ABSTRACT
At large values of the impact energy, many more interesting higher-order Thomas-like encounters are possible with the inclusion of two or more active electrons from the target. For example, in double capture or transfer ionization, which occurs during collisions between a bare nucleus and a helium-like target, the dynamic dielectronic correlation effects become increasingly more important via Thomas scatterings. Discarding a single encounter as a classical pathway for charge exchange, Thomas proposed a double-scattering mechanism by splitting the three-body problem into two consecutive binary elastic collisions, each preserving the momentum and energy law. It is fascinating that double scattering provides a more efficient pathway than a more straightforward single three-body collision for high-energy non-relativistic charge exchange. The mechanism of Thomas electron-electron double scattering was confirmed experimentally in transfer ionization during proton-helium collisions. Conventional single-pass experiments based upon the projectile scattering angle are extremely difficult due to exceedingly small cross sections and intolerably large statistical errors.
