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Potential-Barrier Effects In Photoabsorption. I. General Theory, Anthony F. Starace

Anthony F. Starace Publications

This paper combines parts of the theories of spectroscopy, collisions, and autoionization to provide a unified framework for a quantitative theory of experimental data on 4d-shell photoabsorption in rare earths. The calculations by atomic theory are intended for tentative application to solids. The theory should also apply to 3p-shell photoabsorption in the transition metals and to other cases where the effect of a potential barrier is crucial. A prescription is given for the ab initio numerical calculation of total and partial photoabsorption cross sections, as well as of the profiles, energies, and widths of resonances. A …

Potential-Barrier Effects In Photoabsorption. Iii. Application To 4D-Shell Photoabsorption In Lanthanum, J.L. Dehmer, Anthony F. Starace

Anthony F. Starace Publications

An exploratory calculation of the photoabsorption cross section near the 4d ionization threshold of lanthanum metal is carried out. The level structure of the configuration 4d⁹4f is found to be altered by interaction with the continuum configuration 4d⁹εf. The Fano profile of the resonance above threshold is calculated, as are the oscillator strengths of the discrete states below threshold. Our results provide the ground work for more detailed calculations.

Elastic Scattering Of Low-Energy Electrons At 180° In Co2, Paul Burrow, L. Sanche

Paul Burrow Publications

A technique is described for the study of electrons which are elastically scattered from a gas target into a small solid angle centered at 180° with respect to the direction of the incident electron beam. The method is applied to electron scattering from CO₂. Information is obtained concerning the nature of the compound state in the 4-eV region.

Studies Of Bistable Fluid Devices For Particle Flow Control, Gerald H. Hogland

Dissertations and Theses

This study was directed toward the development of a bistable wall attachment Flip-Flop device which was capable of directionally controlling particle flow. The particles were transported by a fluid stream which under the influence of wall attachment. The dominant criteria in the development of the device was the achievement of the highest recovery of particles at the active output, without destroying the wall attachment of the fluid stream The experiment was conducted in several distinct stages; each of which was concerned with at least one aspect of wa1l attachment or particle flow. Results derived from one test were used to …

Raman-Active Resonance Modes, Overtones, And Anharmonicity In Nacl:Cu+, B.N. Ganguly, Roger D. Kirby, M.V. Klein, G.P. Montgomery Jr.

Roger Kirby Publications

The existence of an impurity-activated E_g resonance mode in NaCl:Cu⁺ has been suggested by several previous experiments. Raman data presented here reveal this resonance directly and also reveal the three components of the first overtone of the 23.5-cm^-1 infrared resonance mode. The frequencies of the E_g resonance and the E_g component of the overtone are shifted as a result of a strong anharmonic coupling. Their line shapes and strengths are considerably altered by an interference between the Raman amplitudes. A reasonable fit to the data has been obtained using a simple theory.

Nuclear-Spin Relaxation In Low-Density Molecular Hydrogen At Room Temperature, Peter A. Beckmann, E. Elliott Burnell, Krovvidi Lalita, Robin L. Armstrong, Kenneth E. Kisman, F. R. Mccourt

Physics Faculty Research and Scholarship

No abstract provided.

Strong, Quasiperiodic Dependence Of Autoionization Shape Parameters On Projectile Energy In H+ + He Collisions, F. D. Schowengerdt, M. Eugene Rudd

M. Eugene Rudd Publications

Profiles of the 2s² (¹S) autoionizing state in He have been observed in the ejected-electron spectrum of H⁺ + He for small angles of ejection and for H⁺ energies of 6 to 150 keV. The shape parameter q shows an increasing dependence on projectile energy as the angle of ejection is decreased, with strong, quasiperiodic oscillations appearing at 10°.

Diffusion-Controlled Reaction Kinetics, David Peak, J W. Corbett

All Physics Faculty Publications

The theory of diffusion-controlled correlated reaction kinetics is developed for the radiation boundary condition (RBC) at the reaction surface. Limited only by the assumptions of purely radial spatial dependence, of a spherical reaction surface, and of continuum diffusion, these results comprise a complete solution for these kinetics. The limiting solutions are obtained for the case of the Smoluchowski boundary condition (SBC) at the reaction surface; numerical solutions are presented, as are the analytic forms of certain limiting cases. The initial recovery for the RBC is linear in time, whereas for the SBC it is well known to be proportional to …

The 6300Å Predawn Enhancement: Excitation By Protoelectrons From The Magnetic Conjugate Point, Vincent B. Wickwar

