scholarly journals A Procedure to Determine Dyson Orbitals from Electron Momentum Spectroscopy: Application to 1,2-Propadiene, 1,3-Butadiene, Cyclopropane and [1.1.1]Propellane

1998 ◽  
Vol 51 (4) ◽  
pp. 691 ◽  
Author(s):  
R. J. F. Nicholson ◽  
I. E. McCarthy ◽  
M. J. Brunger
Keyword(s):  
Inverse Method ◽  
Impulse Approximation ◽  
Reaction Model ◽  
Electron Momentum ◽  
Plane Wave Impulse Approximation ◽  
Molecular Systems ◽  
Hartree Fock ◽  
Fitting Procedure ◽  
Electron Momentum Spectroscopy ◽  
Measured Momentum

We employ a numerical inverse method of extracting the target-ion overlap, or normalised Dyson orbital, directly from experimental electron momentum spectroscopy data by using a quantum- mechanically constrained statistical fitting procedure. This method is used in conjunction with the previously verified, for molecular targets, plane wave impulse approximation (PWIA) reaction model. The present procedure was applied to previously measured momentum distributions (MDs) for the 2e′ and 1e′ valence orbitals of cyclopropane, the 7ag orbital of trans 1,3-butadiene, the 2e orbital of 1,2-propadiene and the 3a′1 orbital of [1.1.1]propellane. We note that this is the first extensive application of the present method to organic molecular systems. In each case the derived normalised Dyson orbital provided a superior representation of the experimental MD than did the corresponding Hartree-Fock orbital. The ramifications of this result are discussed in the text.

scholarly journals Application of DFT and EMS to the Study of Strained Organic Molecules

1998 ◽  
Vol 51 (4) ◽  
pp. 707 ◽  
Author(s):  
W. Adcock ◽  
M. J. Brunger ◽  
M. T. Michalewicz ◽  
D. A. Winkler
Keyword(s):  
Wave Function ◽  
Density Functional ◽  
Impulse Approximation ◽  
Basis Sets ◽  
Functional Theory ◽  
Electron Momentum ◽  
Plane Wave Impulse Approximation ◽  
Electron Momentum Spectroscopy ◽  
Momentum Distributions ◽  
Self Consistent Field

Electron momentum spectroscopy (EMS) studies of the valence shells of [1.1.1]propellane, 1,3-butadiene, ethylene oxide and cubane are reviewed. Binding energy spectra were measured in the energy regime of 3·5–46·5 eV over a range of different target electron momenta, so that momentum distributions (MDs) could be determined for each ion state. Each experimental electron momentum distribution is compared with those calculated in the plane wave impulse approximation (PWIA) using both a triple-? plus polarisation level self-consistent field (SCF) wave function and a further range of basis sets as calculated using density functional theory (DFT). A critical comparison between the experimental and theoretical momentum distributions allows us to determine the ‘optimum’ wave function for each molecule from the basis sets we studied. This ‘optimum’ wave function then allows us to investigate chemically or biologically significant molecular properties of these molecules. EMS-DFT also shows promise in elucidating the character of molecular orbitals and the hybridisation state of atoms.

scholarly journals Satellite Intensities in Photoelectron Spectroscopy and Electron Momentum Spectroscopy-Synchrotron Radiation Studies of Argon 3s and Xenon 5s Photoionisation (hv - 60?130 eV)

1986 ◽  
Vol 39 (5) ◽  
pp. 565 ◽  
Author(s):  
CE Brion ◽  
KH Tan
Keyword(s):  
Synchrotron Radiation ◽  
Photon Energy ◽  
Photoelectron Spectroscopy ◽  
Impulse Approximation ◽  
Main Line ◽  
Magic Angle ◽  
Electron Momentum ◽  
X Ray ◽  
Plane Wave Impulse Approximation ◽  
Electron Momentum Spectroscopy

Binding energy spectra for the main line, satellite lines and associated double ionization continuum for argon 3s and xenon 5s photoionisation have been measured in the photon energy range 60-130 eV using monochromatised synchrotron radiation and magic angle photoelectron spectroscopy. In particular the ratio of satellite to main line intensities has been investigated and compared with the results of earlier experiments using X-ray and ultraviolet photoelectron spectroscopy as well as with recent measurements by electron momentum [i.e. binary (e,2e)] spectroscopy. The results of the presently reported photoelectron measurements show that the satellite intensity relative to that of the main ns -1 line increases with increasing photon energy and approaches the value given by electron momentum spectroscopy. These findings are contrary to predictions based on recent calculations of photoelectron intensities. The present work lends support to the direct interpretation of satellite intensities (pole strengths or spectroscopic factors) in binary� (e, 2e) spectroscopy using the plane wave impulse approximation. The need for improved calculations of photoionisation intensities as well as further photoelectron measurements in the X-ray region is stressed.

