Electron-momentum-specific valence-shell electronic structure of and many-body effects in cis-dichloroethylene: Ionic-state-resolved orientationally averaged electron momentum density measurement by symmetric noncoplanar (e,2e) spectroscopy

Abstract

The ionization energy (IE) spectra and electron momentum distributions (MDs) of the valence shell of cis-dichloroethylene have been obtained using symmetric noncoplanar (e,2e) spectroscopy. The IE spectra were found to be in good accord with earlier photoelectron data and in qualitative agreement with a literature pole-strength spectrum generated by a Green’s function (GF) calculation. In particular, extensive many-body features were observed above ∼22 eV in the IE spectra and found to be consistent with the pole-strength splitting of the three innermost valence states (7a1)−1, (6b2)−1, and (6a1)−1, as predicted by the GF calculation. The measured MDs were compared with ab initio calculations using self-consistent-field wave functions of 4-31G, 6-31G, and 6-31++G** basis sets. The general lack of quantitative agreement between experiment and calculations indicated the need for improved wave functions beyond the 6-31++G** level for the outer-valence orbitals. Moreover, the experimental MDs have provided an unambiguous assignment of the ordering of the D(8b2)−1 and E(2b1)−1 ionic states. A new satellite feature at ∼21 eV was found to have a MD similar to that of the H(7b2)−1 state, confirming the GF result. Furthermore, the many-body features above 26 eV were dominated by s-type angular dependence and could be ascribed predominantly to ionization of the innermost valence orbital 6a1. Finally, the bonding morphology of the valence orbitals was found to be different from other related ethylene derivatives due to ligand substitution effects.