Electronic structure of carbon trioxide and vibronic interactions involving Jahn-Teller states
Electronic structure of CO3 is characterized by equation-of-motion and coupled-cluster methods. C2v and D3h structures are considered. Ground-state equilibrium structures and frequencies are strongly affected by vibronic interactions with low-lying excited states. At D3h geometries, the vibronic interactions are enhanced by the Jahn-Teller character of the excited states. The curvature of the potential energy surface and the existence of the D3h minimum are very sensitive to the correlation treatment and the basis set. The correlation effects are stronger at D3h, in agreement with a smaller HOMO-LUMO gap.