Strong potential second Born theory for electron loss to the continuum in collision with heavy targets

A second-order Born themy is formulaled for the description of forward electron emission from a light projectile in energetic collision with a heavy target atom. This theory is termed 'strong potential second Born theory' $82) because it accounts for electron propagation in the strong tuget potential It is evaluated for the singly inelastic contribution to electron loss, while the first Born approximation is used for the simultaneous projectile-target exciwtion. From the SBZ theory, the 'impulse approximation' of Hartley and Walters is derived. By comparison with experimental data for the Het t Ar system it is shown that both theories account well for the electron intensity, while the asymmetry of the forward peak is only correctly given by SB~. For larger emission angles. consideration of the target potential in the electronic final state is of increasing importuce. Then the SB? becomes inferior to the eleclron impact approximation.