Fullerene Oligomers and Polymers as Carriers of Unidentified IR Emission Bands

Several unidentified infrared emission bands (UIBs) have been assigned to neutral C-60 molecules present in circumstellar and interstellar environments. However, due to the similarity of the infrared (IR) spectra of C-60 in the solid state and in the gas phase, as of yet there is no consensus on the aggregation state of C-60. In this article, we show that even strong covalent chemical bonding might have very little influence on the IR spectrum of C-60, and that therefore such chemically bonded C-60 could be the carrier of the same UIBs. It would best explain observations like the missing emission from C-60 ions and a large variation of relative band intensities between different sources. We demonstrate that such a chemically bonded C-60 can be produced by the co-condensation of C atoms together with C-60 molecules, which leads to the formation of a three-dimensional C-60 polymer film. Such polymerized C-60 molecules cannot easily desorb, while their spectral properties in the visible and IR spectral ranges are almost undisturbed by polymerization.