Ab initio study of the (SO2)(SO2− dimer: structures involving a two-electron SO bond

The structure of the (SO2)2− dimer involving one or two SO bonds has been investigated by means of ab initio calculations at the PUMP4/6–31 + G* / /UMP2/6–31 + G* level. Two minima with one SO bond are found; their formation energies are in reasonable agreement with experimental data. Two bifurcated structures with two equal SO bonds are characterized as transition states. They allow oxygen exchange in each of the SO bound minima. The possible structure of the dimer is discussed in comparison with our previous results in which a SS bound dimer was found.