Photoelectron spectra of inner valence shells. Part 2.—Unsaturated hydrocarbons

Abstract

The photoelectron spectra of some unsaturated hydrocarbons in the region 15–26 eV are presented. As in the previous work on saturated hydrocarbons, ionization potentials for carbon 2s-type molecular orbitals are reported and analysed on the basis of a simple Hückel model. Good agreement with the model is obtained after due consideration of the possible variations in α and β. Benzene is apparently an exceptional case and the reasons for its high 2b_1u energy of 15.45 eV are discussed. It is shown that the ionization potential predictions from a simple Hückel model incorporating a variable bond-length correction compare favourably with the results from more sophisticated quantum-mechanical calculations.