Theoretical study of the extremely small torsional barriers of thiophenol in the ground and the first excited electronic states

- Theoretical study of the extremely small barrier of the SH rotation of thiophenol.
- The performance of MP2, CASSCF(12,11), and DFT (B3LYP, HTCH and ωB97X-D) methods.
- The planar conformer is the stationary structure of both the S0 and the S1 states.
- The spectroscopic properties of the S1 electronic state are obtained at first.
- The barrier of -SH rotation of the S1 state is also very small: 1.89 kcal/mol.