Ionization Energies of Free Molecules and Molecular Solids

Gas phase ionization energies I g, for compounds of interest from electrical and electronic viewpoints can be determined using photoemission techniques. Also reasonably good estimation can be obtained from oxidation potential and energy of charge-transfer absorption in solution. Photoemission techniques are also used for determining ionization energies of molecular solids I s These methods are reviewed, and a table of ionization energies for 120 compounds are given. The difference Δ between I g and I s can be ascribed to the polarization of surrounding molecules and, in some cases, intermolecular band formation. The trends in I g, I s, and Δ for various compounds are discussed. Finally, information from I g and I s is surveyed for the energetics of ionized states and the electronic structure of binary systems.