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1992

Atomic, Molecular and Optical Physics

Articles 1 - 11 of 11

Full-Text Articles in Physics

Collisional Detachment Of Anions Using Fourier Transform Mass Spectrometry, Kevin B. Riehl Dec 1992

Collisional Detachment Of Anions Using Fourier Transform Mass Spectrometry, Kevin B. Riehl

Theses and Dissertations

Fourier Transform Mass Spectrometry (FTMS) is used to make energy resolved ion-neutral reaction measurements at high translational energies (up to several hundred eV). The technique is demonstrated for collisional detachment of anions, and should be easily applied to other inelastic reactions. Collisional detachment cross sections of iodine anions onto gas phase targets of neon, xenon, and trifluoromethyl iodide are measured for 1-300 eV (lab frame). Peak detachment cross sections are roughly 2, 8.5, and 7 Å2, respectively. Ion kinetic measurements show the iodine anion is unreactive in trifluoromethyl iodide at thermal energies. Positive ion chemistry is consistent with …

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Construction Of A Lithium Vapor Oven For Electron Capture And Multiple Ionization Experiments, Oliver Woitke Aug 1992

Construction Of A Lithium Vapor Oven For Electron Capture And Multiple Ionization Experiments, Oliver Woitke

Masters Theses

A Li vapor oven, to be used as a source of Li target atoms in electron capture and multiple ionization experiments, was designed and installed in the beamline of the Van de Graaff accelerator at Western Michigan University. The oven was tested using two different projectile beams, protons and He+. The test results indicate that Li evaporated from the oven in the form of a cloud rather than as a jet spray. For He+ colliding with Li it was found that the projectile single-electron loss yield is about three orders of magnitude larger than the single-electron capture yield, as expected …

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Investigation Of Alignment Dynamics In Mg-Ne And Mg-Ar Two-Photon Fractional Collisions, David Allen Olsgaard Jul 1992

Investigation Of Alignment Dynamics In Mg-Ne And Mg-Ar Two-Photon Fractional Collisions, David Allen Olsgaard

Physics Theses & Dissertations

A new technique is used to observe the dynamics of electronic alignment in a dissociating collision complex. The technique requires the absorption of two optical photons during a single binary collision. Two exciting light fields are tuned into the wings of the 3s1s0-3p1 and 3p1p1-5s1s0 resonances of Mg where strong collisions with rare gas atoms induce transitions between corresponding molecular states. The alignment produced in the intermediate state by the first excitation is probed by the second laser as a function of relative linear laser polarization and laser …

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Direct Measurement Of The Van Der Waals Interaction Between An Atom And Its Images In A Micron-Sized Cavity, V. Sandoghdar, C. I. Sukenik, E. A. Hinds, S. Haroche Jun 1992

Direct Measurement Of The Van Der Waals Interaction Between An Atom And Its Images In A Micron-Sized Cavity, V. Sandoghdar, C. I. Sukenik, E. A. Hinds, S. Haroche

Physics Faculty Publications

The authors have measured by laser spectroscopy the energy of interaction between a sodium atom and its images in the walls of a micron-sized cavity. This cavity-QED study is the first direct quantitative test of the Lennard-Jones van der Waals interaction as a function of controlled atom-surface separation and mean-square electric dipole moment.

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Tamm States In Finite Semiconductor Superlattices: Influence Of Accumulation And Depletion Layers, Roger H. Yu May 1992

Tamm States In Finite Semiconductor Superlattices: Influence Of Accumulation And Depletion Layers, Roger H. Yu

All Faculty Scholarship for the College of the Sciences

We discuss the electronic-level structure of finite semiconductor superlattices and the influence of accumulation and depletion regions on the surface localized states (Tamm states). Exact solutions of the Poisson and Schrödinger equations are obtained self-consistently, through use of a nonuniform jellium model. Both high-energy and low-energy Tamm states are found.

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Evidence For Atomic Processes In Molecular Valence Double Ionization, U. Becker, Oliver Hemmers, B. Langer, A. Menzel, R. Wehlitz, W. B. Peatman Feb 1992

Evidence For Atomic Processes In Molecular Valence Double Ionization, U. Becker, Oliver Hemmers, B. Langer, A. Menzel, R. Wehlitz, W. B. Peatman

Environmental Studies Faculty Publications

Complete molecular valence-electron spectra were measured for CO. Unexpectedly, discrete lines at low kinetic energies were found, superimposed on a continuous energy spectrum representing direct double-ionization processes. The appearance of these lines is discussed in the context of the formation of the C++O+ ion pair near its associated threshold at 38.4 eV. It is ascribed to valence-excited repulsive (CO+)* states, which dissociate to a large part rapidly into atomic fragments before electronic relaxation takes place. From our spectra, partial cross sections for the different processes leading to dissociative valence double ionization are derived.

