“…This distortion reduces the ionization cross -16 -sections at low ion velocities, but increases them at high velocities. At low velocities, the electrons form diatomic molecular orbitals around the projectile and target nuclei, thereby becoming more tightly bound and more difficult to excite, so smaller ionization cross sections are seen (Basbas et al 1973;Anholt and Meyerhof 1977). At high ion velocities, the polarization of the electron clouds decreases the electron-perturbing-nucleus distance, thereby increasing the strength of the perturbing potential, leading to higher ionization cross sections (Basbas et al 1971a(Basbas et al , 1971b(Basbas et al , 1978.…”