All Physics Faculty Publications

Incoherent scatter and tilting filter photometer data from Arecibo Observatory were combined to search for a contribution to the 6300 Å predawn enhancement due to impact excitation by photoelectrons from the magnetic conjugate point. Prior to about 105° conjugate solar zenith angle, calculations of the 6300 Å intensities due to dissociative recombination gave good agreement with the observed intensities. Then, with the arrival of conjugate photoelectrons (confirmed by plasma line enhancements), the observed intensities rose above the calculated, the difference increasing until a plateau was achieved at a conjugate solar zenith angle of about 95°. The difference or residual intensity …

Thomson's E/M Experiment Revisited, Michael Glascock, Don M. Sparlin

Physics Faculty Research & Creative Works

The objective of this experiment is to familiarize the student with the impulse theorem, electron dynamics, and magnetic field contours. He is challenged to obtain accurate as well as precise measurements with suboptimum apparatus through correct analysis. He also investigates the influence of various systematic errors using model calculations on a small computer. © 1972, American Association of Physics Teachers. All rights reserved.

A Correction To Classical Homogeneous Nucleation Theory For Polar Molecules Exhibiting An Electric Double Layer At The Liquid Surface, Daniel R. White, James L. Kassner

Physics Faculty Research & Creative Works

An oriented dipole surface layer is added to the classical liquid drop model of nucleation to account for the surface behavior of substances having polar nonsymmetrical molecules. The preliminary treatment of the change in free energy as given by Abraham is modified to include Fletcher's exponential decay of the degree of orientation. An additional correction for the excess binding energy due to the presence of a foreign molecule in the prenucleation cluster is included to account for the inflections observed in the experimental results of Allen and Kassner. The resulting free energy of formation is combined with the kinetic treatment …

Observation Of The Influence Of Centrifugal Distortion Of The Methane Molecule On Nuclear Spin Relaxation In The Gas., Peter A. Beckmann, M. Bloom, E. E. Burnell

Physics Faculty Research and Scholarship

The spin–lattice relaxation time T₁ was measured in gaseous CH₄ as a function of density at room temperature between 0.006 and 7.0 amagats. T₁ was found to pass through a minimum near 0.04 amagats in agreement with previous, less precise measurements. The spin–rotation interaction is the dominant relaxation mechanism in gaseous CH₄. Since the spin–rotation constants are accurately known for CH₄, the relaxation experiments provide a check on the theory of spin–lattice relaxation for spherical top molecules. In the conventional theory, it is assumed that the correlation function of the spin–rotation interaction is …

Observation Of The Influence Of Centrifugal Distortion Of The Methane Molecule On Nuclear Spin Relaxation In The Gas., Peter A. Beckmann, M. Bloom, E. E. Burnell

Physics Faculty Research and Scholarship

The spin–lattice relaxation time T₁ was measured in gaseous CH₄ as a function of density at room temperature between 0.006 and 7.0 amagats. T₁ was found to pass through a minimum near 0.04 amagats in agreement with previous, less precise measurements. The spin–rotation interaction is the dominant relaxation mechanism in gaseous CH₄. Since the spin–rotation constants are accurately known for CH₄, the relaxation experiments provide a check on the theory of spin–lattice relaxation for spherical top molecules. In the conventional theory, it is assumed that the correlation function of the spin–rotation interaction is …

Diffusiophoretic Forces Between Juxtaposed Atmospheric Particles, Allen L. Williams

Doctoral Dissertations

"The role of diffusiophoretics and Stefan flow in droplet growth by accretion and in-cloud scavenging is examined. A calculation is made for the diffusive forces between two juxtaposed spheres one or both of which are undergoing diffusional growth and the influence of the diffusive force on the trajectories of two spheres, assumed to obey the creeping flow equations is found. The results are: a) the diffusiophoretic force between two water droplets is zero. b) the diffusiophoretic force between a spherical ice particle and a water droplet, although non-zero, is too small to appreciably influence the fall trajectories. c) the diffusiophoretic …

Adsorption Of Rare Gas Atoms On Xenon, Donald E. Hagen

Physics Faculty Research & Creative Works

The problem of adsorption of rare gas atoms on solids is treated for the case of submonolayer films. An energy spectrum calculation method which is suitable for band structure or heat capacity calculations is discussed. It is particularly useful for adsorbate-substrate systems in the region intermediate between "tight binding" and "plane wave" behavior. The method employs a technique introduced by Kohn and Luttinger of using the eigenfunctions corresponding to a particular point in the Brillouin zone as a basis set. The cases of He and Ne adsorbed on Xe are discussed.

