Coincidence studies of capture and ionization in highly charged ${\mathrm{I}}^{\mathit{q}+}$-He and ${\mathrm{U}}^{\mathit{q}+}$-He collisions at medium velocities

Electron capture and ionization processes were investigated for ${\mathrm{I}}^{\mathit{q}+}$-He and ${\mathrm{U}}^{\mathit{q}+}$-He collisions at incident energies 0.1–1.0 MeV/nucleon and for incident charge states q=5–44. Cross sections for single-electron capture, transfer ionization, single ionization, and double ionization were obtained using a projectile-ion recoil-ion coincidence technique. A pronounced interplay among the different electronic processes was observed. Cross sections for single ionization show a rather weak charge-state dependence, in disagreement with recent calculations of McKenzie and Olson [Phys. Rev. A 35, 2863 (1987)]. In a second experiment, photon recoil-ion coincidences were measured to obtain partial cross sections for capture into certain projectile n states. These measurements provide strong evidence that transfer ionization populates lower projectile n states than does single-electron capture. Zero-degree electron spectroscopy, coincident with charge capture for 0.5 MeV/nucleon ${\mathrm{U}}^{30+}$ projectiles revealed that the free electron in transfer ionization is released from the projectile to its continuum and from high-lying Rydberg states of the projectile.