In fast collisions transfer ionization can proceed via different mechanisms:

• the kinematical capture in which the ion compensates the momentum of the captured electrons, accompanied by an independent target ionization by an interaction of the projectile with the second electron in the target.
  
  
• The electron-electron Thomas mechanism, in which the projectile knockst one electron in a hard collision and this electron is scattered at the other electron in the forward direction to be captured. This unique process the continuum electron is emitted with the projectile velocity to 90 deg while the recoiling doubly charged ion is only a spectator, receiving very little momentum.
  
  
• correlated kinematical capture in which one electron is kinematically captured at large impact parameters while the seond electron is shaken of due to the correlation in the initial state. This interesting process gives a grip at a small contribution of the entangled initial state wave function.
  
  

The figure shows that the Thomas mechanism can be clearly separated from the other mechanisms by observing the ion momentum.