Results of a combined photoelectron spectroscopy and first-principles density-functional study of Si N - clusters in the size range 20 ≤ N ≤ 45 are reported and discussed. Evidence for a prolate-to-near-spherical shape transition at N = 27 is presented. It is shown that the tricapped-trigonal-prism (TTP) structural motif Si 9 found in most low-lying clusters Si N -, 9 ≤ N ≤ 19, is replaced or augmented by a series of structural motifs consisting of a bulklike "adamantane" fragment plus a magic-number cluster (Si 6, Si 7, Si 10) or TTP Si 9 in low-lying prolate clusters Si N -, N ≥ 20. For 28 ≤ N ≤ 45, almost all low-lying near-spherical clusters Si N - adopt "stuffed-cage"-like structures where the cages are homologous to carbon fullerenes in the sense that they are composed of only five- and six-membered rings. However the arrangement of the "stuffing" atoms is not yet diamondlike.
ASJC Scopus subject areas
- Physical and Theoretical Chemistry