STABILIZATION CALCULATIONS ON THE PI-STAR ANION STATES OF 1,4-CYCLOHEXADIENE - CONFIRMATION OF THE PI(-)-STAR BELOW PI(+)-STAR ORBITAL ORDERING

The stabilization method is used to calculate the energies of the pi* anion states of 1,4-cyclohexadiene. These calculations show that the ground state anion is 2A(u) while the first excited state anion is 2B2g. This order of the anion states is opposite that which would prevail were only through-space interactions present and is due to the domination of through-bond interactions. Stabilization calculations at Koopmans' theorem and single excitation CI levels of theory give splittings of 1.20 and 0.89 eV, respectively, as compared to the 0.92 eV splitting found experimentally.