Electron-impact excitation cross-section measurements of highly charged heliumlike and lithiumlike ions

Abstract

The cross sections for electron-impact excitation of the heliumlike forbidden line z, intercombination lines y and x, and the resonance line w, together with the associated lithiumlike collisional satellite lines q, r, t, u, and v have been measured for Ti, V, Cr, Mn, and Fe (Z=22--26) on the Livermore electron beam ion trap. The measurements were made near the threshold for excitation of the heliumlike transitions, where no other processes can contribute to the excitation of the lines, and are normalized to the cross sections for radiative electron capture. The uncertainties in the measurements are less than 8% for the heliumlike Fe transitions and between 11% and 15% for the lithiumlike Fe transitions together with a 3% systematic uncertainty from the normalization to theoretical radiative recombination cross sections. We find good agreement with results from a distorted-wave calculation.