Study of the valence electronic structure of the diene class of compounds by electron momentum spectroscopy and Green function methods. I. 1,2-propadiene

Abstract

The complete valence-shell electron separation-energy spectra and momentum distributions are measured for 1,2-propadiene by high momentum-resolution electron-momentum spectroscopy at a total energy of 1500 eV. Many-body calculations of the separation energies and spectroscopic factors using Green function methods are carried out and, for the binding energies, compared with the experimental data. The measured momentum distributions are compared with those calculated in the plane-wave impulse approximation (PWIA) formalism using two respective SCF orbital wavefunctions, the second of which includes d-functions in the basis set. The agreement between the measured momentum distributions and the PWIA-SCF orbital-momentum distributions is, in general, fair, although for the outermost orbitals the SCF wavefunctions underestimate the density at low momentum. The inner valence 1b2 and 1a1 orbitals are found to be severely split by final-state correlation effects.

A high‐resolution electron momentum spectroscopy and density functional theory study into the complete valence electronic structure of allene

“…As such, it is the simplest hydrocarbon to contain two double bonds. Interest in the electronic structure of allene, due in part to its unique ground‐state molecular geometry,1, 2 prompted Braidwood et al3 to undertake the first electron momentum spectroscopy (EMS) study into its properties. Photoelectron spectroscopy (PES) interest in allene is also highlighted by the work of Baker and Turner,4 Thomas and Thompson,5 Bieri et al,6 Yang et al,7 and Baltzer et al8…”

“…Braidwood et al3 measured binding‐energy (ϵ i ) spectra of allene using their low‐resolution noncoplanar symmetric electron‐coincidence spectrometer. The energy resolution (Δ E res ) in that study was 1.40 eV, full width at half maximum (FWHM), and the angular resolution was 1.2° (FWHM).…”

“…Binding‐energy spectra were taken at each ϕ over the energy range ϵ i =8–40 eV using the binning mode 9. From such spectra Braidwood et al3 derived momentum distributions (MDs) for the 2e, 1e+2b 2 2a 1 , 1b 2 , and 1a 1 valence molecular orbitals (MOs). Note that three independent measurements for the MDs were made by Braidwood et al, the MD data for each run being consistent with the results of the others for all MOs.…”

“…Note that three independent measurements for the MDs were made by Braidwood et al, the MD data for each run being consistent with the results of the others for all MOs. Theoretical MDs were also calculated by Braidwood et al3 using a plane wave impulse approximation (PWIA) description for the ionization mechanism9 and a Hartree–Fock (HF) wave function constructed from the GAMESS program 10. Braidwood et al3 found only marginal agreement between their measured and calculated MDs with an illustrative and representative example of this for the 2e highest‐occupied molecular orbital (HOMO) of allene being given in Figure 1.…”

“…Theoretical MDs were also calculated by Braidwood et al3 using a plane wave impulse approximation (PWIA) description for the ionization mechanism9 and a Hartree–Fock (HF) wave function constructed from the GAMESS program 10. Braidwood et al3 found only marginal agreement between their measured and calculated MDs with an illustrative and representative example of this for the 2e highest‐occupied molecular orbital (HOMO) of allene being given in Figure 1. One possible reason for this discrepancy, between the theory and experimental MDs, was that their STO‐3G basis was an inadequate representation for the 2e MO.…”