Quantal and Semiclassical Methods of Slow Ion - Scattering with Applications to NEON(4+) + Helium.

The dynamics of low-energy ion-atom collisions is investigated at a two-state level of approximation. We have proposed a new semiclassical method based upon the two-level theory in spinor representation. The new approach presents a more transparent picture of the present ion -atom scattering for the charge-transfer process. The new results for the transition probability of the system Ne ^{4+} +He compare very well with existing full quantum mechanical methods. Particularly, we give a new view of the S-matrix as a rotation operator which serves to rotate the scattering state. Finally, the single charge-transfer differential cross-sections (sigma(theta)) are calculated at laboratory impact energies from 220 eV to 500 eV for the same system (Ne^{4+} + He) and are compared with the recent experimental data of Tunnell et al. Our calculations explain the experimental data both in quality and quantity. The model scattering potential is used in the sigma(theta) calculation and its construction is discussed.