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Articles 31 - 49 of 49
Full-Text Articles in Physical Sciences and Mathematics
Formation And Desorption Of Negative Ions From Metal Surfaces, Douglas Hugh Baker
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 …
Low-Energy Collisions Of Negative Ions With Atomic Hydrogen, Michael A. Huels
Low-Energy Collisions Of Negative Ions With Atomic Hydrogen, Michael A. Huels
Dissertations, Theses, and Masters Projects
Total cross sections for charge transfer and electron detachment for collisions of a variety of negative ions with atomic hydrogen have been separately determined for laboratory collision energies ranging from about 5 eV to 500 eV. The experiments are performed with an apparatus that utilizes a crossed-beam configuration with a radio-frequency discharge as the source of atomic hydrogen.;For collisions of H{dollar}\sp-{dollar}(D{dollar}\sp-{dollar}) with H the charge transfer cross sections increase monotonically with decreasing energy and display an isotope effect. at the lowest collision energies, the electron detachment cross sections are about one order of magnitude smaller than those for charge transfer; …
A Superconducting Compact Hydrogen Maser Resonator, David B. Opie
A Superconducting Compact Hydrogen Maser Resonator, David B. Opie
Dissertations, Theses, and Masters Projects
The discovery of high critical temperature superconductors (HTSC) has raised the temperature at which the greatly reduced surface resistance, characteristic of superconducting materials, may be exploited. For microwave frequencies below 100 GHz, the surface resistance, R{dollar}\sb{lcub}s{rcub}{dollar}, at liquid nitrogen temperatures (77K) of the new HTSC materials is found to be better than copper measured at the same temperature and frequency. Consequently, the miniaturization of passive microwave components will be among the first applications of these new materials. This dissertation details the development, testing and evaluation of a superconducting compact hydrogen maser resonator made from electrophoretic Y{dollar}\sb1Ba\sb2Cu\sb3{dollar}O{dollar}\sb{lcub}7-\delta{rcub}{dollar} (YBCO). Such a resonator …
Photodetachment Of Hydride Ion In Perpendicular Electric And Magnetic Fields, Aaron David Peters
Photodetachment Of Hydride Ion In Perpendicular Electric And Magnetic Fields, Aaron David Peters
Dissertations, Theses, and Masters Projects
A simple analytic formula for the photodetachment cross section of H$\sp{-}$ in perpendicular electric and magnetic fields is obtained. Oscillations in the spectrum are predicted by the formula, and these oscillations are correlated with closed classical orbits. We point out that the quantum mechanical derivation, using a stationary phase approximation, is in complete agreement with the three-dimensional semiclassical solution to the problem.
The Diffusion Of Muonic Hydrogen Atoms In Hydrogen Gas, Guo Fu Chen
The Diffusion Of Muonic Hydrogen Atoms In Hydrogen Gas, Guo Fu Chen
Dissertations, Theses, and Masters Projects
This experiment measured the time distribution of muonic hydrogen atoms which were formed when negative muons were brought to rest in H{dollar}\sb2{dollar} gas, containing Au target foils, at five pressures (750 mbar, 375 mbar, 188 mbar, 94 mbar and 47 mbar at 4.6 mm foil spacing). A Monte Carlo method is applied for deducing the initial velocity distribution, and preliminary results are obtained. The initial velocity distribution of {dollar}\mu{dollar}H atoms is reasonably well described as a 'Maxwellian' velocity distribution with a mean energy E = 3.4 eV. The corresponding muon mean capture energy is obtained: E{dollar}\sb{lcub}\rm c{rcub}{dollar} {dollar}\approx{dollar} 34 eV …
The Effect Of Closed Classical Orbits On Quantum Spectra: Ionization Of Atoms In A Magnetic Field, Meng Li Du
