Ejection of positive cluster ions from large electron-bombarded 3He or 4He clusters

Electron bombardment of freely flying helium clusters of some 105--107 atoms is observed to yield positive cluster ions of about 68 4He atoms or 85 3He atoms, respectively, aside from ionized clusters of about the original size. The ejection of the small cluster ions from the surface of the large clusters is ascribed to the release of energy resulting from the electrostrictive polarization of the vicinity of a newly formed ion. The observed final sizes of the small cluster ions are found to agree with those following from a macroscopic charged droplet model