Highest Occupied Molecular Orbital of Cyclopentanone by Binary (e, 2e) Spectroscopy

We report the first measurements of the momentum profiles of highest occupied molecular orbital (HOMO) and the complete valence shell binding energy spectra of cyclopentanone with impact energies of 600 and 1200eV by a binary (e, 2e) spectrometer. The experimental momentum profiles of the HOMO orbital are compared with the theoretical momentum distribution calculated using the Hartree--Fock and density functional theory methods with various basis sets. However, none of these calculations gives a completely satisfactory description of the momentum distributions of the HOMO 7b₂. The inadequacy of the calculations could result in the intensity difference of the second maximum at p～1.2a.u. between the experiment and the theory. The discrepancy between experimental and theoretical data in the low-momentum region is explained with the distorted wave effect.