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Standing wave solutions to the inhomogeneous equation for identical particle scattering

Description: The standing wave solution to the inhomogeneous equation describing identical particle scattering is re-examined. Although the form of that solution is correct, its content is shown to be incorrect. A paradigm for constructing the correct solution, based on unitarity, is discussed, and the proper solution is then obtained. A comparison of different standing wave solutions with differing K operators is given. The results are shown to be an extension to the multi-channel case of those derived previously for the potential well case. (auth)
Date: January 1, 1973
Creator: Kouri, D.J. & Levin, F.S.
Partner: UNT Libraries Government Documents Department

Coherent excitation of autoionizing resonances

Description: An electron-electron coincidence [or (e,2e)] technique was used to investigate atomic ionization by electron impact in the neighborhood of autoionizing resonances. Differing binary (I{sup +}) and recoil (I{sup -}) lobe intensities in coplanar (e,2e) ejected-electron angular distributions were analyzed in terms of interference cross-terms, between opposite parity final-state continua, that change sign when {theta}{sub ej} {yields} {theta}{sub ej} + 180{sup o} in the angular distributions. The magnitude of these cross-terms varies rapidly with ejected-electron energy across overlapping autoionizing resonances. The energy variation in the interference terms may be examined by obtaining the sum (I{sup +} + I{sup -}) and difference (I{sup +} - I{sup -}) of (e,2e) energy spectra measured at ejected-electron angles 180{sup o} apart.
Date: October 3, 2002
Creator: Martin, N.L.S.
Partner: UNT Libraries Government Documents Department

Coherent excitation of autoionizing resonances by electron impact. Annual report, March 1995 - April 1996

Description: Experimental investigations are being carried out into interference effects caused by the coherent population, by electron impact, of autoionizing levels and continua of differing total angular momentum and parity. The work provides information on the atomic excitation and ionization mechanisms by charged particle impact. The experimental technique being used is electron-electron coincidence [or (e, 2e)] spectrometry. Differing binary (I{sup +}) and recoil (I{sup -}) lobe intensities in coplanar (e, 2e) ejected-electron angular distributions may be modeled by interference cross-terms, between opposite parity final-state continua, that change sign when {theta}{sub ej} {r_arrow} {theta}{sub ej} + 180{degrees} in the angular distributions. The magnitude of these cross-terms varies rapidly with ejected-electron energy across overlapping autoionizing resonances. The energy variation in the interference terms may be examined by obtaining the sum (I{sup +} + I{sup -}) and difference (I{sup +} - I{sup -}) between (e, 2e) energy spectra measured at ejected-electron angles 180{degrees} apart. 5 refs., 1 fig.
Date: December 1, 1995
Creator: Martin, N.L.S.
Partner: UNT Libraries Government Documents Department

Electron-atom collision studies using optically state-selected beams. Final report, May 15, 1991--May 14, 1994

Description: As stated in the original proposal, the goal of the project has been to perform electron-scattering experiments on a few model systems with emphasis on resolving all the quantum-state variables possible. The purpose of these experimental studies has been to provide a set of measurements of unprecedented accuracy and completeness that can be used as benchmarks for comparison with theoretical calculations. During the period covered by this report, the work has concentrated on measuring low-energy electron scattering from sodium and chromium. Sodium provides an ideal one-electron test case, since it has a single loosely bound valence electron, making it approachable by even the most complex electron scattering calculations. In addition, the atom has a strong optical transition from the 3{sup 2}S{sub 1/2} ground state to the 3{sup 2}P{sub 3/2} excited state whose wavelength (589 nm) matches the peak output of the laser dye rhodamine 6G. Thus optical pumping techniques can be readily applied in the laboratory, leading to either a population of ground state atoms in which the spin of the valence electron is oriented either up or down in the laboratory, or a spin polarized pure angular momentum state of the excited 3{sup 2}P{sub 3/2} state. Such an excited state makes possible superelastic scattering, where the internal energy of the atom is transferred to the electron during the collision. This turns out to be a very efficient way to study the inelastic scattering process. Unlike sodium, chromium provides an extremely exacting test for theoretical methods because of its very complex electronic structure, not because it is simple. With a valence configuration consisting of five electrons in a half-filled 3d shell, plus another electron in a 4s shell, this atom provides a test case that can challenge even the simplest approximations.
Date: March 15, 1998
Creator: Kelley, M.H. & McClelland, J.J.
Partner: UNT Libraries Government Documents Department

Theory of Ionization by Electron Collisions

Description: The problem of calculating comprehensive sets of cross sections for ionization of atoms and molecules is reviewed. Emphasis is put on targets that are already ionized and lower-energy collisions for which the incident electron must be treated on a par with target electrons. The physical circumstances are discussed in which perturbation methods should be adequate, and special investigations are recommended to identify the relevant ranges of parameters more precisely and dependably. A new R-matrix approach is outlined which should permit rather simple, approximate, but dependable calculations when the perturbation methods fail.
Date: June 1976
Creator: Fano, Ugo & Inokuti, Mitio
Partner: UNT Libraries Government Documents Department

Channel T and K operators and the Heitler damping equation for identical particle scattering

Description: Coupled integral equations linking the direct and exchange (rearrangement) K operators are proposed in analogy to similar ones linking the direct and exchange T operators. It is shown that these pairs of coupled equations lead to the damping equation which was used previously on identical particle scattering and which expresses the unitarity condition. Other formulations of integral equations for the K operator are also discussed. (auth)
Date: January 1, 1973
Creator: Kouri, D.J. & Levin, F.S.
Partner: UNT Libraries Government Documents Department

