Theoretical study of the electronic states of CS2++

Three-dimensional potential energy functions (PEFs) have been generated for the X3Σg−, a1Δg, b1Σg+, and c1Σu− states of CS2++ using internally contracted multi-reference configuration interaction approach. The analytic forms of the PEFs have been employed in the calculations of the vibrational energy levels, the wave functions, and the Franck–Condon factors for the direct ionization process CS2→CS2+++2e. As in CS2 and CS2+, strong anharmonic resonances are found in all four states. The spectra are predicted to consist of vibrational progressions of Fermi polyads. For the 1Δg state the Renner–Teller problem has been solved and the pattern of the bending levels has been analyzed. For 14 electronic states one-dimensional collinear cuts along the charge separation path CS++S+ have been calculated and the corresponding barrier heights of the predissociating states have been determined. The experimental onset for the charge separation paths CS2++→CS++S+ at about 30 eV is found to be consistent with the calculated barrier height on the PEF of the X3Σg− state.