The infrared spectrum of protonated buckminsterfullerene C 60 H

Although fullerenes have long been hypothesized to occur in interstellar environments, they have only recently been unambiguously identified through spectroscopy1–4. C60, C70 and C60+ now constitute the largest molecular species individually identified in the interstellar medium. Fullerenes have substantial proton affinities and it has been suggested that C60H+ is likely the most abundant interstellar analogue of C60 (ref. 5). We present here a laboratory infrared (IR) spectrum of gaseous C60H+. Symmetry breaking in C60H+ 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, which have been associated with high C$${}_{60}$$ abundances, indicates that C60H+ is a plausible contributor to their IR emission. Protonated buckminsterfullerene (C60H+) may be the most abundant interstellar analogue of C60, and its gas-phase laboratory infrared spectrum is presented here. C60H+ has more infrared active modes than C60, giving it a richer spectrum that may be detectable with future infrared space missions.