Theoretical studies of atmospheric triatomic molecules. New a b i n i t i o results for the 1Πg–1Δu vertical state ordering in CO2a)

Vertical energy levels are computed with MC–CI wave functions for the 1Δu valence state and the 1Πg mixed character state of CO2, and for the 2Πg state of CO+2. Using the computed MC–CI results and results from previous work, vertical energy levels for the low-lying valence states, mixed character states, and Rydberg states of CO2 are determined. An adiabatic correlation diagram for these states is constructed for the process CO2→CO+O. Qualitative features in the potential energy surfaces which arise from the ordering are discussed. Comparisons with theory and experiment are given.