Study of the valence electronic structure of the diene class of compounds by electron momentum spectroscopy and Green function methods. I. 1,2-propadiene

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The complete valence-shell electron separation-energy spectra and momentum distributions are measured for 1,2-propadiene by high momentum-resolution electron-momentum spectroscopy at a total energy of 1500 eV. Many-body calculations of the separation energies and spectroscopic factors using Green function methods are carried out and, for the binding energies, compared with the experimental data. The measured momentum distributions are compared with those calculated in the plane-wave impulse approximation (PWIA) formalism using two respective SCF orbital wavefunctions, the second of which includes d-functions in the basis set. The agreement between the measured momentum distributions and the PWIA-SCF orbital-momentum distributions is, in general, fair, although for the outermost orbitals the SCF wavefunctions underestimate the density at low momentum. The inner valence 1b2 and 1a1 orbitals are found to be severely split by final-state correlation effects.