Electronic absorptions of C₅⁺ detected in the visible through action spectroscopy in a cryogenic trap

The ²Π_g←X²Σ_u⁺ electronic spectrum of C₅⁺ in the gas-phase with origin band at 513nm is reported following experiments in a cryogenic ion trapping instrument. Buffer gas-cooled C₅⁺ ions, generated by laser vaporisation of graphite, were investigated using two action spectroscopy approaches. Laser-induced dissociation of weakly bound C₅⁺−He_n complexes synthesised in the trap reveal a linear dependence of the absorption energies on n allowing prediction of those of the bare ion C₅⁺. These results are confirmed in two colour experiments on C₅⁺, by monitoring fragmentation into the C₃⁺ + C₂ product channel. The data are supplemented with high-level electronic structure calculations which support the assignment of D_∞h symmetry to the ground electronic state. These laboratory results provide the requisite data needed for spectroscopic detection of this structure in terrestrial and extraterrestrial environments.