Rotational analysis of the threshold photoelectron spectra of room temperature and jet-cooled CO2

The rotational structure associated with the X̃ 2Πg (000) ground ionic state of CO+2 has been investigated by threshold photoelectron spectroscopy and semiempirical calculations based on the distribution of Rydberg state levels at n=2000. The calculations are in very good agreement with the rotationally resolved spectra for the X̃ 2Πg,3/2 and X̃ 2Πg,1/2 spin–orbit levels for both room temperature and supersonically cooled ground state CO2. Intensity anomalies are partly explained by decay mechanisms involving rotational and spin–orbit autoionization.