KLL dielectronic recombination resonances, where a free electron is captured into the L shell and at the same time a K shell electron is excited into the L shell, have been measured for open shell iodine ions by measuring the detected yield of escaping ions of various charge states and modeling the charge balance in an electron beam ion trap. In the modeling, the escape from the trap and multiple charge exchange were considered. Extracted ions were used to measure the charge balance in the trap. The different charge states were clearly separated, which along with the correction for artifacts connected with ion escape and multiple charge exchange made the open shell highly charged ion measurements of this type possible for the first time. From the measured spectra resonant strengths were obtained. The results were 4.27͑39͒ ϫ
This paper reports a systematic study of the dependence on atomic number of the dielectronic recombination resonance strengths for He-like, Li-like and Be-like ions. Recent measurements of dielectronic recombination resonance strengths for the KLL and KLM manifolds for iron, yttrium, iodine, holmium, and bismuth are also described. The resonance strengths were normalized to calculated electron impact ionization cross sections. The measured resonance strengths generally agree well with theoretical calculations using the distorted wave approximation. However, KLM resonance strength measurements on high atomic number open-shell ions gave higher values than those suggested by calculations. Using recently measured data, along with existing results, scaling laws have been generated as a function of atomic number for He-like, Li-like, and Be-like ions in the KLL and KLM manifolds.
We present a clear observation of a resonant contribution to electron impact ionization of Li-like highly charged ions ͑I 50+ ͒. Li-like ions are the simplest in which resonant-excitation double autoionization ͑REDA͒ can occur. REDA was observed by measuring the ratio of the numbers of trapped ions of two neighbring charge states as a function of electron energy under equilibrium conditions using an electron beam ion trap. The resonant strength was determined by normalizing the experimental data to theoretical ionization cross sections at the nonresonant interaction energies. Good agreement was found between the observed and calculated resonant strengths for this observation of REDA in Li-like highly charged ions.
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