Ab initioinvestigations of the unimolecular decay of CS+2for internal energies lower than 10 eV

One-dimensional potential energy curves of the lowest doublet and quartet states of CS + 2 and their mutual spin–orbit interactions have been calculated using the complete active space self-consistent field and internal contracted multi-reference configuration interaction methods. Between the A 2 Π u and the C 2 Σ + g states, four doublet satellite states (two 2 Π u , one 2 Π g and one 2 Φ u ) in addition to the valence B 2 Σ + u state are found. The two 2 Π u states have been already observed in the photoelectron spectra where they were associated with a long vibronic progression. Several quartet states have been also located in the 3–10 eV internal energy range. The avoided crossing regions and the conical intersections for the doublets and the quartets are located. The predissociation mechanisms of the doublet states of CS + 2 leading to the first dissociation limit (S + ( 4 S u ) + CS(X 1 Σ + )) are also discussed. They are found to involve vibronic and/or spin–orbit interactions between the doublet and the quartet states.