Probing Dyson orbitals with Green's Function theory and Electron Momentum Spectroscopy

Results of an experimental study of the valence electronic structure of difluoromethane employing high-resolution Electron Momentum Spectroscopy with various impact energies are reported. One-particle Green's Function theory is utilized, for the first time, for computing accurate spherically averaged electron momentum distributions. These are derived from Dyson orbitals obtained using the third-order Algebraic Diagrammatic Construction (ADC(3)) scheme. The corresponding eigen-energies also accurately reproduce the (e, 2e) ionization spectrum. Shortcomings of empirical analyses of (e, 2e) experiments based on Kohn-Sham orbitals and eigen-energies are comparatively discussed. A failure of the target Hartree-Fock approximation is noted for the momentum distribution pertaining to the 1b1 + 3b2 + 5a1 levels.