Electron momentum spectroscopy experiments and calculations for the production of excited states of He+ and

1996 ◽  
Vol 74 (11-12) ◽  
pp. 748-756 ◽  
Author(s):  
N. Lermer ◽  
B. R. Todd ◽  
N. M. Cann ◽  
C. E. Brion ◽  
Y. Zheng ◽  
...  
Keyword(s):  
Excited States ◽  
Cross Section ◽  
Cross Sections ◽  
Impulse Approximation ◽  
Final State ◽  
Electron Momentum ◽  
Plane Wave Impulse Approximation ◽  
Highly Sensitive ◽  
Electron Momentum Spectroscopy ◽  
Explicitly Correlated

The (e,2e) cross-section for transitions to the n = 2 final state of He+ and the 2sσg, final state of [Formula: see text] have been measured, relative to the cross-section for the transitions to the respective ground state ions, using a highly sensitive momentum dispersive multichannel electron momentum spectrometer. The experimental results for He are compared with plane wave impulse approximation (PWIA) cross-section calculations carried out using two previously published GI wavefunctions and also with two cross-section calculations based on explicitly correlated wavefunctions with energy errors of less than 10 nHartree. The H2 results are compared with calculations by J.W. Liu and V.H. Smith Jr. (Phys. Rev. A, 31, 3003 (1985); erratum: Phys. Rev. A, 39, 3703 (1989)). For both He and H2, significant differences are observed between the measured relative cross-sections and those calculated using the PWIA. While the measurements for He differ from previous work, the results for H2 are consistent with some earlier measurements.

scholarly journals Electron Momentum Spectroscopy

1986 ◽  
Vol 39 (5) ◽  
pp. 587 ◽  
Author(s):  
IE McCarthy
Keyword(s):  
Impulse Approximation ◽  
High Electron ◽  
Final States ◽  
Final State ◽  
Structure Information ◽  
Plane Wave Impulse Approximation ◽  
Ion Structure ◽  
Spectroscopic Factors ◽  
Electron Momentum Spectroscopy ◽  
Energy And Momentum

For sufficiently high electron energies (greater than a few hundred eV) and sufficiently low recoil momenta Oess than a few atomic units) the differential cross section for the non-coplanar symmetric (e,2e) reaction on an atom or molecule depends on the target and ion structure only through the target-ion overlap. Experimental criteria for the energy and momentum are that the apparent structure information does not change when the energy and momentum are varied. The plane-wave impulse approximation is a sufficient description of the reaction mechanism for determining spherically averaged squares of momentum-space orbitals for atoms and molecules and for coefficients describing initial- and final-state correlations. For mainly uncorrelated initial states, spectroscopic factors for final states belonging to the same manifold are uniquely determined. For molecules, summed spectroscopic factors can be compared for different ion manifolds. For atoms, summed spectroscopic factors and higher-momentum profiles require the dist~rted-wave impulse approximation.

EMS studies of larger molecules of chemical and biochemical interest

1996 ◽  
Vol 74 (11-12) ◽  
pp. 773-781 ◽  
Author(s):  
J. J. Neville ◽  
Y. Zheng ◽  
B. P. Hollebone ◽  
N. M. Cann ◽  
C. E. Brion ◽  
...  
Keyword(s):  
Density Functional ◽  
Polyatomic Molecules ◽  
Target Compound ◽  
Frontier Orbitals ◽  
Functional Theory ◽  
Electron Momentum ◽  
Hartree Fock ◽  
Electron Momentum Spectroscopy ◽  
Key Factor ◽  
Increased Sensitivity

The challenges involved in extending electron momentum spectroscopy (EMS) studies beyond small polyatomic molecules to more complicated systems are discussed. EMS results for the highest occupied (frontier) molecular orbitals of glycine (NH2CH2COOH) and dimethoxymethane ((CH3O)2CH2) demonstrate possible approaches to overcoming such challenges as closely spaced valence orbitals, low volatility, and the conformational mobility of the target compound. The increased sensitivity available from recently developed multichannel electron momentum spectrometers is a key factor in overcoming these challenges and making such EMS studies feasible. The utility of Kohn–Sham density functional theory (DFT) for EMS calculations on larger molecules such as glycine and dimethoxymethane using the recently formulated target Kohn–Sham approximation is also investigated as experimental momentum profiles are compared with theoretical momentum profiles generated via Kohn–Sham DFT and a range of Hartree–Fock calculations. The Kohn–Sham DFT calculations provide better agreement with experiment for the frontier orbitals of glycine and dimethoxymethane than even the near Hartree–Fock limit results.

Quantitative treatment for extracting coherent elastic scattering from X-ray scattering experiments

1999 ◽  
Vol 32 (2) ◽  
pp. 322-326 ◽  
Author(s):  
Khalid Laaziri ◽  
J. L. Robertson ◽  
S. Roorda ◽  
M. Chicoine ◽  
S. Kycia ◽  
...  
Keyword(s):  
Impulse Approximation ◽  
Coherent Scattering ◽  
High Energy ◽  
Compton Profile ◽  
Detector Resolution ◽  
X Ray ◽  
Hartree Fock ◽  
Fitting Procedure ◽  
X Ray Scattering ◽  
Peak Function

A fitting procedure for separating the inelastic and elastic contributions to the total scattering in diffuse-scattering experiments at high energy using energy-dispersive X-ray techniques is presented. An asymmetric peak function is used to model the elastic peak. The inelastic scattering peak is modeled using a theoretical Compton profile, calculated using the impulse approximation (Hartree–Fock wave functions were used), convoluted with the detector resolution. This procedure, which requires only two free parameters, is shown to be extremely effective in extracting the integrated elastic intensity of coherent scattering at each wave vector, even at low scattering angles where the Compton scattering is not well resolved.

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