THEORETICAL-STUDY OF THE ELECTRONIC-SPECTRA OF THE BIPHENYL CATION AND ANION

The electronic spectra of the cation and anion of biphenyl have been s tudied using multiconfigurational second-order perturbation theory (CA SPT2) and a basis set of ANO type, including polarization functions on the carbon atoms. For both cation and anion, two main transitions are obtained. The calculations for the cation give the intense vertical t ransitions placed at 1.9 and 3.2 eV in agreement with experimental evi dence. A number of weak transitions are in addition found in the energ y interval 1.1-4.6 eV. For the anion the strongest vertical transition s are calculated at 2.1 and 3.0 eV. The adiabatic electron affinity fo r biphenyl in the gas phase is computed to be -0.30 eV. The localized solutions obtained for the ground and excited states therefore corresp ond to shape resonances. The results are used for the interpretation o f the polaron states of doped poly(paraphenylene). It is concluded tha t simple molecular orbital models used in earlier work do not give a p roper description of the excitation process.