The Potential Energy Surfaces of the Ground and Excited States of Carbon Dioxide Molecule

Potential energy surfaces (PESs) of the (1)A(1)((1)Sigma(+)(g)), B-1(2) and B-3(2) electronic states of CO2 have been computed as a function of the two bond distances and the bond angle. The calculations were based on the complete active space self consistent field (CASSCF) and multiconfigurational second-order perturbation theory (CASPT2) electronic structure models. From our calculations no crossing point between B-1(2) and B-3(2) states was found, but there is a crossing point located between B-1(2) and (3)A(2) state on the PESs. The energy of the crossing point is lie 0.23 eV above the CO + O (P-3), which is in agreement with the value of 0.27 eV on the experiment. This implies that the mechanism of the recombination of an oxygen atom with a carbon monoxide molecule: CO(X-1 Sigma(+), nu) + O(P-3) -> (CO2)-C-3* -> (CO2)-C-1*(X-1 Sigma(+), nu = 0) + O(D-1) may occur through the (3)A(2) state crossing the 1B2 state. The equilibrium geometries and adiabatic excitation energies of B-1,3(2), 1,(3)A(2) states of CO2 were reported and discussed in this paper, too.