Observation of shell structures in the growth of microcluster ions

Abstract

We have observed shell structure manifested in the size distributions of various non-metallic cluster ions sequentially grown on seed positive ions generated by electron impact ionization in a pulsed supersonic jet. The data suggest the identification of the core ion and the placement of equivalent ligands about the core during the embryonic stages of cluster growth. A crown structure similar to that of H 3 +·(H 2) n , is indicated for H 3O +·(H 2) n ( n⪕4). Pentagonal bipyramid structures with five neutrals surrounding a dimer ion core are suggested by the (CO) n + ( n⪕19) and (N 2) n + ( n⪕14) cluster size distributions, whereas (CO 2) n + ( n⪕ 16) clusters appear to have a relatively amorphous structure. Variations in the cluster size distributions of Xe n + ( n⪕26) are correlated with the elongated icosahedral structure.