A Study Of Phosphorus Adsorption And Desorption Kinetics On Silicon (111) Surfaces, L. E. Davis, L. L. Levenson, J. J. Melles

Physics Faculty Research & Creative Works

Low energy electron diffraction (LEED) and Auger electron spectroscopy (AES) methods were used to characterize the (111) surface of Si wafers before and after the deposition of P2 molecules. Before deposition, the well-known Si(111)-7 LEED pattern was easily obtained by thermal cleaning at 1200 °C. Cleaning was done by electron bombardment in a vacuum chamber with a base pressure of ∼ 10-10 Torr. After cleaning, AES showed that about 10-2 atomic layer of carbon was the only surface contaminant. The sensitivity of our cylindrical AES apparatus for phosphorus was about 10-3 atomic layer. We found that ∼5x10-2 atomic layer of …

An Inexpensive Electrical Vacuum Feedthrough, D. R. Kastelein, Richard A. Anderson, Kaare J. Nygaard

Physics Faculty Research & Creative Works

No abstract provided.

Excited-Ion Lifetimes Using Penning-Ionizing Collisions, William F. Parks, Laird D. Schearer

Physics Faculty Research & Creative Works

We show that in the Penning-ionizing collision He(23S1)+X→He(11S0)+(X+)*+e the precession of the Hem spin at its Larmor frequency forces the J polarization of the Penning ion to rotate at the same frequency but shifted in phase. The tangent of the phase shift is proportional to the lifetime of the ionic state and presents a unique method for measuring excited-ion lifetimes. © 1972 The American Physical Society.

Application Of The Weiss Molecular Field Theory To The B‐Site Spinel, W. E. Holland, Harry A. Brown

Physics Faculty Research & Creative Works

A molecular field treatment of the B‐site spinel was used to determine the ordering temperatures and the asymptotic Curie temperature in terms of the exchange integrals. The theory was developed from a 16‐sublattice model and took into account interactions between an atom and its nearest to fourth‐nearest neighbors. Experimental values of the ordering temperatures and the asymptotic Curie temperature were then used to determine the exchange integrals for the systems Hg1−xCdx Cr2 S4, CdCr2S4(1−y)Se4y, and Zn1−xCdxCr2Se4. Copyright © 1972 WILEY‐VCH Verlag GmbH & Co. KGaA

Time-Dependent Ionization Equilibrium And Line Radiation Under Flarelike Conditions, Menas Kafatos, W. H. Tucker

Mathematics, Physics, and Computer Science Faculty Articles and Research

The results of calculations for time-dependent ionization equilibrium and line emission are presented and compared with the values obtained under the assumption that steady-state conditions prevail. In the models considered, it is assumed that the electron density is constant (=10^3 cm^-3) and that the temperature increases by a factor of 10 from 3 x 10^6 K on timescales ranging from 100 to 300 s and decays back to 3 x 10^6 K on a timescale ranging from 600 to 1400 s. Ions of oxygen and silicon are considered, and it is found that the spectrum is softer during the rise …

Collisional Excitation Of N+ At 50 Kev, D. H. Crandall, G. York, V. Pol, John T. Park

Physics Faculty Research & Creative Works

The excitation spectrum of N+ has been observed by examining the energy lost by a 50- keV N+ beam passing through a He target. The spectrum exhibits dramatic features with large cross sections. Determination of the approximate ratio of metastable to ground-state ions in the primary ion beam has permitted measurement of excitation cross sections from both ground-state and metastable N+ ions colliding with He target atoms. © 1972 The American Physical Society.

Gas-To-Particle Conversions Of So₂-No₂-H₂O-Air Gas Mixtures Under Specific Uv Irradiation, James Leonard Fowler

Masters Theses

"In these series of experiments, mixtures of sulfur dioxide and nitrogen dioxide were irradiated in an absorption cell with monochromatic radiation found in the tropospheric region of the atmosphere. The irradiated mixtures were then introduced into a Wilson type cloud chamber to investigate the effects of these specific wavelength induced gas to particle conversions on nucleation. Results showed that sulfur dioxide could not be the sole agent for the formation of condensation nuclei. A mixture of sulfur dioxide and nitrogen dioxide irradiated at 3660 angstroms produced copious droplet formation identifying nitrogen dioxide as an integral reactant in nuclei production"--Abstract, page …

Some Bonding Aspects Of Cobalt Ions In Phosphate Glasses, Tewfik Boutros Absi

Archived Theses and Dissertations

No abstract provided.

