Resonance enhancement of electron collision rates for fluorinelike ions

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Abstract
The distorted-wave approximation and similar weak-coupling methods are frequently used to calculate electron collision cross sections for studies of astrophysical and laboratory plasmas. Autoionizing resonances neglected in these approximations can significantly enhance the calculated rates for collisional excitation of some transitions in highly charged ions. We investigated the effects of such resonances on the excitation rates for n=2 to n=2 transitions in fluorinelike Fe, Se, Mo, Ag, Xe, and Eu. The background excitation rates were calculated using a relativistic distorted-wave approximation, and the detailed Auger and radiative rates were calculated using a multiconfiguration Dirac-Fock model. The largest effect is on the electric-dipole-forbidden transitions. The enhancement diminishes with increasing atomic number for all transitions.