Electronic States of Organic Molecules. 3. Photoelectron Spectra of Cycloalkenes and

Abstract: The photoelectron spectra (He(1) and He(I1)) of a series of cycloalkenes (c3-C~) and methylenecycloalkenes (C3-C,) are presented along with those of related open chain compounds. The calculated MO energies using a 4-31G basis set are also given. A good correlation between ionization potentials and MO energies was found, but the correlation did not have a zero intercept. The correlation was useful in assigning the bands in the photoelectron spectra of the larger molecules for which over-lapping bands could not experimentally be resolved and suggests a relationship between the neutral molecule MO energy and the sum of the correlation and reorganization energies on going to the ion. One of the most important of the techniques which give information concerning ground state molecular orbital energy levels is photoelectron ~pectroscopy. ~ To the extent that Koopmans ’ theorem4 is applicable, the Hartree-Fock orbital energies are obtained directly. It seems likely that it will be possible in the near future to calculate the error associated with relating ionization potentials to MO energy level^. ^ The pho-toelectron spectra are also an important tool in achieving an understanding of the optical spectra