Effects of autoionizing resonances on electron-impact excitation rates and gain calculations for Ni-like tantalum

Abstract

The electron-impact excitation-rate coefficients for the 3d to 4l transitions in Ni-like tantalum were calculated using the distorted-wave and the multiconfiguration Dirac-Fock methods. As for the few-electron cases, the effects of autoionizing resonances are found to be very important for most transitions. In some transitions, resonances can enhance the rate coefficients by as much as a factor of 5. A collisional-radiative model was employed to study the effects of resonances on the laser gains. We found that the inclusions of the resonance excitation-rate coefficients in the calculations significantly reduce the gain coefficients for the two J=0→1 lasing transitions but fail to explain the large discrepancies between the predicted and measured lasing spectrum.