Experimental Investigation of Electron Capture by Highly Charged Ions of Medium Velocities

Collisions between highly charged ions of medium velocities and light atoms, which result in capture of electrons by the ion, are discussed. It is shown that measured total-capture cross sections in general agree well with the various theoretical results. Recently obtained experimental cross sections for the population by the captured electron of specific n, l levels of the ion are presented and compared to the existing theoretical calculations. Measurements of cross sections for charge-change collisions, where both the ion and the target-atom charge are known before and after the collision, are presented. It is shown that in general, a large part of the collisions, which lead to single-electron capture, result in the removal of two (or more) electrons from the target atom. A number of mechanisms leading to this outcome of the collisions have been suggested. Information as to which of the possible mechanisms is the dominating one has been obtained from recent measurements of the doubly differential cross-section for emission of electrons in the forward direction.