Observation Of A Broad Resonance In The 23S Excitation Of Helium By Electron Impact, G. B. Crooks, R. D. Dubois, D. E. Golden, M. Eugene Rudd

M. Eugene Rudd Publications

We have observed a broad P-wave resonance at about 50 eV primary energy in the angular distribution of electrons scattered after excitation of the 2³S state of helium. The resonance has a width of about 15 eV and affects the differential excitation cross section by more than 3 orders of magnitude. It is suggested that this resonance is associated with the temporary formation of triply excited states of the negative helium ion.

Detection Of Energetic Heavy Ions, Robert Katz, S. C. Sharma, Mehdi Homayoonfar

Robert Katz Publications

The delta-ray theory of track structure, applied earlier to such 1-or-more hit detection systems as the inactivation of dry enzymes and viruses, the NaI(Tl) scintillation counter, and nuclear emulsion, is extended to the silver activated phosphate glass dosimeter, the LiF thermoluminescent dosimeter, the creation of free radicals in solid biological substances, solid and liquid organic scintillators, and the ferrous sulfate (Fricke) dosimeter. The response of these systems to both gamma-rays and heavy ions is characterized by two parameters: 1) D_γ³⁷, the dose of gamma-rays at which 37% of the sensitive elements remain unaffected by the radiation, and …

Radiative And Predissociative Lifetimes Of The A²Σ⁺ State Of Oh, Robert Allen Sutherland

Doctoral Dissertations

"Lifetime measurements have been made on the A²Σ⁺ state of OH by the delayed coincidence technique in conjunction with an interrupted rf discharge through water vapor. Lifetimes are reported for rotational states up to K = 29 and K = 20 in the v = 0 and v = 1 vibrational levels respectively and on the unresolved levels of v =2. A predissociation, previously predicted from relative intensity measurements, resulting from a curve crossing by the repulsive 4 Σˉ state, was observed for the rotational states above K = 23 of v = 0, for those above K = 14 …

Time Resolved Measurements Of Droplet Growth In A Wilson Cloud Chamber, Michael Anthony Vietti

Doctoral Dissertations

"The growth rates of water drops in a Wilson expansion cloud chamber are measured with air, argon and helium as the carrier gas, in the size range of .5 to 10 microns. The drops growing in the supersaturated chamber exhibit oscillations in the scattered intensity as predicted by Mie theory. Scattered intensity is measured at 30 degrees to the He-Ne laser beam. Supersaturation ratios during growth range from S =1.2 to S = 3.5 for all three gases. The initial temperature is measured and the pressure is monitored continuously so that droplet growth theory can be compared with experiment. Three …

Ionization Mechanisms In Cesium, Yu Bong Hahn

Doctoral Dissertations

"Autoionizing states in Cs between 12 and 20 eV have been studied by electron impact. The retarding-potential-difference(RPD) method was used to obtain an electron beam with energy spread of about 0.1 eV. To determine the threshold energies, inelastically scattered electrons were analyzed by the trapped-electron method. We have been able to identify about 20 levels, and the agreement with spectroscopic data is excellent. A peak appearing at 12.80 eV is probably due to the quartet states observed by Feldman and Novick"--Abstract, page 2. "The structure in the electron impact ionization cross section in cesium can be partially accounted for by …

The Eikonal Distorted Wave Born Approximation For The Excitation Of Hydrogen By Impact With Hydrogen And Helium In The Intermediate Energy Range, Richard Homer Shields

Doctoral Dissertations

"An eikonal approximation is applied to atom-atom scattering in the intermediate energy range. The theory and the form of the eikonal approximation are reviewed. Also a brief survey of previous theoretical methods for all energy ranges is included.

In particular, the differential and total cross sections for the excitation of hydrogen to the 2s and 2p states by impact on hydrogen and helium atoms have been calculated using the eikonal distorted wave Born approximation (DWBA) for the incident energy range of 2.25-100 keV. The eikonal DWBA differential cross sections are compared to the differential cross sections given by the first …

Shubnikov-De Haas Effect And Magnetic Breakdown In Be , David J. Sellmyer, I.S. Goldstein, B.L. Averbach

David Sellmyer Publications

Magnetic breakdown in the basal plane of Be was investigated in fields up to 150 kG. Geometrical aspects of the open orbits caused by breakdown are discussed. An estimate of 30 kG for the characteristic breakdown field is obtained by applying the theory of Falicov et al. Shubnikov-de Haas frequency measurements are reported for the central-cigar cross section. These measurements are relevant to a recent conjecture that the Onsager-Lifshitz quantization scheme may be violated in the presence of magnetic breakdown.