Ab initio study of CO2 −⋅CO2↔C2O4 − isomerization

The potential energy surface (PES) relevant to the isomerization of (CO2)2 − has been investigated by ab initio calculations including the effects of electron correlation. The surface plotted against appropriate angle parameters shows two shallow minima and a deep valley, which correspond to the CO2 −⋅CO2 (C2v), CO2 −⋅CO2 (Cs) and C2O4 − (D2d) structures, respectively. The transition states for the C2v↔Cs↔D2d interconversion are located well below the CO2 −+CO2 dissociation limit, which allows (CO2)2 − with sufficient internal energies to fluctuate among the isomeric forms. The calculations have also revealed quantitatively the behavior of the excess charge flow during the CO2 −⋅CO2↔C2O4 − electronic isomerization.