Impact parameter dependent k-shell ionization probabilities in ion-atom collisions with different asymmetry

We present experimental probabilities P_κ(θ) for target K-shell ionization in 1.26 MeV/u He → Te, Dy; N → In, Nd collisions up to very large scattering angles (θ 170°). The P_κ(θ) are nearly constant for θ > 10°. Groups of collision systems with about the same sum of projectile and target nuclear charge (Z_P + Z_T = united atom system) and collision velocity were s probabilities are within these groups of collision systems nearly proportional to the square of the projectile nuclear charge even up to Z_p/Z_T = 0.7. The calculations in the semiclassical approximation (SCA) by Trautmann et al. are compatible with the experimental results when the recoil effect is included and wave functions of the united atom system are used.