The emission of energetic electrons from atoms by fast ions considered as a charge-transfer process

The ejection of energetic electrons from atoms by fast ions is described using as final electron states the continuum orbitals in the field of the projectile. The electronic distribution in the first-order Born approximation is equal to the distribution for direct ionisation where the final electron state is described by a plane wave times the Coulomb factor centred on the projectile. In the second-order Born approximation the distribution of ejected electrons is significantly decreased, and it is shown that it is equivalent to the correct distribution for direct ionisation in first order times the Coulomb factor around the projectile. For the case of ejected electrons with negligible momentum in the frame of the projectile, it is shown that the electron distribution centred on the projectile is isotropic to order nu -12 , while the double scattering term in nu -11 depends on the direction of motion of the electron.