Orbital imaging for the valence shell of sulphur dioxide: comparison of EMS measurements with near Hartree-Fock limit and density functional theory

The momentum distributions of the valence orbitals of sulphur dioxide have been studied by electron momentum spectroscopy (EMS), Hartree-Fock (HF) and density functional theory (DFT) calculations. The experiments were perform ed using an energy dispersive multichannel EMS spectrometer at an impact en ergy of 1200 eV plus the binding energy and in symmetric non-coplanar kinem atics. The valence-shell binding energy spectra have been measured for all valence orbitals over the energy range 8-60 eV. Calculated synthetic bindin g energy spectra derived from many-body Green's function and DFT calculatio ns are compared with experiment. In the inner valence region, strong splitt ing of the 3b(2) and 5a(1) ionization is observed due to final state electr on correlation effects. The measured momentum profiles of the valence orbit als are compared with HF calculations at the level of the target HF approxi mation, and with DFT calculations using B3LYP functionals at the level of t he target Kohn-Sham approximation, with basis sets ranging from minimum (ST O-3G) to large (AUG-cc-pV5Z(-h)). Generally, the shapes of the experimental momentum profiles are well reproduced by HF and DFT calculations using lar ge diffuse basis sets. However, small discrepancies still exist between all theoretical treatments and experiment in the low momentum region for the ( 4b(2)+7a(1)+2b(1)) and 6a(1) orbitals. (C) 2000 Elsevier Science B.V. All r ights reserved.