Dynamic response of target electrons upon low and medium energy ion impact

We found that differential scattering cross sections for medium and low energy He+ and Ne+ impact on high Z-atoms were significantly enhanced compared with those calculated from the inter-atomic potential based on the Hartree-Fock-Slater atomic model coupled with the bare nuclear charge of a projectile. The enhanced scattering cross sections determined experimentally are reproduced well by a simple model that the center of gravity of target electrons is shifted toward the projectile during a large-angle collision. The shift d→ from the target nucleus is expressed as a function of inter-nuclear distance r→ in terms of a dipole moment μ→=Z2ed→=αZ1er→/r3 (Z1 and Z2: atomic numbers of projectile and target, α: polarizability, e: electron charge). The effective polarizability β (≡αZ1/Z2) is expressed as a function of ion velocity v [107 cm/s], in the form β = 0.079 exp[−0.46v].