The Photoelectron Spectrum of [18]Annulene

The PE. spectrum of 18]annulene has been measured and correlated with MO-calculations. The experimental ionization energies can only be explained by computing the electronic states of the cation, that is by taking into account the electron correlation and reorganization in the ionic states. The results allow a discussion of the structure of the neutral molecule; they are consistent with a D_6hpoint group of symmetry.