Green's function study of the one-electron and shake-up ionization spectra of unsaturated hydrocarbon cage compounds

The valence one‐electron and shake‐up ionization spectra of stella‐2,6‐diene, stella‐2,6‐dione, bicyclo‐[2.2.2]‐octane‐2,5‐dione, and bicyclo‐[2.2.1]‐heptane‐2,5‐dione have been exhaustively studied, up to the double ionization threshold and beyond, by means of one‐particle Green's function theory. This study is based on calculations employing the outer‐valence Green's function and the third‐order algebraic diagrammatic construction schemes, along with a variety of basis sets. A comparison is made with available ultraviolet (He I) photoelectron and (e, 2e) electron‐impact ionization spectra, with main focus on the identification of spectral fingerprints for cyclic strains and through‐bond π‐conjugation. As a byproduct, our results demonstrate that it is impossible to reliably assign complex (e, 2e) ionization spectra by resorting only to Hartree–Fock or Kohn–Sham orbital energies and to the related electron momentum distributions. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2006