ISOTOPIC COMPOSITIONS OF INDIVIDUAL POLYCYCLIC AROMATIC-HYDROCARBONS FROM THE MURCHISON METEORITE

We have made the first determination of the C-12/C-13 ratios of individual polycyclic aromatic hydrocarbons (PAHs) isolated from the Murchison carbonaceous meteorite. A range in carbon isotopic composition of some 16 parts per thousand between individual PAHs is observed, with increasingly complex PAHs becoming progressively enriched in C-12. The data are consistent with a mechanism involving the synthesis of higher molecular weight species from lower homologues. We consider how the carbon isotopic information fits in with proposed mechanisms of PAH synthesis in extraterrestrial environments, and the relationship of PAHs to the complex macromolecular material present in meteorites.