Ionization in ion-atom collisions

From a theoretical point of view the theory of ionisation is still rather incomplete, the main problem being the representation of the final electronic state where the ionised electron travels in the presence of two Coulomb potentials (target and projectile). Due to the long-range ionic tail of the Coulomb potential the 'free particle' cannot be represented by a plane wave. The difficulty arises from the fact that the Schrodinger equation for the three-body problem cannot be solved exactly. However an exact asymptotic form can be obtained. The main objective of this thesis is to review the continuum distorted-wave (CDW) and continuum distorted-wave eikonal-initial-state (CDW-EIS) models, which at least satisfy the exact asymptotic conditions in the initial and final states. Both of these approximations are based on distorted wave perturbation theory. In this thesis, we review the two-centre effects on the electron yield due to the long-range nature of the Coulomb potential, which the continuum distorted-wave models should theoretically account for. This allows for a detailed study of the experimental results obtained from ejected electron spectroscopy, recoil-ion momentum spectroscopy and projectile scattering detection in coincidence with the recoil-ion charge state. It has also allowed for an investigation into the disputed 'saddle-point' electrons where the ejected electron is stranded on the saddle-point of the two-centre potential between the residual target and receding ion. Finally in chapter 5 a new generalised version of the CDW-EIS approximation is derived. In this, the CDW final state is generalised to non-zero magnetic quantum numbers, which led to a more complete set of states. (author)