A THEORETICAL-STUDY OF THE ELECTRONIC-SPECTRUM OF BIPHENYL

The electronic spectrum of biphenyl in the energy range up to 6.0 eV h as been studied using multiconfigurational second-order perturbation t heory (CASPT2) and a basis set of ANO type, including polarization fun ctions on all carbon atoms. The calculated spectrum gives conclusive a ssignments to all valence excited singlet states and the low-lying tri plet states. The change of the torsional angle between the two benzene rings in the different excited states is shown to be of considerable importance and explains the different excitation energies observed in the gas phase as compared to solution or crystalline biphenyl at low t emperatures. The intense transition to the 1 B-1(1u), state is mostly affected. The first Rydberg transition (3s) is found at 5.6 eV. The ap pearance of a state of (1)A(g), symmetry at energies around 5.0 eV is ruled out. The first state of this symmetry appears at 5.9 eV.