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

Abstract

A study of the electronic structure of the complete valence shell of allene (1,2-propadiene) is reported. New high-resolution binding-energy spectra were measured in the energy regime 6-34.5 eV over a range of different target electron momenta, so that momentum distributions (MDs) could be determined for each molecular orbital. These data supersede the low-resolution work of Braidwood et al. [J Phys B 27 (1994[J Phys B 27 ( ) 2075[J Phys B 27 ( -2087, and also clarify some ambiguities with the earlier results. Theoretical MDs were calculated using a plane wave impulse approximation (PWIA) model for the reaction mechanism and density functional theory (DFT) for the wave function. Three basis sets, at the local spin density (LSD) approximation level and, additionally, incorporating nonlocal corrections such as the generalized gradient approximation (GGA), were studied. A critical comparison between the experimental and theoretical MDs was made, and it allowed us to determine the "optimum" wave function for allene from the basis sets we considered. This wave function is then used to derive allene's chemically interesting molecular properties. A summary of some of these results and a comparison of them with those of other workers is also presented with the level of agreement typically being good.

Understanding glycine conformation through molecular orbitals

“…1 ͑conformers I, II, III, and IV͒. [14][15][16][18][19][20][21][22][23] Based on the individual conformer geometries, three parallel calculations, namely, RHF/TZVP, OVGF/TZVP, and DFT-SAOP/ATZP were conducted for molecular properties, such as outer valence VIEs and dipole moments. [14][15][16][18][19][20][21][22][23] Based on the individual conformer geometries, three parallel calculations, namely, RHF/TZVP, OVGF/TZVP, and DFT-SAOP/ATZP were conducted for molecular properties, such as outer valence VIEs and dipole moments.…”

High-resolution electron momentum spectroscopy of molecules

“…This SCF calculation used the optimised structural geometry of Wiberg. 39 Some of the DFT results we obtained, 17 for the ground electronic state of allene, with the DZVP, DZVP2 and TZVP basis sets and XC functionals are summarised in Tables 1 and 2. It is clear from these tables that the calculated electronic structure and the calculated harmonic vibrational frequencies are rather sensitive to the basis set and XC functional used in the computation.…”

“…"peak", which they had to include in their analysis to account for the measured coincidence signal in their binding-energy spectra, could arise due to either the low energy resolution employed by Braidwood et al, 62 making the unique spectral deconvolution of overlapping features problematic, and/or as a result of employing Gaussian functions in their 62 spectral deconvolution whereas the line profiles could in principle be quite asymmetric. Consequently Wang et al 17 performed new high-resolution (∆E res ≈ 0.49 eV FWHM) EMS measurements, under almost identical kinematic conditions as Braidwood et al, in order to resolve some of these ambiguities and also to provide a stringent cross check for the previously reported MDs. In addition, Wang et al 17 also used their measurements to investigate the validity of the spectroscopic sum rule (see eqn.…”

“…Consequently Wang et al 17 performed new high-resolution (∆E res ≈ 0.49 eV FWHM) EMS measurements, under almost identical kinematic conditions as Braidwood et al, in order to resolve some of these ambiguities and also to provide a stringent cross check for the previously reported MDs. In addition, Wang et al 17 also used their measurements to investigate the validity of the spectroscopic sum rule (see eqn. ( 8)) for allene, which was the first time this was attempted for molecules.…”

“…HREMS of atoms and molecules originated at Flinders University in 1997 with the commissioning of their (e,2e) monochromator. 12, 13 Since that time it has been applied to several atoms 14 and molecules, [15][16][17][18] with its particular importance being that it has enabled conventional EMS to be extended to larger molecules, which are often the species where questions pertaining to the nature of their chemical bonding remain open.…”