Mid-infrared spectroscopy of 1-cyanonaphthalene cation for astrochemical consideration.

We present the low temperature gas-phase vibrational spectrum of ionised 1-cyanonaphthalene (1-CNN+) in the mid-infrared region. Experimentally, 1-CNN+ ions are cooled below 10 K in a cryogenic ion trapping apparatus, tagged with He atoms and probed with tuneable radiation. Quantum-chemical calculations are carried out at a density functional theory level. The spectrum is dominated by the CN-stretch at 4.516 µm, with weaker CH modes near 3.2 µm.

Electronic Spectroscopy of Monocyclic Carbon Ring Cations for Astrochemical Consideration.

Gas phase electronic spectra of pure carbon cations generated by laser vaporization of graphite in a supersonic jet and cooled to below 10 K and tagged with helium atoms in a cryogenic trap are presented. The measured C2n+-He with n from 6 to 14, are believed to be monocyclic ring structures and possess an origin band wavelength that shifts linearly with the number of carbon atoms, as recently demonstrated through N2 tagging by Buntine et al. ( J. Chem. Phys. 2021, 155, 214302). The set of data presented here further constrains the spectral characteristics inferred for the bare C2n+ ions to facilitate astronomical searches for them in diffuse clouds by absorption spectroscopy.

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 Šand 9645 Šwere 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.

Pathway to the identification of C60+ in diffuse interstellar clouds.

The origin of the attenuation of starlight in diffuse clouds in interstellar space at specific wavelengths ranging from the visible to the near-infrared has been unknown since the first astronomical observations around a century ago. The absorption features, termed the diffuse interstellar bands, have subsequently been the subject of much research. Earlier this year four of these interstellar bands were shown to be due to the absorption by cold, gas phase [Formula: see text] molecules. This discovery provides the first answer to the problem of the diffuse interstellar bands and leads naturally to fascinating questions regarding the role of fullerenes and derivatives in interstellar chemistry. Here, we review the identification process placing special emphasis on the laboratory studies which have enabled spectroscopic measurement of large cations cooled to temperatures prevailing in the interstellar medium.This article is part of the themed issue 'Fullerenes: past, present and future, celebrating the 30th anniversary of Buckminster Fullerene'.