A THEORETICAL-STUDY OF THE ELECTRONIC-SPECTRA OF PYRIDINE AND PHOSPHABENZENE

The electronic excitation spectra of pyridine and phosphabenzene have been studied using theoretical methods. The electronic states are desc ribed by wave functions derived from second-order perturbation theory based on multiconfigurational reference functions. The study includes singlet and triplet valences excited states as well as a number of Ryd berg states. For both molecules the transition energies to the two low est pi --> pi excited singlet states are known from experiment and re produced with an accuracy of 0.15 eV or better, while the n --> pi tr ansition energies are predicted with a somewhat uncertain error of abo ut 0.2 eV. The calculations suggest the lowest n --> pi transition de tected experimentally in pyridine corresponds to an adiabatic transiti on. 43 electronic states have been determined in each of the molecules .