Aromatic components in cometary materials

Abstract

The Raman spectra of interplanetary dust particles (IDPs) collected in the stratosphere show that two bands at about 1350 and 1600 delta/cm and a broader feature between 2200 and 3300 delta/cm that are characteristic of aromatic molecular units with ordered domains smaller than 25 A in diameter. This suggests that the carbonaceous material in IDPs may be similar to the polymeric component seen in meteorites, where this material is thought to consist of aromatic molecular units that are randomly interlinked by short aliphatic bridges. The features in the Raman spectra of IDPs are similar in position, and relative strength to interstellar infrared emission features that have been attributed to vibrational transitions in free molecular polycyclic aromatic hydrocarbons. Taken together, these observations suggest that some fraction of the carbonaceous materials in IDPs may have been produced in circumstellar dust shells and only slightly modified in interstellar space.