Infrared spectroscopy of fullerene C60/anthracene adducts

Recent Spitzer Space Telescope observations of several astrophysical environments such as planetary nebulae, reflection nebulae and R Coronae Borealis stars show the simultaneous presence of mid-infrared features attributed to neutral fullerene molecules (i.e. C60) and polycyclic aromatic hydrocarbons (PAHs). If C60 fullerenes and PAHs coexist in fullerene-rich space environments, then C60 may easily form adducts with a number of different PAH molecules, at least with catacondensed PAHs. Here we present the laboratory infrared spectra (∼2–25 μm) of C60 fullerene and anthracene Diels–Alder mono- and bis-adducts as produced by sonochemical synthesis. We find that C60/anthracene Diels–Alder adducts display spectral features strikingly similar to those from C60 (and C70) fullerenes and other unidentified infrared emission features. Thus, fullerene adducts – if formed under astrophysical conditions and are stable/abundant enough – may contribute to the infrared emission features observed in fullerene-containing circumstellar/interstellar environments.