Ab initio study of (CO2)n−: structures and stabilities of isomers

The geometrical structures and stabilities of (CO2)n− with the size range 3⩽n⩽6 are investigated by ab initio calculations including the effects of electron correlation. The calculations have shown that the structures of (CO2)n− can be formulated by either CO2−·(CO2)n−1 or C2O4−·(CO2)n−2, and that the geometry of the (CO2)2− dimer remains more or less in all the optimized structures. In all the sizes investigated in the present study, the most stable isomers are of the C2O4−·(CO2)n−2 form, being consistent with the results obtained in photoelectron spectroscopic studies.