Excitation and Ionization In Fast Ion-Atom Collisions Due to Projectile — Electron — Target — Electron Interactions

Abstract

ABSTRACf. Recent investigations of excitation and ionisation in collisions of fast highly-charged projectiles with H2 and He targets have shown that effects due to projectile-electron -targetelectron interactions can be clearly identified. The interacting electrons, traditionally assigned only a passive screening role, are now seen to acquire a new dynamic role, contributing a significant part of the excitation cross section, measuring up to 60%, as in the case of K-shell projectile ionisation at collision energies of a few Me V lu. Experimental signatures for these dynamic, twocentre e-e interactions can be found in the observation of excitation thresholds, resonances and electron exchange processes, traditionally associated with excitation of ions by free electrons.Improved applications of the Born and Impulse Approximations have been successful in accounting for the new data. A brief account of these investigations is presented.

Mixed-State Ionic Beams: An Effective Tool for Collision Dynamics Investigations

“…Existing theories that have successfully predicted total cross-sections for these processes can now be tested to the next order of sophistication and accuracy by comparing to state-selective differential cross section measurements. Furthermore, few-electron systems as found on highly charged ions provide some of the simplest testing grounds for studying the many-particle problem at large, and in particular, the role played by electron-electron interactions [12][13][14][15][16][17][18][19][20][21][22]. By limiting the number of electrons on the projectile and by using simple targets such as He or H 2 , considerable simplification of the collision system is attained.…”