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Auger Spectra And Band Structure Of La1.85Sr0.15Cuo4 And La1.85Ba0.15Cuo4, R. Bar-Deroma, J. Felsteiner, R. Brener, J. Ashkenazi, D. Van Der Marel Jan 1992

Auger Spectra And Band Structure Of La1.85Sr0.15Cuo4 And La1.85Ba0.15Cuo4, R. Bar-Deroma, J. Felsteiner, R. Brener, J. Ashkenazi, D. Van Der Marel

Physics Articles and Papers

High-resolution Auger electron spectra of La1.85Sr0.15CuO4 and La1.85Ba0.15CuO4 have been measured. The experimental Auger line shapes of the oxygen KLL and copper L2,3VV transitions are compared with those generated from local-density-approximation linear-muffin-tin-orbital band-structure calculations. An analysis based on this comparison is used to determine the Coulomb parameters Up and Ud of the oxygen and copper atoms, respectively. For this purpose, an extended version of Cini and Sawatzky’s expression for the theoretical Auger line shape is used, taking into account the multiplet structure of the Auger final …

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Magnetism With Generalized-Gradient-Approximation Density Functionals, D.J. Singh, J. Ashkenazi Jan 1992

Magnetism With Generalized-Gradient-Approximation Density Functionals, D.J. Singh, J. Ashkenazi

Physics Articles and Papers

We report generalized-gradient-approximation (GGA) density-functional studies of Cr, V, and Pd, using an all-electron, general-potential linearized-augmented-plane-wave technique. These calculations were undertaken in order to assess the utility of the GGA as an improvement over the local-density approximation in describing transition-metal magnetism. It is found that although the tendency towards magnetism is enhanced, both V and Pd are correctly predicted to be nonmagnetic with the recent GGA functional of Perdew (PW GGA-II) as with the Langreth-Mehl-Hu (LM) functional. Calculations for commensurate antiferromagnetic Cr show that the PW GGA-II predicts an overly large moment of 1.4μB while the LM functional yields …

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Nonuniversality In The Kondo Effect, M. Naghashpour, S. E. Barnes Jan 1992

Nonuniversality In The Kondo Effect, M. Naghashpour, S. E. Barnes

Physics Articles and Papers

We have analytically evaluated, up to fourth order, all logarithmic terms in the perturbation expansion of the magnetization scrM for the Kondo model. All nonlogarithmic terms have been evaluated up to third order. When these results are compared with the claimed universal function scrM(H/TH) calculated with the Bethe ansatz, we find that the two cannot be made to agree whatever the form of TH. We conclude that such universal functions do not exist.

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Density Effect In Cu K-Shell Ionization By 5.1-Gev Electrons, W. E. Meyerhof, D. G. Jensen, D. M. Kawall, S. E. Kuhn, D. W. Spooner, Z. E. Meziani, D.. N. Faust Jan 1992

Density Effect In Cu K-Shell Ionization By 5.1-Gev Electrons, W. E. Meyerhof, D. G. Jensen, D. M. Kawall, S. E. Kuhn, D. W. Spooner, Z. E. Meziani, D.. N. Faust

Physics Faculty Publications

We have made an absolute measurement of the Cu K-shell impact ionization cross section by 5.1-GeV electrons, which demonstrates directly a density effect predicted by Fermi in 1940. By determining the ratio of the K x-ray yield from a thin front and back layer of the target by a novel grazing emission method, we have verified the effect of transition radiation on the x-ray production, suggested by Sorensen and reported by Bak et al.

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Formation And Desorption Of Negative Ions From Metal Surfaces, Douglas Hugh Baker Jan 1992

Formation And Desorption Of Negative Ions From Metal Surfaces, Douglas Hugh Baker

Dissertations, Theses, and Masters Projects

Investigations of negative ion and electron emission from gas-covered metal surfaces due to the impact of low energy (30-300 eV) positive ions and, separately, photons (2-5 eV) are presented. In both cases, the negative ion formation process is thought to occur via electron tunneling from the surface or its substrate to a sputtered or photodesorbed neutral atom or molecule.;In particular, absolute total negative ion and electron yields for collisions of positive alkali ions with a gas-covered Mo substrate have been measured. Mass analysis of the sputtered negative ions show that O{dollar}\sb2\sp-{dollar} is the dominant ion at low impact energies. This …

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