Spin-orbit coupling and dissociation of CO2 molecules

Potential surfaces of the CO₂ molecule for the ground and excited ³ B ₂, ¹ B ₂ electronic states are calculated by quantum chemistry methods. The calculation of the spin-orbit coupling in the molecule shows a large the matrix element, which removes the prohibition for the dissociation-recombination process CO₂(X ¹Σ) + M ? CO(X ¹Σ) + O(³ P) + M. The barrier on the potential curve for ³ B ₂, the energy of which exceeds the limit of dissociation into components in the ground states, explains the data on the dissociation and recombination energies measured in experiments with shock tubes. The absorption cross section of CO₂ molecules in the UV spectral region measured at high temperatures allowed us to plot branches of potential curves near their minima for two upper singlet states assigned to the ¹ B ₂ and ¹ A ₂ symmetry.