New rotational analyses and vibronic coupling of the Ã2Πu→X̃2Πg electronic transition of the CO2+ molecular ion.

In the present work, the Ã2Πu→X̃2Πg (Fox-Duffendack-Barker) electronic transition of the CO2+ molecular ion has been investigated using high-resolution Fourier transform emission spectroscopy in the 20,000 - 33,000 cm-1 range. A total of 62 bandheads were assigned and rotationally analysed, including 17 subbands subjected to detailed rotational analysis for the first time. This investigation allowed the determination of spectroscopic constants for the 102, 202, 302 and 402 levels of the X̃2Πg ground state, reported here for the first time. Precise wavenumber measurements produced improved molecular constants and band origins, establishing more reliable parameters than those previously available in the literature. Based on this refinement, a comprehensive set of spin-vibronic term values was derived and validated by comparing it with previous results available in the literature.