Buckyball-metal complexes as promising carriers of astronomical unidentified infrared emission bands

TL;DR

This study presents laboratory spectra and theoretical analysis of fullerene-metal complexes, suggesting they could be key carriers of unidentified infrared emission bands in space, expanding our understanding of cosmic carbon chemistry.

Contribution

It is the first to provide laboratory spectra of gas-phase fullerene-metal complexes and links these to astronomical infrared observations, proposing them as carriers of unidentified emission bands.

Findings

Fullerene-metal complexes match observed infrared bands in planetary nebulae.

Complexes of C60 with common metals show similar spectral patterns.

Proposed complexes could form and survive in astrophysical environments.

Abstract

Infrared emission bands with wavelengths between 3-20 {\mu}m are observed in a variety of astrophysical environments [1,2]. They were discovered in the 1970s and are generally attributed to organic compounds [3,4]. However, over 40 years of research efforts still leave the source of these emission bands largely unidentified [5-7]. Here, we report the first laboratory infrared (6-25 {\mu}m) spectra of gas-phase fullerene-metal complexes, [C60-Metal]+ (Metal = Fe and V), and show with density functional theory calculations that complexes of C60 with cosmically abundant metals, including Li, Na, K, Mg, Ca, Al, V, and Fe, all have similar infrared spectral patterns. Comparison with observational infrared spectra from several fullerene-rich planetary nebulae demonstrates a strong positive linear cross-correlation. The infrared features of [C60-Metal]+ coincide with four bands attributed earlier to neutral C60 bands, and in addition also with several to date unexplained bands. Abundance and collision theory estimates furthermore indicate that [C60-Metal]+ could plausibly form and survive in astrophysical environments. Hence, [C60-Metal]+ are proposed as promising carriers, in supplement to C60, of astronomical infrared emission bands, potentially representing the largest molecular species in space other than the bare fullerenes C60, C60+, and C70. This work opens a new chapter for studying cosmic fullerene species and carbon chemistry in the Universe.