The infrared spectrum of protonated buckminsterfullerene, C60H+

TL;DR

This study provides the first laboratory IR spectrum of protonated buckminsterfullerene (C60H+), demonstrating its potential role in interstellar IR emission and validating theoretical models for its spectral features.

Contribution

It presents the first experimental IR spectrum of gaseous C60H+, compares it with theoretical predictions, and suggests C60H+ as a contributor to interstellar IR emission in planetary nebulae.

Findings

The IR spectrum of C60H+ is richer than that of C60 due to symmetry breaking.

B3LYP/6-311+G(d,p) accurately reproduces the experimental spectrum.

C60H+ plausibly contributes to IR emission observed in certain planetary nebulae.

Abstract

Although fullerenes have long been hypothesized to occur in interstellar environments, their actual unambiguous spectroscopic identification is of more recent date. C60, C70 and C60+ now constitute the largest molecular species individually identified in the interstellar medium (ISM). Fullerenes have significant proton affinities and it was suggested that C60H+ is likely the most abundant interstellar analogue of C60. We present here the first laboratory infrared (IR) spectrum of gaseous C60H+. Symmetry breaking relative to C60 produces an IR spectrum that is much richer than that of C60. The experimental spectrum is used to benchmark theoretical spectra indicating that the B3LYP density functional with the 6-311+G(d,p) basis set accurately reproduces the spectrum. Comparison with IR emission spectra from two planetary nebulae, SMP LMC56 and SMC16, that have been associated with high C60 abundances, indicate that C60H+ is a plausible contributor to their IR emission.