RAMAN AND INFRARED-SPECTRA OF POLYCYCLIC AROMATIC HYDROCARBON MOLECULES OF POSSIBLE ASTROPHYSICAL INTEREST

We present the results of a laboratory analysis performed by means of Raman and infrared spectroscopy on six polycyclic aromatic hydrocarbons (PAHs): chrysene, triphenylene, perylene, benzo[alpha] pyrene, pentacene, and coronene. These are among the most stable and the most abundant PAHs suggested as an important constituent of interstellar matter. The Raman spectrum of PAHs exhibits intense peaks around 1350 and 1600 cm-1, falling close to the two broad bands observed from interplanetary dust particles (IDPs). They are sharper, however, and therefore appear less appropriate to simulate the Raman spectra of IDPs than the spectra of amorphous carbons. In addition, although the family of PAHs analyzed in the present study may be considered as a good representative of the molecules proposed to reproduce the class of "unidentified" infrared bands (UIBs), the analysis of their IR spectra suggests that physical processes, capable of altering the spectral properties of PAHs, have to be invoked to obtain a better match with astronomical spectral. Other molecules and/or a solid grain component might be included, too.