Triply Differential Single-Ionization Cross Sections in Fast Ion-Atom Collisions at Large Perturbation

We present experimental triply differential single-ionization cross sections for electrons emitted into the scattering plane in 3.6 MeV amu ^-1 Au ⁵³⁺ + He collisions, i.e. for a large perturbation. The data show that the post-collision interaction between the scattered projectile and the ionized electron strongly affects the recoil peak, but it influences the binary peak rather weakly. Surprisingly, the continuum distorted wave-eikonal initial state model, which describes differential electron spectra very well, fails to reproduce our data even qualitatively. Most notably, it does not show a recoil peak.