ELECTRON-IMPACT IONIZATION AND DIELECTRONIC RECOMBINATION OF SODIUM-LIKE IRON IONS

Absolute rates and cross sections for dielectronic recombination and ionization of Na-like Fe15+ (1s(2)2s(2)2p(6)3s) ions were measured at electron impact energies between 0 and 1030 eV using the Heidelberg heavy ion storage ring TSR with the cooling device as an electron target. In the region where excitation-autoionization and related resonant processes are relevant, variations of the ionization cross sections below 0.5% were observed with an energy resolution of 4 to 5 eV FWHM. The theoretical calculations are in good overall agreement with the measured cross sections but do not reproduce all the details of the rich resonance structures revealed by our experiment. In the lower energy range we made use of the magnetically expanded electron beam with a transverse temperature corresponding to only kT perpendicular to = (15 +/- 3) meV. This resulted in an excellent energy resolution in the measurements of dielectronic recombination associated with 3s --> 3p, 3d, 4l core excitations. Here, theory and experiment are in very good agreement.