A joint experimental and theoretical study of the valence electron momentum distributions of trans-stilbene

Abstract

This paper reports an experimental and theoretical study on the valence orbital momentum distributions of trans-stilbene. Experimentally, an (e, 2e) electron-impact ionization measurement is performed to obtain momentum profiles of the outer valence orbitals. Theoretically, calculations of the momentum profiles are carried out at the level of density functional theory, including the influences of thermally induced torsional motions of phenyl rings as well as contributions from other vibrational modes. The theoretical analysis shows that despite the structural flexibility of trans-stilbene, molecular vibration does not significantly affect the momentum profiles. The experimental results for the high-lying occupied π orbitals reveal that the position of the maximum in each momentum profile reflects the bonding character of the corresponding orbital. It provides a basis to apply electron momentum spectroscopy to large π-conjugated molecules, such as oligomers of conducting polymers.