A theoretical study on the strength of two-center three-electron bonds in the NO3 radical adducts of reduced sulfur molecules, H2S, CH3SH, CH3SCH3, and CH3SSCH3

It is widely known that addition of a radical species to the sulfur atom of a reduced sulfur molecule results in formation of a two-center three-electron (2c-3e) bond, but relatively few investigations have been reported for the 2c-3e bond between the NO3 radical and a sulfur molecule. This article presents results of gas-phase DFT and ab initio investigations on the 2c-3e type adducts of the NO3 radical with reduced sulfur molecules. By using correlation consistent basis sets, geometry optimizations at the MP2 and BH&HLYP levels and single-point energy evaluations at the CCSD(T) level were carried out. Our estimates for the dissociation enthalpies (ΔH (298 K)) of the 2c-3e S–O bonds in the NO3 radical adducts of the CH3SH, CH3SCH3, and CH3SSCH3 molecules are 7∼10, 15∼16, and 10∼12 kcal/mol, respectively, but our calculations suggest that the H2S molecule will not actually form a 2c-3e adduct with the NO3 radical.