Coexistence of 1,3-butadiene conformers in ionization energies and Dyson orbitals

Abstract

The minimum-energy structures on the torsional potential-energy surface of 1,3-butadiene have been studied quantum mechanically using a range of models including ab initio Hartree-Fock and second-order Møller-Plesset theories, outer valence Green's function, and density-functional theory with a hybrid functional and statistical average orbital potential model in order to understand the binding-energy ͑ionization energy͒ spectra and orbital cross sections observed by experiments. The unique full geometry optimization process locates the s-trans-1,3-butadiene as the global minimum structure and the s-gauche-1,3-butadiene as the local minimum structure. The latter possesses the dihedral angle of the central carbon bond of 32.81°in agreement with the range of 30°-41°obtained by other theoretical models. Ionization energies in the outer valence space of the conformer pair have been obtained using Hartree-Fock, outer valence Green's function, and density-functional ͑statistical average orbital potentials͒ models, respectively. The Hartree-Fock results indicate that electron correlation ͑and orbital relaxation͒ effects become more significant towards the inner shell. The spectroscopic pole strengths calculated in the Green's function model are in the range of 0.85-0.91, suggesting that the independent particle picture is a good approximation in the present study. The binding energies from the density-functional ͑statisticaly averaged orbital potential͒ model are in good agreement with photoelectron spectroscopy, and the simulated Dyson orbitals in momentum space approximated by the density-functional orbitals using plane-wave impulse approximation agree well with those from experimental electron momentum spectroscopy. The coexistence of the conformer pair under the experimental conditions is supported by the approximated experimental binding-energy spectra due to the split conformer orbital energies, as well as the orbital momentum distributions of the mixed conformer pair observed in the orbital cross sections of electron momentum spectroscopy.

Intrinsic Information Content of NMR Dipolar Couplings: A Conformational Investigation of 1,3‐Butadiene in a Nematic Phase

“…Here, we will discuss with some details what was obtained when using the U int ({f}) value of ref. [7], calculated at the MP2/cc-pVTZ level (anyway, very similar results were obtained when using U int ({f}) from more recent theoretical investigations [9,11,12] ). The two distributions differ slightly in the 908 < f < 1808 range in that the experimental curve is more peaked at a lower f with respect to the quantum mechanical calculations; the latter technique predicts also a higher population of the planar s-cis form.…”

Intramolecular interactions of L‐phenylalanine: Valence ionization spectra and orbital momentum distributions of its fragment molecules

“…53,[55][56][57] For benzene, the ionization energies generated by the SAOP/TZ2P model exhibit comparable accuracy of the more sophisticated ADC(3) and OVGF/TZVP models and agree well with the experiment in almost the entire valence spectrum. It is a known fact that the SAOP model produces less accurate vertical IP for the highest occupied molecular orbitals (HOMO) for some molecules, [58][59][60] although this is not the case for alkanes (Yang et al, in preparation). As seen in Table 2, the SAOP model overesti- mates vertical ionization energies of the three outermost states of benzene.…”

Valence orbital response to pseudorotation of tetrahydrofuran: A snapshot using dual space analysis

“…The orbital symmetries of these conformations produced by the pseudorotation exhibit changes in point groups quite different from those produced by conformers arising from rotations around a single bond such as n-butane. 2,4,40 The conformers of THF represent the local minima which connect via the C 1 transition state on the PES.…”

“…1 As another example, the determination of torsional potentials around the C-C single bond in 1,3-butadiene and conjugated systems still remains a very active research area. 2 Indeed, understanding the equilibrium between the s-trans and s-cis conformers is an important factor when rationalizing the mechanism involved in fundamental reactions in organic chemistry such as cheletropic and Diels-Alder cycloadditions. 3 As a biological illustration of the importance of conformational analysis one could mention that experimental and theoretical conformational studies on biomolecules, such as amino acids, have been the focus of a great deal of attention in recent literature because of their biological significance as building blocks of peptides and proteins.…”