We have made the first determination of the 12C/13C 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 12C. 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.
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Gilmour et al. (1994) studied this question.