The impact energy dependence of momentum profiles of glyoxal and biacetyl and comparison with theory at their high-energy limits

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.