The vacuum ultraviolet pulsed field ionization–photoelectron (PFI–PE) spectra for CO2 have been measured in the energy range of 13.6–14.7 eV, revealing complex vibronic structures for the ground CO2+(X 2Πg) state. Many vibronic bands for CO2+(X 2Πg), which were not resolved in previous photoelectron studies, are identified in the present measurement based on comparison with available optical data and theoretical predictions. As observed in the HeI photoelectron spectrum of CO2, the PFI–PE spectrum is dominated by the symmetry allowed ν1+ (symmetric stretch) vibrational progression for CO2+(X 2Πg). However, PFI–PE vibronic bands due to excitation of the symmetry disallowed ν2+ (bending) and ν3+ (asymmetric stretch) modes with both odd quanta, together with the symmetry allowed even quanta excitations, are clearly discernible. The simulation of rotational contours resolved in PFI–PE vibronic bands associated with excitation to the 1+=0–1,ν2+=0–2,ν3+=0) vibrational levels has yielded accurate ionization energies for the formation of these vibronic states from CO2(X 1Σg+).

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