Metal, semiconductor, and carbon cluster studies including the discovery and characterization of carbon-60:Buckminsterfullerene

[摘要] Experiments using the laser vaporization technique for production of metal clusters have been performed. The reactions of neutral metal clusters with various gases have been studied using a fast flow reactor. Dramatic reactivity variations were observed which depended on cluster size, metal, and reactant.A laser vaporization disc source has been developed for the study of semiconductor clusters. Some preliminary studies on neutral germanium and silicon clusters were performed. Their ionization potentials have been bracketed and the clusters were found to fragment by a fissioning process and to have long lived (100 nanoseconds) excited electronic states.A detailed study has been undertaken into carbon clusters. Laser synthesis of astrophysically important polyyne molecules such as H-C-(C-C)$sb{m 2n}$-N has been done. Chains containing up to 22 carbon atoms are formed in a vaporized carbon and reactant gas plasma.A photophysically stable and chemically inert cluster, C$sb{60}$, has been discovered and hypothesized to have the structure of a truncated icosahedron. All even clusters in the 60 atom size range were found to be inert to highly reactive gases, while odd clusters readily reacted. The results are consistent with a whole series (30-90 atoms) of closed cage-like structures. Closure of even clusters only is possible via the inclusion of twelve pentagons into a hexagonal network. Odd clusters show neither the photophysical nor chemical stability of the even clusters. A mechanism for the formation of spherical soot particles has been developed.Stable organometallic complexes of the formula C$sb{m 2n}$M (20 $<$ n $<$ 40 and M = La, Ba, Sr, Ca) have been laser synthesized. The dominant complex observed was C$sb{60}$M$sp+$. These species are photophysically stable, chemically inert, and no C$sb{m 2n}$M$sb2$ species were detected.The ultraviolet and visible absorption spectrum of C$sb{60}$ has been measured. Because excited electronic states are not expected to live long in a molecule of this size, a unique spectroscopy independent of excited state lifetime was developed. Predissociation spectroscopy was performed on the cold van der Waals complexes C$sb{60}$--CHCL$sb2$ and C$sb{60}$--benzene. A single sharp (50 cm$sp{-1}$ wide) absorption band was found at 3860 A and 3863 A for the two complexes respectively. This peak is tentatively assigned to the 0-0 band of the lowest $sp1$T$sb{m 1u}$ $gets$ $sp1$A$sb{m g}$ (LUMO+1 $gets$ HOMO) transition of a truncated icosahedral carbon shell structure.

[发布机构] Rice University

[效力级别] physics