A Theoretical Study of Infrared Spectra of Highly Positively Charged C60 Fullerenes and Their Relevance to Observed UIE Features

Abstract

Abstract By applying first principles quantum chemical calculations, we present a complete catalog of the theoretically expected mid-infrared signatures of cationic forms of fullerene with the general formula of C 60 q + (q = 1–26). The structural stability and bonding of these exotic species have been reported by us elsewhere. It is found that not only can some of these cations contribute significantly to the flux of the 17.4 and 18.9 μm bands of fullerene that are observed in some planetary nebulae but they also show strong bands that match the position of key astronomical unidentified infrared emission at 11.21, 16.40 and 20–21 μm, which makes them key species for identification. It is also found that the IR signatures of the group of these cations with q = 1–6 are well separated from the 6.2 μm band that is associated with free/isolated aromatic hydrocarbon molecules. This is particularly important in the discrimination and exploration of the coexistence of complex hydrocarbon organics and fullerenes in astronomical sources. To provide insight into the effect of ionization on the IR spectrum of fullerene, particularly at the long-wavelength range, the quantitative analysis of the origin of key bands of these cations is presented. Finally, the potential target(s) among these species, specifically aromatic C 60 10 + , are discussed for further astrochemical observations.