The Effect Of Closed Classical Orbits On Quantum Spectra: Ionization Of Atoms In A Magnetic Field, Meng Li Du
Dissertations, Theses, and Masters Projects
A quantitative theory of oscillatory spectra for atoms in a magnetic field is developed. When an atom is placed in a magnetic field, and absorption spectrum into states close to the ionization threshold is measured, it is found that the absorption as a function of energy is a superposition of many sinusoidal oscillations. Such interesting and surprising phenomenon are fully explained and described by the theory.;The theory is based on three approximations: (1) Near the atomic nucleus, the diamagnetic field is negligible. (2) Far from the nucleus, the wave propagates semiclassically. (3) Waves returning to the nucleus are similar to …
Slow Collisions Of Hydride Ion And Deuteride Ion With Sodium, Potassium And Cesium, Yicheng Wang
Slow Collisions Of Hydride Ion And Deuteride Ion With Sodium, Potassium And Cesium, Yicheng Wang
Dissertations, Theses, and Masters Projects
The cross sections of charge transfer and electron detachment in collisions of H$\sp{-}$ and D$\sp{-}$ with Na, K and Cs have been measured for collision energies ranging from 3 to 300 eV. Both charge transfer and electron detachment are significant electron-loss mechanisms for H$\sp{-}$(D$\sp{-}$); both processes exhibit velocity-dependent isotope effects for H$\sp{-}$ and D$\sp{-}$. $\sigma\sb{\rm cg}$(E) displays high energetic thresholds for Na and K (about 20 eV for H$\sp{-}$ + Na and 40 eV for H$\sp{-}$ + K) yet no obvious one for Cs. $\sigma\sb{\rm e}$(E) does not depend on the target as much as $\sigma\sb{\rm ct}$(E) and displays near …
Low-Energy Collisions Of Alkali-Metal Anions, David M. Scott
Low-Energy Collisions Of Alkali-Metal Anions, David M. Scott
Dissertations, Theses, and Masters Projects
Measurements of the total cross section for electron detachment, (sigma)(,e)(E), are presented for low-energy (E(,1ab) < 300 eV) collisions of Na('-), K('-), and Cs('-) with atomic and molecular targets. For many of the atomic (rare-gas) targets, the energy dependence of (sigma)(,e)(E) is striking: virtually no detachment is observed until relatively high collision energies (50 eV in the center-of-mass frame) are reached, in contradistinction to what has been observed for similar collisions involving H('-). The thresholds for alkali anion detachment are approximately equal to the thresholds for excitation observed in collisions of neutral alkali atoms with these same targets. The similarity between the dynamics of the neutral system and that of the negative ion system, together with the observation (at greater energies) of detachment accompanied by excitation of the alkali parent, suggests that electron detachment may be mediated by a two-electron process in some cases. A simple curve-crossing mechanism adequately reproduces the observed (sigma)(,e)(E) for several of these rare-gas targets.;Measurements of both (sigma)(,e)(E) and the cross section for charge transfer (sigma)(,i)(E) have also been completed for H(,2), D(,2), N(,2), O(,2), CO, CO(,2), SO(,2), N(,2)O, CH(,4), and SF(,6) targets. Electron detachment is the dominant process for all of these targets except O(,2), SO(,2), and SF(,6), with thresholds on the order of a few eV. Structure in (sigma)(,e)(E) for the CO(,2) target has been attributed to charge transfer to a metastable state of CO(,2)('-)(('2)A(,1)). Similarly, in the case of N(,2)O, both (sigma)(,e)(E) and (sigma)(,i)(E) exhibit behavior which suggests that a temporary negative ion state is formed during the collision. In the case of the O(,2), SO(,2), and SF(,6) targets, charge transfer is observed to have particularly large cross sections (>100 (ANGSTROM)('2)) at low collision energies.
