Projectile excitation in strongly asymmetric ion-atom collisions

Abstract. In an ion-atom collision at velocity U such that U>> Z,, the nuclear charge of the target, the first Born approximation is expected to be valid. However, i f at the same time Z,>> Z, , where Z, is the projectile nuclear charge, the first Born approximation is never valid at non-relativistic velocities since the projectile field cannot be regarded as a perturbation. A theory of inelastic processes in such ion-atom collisions is presented and applied specifically to the case of excitation of K-shell projectile electrons by the initially neutral target atom. The theory is formulated in such a way as to emphasise the polarisation of the target by the strong projectile ionic field and to see immediately the departures from the first Born approximation. The principal effects are that the target nucleus and electrons act coherently in exciting the projectile, rather than incoherently as in the first Born approximation, and that collisions in which the target remains in its ground state are greatly suppressed compared with the first Born result. 1