Electron transfer processes in collisions of highly charged energetic (0.1-1.0 MeV/nucleon) ions with helium atoms

We have investigated charge transfer in collisions of energetic (0.1-1 MeV/nucleon) highly charged ions with helium atoms with the principal aim of clarifying the nature of two-electron processes. The sensitivity of partial charge-changing cross sections (i.e., single- and double-charge transfer, transfer ionziation (TI), and single and double ionization) to core configuration and scaling rules for one- and two-electron process were investigated with iodine ions (q = 5+ → 26+) and uranium ions (q = 17+ → 44+) using an ion-charge state, recoil-ion coincidence method. Using zero-degree electron spectroscopy in coincidence with charge transfer, we found that at the higher energies, as in the case of 0.1 MeV/nucleon ions previously reported. TI involves the transfer of two electrons to a higher correlated state followed by loss of one electron to the continuum. In addition, we observe very high Rydberg electrons in coincidence with TI, implying a possible up-down correlation in the pair transfer. In addition, we made measurements of VUV photons emitted at the collision in coincidence with He+ and He2+ recoils. The results show that TI leads to capture into lower n states than single-charge transfer. (orig.)