The role of linear and spheroïdal carbon molecules in interstellar grain formation

The recent discovery that a uniquely stable, spheroidal, carbon molecule consisting of 60 atoms, C 60 Buckminsterfullerene, forms spontaneously when carbon vapour nucleates has opened up a new and exciting perspective on the chemical and physical properties of carbon. The observations, shed new light on the detailed mechanism of the carbon clustering process itself and appear to have particularly important implications as far as carbon particle formation is concerned in such varied scenarios as combustion chemistry and circumstellar dust formation. The new perspective appears to offer the possibility of an understanding of many hitherto unexplained aspects of the behaviour of solid and fluid forms of condensed carbon. The discoveries were made during laboratory experiments aimed at an understanding of the relationships between carbon chain molecules and macroscopic carbon grains in circumstellar shells and interstellar space. The results suggest that in addition to the chains and grains, the C60 molecule, probably in the form of the ion C60+ in the less shielded regions, is ubiquitously present and perhaps responsible for some of the interstellar spectroscopic features such as the some of the Diffuse Interstellar Bands. Further study of small carbon particles which form in the gas phase has resulted in the discovery that they have quasi-icosahedral spiral shell structures. It seems highly likely that related species which include hydrogen are responsible for some of the Unidentified Infrared Bands. The rôle that C60, C60 + and icospiral carbonaceous particles play in the interstellar medium should soon be accessible to verification by a combination of laboratory experiment and astronomical spectroscopy