Theoretical characterization of the thiosulfeno radical, HS2

We have investigated the structural and thermodynamic properties of the HSS radical at the CCSD(T) and B3LYP levels of theory, in conjunction with the correlation consistent basis sets. The structural parameters obtained at the CCSD(T) level are in good agreement with experiment, with the exception of the SH bond distance, which is 0.0055 Å shorter than the experimental result. The excitation energy to the lowest excited state, 2A′ is in excellent agreement with experiment, 20.59 vs. 20.80 kcal/mol, CCSD(T)/CBS and experiment, respectively. The ground state of HSS+ is predicted to be 1A′, but there is a very low lying triplet state 3A″. The gap between the 1A′ and 3A″ states is 8.40 and 2.90 kcal/mol at the CCSD(T)/CBS and B3LYP/6-311 + G(3df,2p) levels, respectively. The predicted IP(HS2) = 213.9 kcal/mol is close to the determined for HSSH, 208.9 kcal/mol. The estimated Δ H f , 298 0 ( HSSH ) = 3.63 ± 1 kcal / mol is in good agreement with the experimental results available 3.8 and 4 kcal/mol. However, some discrepancies exist for HSS, we recommend Δ H f , 298 0 ( HSS ) = 25.02 ± 1 kcal / mol .