Showing papers by "Michael J. Brunger published in 2005"

Positron and electron scattering from tetrahydrofuran

Abstract: We report results of total cross-section measurements for positron and electron scattering from the chemically and biologically important molecule tetrahydrofuran. We believe this is the first time such data have been reported in the literature. The positron measurements were conducted over the energy range of 0.1–20.0 eV, with the cross section being found to be strongly peaked at the lower energies. The electron energy range was 2–21 eV, with this cross section's main feature being a broad shape resonance with a peak at ~7.5 eV.

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 Moller-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 energy) 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 potentials) mod...

Investigation into the valence electronic structure of norbornene using electron momentum spectroscopy, Green's function, and density functional theories.

Abstract: Results of a study of the valence electronic structure of norbornene (C7H10), up to binding energies of 30 eV, are reported. Experimental electron momentum spectroscopy (EMS) and theoretical Green's function and density functional theory approaches were utilized in this investigation. A stringent comparison between the electron momentum spectroscopy and theoretical orbital momentum distributions found that, among the tested models, the combination of the Becke−Perdew functional and a polarized valence basis set of triple-ζ quality provides the best representation of the electron momentum distributions for all 19 valence orbitals of norbornene. This experimentally validated model was then used to extract other molecular properties of norbornene (geometry, infrared spectrum). When these calculated properties are compared to corresponding results from independent measurements, reasonable agreement is typically found. Due to the improved energy resolution, EMS is now at a stage to very finely image the effect...