The first experimental observation of electronic transitions in C2+ and C2D+

High-resolution translational energy spectroscopy (up to 0.1 eV) has been carried out on 8 kV of C₂⁺ and C₂D⁺. The spetra obtained with C₂⁺ formed by different methods show considerable differences which are attributed to the formation of different spin states of the ion. Tentative assignments for the observed transitions have been made including one corresponding to excitation of the ⁴∑_g^? —X ⁴∑_g^? system, which may be useful as a probe of interstellar C₂⁺. Two broad transitions have been seen in the translational energy spectrum of C₂D⁺ which are in reasonable agreement with existing theoretical calculations. Tentative assignments are proposed for these transitions.