Infrared spectral fingerprint of neutral and charged endo- and exohedral metallofullerenes

TL;DR

This study provides detailed simulated mid-infrared spectra of various metallofullerenes, highlighting their potential spectral signatures in space, aiding future astronomical detection efforts with telescopes like JWST.

Contribution

The paper presents the first comprehensive set of simulated IR spectra for twenty-eight neutral and charged metallofullerenes, facilitating their identification in astrophysical environments.

Findings

Identified key IR spectral regions for metallofullerenes.

Provided publicly available spectra for astronomical use.

Highlighted effects of metal binding on spectral features.

Abstract

Small metal-containing molecules have been detected and recognized as one of the hybrid species efficiently formed in space; especially in the circumstellar envelopes of evolved stars. It has been predicted also that more complex hybrid species like those formed by metals and fullerenes (metallofullerenes) could be present in such 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 um) spectra of twenty-eight 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 on 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 where, depending on the metal binding nature, there should be a major spectral contribution from each of the metallofullerenes. The metallofullerenes IR spectra are made publicly available to the astronomical community, especially James Webb Space Telescope users, for comparisons that could eventually lead to the detection of these species in space.