Theory of binary encounter electrons in ion-atom collisions

An intuitive model of the binary encounter peak in the energy and angular distribution of ionization electrons employs the elastic scattering amplitude for electron-projectile scattering. When the projectile carries some electrons, electron exchange contributes to the elastic scattering. We show that the elastic scattering model, including exchange, derives from a distorted-wave strong-potential Born approximation for ionization to the projectile continuum. This theory incorporates both the binary encounter peak and the continuum capture cusp. (author)