On the stabilization of the sulfate dianion by sulfur dioxide in the gas phase. Theoretical studies on structure and stability of SnO2n+2 anions, n = 1–4

The stabilization with respect to electron detachment of the sulfate dianion SO 4 2 - in gas phase by addition of SO2 molecules is being studied. Geometries of SO 4 2 - (SO2)n and SO 4 1 - (SO)n for n = 1–3 have been optimized using the B3PW91 method. The energies of the smaller clusters have been recalculated at the CCSD and CCSD(T) level based on the B3PW91 geometry. In the gas phase the sulfate monoanion is more stable than the dianion, the latter having an adiabatic electron detachment energy of −1.57 eV. However, with the addition of two SO2 molecules the dianion becomes more stable by 0.38 eV (CCSD energies). The vertical electron detachment energy, while negative for the lone sulfate dianion (−1.26 eV), turns positive with the addition of a single SO2 molecule (0.64 eV). Chemically bonded monoanions S 2 O 6 1 - and S 3 O 8 1 - , as well as dianions S 2 O 6 2 - , S 3 O 8 2 - and S 4 O 10 2 - , have been identified.