Atomic, Molecular and Optical Physics Commons^™

Measurement Of The Casimir-Polder Force, C. I. Sukenik, M. G. Boshier, S. Cho, V. Sandoghdar, E. A. Hinds

Physics Faculty Publications

The authors have studied the deflection of ground-state sodium atoms passing through a micron-sized parallel-plate cavity by measuring the intensity of a sodium atomic beam transmitted through the cavity as a function of cavity plate separation. This experiment provides clear evidence for the existence of the Casimir-Polder force, which is due to modification of the ground-state Lamb shift in the confined space of a cavity. The results confirm the magnitude of the force and the distance dependence predicted by quantum electrodynamics.

Temporal Development Of Electric Field Structures In Photoconductive Gaas Switches, K. H. Schoenbach, J. S. Kenney, F.E. Peterkin, R. J. Allen

Bioelectrics Publications

The temporal development of the electric field distribution in semi‐insulating GaAs photoconductive switches operated in the linear and lock‐on mode has been studied. The field structure was obtained by recording a change in the absorption pattern of the switch due to the Franz–Keldysh effect at a wavelength near the band edge of GaAs. In the linear mode, a high field layer develops at the cathode contact after laser activation. With increasing applied voltage, domainlike structures become visible in the anode region and the switch transits into the lock‐on state, a permanent filamentary electrical discharge. Calibration measurements show the field intensity …

High-Energy Behavior Of The Double Photoionization Of Helium From 2 To 12 Kev, Jon C. Levin, Ivan A. Sellin, B. M. Johnson, Dennis W. Lindle, R. D. Miller, Y. Azuma, H. G. Berry, D.-H. Lee, N. Berrah

Chemistry and Biochemistry Faculty Research

We report the ratio of double-to-single photoionization of He at several photon energies from 2 to 12 keV. By time-of-Aight methods, we find a ratio consistent with an asymptote at 1.5%±0.2%, essentially reached by h v≈4 keV. Fair agreement is obtained with older shake calculations of Byron and Joachain [Phys. Rev. 164, 1 (1967)], of Aberg [Phys. Rev. A 2, 1726 (1970)], and with recent many-body perturbation theory (MBPT) of Ishihara, Hino, and McGuire [Phys. Rev. A 44, 6980 (1991)]. The result lies below earlier MPBT calculations by Amusia et al. [J. Phys. B 8 …

Determination Of The Neutron Spin Structure Function, P. L. Anthony, R. G. Arnold, H. R. Band, H. Borel, P.E. Bosted, V. Breton, G. D. Cates, T. E. Chupp, F. S. Dietrich, J. Dunne, R. Erbacher, J. Fellbaum, H. Fonvielle, R. Gearhart, R. Holmes, E. W. Hughes, J. R. Johnson, D. Kawall, C. Keppel, S. E. Kuhn, R. M. Lombard-Nelsen, J. Marroncle, T. Maruyama, W. Meyer, Z. E. Meziani, H. Middleton, J. Morgenstern, N. R. Newbury, G. G. Petratos, R. Pitthan, R. Prepost, Y. Roblin, S. E. Rock, S. H. Rokni, G. Shapiro, T. Smith, P. A. Souder, M. Spengos, F. Staley, L. M. Stuart, Z. M. Szalata, Y. Terrien, A. K. Thompson, J. L. White, M. Woods, J. Xu, C. C. Young, G. Zapalac, E142 Collaboration

Physics Faculty Publications

The spin structure function of the neutron g₁ⁿ has been determined over the range 0.03 < x < 0.6 at an average Q² of 2 (GeV/c)² by measuring the asymmetry in deep inelastic scattering of polarized electrons from a polarized ³He target at energies between 19 and 26 GeV. The integral of the neutron spin structure function is found to be f-¹₀ gⁿ₁(x)dx = -0.022 ± 0.011. Earlier reported proton results together with the Bjorken sum rule predict f-¹₀ gⁿ₁(x)dx = -0.059 ± 0.019.

