EFFECTS OF COSTER-KRONIG TRANSITIONS ON ELECTRON-IMPACT EXCITATION RATES FOR FLUORINELIKE IONS IN THEIR GROUND-STATES

The contributions of Coster-Kronig resonances to the electron-impact e xcitation rate coefficients have been calculated for six F-like ions w ith Z = 26, 34, 42, 47, 54, and 63. The calculations are carried out u sing the relativistic distorted-wave approximation and the multiconfig uration Dirac-Fock model. We found that resonance excitation via Coste r-Kronig transitions is the dominant excitation mechanism at low tempe ratures for Z less-than-or-equal-to 34 and is as important as the dire ct excitation for heavier ions. In addition, we found that the effects of relativity can reduce the rate coefficients by more than an order of magnitude at electron temperatures T < 100 eV.