On the correlation between photoelectron and electronic spectra in trans ‐ azomethane

A possibility of correlating electronic and photoelectron spectra is discussed, using trans ‐azomethane as an example. The Coulomb and exchange integrals required were obtained by three semi‐empirical SCF‐methods: MINDO/2, CNDO/2, and a modified CNDO method. The orbital energies were taken as minus the corresponding experimental ionization potentials. The sequence of the transition energies Δ E ( n s → π*) Δ E ( n a → π*) < Δ E (π → π*) is found to be different from the ionization potential sequence IP ( n s ) < IP (π) < IP ( n a ), in agreement with previous spectroscopic studies; the results support the latest view that the π → π* transition of the azo group occurs at around 12 eV.