Long carbon chain molecules in circumstellar shells

It has been proposed that long-chain carbon molecules abundant in various interstellar regions can be produced by facile reactions between carbon clusters produced by graphite vaporization and the simpler reagents present in the ISM. The results of recent laboratory experiments which support this hypothesis are reviewed. The properties of the species of linear carbon chains, spherical shell carbon clusters, and macroscopic particles produced in these experiments are summarized. The experiments show that high-temperature processes are a viable simultaneous source of polyynes as well as carbonaceous grains. In particular, they suggest that wherever polyynes are abundant, the associated grains are likely to be carbonaceous and that both may be of circumstellar origin. 55 references.