Resonant excitation channels in the 3d(10)-3d(9)4s and 3d(10)-3d(9)4p transitions of nickel-like Mo14+ and Zr12+

At energies below the threshold for direct electron impact excitation, resonant excitations can make a significant contribution to the total excitation rate of a given energy level. In this paper, the rates of resonant excitation into the levels of the 3d(9)4s and 3d(9)4p configurations of Mo14+ have been calculated using a fully relativistic, multiconfiguration atomic structure code and detailed accounting of energy levels. By including the effects of resonant excitations in collisional-radiative models for the spectrum of Ni I-like Mo14+ and (by isoelectronic scaling) Zr12+, the ratio of the emissivity of the 3d(10)-4d(9)4s E2 transitions to the emissivity of the 3d(10)-3d(9)4p El transitions is greatly enhanced, and sensitivity to electron temperature in the ratio is introduced. This ratio is density sensitive for n(e) greater than or equal to 10(13) cm(-3), and therefore, given knowledge of either local temperature or density conditions, the E2-E1 ratio can serve as a diagnostic for local conditions in magnetically confined fusion plasmas. The current work demonstrates the need to include resonant excitations in collisional-radiative models of the soft x-ray emission of nickel-like ions. Good agreement is found between measurements of El and E2 Line brightness ratios made in a tokamak plasma, and the predictions of collisional-radiative models in the present work.