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Fullerene Oligomers and Polymers as Carriers of Unidentified IR Emission Bands

Several unidentified infrared emission bands (UIBs) have been assigned to neutral C60 molecules present in circumstellar and interstellar environments. However, due to the similarity of the infrared (IR) spectra of C60 in the solid state and in the gas phase, as of yet there is no consensus on the aggregation state of C60. In this article, we show that even strong covalent chemical bonding might have very little influence on the IR spectrum of C60, and that therefore such chemically bonded C60 could be the carrier of the same UIBs. It would best explain observations like the missing emission from C60 ions and a large variation of relative band intensities between different sources. We demonstrate that such a chemically bonded C60 can be produced by the co-condensation of C atoms together with C60 molecules, which leads to the formation of a three-dimensional C60 polymer film. Such polymerized C60 molecules cannot easily desorb, while their spectral properties in the visible and IR spectral ranges are almost undisturbed by polymerization.