Matthew Anthony Haynes

Exchange effects in low energy electron impact ionization of the inner and outer shells of argon

First order distorted wave Born approximation (DWBA) triple differential cross sections are reported for low-energy electron-impact ionization of the inner 3s and outer 3p shells of argon. Previous DWBA works have demonstrated that experiment and theory are not in accord for low energy ionization of inert gases and here we investigate the importance of exchange scattering. Different approximations for treating exchange scattering are investigated. It is shown that exchange scattering is particularly important for 3s ionization. Even with a proper treatment of exchange, the first order calculations are still not in satisfactory agreement with experiment. Consequently higher order effects will have to be included to achieve a satisfactory description of the low-energy ionization process. We also investigated both the Hartree-Fock and optimized potential methods for calculating atomic wavefunctions and static potentials and found that both methods produced almost the same cross sections.

Low energy triple differential cross sections for argon 3s electron impact ionization.

The triple differential cross section for electron impact ionization of the 3s orbital in argon has been measured in the coplanar asymmetric geometry, at a low incident energy of 113.5 eV (less than five times the binding energy) and ejected electron energies of 2, 5, 7.5 and 10 eV. Comparison of two distorted-wave Born approximation calculations with the experimental data reveals very poor agreement.

Investigating inner shell ionisation via the (e,2e) technique

The (e, 2e) technique has been applied successfully to valence shell ionisation of many targets, but studies of inner shell ionisation by this technique have been limited. The triple difierential cross section for the latter process exhibits behaviour which is very difierent to that observed for valence shell ionisation, particularly when the energy of the slow ejected electron is decreased below the binding energy of the inner shell orbital. Our recent results for inner shell ionisation of argon and krypton will be discussed, and comparisons made with distorted wave calculations. The importance and utility of the (e, 2e) technique in investigating electron impact ionisation may be gauged from the range of target species and kinematical conditions over which measurements have been performed. The primary theme of this workshop is the application of the (e, 2e) technique in electron momentum spectroscopy (EMS), where structural information about the electron motion in the target may be obtained. However, another emphasis in the application of the (e, 2e) technique is in studies of the dynamics of the ionisation process itself. Aspects of the collision such as distortions in the incident and outgoing channels, the in∞uence of multiple scattering, decay processes following the ionisation and electron{electron correlation efiects such as post collision interaction have been studied. Valence shell ionisation of numerous atomic targets has been studied in considerable detail, with most attention being directed to simple targets such as helium and hydrogen, where the target wavefunctions are well known. For other atoms, uncertainties in the target description can complicate the theoretical description of the collision; nevertheless good progress has been made in the theoretical approaches to this problem. For larger atoms, core ionisation becomes a possibility. Associated with the primary core-hole formation is the possibility of Auger emission. Indeed, for targets other than very heavy atoms, the Auger decay process dominates over photon decay. The process may be represented as follows:

Low Energy Inner Valence Ionization of the Rare Gases

Recent measurements are presented of the triple differential cross section for electron impact ionization of the inner valence shells of argon and krypton at low to intermediate energies, and both coplanar symmetric and asymmetric geometries. Comparison is made with some of the latest available theoretical calculations performed in the distorted wave Born approximation formalism.

Low Energy Inner-Valence Electron Impact Ionization of Argon

We present here experimental results for the triple differential cross section (TDCS) for low energy electron impact ionization of a heavy target in the coplanar asymmetric geometry. We have investigated ionization of the 3s inner-valence orbital in argon, at an incident energy of 113. 5 eV (< 5 times the binding energy of 29. 3 eV), scattering angle of 15° and ejected electron energies of 2, 5, 7. 5 and 10 eV. The choice of target orbital and kinematics was prompted by the existence of published results of distorted-wave Born approximation calculations which predicted interesting structure in both the binary and recoil regions of the TDCS. The experimental measurements have been performed in a new low energy coincidence spectrometer. We compare our experimental results with two distorted wave Born approximation calculations. There are very large deviations between theory and experiment at all ejected electron energies investigated.