Radiative dielectronic recombination and correlated processes

A new quasi-resonant radiative dielectronic recombination (RDR) process is formulated as an off-shell extension of the dielectronic recombination. It is an electron-ion recombination process in which dielectronic-excitation capture is accompanied by simultaneous radiation emission, and can occur at all continuum energies of the electron being captured. The RDR can be the dominant mode of recombination at off-resonance energy regions, and may provide an important distortion correction to the direct recombination. The distinct signature of the RDR is the quasi-discrete low energy x-rays emitted during the capture, shifted down in energy by the excitation energies of the core electrons. The analog of the RDR must also take place in the ion-atom collisions, as radiative transfer excitation (XTE). Evaluation of the RDR cross section is difficult because of the correlated nature of the transition operator, but detailed qualitative discussions of the RDR are presented. A crude estimate of the cross section is obtained and compared with the other recombination modes. The radiative Auger effect is roughly an inverse of RDR, and the charge dependence of its cross section is improved, using a correlated vertex.