DYNAMIC SCREENING AND WAKE EFFECTS ON ELECTRONIC EXCITATION IN ION SOLID AND ION SURFACE COLLISIONS

The collective electronic response in a solid effectively alters ionic and atomic potentials giving rise to dynamic screening and to a "wake" of density fluctuations trailing ions as they propagate through the solid. The presence of dynamic screening modifies electronic excitation processes of projectiles in ion-solid collisions as compared to binary ion-atom collisions. We review recent theoretical and experimental studies directed al the search for and identification of signatures of dynamic screening and wake effects. Examples include the formation of excited projectile bound states under channeling conditions, radiative electron capture, the search for "wake-riding" electrons in antiproton-solid collisions, and the neutralization of highly charged ions near surfaces.