Theoretical studies on anionic clusters of sulfate anions and carbon dioxide, SO 4 −1/−2 (CO2) n , n = 1−4

Abstract

Geometry optimizations were performed on monoanionic and dianionic clusters of sulfate anions with carbon dioxide, SO4−1/−2(CO2)n, for n = 1–4, using the B3PW91 density functional method with the 6-311 + G(3df) basis set. Limited calculations were carried out with the CCSD(T) and MP2 methods. Binding energies, as well as adiabatic and vertical electron detachment energies, were calculated. No covalent bonding is seen for monoanionic clusters, with O3SO–CO2 bond distances between 2.8 and 3.0 A. Dianionic clusters show covalent bonding of type [O3S–O–CO2]−2, [O3S–O–C(O)O–CO2]−2, and [O2C–O–S(O2)–O–CO2]−2, where one or two oxygens of SO4−2 are shared with CO2. Starting with n = 2, the dianionic clusters become adiabatically more stable than the corresponding monoanionic ones. Comparison with SO4−1/−2(SO2)n and CO3−1/−2(SO2)n clusters, the binding energies are smaller for the present SO4−1/−2(CO2)n systems, while stabilization of the dianion occurs at n = 2 for both SO4−2(CO2)n and SO4−2(SO2)n, but only at n = 3 for CO3−2(SO2)n.