Photoelectron spectra of polycyclic aromatic hydrocarbons

Abstract

The high-resolution He(I) PE spectra of anthracene, phenanthrene, pentacene, perylene, chrysene, 1,2-benzanthracene, 1,2-benzpyrene, benzo[g, h, i]perylene and ovalene are presented and their essential features briefly discussed on the basis of HMO, Pariser–Parr–Pople, extended Hückel and MINDO/2 calculations. With the exception of a few closely spaced orbitals in the larger hydrocarbons, the four theoretical treatments yield the same π level ordering, thus allowing a tentative assignment of 56 observed ionization potentials in the 6–11 eV region to computed π levels. Increasing the size of the hydrocarbon shifts the onset of the σ bands only slowly to lower ionization potentials.