The Distorted Wave Born Approximation Theory Of Electron-Impact Ionization Of Ar In The Coplanar Doubly Symmetric Geometry

The ionization of atoms and molecules by charged particle impact is one of the fundamental few-body interaction processes in physics. The (e,2e) process, of which the colliding particle is electron, has been developing for almost40years. It is a powerful tool for investigating the electronic structure of matter, and presents a valuable test of all kinds of theoretical models. In genaral, the (e,2e) process means that, an incident electron of well-defined momentum collided with a target particle; after the collision, two electrons slip out and are detected in coincidence, while the residual ion is left in either initial or excited state.One of the commonly used geometries in (e,2e) experiments is the coplanar doubly symmetric geometry, in which one must treat the two outgoing electron equally, thus it provides the most demanding test of all collision theories. As there has been an extensive success in the study of high energies (e,2e) on the simpler targets (H, He, etc.), experiments and theories are further developing toward complex atoms or molecules. The electron impact ionization of Ar shows some characteristic structures in a coplanar doubly symmetric geometry, and consequently it is of special interest.Since the few-body problem is not analytically solvable, many approximate models have been developed. One of the most successful theoretical approaches is the distorted wave Born approximation (DWBA). As is well known, the (e,2e) processes in the intermediate energies regime are extremely difficult to study theoretically, since many approximations used at higher energies fail; whereas the triple differential cross sections (TDCS) will be greatest if the incident electron energies are3to7times of the ionization threshold of the target. So it is of great significance for the reseaching from low to intermediate energies.In this thesis, the first-order distorted wave Born approximation has been performed for single ionization of Ar (3p) by electron impact in a coplanar doubly symmetric geometry from low to intermediate energies. The theoretical TDCSs are compared with the related experimental data reported by Nixon and Murray. It is found that when the incident electron energies are40eV above the threshold, the binary and recoil collision mechanism wil be dominant as the energies increased, but not in the lower energies, where the distortion effects are found to be important. In order to completely describe the electron impact ionization of argon, it is imperative that many kinds of scattering mechanisms should be considered in the model.By taking into account the post-collision interaction (PCI), the effective charges in the outgoing channel and the effective potential in the incoming channel, etc., the agreements of experiment and theory are remarkably improved. In brief, for low to intermediate enegies, the PCI must be considered, but the Gamow factor tends to overestimate the effect of PCI for the incident electron energies are1to3times of the ionization threshold of the target; in the same regime, the effective charges are extremely important, by using which the modified calculations have proven to be very successful in reproducing the experiment data, but it isn’t accurate for the near axis angles; the effective potential can modify the cross section amplitudes in the backward direction, which may be considered as a complement of the recoil collision mechanism. These results indicate that, for the impact ionization processes from low to intermediate energies, it is better to simultaneously investigate all the factors mentioned above, especially the effective charges.