Autoionizing resonances in electron-impact excitation of oxygenlike selenium.

Abstract

We have investigated the contributions of doubly excited, autoionizing resonances to the rate coefficients for electron-impact excitation of the n=2 to n=2 transitions in oxygenlike selenium. The cross sections for direct excitation were calculated using a relativistic distorted-wave approximation. The detailed Auger and radiative rates required for evaluating the resonance contributions were calculated using a multiconfigurational Dirac-Fock model. The largest effect is on the electric-dipole-forbidden transitions. For some J=0 to J=0 transitions involving two-electron excitations, the resonances enhance the collisional excitation rates by factors up to ${10}^{4}$ at electron temperatures relevant for laboratory plasmas.