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 Ų, respectively. Ion kinetic measurements show the iodine anion is unreactive in trifluoromethyl iodide at thermal energies. Positive ion chemistry is consistent with …

Cathodoluminescence Spectroscopy Of Zinc Germanium Phosphide Zngep2, Michael R. Gregg

Theses and Dissertations

Zinc Germanium Phosphide (ZnGeP₂) is a nonlinear semiconductor suitable for use as a laser tuning element over the two to six micron wavelength range. Although this crystal has been studied in the past, its luminescent properties are not yet well understood. In this present study, ZnGeP₂ has been examined using cathodoluminescence spectroscopy (CL). Specifically, the spectral dependence of the CL was obtained as a function of electron beam energy, beam current and temperature. The resulting CL was found to be polarized with a peak structure that was dependent on the polarization. This peak structure observed by CL …

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 …

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 …

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.

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.

Design And Construction Of A Channel Electron Multiplier Based Mossbauer Spectroscopy System, Daniel J. Robbins

Theses and Dissertations

A channel electron multiplier (cem) detector system was designed and built to provide a signal to a Mossbauer spectroscopy system in an effort to obtain a better signal-to-noise ratio than achievable with a proportional counter system. Three cems are contained in a vacuum chamber built using standard components. Gamma, rays of 14.4-keV energy from a ⁵⁷Co source enter from outside the chamber through a window and are absorbed by an ⁵⁷Fe target near the cems. The target emits internal conversion electrons which are collected by the cems and a Mossbauer spectrometer collects the signal. The system produces a …

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.

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 La_1.85Sr_0.15CuO₄ and La_1.85Ba_0.15CuO₄ have been measured. The experimental Auger line shapes of the oxygen KLL and copper L_2,3VV 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 U_p and U_d 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 …

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 1.4μ_B while the LM functional yields …

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/T_H) calculated with the Bethe ansatz, we find that the two cannot be made to agree whatever the form of T_H. We conclude that such universal functions do not exist.

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.

Surface Structure Of √3x√3r 30 Cl/Ni(111) Determined Using Low-Temperature Angle-Resolved-Photoemission Extended Fine Structure, Li-Qiong Wang, Z. Hussain, Z. Q. Huang, A. E. Schach Von Wittenau, Dennis W. Lindle, D. A. Shirley

Chemistry and Biochemistry Faculty Research

A surface structural study of the √3 × √3 R30° Cl/Ni(111) adsorbate system was made using low-temperature angle-resolved photoemission extended fine structure. The experiments were performed along two emission directions, [111] and [110], and at two temperatures, 120 and 300 K. The multiple-scattering spherical-wave analysis determined that the Cl atom adsorbs in the fcc threefold hollow site, 1.837(8) Å above the first nickel layer, with a Cl-Ni bond length of 2.332(6) Å, and an approximate 5% contraction between the first and the second nickel layers (the errors in parentheses are statistical standard deviations only).

Formation Of Positronium In E+ + H- Collisions, Jack C. Straton, Richard J. Drachman

Physics Faculty Publications and Presentations

Cross sections for positronium formation by capture from the negative hydrogen ion are given. Orthogonalization corrections to the Coulomb (first-order) Born approximation (CBA) differential and total cross sections are calculated using approximate H- wave functions of both Löwdin [Phys. Rev. 90, 123 (1953)] and Chandrasekhar [Astrophys. J. 100, 176 (1944)]. The present calculation of the CBA cross sections using the post interaction for Löwdin’s wave function (LCBAPS) disagrees with the calculation of Choudhury, Mukherjee, and Sural (CMS) [Phys. Rev. A 33, 2358 (1986)], whereas our results using the prior interaction agree. Thus, where CMS found an order …

Resonant Electron Transfer And K-Shell Excitation Of Lithiumlike Projectiles In Collisions With Molecular Hydrogen, M. Anwar Kamal

Masters Theses

An experimental investigation of resonant transfer and excitation (RTE) for collisions of Mg⁹⁺ (lithiumlike) projectile ions with a molecular hydrogen gas target has been made. The experimental cross sections for projectile K-shell x rays coincident with electron capture in the energy of 33- to 60-MeV are found to be in good agreement with theoretical RTE calculations. The present results confirm the agreement between experiment and theory which has been reported for RTE involving K-shell excitation for projectiles with atomic numbers between 9 and 92 incident on H₂ and He targets.

