Theoretical studies on clusters of carbonate with carbon dioxide, CO3~(1-/2-)(CO2)_n, for n = 1-5 -Comparison of carbonate clusters with sulfate clusters

摘要

Density functional theory (DFT) calculations were performed on the geometries and energies of CO3~(1-/2-)(CC>2)_n clusters with n = 1-5. For small clusters (n = 1 or 2), coupled cluster energies were obtained. Up to three CO2 molecules are bound covalently to the dianion. Only weak electrostatic bonds were found in the monoanions. Calculated binding energies for the monoanions are in reasonable agreement with experimental values. The calculated adiabatic electron detachment energy for the dianion is -0.07 eV at n = 5, indicating that at least six CO2 molecules will have to be added to CO3~(2-) before the dianionic cluster becomes, in the gas phase, more stable than the monoanionic one. In comparison, for sulfate - carbon dioxide clusters, stabilization occurs at n = 2. Carbonate clusters are compared with sulfate clusters for three solvent molecules: CO2, SO2, and H2O. Carbonate clusters have larger binding energies than sulfate clusters. For a given dianion, binding energies are largest for SO2 and smallest for H2O. However, in all cases, stabilization of the carbonate dianion by clustering is more difficult to achieve than stabilization of the sulfate dianion.