The S1 states of o-, m-, and p-benzyne studied using multiconfiguration second-order perturbation theory

Electronic states of o-, m-, and p-benzyne have been studied based on the CASPT2 (multiconfiguration second-order perturbation theory) geometry optimization calculations. The results for the S0, T1, and anionic states of the three benzynes are in good agreement with experiment. Based on adiabatic excitation energy (T0) calculations, the S1 states of o-, m-, and p-benzyne are determined to be 11B1, 11B1, and 11B1g, with the T0 values of 3.46, 2.97, and 2.70 eV, respectively. For each benzyne the S1 and T1 states have different space-symmetries.