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.