F. Catoire

Investigation of the (e, 2e) single ionization of He and Ar at large energy loss close to minimum momentum transfer

We report new coplanar (e, 2e) measurements for ionization of He and Ar under kinematics characterized by large energy transfer and close to minimum momentum transfer from the projectile to the target. These kinematics have remained rather unexplored to date due to the smallness of the corresponding cross sections. They could be investigated here thanks to the high sensitivity of our multi-collection spectrometer. The experimental results are used as a sensitive test of state-of-the-art available theoretical models for multi-electron atoms, namely the BBK and a hybrid DWBA+R-matrix (close coupling) models. An overall satisfactory agreement with experiment is obtained for the hybrid DWBA results for both targets. However, a close inspection of the remaining discrepancies calls for further refinement of the theory.

Double ionization of helium by electron impact: angular distributions at low incident energy

A complete analysis of our recent (e, 3e) experiments on helium at 601 eV incident energy (Lahmam-Bennani et al 2003 Phys. Rev. A 67 010701) is conducted by using an approximate 6C model which accounts for the interaction between all four particles (the scattered electron, the two ejected electrons and the nucleus) in the final state. An accurate wavefunction for the initial state is also used. The agreement between experiments and theory is not always good even though most peaks and dips can be explained. Comparison is also made with the results of the first Born-BBK approximation as well as with approximate second Born results.

Coincidence angular correlation in electron impact single or double ionisation of atoms and molecules

Experimental results obtained with our multi parameter multi-coincidence spectrometer are presented for the (e,3e) double ionisation of Ar and (e,2e) single ionisation of small molecules. The (e,3e) measurements are discussed in terms of competition between the two double ionisation processes present under the chosen kinematics, and qualitative conclusions are given. The results for the ionisation of H2 and the outer orbital of N2 are compared with the predictions of the most elaborate available theoretical models for description of the molecular ionisation process. Overall reasonable agreement is observed and tentative interpretations for the discrepancies are discussed.

Double ionization of argon by electron impact: use of the approximate 6C model

We study the electron impact double ionization of argon in the case where two, or else, three of the outgoing electrons (one scattered and two ejected) have the same energy. Each electron in the final (continuum) state is described by a Coulomb wave and account is taken for the interaction between these three electrons. We also include exactly all the exchange effects for the first time. The results of our model are compared to the recent experiments of Catoire et al (2004, Photonic, Electronic and Atomic Collisions ed R Schuch et al (Phys. Scr. T110 228–32); 2005, Electron and Photon Impact Ionization and Related Topics ed B Piraux (Bristol: Institute of Physics) p 53).

Interference Of Exchange And Processes In The Case Of Double Ionisation Of Argon

The (e,3e) angular distributions for the double ionisation of Ar where at least two of the three outgoing electrons have the same kinetic energy (205 eV) as the Auger electron issued from a 2p‐ionisation and the subsequent electronic relaxation have been theoretically investigated at three different impact energies within a first Born model and including electron exchange and interference of processes. The results are compared with recent (e,3‐1e) measurements under the same kinematics. Possible dominant ionisation mechanisms are tentatively identified in each case.