Electronic structure computational study of H and Mu addition to CS double bonds

High-level ab initio electronic structure calculations have been performed for H(Mu) addition to the C and S atoms of CS-containing molecules in order to understand the preferential addition site. It is found that the barrier height for the C-addition is generally high, while the S-addition occurs with a very low barrier or without a barrier. Thus, the S-addition processes are kinetically favored. However, the situation of the thermodynamics stability for C- and S-adducts is somewhat complicated. In the case of the H(Mu) + H2CS and (CH3)2CS reactions, the C-adducts are more stable than the S-adducts for both H and Mu additions. For larger CS-containing compounds, S-adducts are more stable than the C-adducts in Mu addition, while the S-adducts are less stable than the C-adducts in H addition. This means that H and Mu addition reactions can give different reaction mechanisms and thus different final reaction products depending on the parent molecules. This behavior mainly comes from large zero-point energy corrections of muoniated radicals.