Theoretical studies of sulfite – sulfur dioxide clusters, SO32−(SO2)n: structure and stability of SnO2n+1 anions, n = 1–5

Density functional calculations using the B3PW91 functional with the 6-311+G(3df) basis set were performed on the addition of n = 1–4 SO2 molecules to SO3− and SO32−. Geometry optimizations were performed for a large number of possible structures. At n = 4, the dianionic cluster becomes adiabatically more stable than the monoanionic one, with an adiabatic electron detachment energy of 0.30 eV. Monoanionic clusters are characterized by the O–S–O–SO3 moiety having long O–S bonds to SO2 molecules. Dianionic clusters, however, prefer S–S bonding of O3S–O–S(O) with SO2.

Theoretical studies on clusters of carbonate with carbon dioxide, CO31–/2–(CO2)n, forn= 1–5 — Comparison of carbonate clusters with sulfate clusters

Density functional theory (DFT) calculations were performed on the geometries and energies of CO31–/2–(CO2)nclusters with n = 1–5. For small clusters (n = 1 or 2), coupled cluster energies were obtained. Up to three CO2molecules 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 CO2molecules will have to be added to CO32–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 SO2and 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.