High-Resolution Spectroscopy of the X-A Transition of the Carbon Monoxide Dication CO²⁺

We report rovibronic spectra of the A ³Σ^+$v'=0-2$ - X ³Π_Ω\(v=0\) rovibronic transitions $|Ω|=0, 1$ and 2 of the CO²⁺ doubly-charged molecular ion. Spectra were recorded at high resolution $sim 5$ cm$^-1$ in a fast beam of CO²⁺ molecules by detecting the Coulomb explosion of the molecules upon excitation to the A state. Measurements were guided by ab initio calculations which then assisted the assignment of the observed spectral features. Our results resolve the spin-orbit splittings of the ground vibronic state X ³Π_Ω\(v=0\), but not the rotational structure of the bands due to spectral congestion, and provide spectroscopic information on CO²⁺ with unprecedented resolution. In doing so they expand our knowledge of this benchmark doubly charged molecular ion and expand the short list of doubly charged molecules studied at high resolution.