Cross sections for total K-shell x-ray production and …

Electron-Energy And –Angular Distributions In The Double Photoionization Of Helium, R. Wehlitz, Franz Heiser, Oliver Hemmers, B. Langer, A. Menzel, U. Becker

Environmental Studies Faculty Publications

Photoelectron spectra of helium have been measured at different angles and at various energies above the double-ionization threshold up to 120 eV to investigate the behavior of the energy and angular distributions, of shake-off electrons. Both energy and angular distributions clearly show a U-shaped profile which turns to a flat curve near threshold pointing to a uniform intensity distribution over the kinetic energy for all angles in this excitation energy regime. Our results for the angular-distribution asymmetry parameter indicate qualitative agreement with theoretical predictions but fail to provide them quantitatively.

Gaseous Component Identification With Polymeric Film Sensor, Edward S. Kolesar Jr.

AFIT Patents

A sensor having an interdigitated gate electrode field effect transistor (IGEFET) coupled to an electron beam evaporated copper phthalocyanine thin film is used to selectively detect parts-per-billion concentration levels of atmosphere contaminants such as nitrogen dioxide (NO₂) and diisopropyl methylphosphonate (DIMP). The sensor is excited with a voltage pulse, and its time- and frequency-domain response are examined. The envelopes of the magnitude of the normalized difference frequency spectrums reveal features which unambiguously distinguish the NO₂ and DIMP exposures.

Anisotropy Of Polarized X-Ray Emission From Molecules, S. H. Southworth, Dennis W. Lindle, R. Mayer, P. L. Cowan

Chemistry and Biochemistry Faculty Research

Strongly anisotropic, polarized Cl K-V x-ray emission from gas-phase CF₃Cl has been observed following resonant excitation with a linearly polarized x-ray beam. Distinctively different angular distributions are observed for x-ray emission involving molecular orbitals of different symmetries. A classical model of the x-ray absorption-emission process accurately describes the observed radiation patterns.

Measurement Of The Ratio Of Double-To-Single Photoionization Of Helium At 2.8 Kev Using Synchrotron Radiation, Jon C. Levin, Dennis W. Lindle, N. Keller, R. D. Miller, Y. Azuma, N. Berrah Mansour, H. G. Berry, Ivan A. Sellin

Chemistry and Biochemistry Faculty Research

We report the first measurement of the ratio of double-to-single photoionization of helium well above the double-ionization threshold. Using a time-of-flight technique, we find He⁺⁺/He⁺=1.6±0.3% at hν=2.8 keV. This value lies between calculations by Amusia (2.3%) and by Samson, who predicts 1.2% by analogy with electron-impact ionization cross sections of singly charged ions. Good agreement is obtained with older shake calculations of Byron and Joachain, and of Åberg, who predict 1.7%.

Fock-Tani Hamiltonian For Reactions Involving Two-Electron Atoms, Jack C. Straton

Physics Faculty Publications and Presentations

The Fock-Tani Hamiltonian is found for scattering processes involving up to two ions and two electrons. Possible bound-state species include one or two electrons bound on an ion fixed at the origin, and a one-electron projectile atom. A diagrammatic technique is illustrated that simplifies the algebra of the transformation. Coulomb- or plane-wave states are automatically generated by the same asymptotic Hamiltonian for all arrangement channels.

