PREDICTION OF THE LOWEST-ENERGY NON-KOOPMANS DOUBLET STATES AND THE FIRST IONIZATION-POTENTIALS OF POLYCYCLIC AROMATIC SYSTEMS FROM THEIR TRIPLET-STATE ENERGIES

This paper presents some new relations connecting the triplet-state en ergy of an alternant aromatic hydrocarbon with that of its excited dou blet state as well as its first ionization potential. The energy relat ion between the doublet and triplet states is basically a simplified v ersion of the SDT relation but the predictive power of the proposed co rrelation is considerably better in spite of the drastic assumptions m ade in the model. Incorporation of molecular size in the doublet-tripl et correlation has no appreciable effect on the predictions, but its i nclusion in the ionization potential vs. triplet-state energy relation leads to a significant improvement in the results. It is explained on the basis of our new finding that the Coulomb term appearing in the e xpression for the ionization potential behaves in the same manner as t he molecular size, which thus accounts for electron interaction in the model. The proposed correlations provide a simple but powerful means to estimate the first ionization potentials and excited doublet-state energies of polycyclic aromatic hydrocarbons directly from the knowled ge of their triplet-state energies.