The Jahn Teller distorted states, 2 B 2g and 2 B 1g of the benzene radical cation have been studied by using ab initio MPn and SDCI methods. The calculations indicate that 2 B 2g is the ground state of the benzene cation and that 2 B 1g is higher in energy than 2 B 2g and represents a saddle point. The calculated isotropic and anisotropic hyperfine coupling constants for the 2 B 2g state are in excellent agreement with those obtained from the ESR experiments. It is concluded that the benzene cation is in the 2 B 2g Jahn Teller distorted state.