Double Ionization Of Helium By Intermediate To High Velocity He+ Projectiles, Jun Forest

Masters Theses

Ionization of helium target atoms by He⁺ projectiles colliding with helium at energies of 0.125 to 3.0 MeV/u is investigated. Cross sections for single and double ionization, and ratios o f double-to-single ionization are determined for each outgoing projectile charge state, and are compared to previous studies. For the lowest energies investigated, the ratios are consistent with the two-step mechanism in which the projectile interacts separately with each target electron. At the highest energies, the ratios reach nearly constant values indicating approach to the high velocity limit. At these high energies, however, the ratios are all higher than the …

Resonant Electron Transfer And K-Shell Excitation Of FQ+ (Q=6,8) In Collisions With Neutral He And H2 Targets, Konstantinos E. Zaharakis

Masters Theses

Measurements of resonant transfer and excitation (RTE) were conducted for 16.5-38 MeV F⁶⁺ (Li-like) ions colliding with H₂. In the RTE process electron capture and projectile excitation take place simultaneously due to the electronelectron interaction. In previous work, for the same collision system, at the Oak Ridge National Laboratory (Oak Ridge, TN) , the magnitude of the measured RTE cross sections was found to be nearly a factor of two smaller than theory. In order to investigate RTE in F⁶⁺ H₂ collisions more completely, we undertook measurements at Western Michigan University using the EN tandem …

Double Excitation Of Helium By Fast Particles Of Charge Z, James H. Mcguire, Jack C. Straton

Physics Faculty Publications and Presentations

Results of calculations of double excitation of helium to n=2 states for fast projectiles of charge Z are presented. Nonzero Z³ contributions for single and double excitation occur only when time-ordering contributions from the second-order amplitude are nonzero. For double excitation, electron correlation must also be nonzero to obtain Z³ terms. The time-ordering effects arise from virtual off-energy-shell intermediate states. As with second-order amplitudes for Thomas singularities in electron capture, the energy-nonconserving amplitude is connected to the second-order energy-conserving amplitude by a dispersion relation. Comparison is made with experiment.

Rotationally Resolved Laser Spectroscopy Of The 3s2Σ+ ← 2p2ii Transition In 6li20ne And 7li20ne Van Der Waals Molecules, Chang Jae Lee

Physics Theses & Dissertations

The rotationally resolved absorption spectrum of the ⁶Li²⁰Ne and ⁷Li²⁰Ne 3s²Σ⁺ ← 2p² II transition has been observed. For each isotope, thirteen vibrational transitions from four vibrational levels (v"=0, 1, 2, and 3) of the lower 2p² II to six (v’=0, 1, 2, 3, 4, and 5) of the upper 3s*Σ⁺ electronic state have been rotationally analyzed. Adiabatic potentials and dissociation energies for both states have been obtained through an inverse perturbation analysis. For the 2p²II state, a well depth of 212(5) cm^-1 and an …

Molecular-Orbital Studies Via Satellite-Free X-Ray Fluorescence: Cl-K Absorption And K–Valence-Level Emission Spectra Of Chlorofluoromethanes, Rupert C. Perera, P. L. Cowan, Dennis W. Lindle, R. E. Lavilla, T. Jach, R. D. Deslattes

Chemistry and Biochemistry Faculty Research

X-ray absorption and emission measurements in the vicinity of the chlorine K edge of the three chlorofluoromethanes have been made using monochromatic synchrotron radiation as the source of excitation. By selectively tuning the incident radiation to just above the Cl 1s single-electron ionization threshold for each molecule, less complex x-ray-emission spectra are obtained. This reduction in complexity is attributed to the elimination of multielectron transitions in the Cl K shell, which commonly produce satellite features in x-ray emission. The resulting "satellite-free" x-ray-emission spectra exhibit peaks due only to electrons in valence molecular orbitals filling a single Cl 1s vacancy. These …

Relativistic Wave Equation For Anyons, R. Jackiw, V. Parameswaran Nair

Publications and Research

Construction of one-particle states as unitary representations of the Poincare algebra in 2 + 1 dimensions shows that an anyon has one polarization state. However, for nonzero spin manifestly linear and covariant realizations of Lorentz transformations require more than one field component, and an infinite number is needed when the value of spin is not an integer or half-integer. We discuss the relation between these two aspects of Poincare symmetry. In particular, we construct a relativistic equation for anyons where the number of physical polarizations is reduced to one by virtue of a gauge symmetry or equivalent constraint.