Dissociative and non-dissociative electron capture inmedium-velocity cluster-atom collisions; evidence ofcontributions due to multi-electron processes

Abstract

Dissociative and non-dissociative electron capture crosssections for medium-velocity collisions of carbon ionic clusterprojectiles with helium atoms have been measured (v = 2,2.6and 4 au Cn+ n⩽5). This has been done using a4π multifragment detector operating either in the full-efficiency mode for the extraction of total electron capturecross sections, or in a partial-efficiency mode(anticoincidence method) for the extraction of the dissociativeand non-dissociative parts. The dissociative part has beenfound to be the largest one in all cases, increasing with nand v. The role of the cluster temperature, not preciselyknown, may be important but cannot explain all the observedexperimental results, in particular the appearance of quitelarge branching ratios for dissociation into three fragments (n⩾3). In order to explain this multifragmentation, themulti-electron process of capture-projectile excitation isinvoked. Another multi-electron process is directlyextracted from these collisions, namely, thetransfer-ionization two-electron process whose relativecontribution with respect to single capture is found toincrease with the velocity.