Infrared Spectral Fingerprint of Neutral and Charged Endo- and Exohedral Metallofullerenes

Abstract

Small metal-containing molecules have been detected and recognized as one of the hybrid species that are efficiently formed in space, especially in the circumstellar envelopes of evolved stars. It has also been predicted that more complex hybrid species such as those formed by metals and fullerenes (metallofullerenes) could be present in these circumstellar environments. Recently, quantum-chemical simulations of metallofullerenes have shown that they are potential emitters contributing to the observed mid-IR spectra in the fullerene-rich circumstellar environments of different types of evolved stars. Here we present the individual simulated mid-IR (∼5–50 μm) spectra of 28 metallofullerene species. Both neutral and charged endo- and exohedral metallofullerenes for seven different metals (Li, Na, K, Ca, Mg, Ti, and Fe) have been considered. The changes induced by the metal–C60 interaction in the intensity and position of the spectral features are highlighted using charge-density difference maps and electron-density partitioning. Our calculations identify the fundamental IR spectral regions in which, depending on the metal binding nature, there should be a major spectral contribution from each of the metallofullerenes. The IR spectra of the metallofullerenes are made publicly available to the astronomical community, especially users of the James Webb Space Telescope, for comparisons that could eventually lead to the detection of these species in space.