Energy Dependence of the Line Ratio I(233.9 Å)/I(243.8 Å) in Fe xv Observed with an Electron Beam Ion Trap

We present the energy dependence of the intensity ratio between the 3 s 3 p 3 P 2 —3 s 3 d 3 D 3 transition at 233.9 Å and the 3 s 3 p 1 P 1 —3 s 3 d 1 D 2 transition at 243.8 Å in Fe xv studied with an electron beam ion trap over an energy range that spans resonance excitation regions. Clear resonance structures are observed in the electron energy range of 400–600 eV. The energy dependence obtained in the experiment is compared with a collisional-radiative model calculation, including resonance excitations, and overall agreement is found. It is shown that the ratio strongly reflects the population of the 3 s 3 p 3 P 2 metastable state, which is the lower state of the 233.9 Å transition.