Symmetry-Resolved Vibrational Spectroscopy for the C 1s[-1]2πu Renner-Teller Pair States in CO2

Symmetry-resolved excitation spectra have been measured for the Renner-Teller pair states A1 and B1 split from the core-excited C 1s[-1]2πu state in CO2. A vibrational progression with the spacings of ∼145 meV is found in both the A1 and B1 spectra at different energies and assigned to the symmetric stretching mode caused in the B1 linear state, with the help of ab initio calculations. Appearance of the vibrations in the A1 spectrum is interpreted as due to nonadiabatic coupling between the A1 and B1 states via the bending motion