What is the mechanism of the OSO ring formation in sulfur tetroxide (SO4(C2v)) molecule?

► The mechanism of the OSO ring formation in SO4(C2v) molecule has been investigated, theoretically. ► There are no favorable paths in the SO2 + O2(3∑g-), SO2 + O2(1Δg) and O(3P) + SO3 reactions. ► The O(1D) + SO3 reaction is suitable for the OSO ring formation on the singlet PES.