ELECTRON-IMPACT IONIZATION OF LITHIUM-LIKE IONS - TI-19-20+, CR-21+, MN-22+, AND FE-23+(, V)

The Livermore electron-beam ion trap has been used to measure cross se ctions for electron-impact ionization of lithiumlike Ti, V, Cr, Mn, an d Fe. The measurements were made using two variations of an x-ray tech nique that correlates ionization events with dielectronic-recombinatio n photons. The cross sections were determined at one energy correspond ing to approximately 2.3 times threshold. Ionization cross sections ar e measured (i) relative to the theoretical cross section for radiative recombination onto the n = 2 shell for lithiumlike ions and (ii) rela tive to the theoretical cross section for direct excitation of the lit hiumlike line q[1s2s(3S)2p P-2(3/2) --> 1s(2)2s S-2(1/2)]. The uncerta inties in the ionization cross sections are estimated to be about 10% from the experiment together with a systematic uncertainty from the ch oice of normalization, which is 3% for radiative recombination and 10% for direct excitation. Good agreement is found with relativistic dist orted-wave calculations.