Title: Isolation and spectroscopy of C₂H⁺ ions in helium droplets  

Abstract:

Ethynylium (C2H + ) may be an important intermediate in astrochemistry, however due to its high reactivity, C2H + remains poorly studied by laboratory techniques. Immersion of single acetylene molecules in the droplets followed by electron impact ionization effectively generates and isolates C2H + cations in an inert cryogenic environment, enabling spectroscopic measurements. We find that in the C-H stretching range, the C2H + spectrum appears as a triplet with splitting of 33.6 cm-1 and 37.5 cm-1. The splitting is temporarily assigned to the product of interactions between the CH stretching mode and overtones of the bending mode.