∗Work performed under the auspices of the Office of Basic Energy Sciences of the U. S. Department of Energy.Author Institution:A series of large scale configuration interaction calculations have been carried out on the SO2 molecule. The ``ring’’ isomer of SO2 was found to lie 95 kcal/mole above the ``normal’’ isomer. In addition, a ``superoxide’’ isomer of SO2 i.e., a structure with a terminal sulfur atom, lies <12 kcal/mole above the ring isomer, or ∼25 kcal/mole below the S−O2 dissociation limit. The super-oxide isomer of SO2 has been implicated in the oxidation of CS2 and OCS