Indigenous polycyclic aromatic hydrocarbons in circumstellar graphite grains from primitive meteorites

We report the measurement of polycyclic aromatic hydrocarbons (PAHs) in ind ividual circumstellar graphite grains extracted from two primitive meteorit es, Murchison and Acfer 094. The C-12/C-13 isotope ratios of the grains in this study range from 2.4 to 1700. Roughly 70% of the grains have an apprec iable concentration of PAHs (500-5000 parts per million [ppm]). Independent molecule-specific isotopic analyses show that most of the PAHs appear isot opically normal, but in several cases correlated isotopic anomalies are obs erved between one or more molecules and their parent grains. These correlat ions are most evident for C-13-depleted grains. Possible origins of the PAH s in the graphite grains are discussed.