We report an electron momentum spectroscopy study of the two outermost
orbitals of the dicarbonyls, glyoxal and biacetyl. The experiments were performed
at impact energies of 800, 1200 and 1600 eV using a recently developed
multichannel (e, 2e) spectrometer. The experimental momentum profiles clearly
show remarkable variations in the low-momentum region with increasing impact
energy. Furthermore, it has been found that the two molecules reach their
high-energy limits at different impact energies, indicating that the range of
validity of the plane-wave impulse approximation (PWIA) largely depends on the
target in question. The results at 1600 eV are employed for comparisons with
PWIA calculations using Hartree–Fock and density functional theory (DFT).
While the DFT calculations reproduce well the observations for glyoxal,
considerable discrepancies between experiment and theory exist for biacetyl.