Fullerenes in Space

In 1985 the football structure of C₆₀ , buckminsterfullerene was proposed and subsequently confirmed following its macroscopic synthesis in 1990. From the very beginning the role of C₆₀ and C₆₀⁺ in space was considered, particularly in the context of the enigmatic diffuse interstellar bands. These are absorption features found in the spectra of reddened star light. The first astronomical observations were made around one hundred years ago and despite significant efforts none of the interstellar molecules responsible have been identified. The absorption spectrum of C₆₀⁺ was measured in a 5 K neon matrix in 1993 and two prominent bands near 9583 Å and 9645 Å were observed. On the basis of this data the likely wavelength range in which the gas phase C₆₀⁺ absorptions should lie was predicted. In 1994 two diffuse interstellar bands were found in this spectral region and proposed to be due to C₆₀⁺ . It took over 20 years to measure the absorption spectrum of C₆₀⁺ under conditions similar to those prevailing in diffuse clouds. In 2015, sophisticated laboratory experiments led to the confirmation that these two interstellar bands are indeed caused by C₆₀⁺ , providing the first answer to this century old puzzle. Here, we describe the experiments, concepts and astronomical observations that led to the detection of C₆₀⁺ in interstellar space.