ELECTRONIC-SHELL-STRUCTURE EFFECTS IN CSN+

Relative mass abundances of singly charged cesium-cluster ions (Csn+) extracted from a liquid-metal ion source show sharp decremental steps at n=3, 5, 9, and 21 and a pronounced minimum at Cs10+. In the region of n>9, Cs13+ shows a maximum in the relative abundance. The time-of-flight technique is used to obtain the mass spectrum. The prominent features observed at n=9 and 21 are interpreted using the shell structure of simple metal clusters. Cs9+ and Cs21+, which contain 8 and 20 valence electrons, respectively, form closed-shell configurations with enhanced relative stabilities. © 1990 The American Physical Society.