Rydberg Atoms In Parallel Electric And Magnetic Fields, Robert Leonard Waterland
Rydberg Atoms In Parallel Electric And Magnetic Fields, Robert Leonard Waterland
Dissertations, Theses, and Masters Projects
I have calculated the energy spectrum of a highly excited atom which lies in parallel, static electric and magnetic fields. In parallel fields the Coulomb quantum numbers n and m are still "good" quantum numbers but 1 is not: the calculation is for n = 30, m = 1 atoms.;The eigenvalues were obtained by semi-classical quantisation of first-order classical perturbation theory and have been calculated for a large range of electric and magnetic field strengths. The results are in good agreement with those found from first-order degenerate quantum perturbation theory.;The semi-classical analysis provides a correlation diagram connecting the Stark effect …
Electron Detachment In Negative Ion-Molecule Collisions, Mohammed Saiful Huq
Electron Detachment In Negative Ion-Molecule Collisions, Mohammed Saiful Huq
Dissertations, Theses, and Masters Projects
Absolute total cross sections for electron detachment, reactive scattering, charge transfer and dissociative charge transfer have been measured for collisions of hydrogen and halogen negative ions with various molecular targets. The reactants investigated involve H('-), D('-), F('-), Cl('-), Br('-) and I('-) ions as projectiles and H(,2), D(,2), HD, N(,2), CO, O(,2), CO(,2), CH(,4) and Cl(,2) molecules as targets. The energy range of these experiments extended from about 1 eV to about 300 eV in the lab.;The threshold behavior of the detachment cross sections for the reactants H('-)(D('-)) + H(,2),D(,2) and HD has been determined. The thresholds for detachment for both …
A Theory Of Associative Detachment, Susan Elizabeth. Haywood
A Theory Of Associative Detachment, Susan Elizabeth. Haywood
Dissertations, Theses, and Masters Projects
In this thesis a theory of associative detachment (A('-) + B (--->) AB + e) is presented. The theory is based on the close-coupling theory of Wang and Delos, but is more general in that final states of the nuclei (AB) are treated quantum mechanically. This is necessary since the molecule may be in any one of several vibrational states. The Schroedinger equation is reduced to an infinite set of coupled equations using carefully chosen assumptions. The coupled equations are uncoupled and the resulting equation for the wave function of the negative ion is solved to zero and first …
A General Theory Of Electron Detachment In Negative Ion Collisions, Tzuu-Shin Wang
A General Theory Of Electron Detachment In Negative Ion Collisions, Tzuu-Shin Wang
Dissertations, Theses, and Masters Projects
In this thesis a general theory of electron detachment in slow collisions of negative ions with atoms is presented. The theory is based upon a semiclassical close-coupling framework, following the work of Taylor and Delos. The Schrodinger equation is reduced, under certain assumptions, to a non-denumerably infinite set of coupled equations. We develop a new method for solving these equations that is more general than the methods used by Taylor and Delos. A zero-order approximation of our solution is applied to the case of H('-)(D('-)) on Ne collisions, the results are compared with the experimental data, and we find good …
Theory Of Electron Detachment In Collisions Of Negative Ions With Atoms, Ronald David Taylor
Theory Of Electron Detachment In Collisions Of Negative Ions With Atoms, Ronald David Taylor
Dissertations, Theses, and Masters Projects
No abstract provided.
Semiclassical Calculation Of Vibrational Energy Levels Of Nonseparable Systems, Randall T. Swimm
Semiclassical Calculation Of Vibrational Energy Levels Of Nonseparable Systems, Randall T. Swimm
Dissertations, Theses, and Masters Projects
No abstract provided.
Studies Of Negative Ion-Atom Scattering At Low Collision Energies, Barry T. Smith
Studies Of Negative Ion-Atom Scattering At Low Collision Energies, Barry T. Smith
Dissertations, Theses, and Masters Projects
No abstract provided.
Studies Of Elastic And Inelastic Scattering Of H⁻ And D⁻ By Inert Gas Atoms, Siu-Kwong Lam
Studies Of Elastic And Inelastic Scattering Of H⁻ And D⁻ By Inert Gas Atoms, Siu-Kwong Lam
Dissertations, Theses, and Masters Projects
No abstract provided.
An Investigation Of One And Two State Molecular Systems Based On The Results Of Elastic Differential Scattering Experiments, Stephen Michael Bobbio
An Investigation Of One And Two State Molecular Systems Based On The Results Of Elastic Differential Scattering Experiments, Stephen Michael Bobbio
Dissertations, Theses, and Masters Projects
No abstract provided.
Low Energy Studies Of The Experimental Elastic Differential Cross-Sections For The Systems Proton-Helium, Proton-Neon And Signly Ionized Helium-Helium, William Guy Rich
Low Energy Studies Of The Experimental Elastic Differential Cross-Sections For The Systems Proton-Helium, Proton-Neon And Signly Ionized Helium-Helium, William Guy Rich
Dissertations, Theses, and Masters Projects
No abstract provided.
Measurements Of Stark Widths Of Argon Ion Lines, Nelson Wayne Jalufka
Measurements Of Stark Widths Of Argon Ion Lines, Nelson Wayne Jalufka
Dissertations, Theses, and Masters Projects
No abstract provided.