Topology of conical/surface intersections among five low-lying electronic states of CO₂: Multireference configuration interaction calculations

Multi-reference configuration interaction with single and double excitation method has been utilized to calculate the potential energy surfaces of the five low-lying electronic states ¹A₁, ¹A ₂, ³A₂, ¹B₂, and ³B₂ of carbon dioxide molecule. Topology of intersections among these five states has been fully analyzed and is associated with double-well potential energy structure for every electronic state. The analytical potential energy surfaces based on the reproducing kernel Hilbert space method have been utilized for illustrating topology of surface crossings. Double surface seam lines between ¹A₁ and ³B₂ states have been found inside which the ³B₂ state is always lower in potential energy than the ¹A₁ state, and thus it leads to an angle bias collision dynamics. Several conical/surface intersections among these five low-lying states have been found to enrich dissociation pathways, and predissociation can even prefer bent-geometry channels. Especially, the dissociation of O( ³P) + CO can take place through the intersection between ³B₂ and ¹B₂ states, and the intersection between ³A₂ and ¹B₂ states.