Observation of resonant-excitation double autoionization in electron-I50+ collisions

We present a clear observation of a resonant contribution to electron impact ionization of Li-like highly charged ions (I50+). Li-like ions are the simplest in which resonant-excitation double autoionization (REDA) 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.