Complete breakdown of the quasiparticle picture for inner-valence electrons: Hydrogen cyanide and formic acid

The position and the relative intensity of the lines in the ionization spectrum of HCN and HCOOH are calculated by a many-body Green's function method. The results show that the concepts developed for the interpretation of the photoelectron spectra of the outer-valence shell of atoms and molecules are inapplicable in the inner-valence region. There is no longer any simple correspondence between the occupied molecular orbitals and the bands observed in the ionization spectrum. Correlation effects are so strong that the usual distinction between main lines and satellite lines cannot be maintained. The theoretical results are used to interpret published He II photoelectron spectra of HCN and HCOOH.