spontaneous radiative and Auger transitions) of an arbitrary initial inner-shell-electron vacancy distribution. The initial vacancy distribution may be created by electron or photon impact. We have also developed a unified description of the combined electron-ion photo-recombination process, taking into account the quantum-mechanical interference between radiative and dielectronic recombination. Results of calculations for Fe ions are discussed, which are expected to be valid at low densities. Implications for the detailed kinetics and spectral modeling of dense photoionized plasmas are discussed. Published by Elsevier Science Ltd.