Fully Differential Cross Sections for the Single Ionization of Helium by Ion Impact

We present experimental and theoretical fully differential cross sections for the single ionization of He by heavy-ion impact for electrons emitted into the scattering plane. Data were obtained for 2 MeV amu ^-1 C ⁶⁺ and 3.6 MeV amu ^-1 Au ^Q+ (Q = 24, 53) projectiles, corresponding to perturbations (projectile charge to velocity ratio) ranging from 0.7 to 4.4, a regime which is inaccessible for electron-impact ionization. We observe a decreasing recoil, peak intensity (relative to the binary peak) and at the same time an increasing peak in the forward direction with increasing perturbations. Large discrepancies between the experimental data and theoretical predictions are found, which can at least be partly attributed to the use of hydrogenic wavefunctions.