EXCITATIONS FROM THE NONBONDING ORBITALS IN PARABENZOQUINONE

Abstract

Ab initio configuration interaction calculations using minimal and double-zeta basis sets have been performed on the $^{1,3} n\pi^{*}$ and $^{2}n$ cation states of parabenzoquinone. The calculations show that the best single-determinant description of these states has the excitation strongly localized on a single oxygen atom, which agrees with the earlier work of $Jonkman.^{1}$ Enforcing a delocalized (molecular orbital) description increases the energy of the excitation by over 2.5eV. The orbitals polarize in response to the localized excitation. A corresponding orbital $analysis^{2}$ shows that the polarization occurs primarily in the $\pi$-orbital space. Various wave-functions were tried to determine the minimum requirements for describing the states in terms of interacting local excitations. The possibility of pseudo Jahn-Teller distortions in the excited states was studied using the PRDDO method.