Electron collisions with coherently prepared atomic targets

Description: The subject of electron scattering by laser-excited atoms is briefly reviewed. To demonstrate some aspects of these electron collision processes, the authors describe the procedures and the results of a joint experimental and theoretical study concerning elastic scattering by coherently excited {sup 138}Ba (...6s6p {sup 1}P{sub 1}) atoms. Examples of experimental and theoretical collision parameters and magnetic sublevel differential cross sections for elastic scattering are given and compared. The convergent close coupling calculations (with the neglect of spin-orbit interaction) are in good agreement with experiment at 20 eV impact energy and 10, 15 and 20{degree} scattering angles and can be expected to yield reliable integral magnetic sublevel and alignment creation cross sections. The role of these quantities in plasma polarization spectroscopy is pointed out.
Date: February 1, 1998
Creator: Trajmar, S.; Kanik, I.; LeClair, L.R.; Khakoo, M.S.; Bray, I.; Fursa, D. et al.
Partner: UNT Libraries Government Documents Department

Coherent excitation of autoionizing resonances by electron impact. Annual report, September 1991 - January 1993

Description: This report describes experimental investigations of interference effects, in the Group IIB transition metal atoms Zn, Cd, and Hg, caused by the coherent excitation, by electron impact, of autoionizing levels of differing total angular momentum. The work will provide information on both the excitation mechanism by charged particle impact and the spectroscopy of autoionizing levels. 4 refs., 2 figs.
Date: July 1, 1992
Creator: Martin, N.L.S.
Partner: UNT Libraries Government Documents Department

Electron-impact ionization of atomic hydrogen

Description: Since the invention of quantum mechanics, even the simplest example of collisional breakup in a system of charged particles, e{sup {minus}} + H {r_arrow} H{sup +} + e{sup {minus}} + e{sup {minus}}, has stood as one of the last unsolved fundamental problems in atomic physics. A complete solution requires calculating the energies and directions for a final state in which three charged particles are moving apart. Advances in the formal description of three-body breakup have yet to lead to a viable computational method. Traditional approaches, based on two-body formalisms, have been unable to produce differential cross sections for the three-body final state. Now, by using a mathematical transformation of the Schrodinger equation that makes the final state tractable, a complete solution has finally been achieved, Under this transformation, the scattering wave function can be calculated without imposing explicit scattering boundary conditions. This approach has produced the first triple differential cross sections that agree on an absolute scale with experiment as well as the first ab initio calculations of the single differential cross section.
Date: February 14, 2000
Creator: Baertschy, Mark D.
Partner: UNT Libraries Government Documents Department

Cross Sections for Electron Inelastic Collisions with Argon

Description: A complete set of optical oscillator strengths and electron-impact cross sections for the argon atom is presented in tabular form. A large variety of experimental data and theoretical calculations was studied, and various checks based on theory (including the constraint of sum rules) were critically performed. Data were analyzed mainly by a semi-empirical method that stresses the close relation of photoabsorption with electron-atom collisions.
Date: July 1980
Creator: Eggarter, E. & Inokuti, Mitio
Partner: UNT Libraries Government Documents Department

A discrete variable representation for electron-hydrogen atom scattering

Description: A discrete variable representation (DVR) suitable for treating the quantum scattering of a low energy electron from a hydrogen atom is presented. The benefits of DVR techniques (e.g. the removal of the requirement of calculating multidimensional potential energy matrix elements and the availability of iterative sparse matrix diagonalization/inversion algorithms) have for many years been applied successfully to studies of quantum molecular scattering. Unfortunately, the presence of a Coulomb singularity at the electrically unshielded center of a hydrogen atom requires high radial grid point densities in this region of the scattering coordinate, while the presence of finite kinetic energy in the asymptotic scattering electron also requires a sufficiently large radial grid point density at moderate distances from the nucleus. The constraints imposed by these two length scales have made application of current DVR methods to this scattering event difficult.
Date: August 1, 1994
Creator: Gaucher, L. F.
Partner: UNT Libraries Government Documents Department

Direct detection of neutral metal atoms in electron-stimulated desorption: Al from CH{sub 3}O/Al(111) - velocity distribution and absolute yield

Description: Electron-stimulated desorption of neutral aluminum from the system CH{sub 3}O/Al(111) has been directly monitored via quasiresonant photoionization with 193 nm excimer laser light and confirmed by two-step resonant ionization, utilizing the Al 3d {sup 2}D manifold. Velocity distribution measurements for the neutral Al peak at {approximately} 800 m/s for 1 keV incident electron energy. An absolute yield of 3.2 x 10{sup {minus}6} Al atoms/electron was determined by comparison with sputtering measurements in the same apparatus. This is the first observation of electron-stimulated metal desorption from adsorbate-covered metallic surfaces.
Date: June 1, 1994
Creator: Whitten, J. E.; Young, C. E.; Pellin, M. J.; Gruen, D. M. & Jones, P. L.
Partner: UNT Libraries Government Documents Department

The two-electron problem and prospects for atomic collision theory on a numerical lattice

Description: An exact numerical treatment of fully correlated two-electron systems is described and placed in context with themes characterizing Chris Bottcher`s research regarding time-dependent, lattice approaches to the quantum mechanical solution of atomic collision problems. Tests of the method are summarized in which low-lying bound state are computed and the time-dependence of autoionization is described. Finally, prospects for treating the near-threshold electron-impact ionization of hydrogen and photoionization are discussed, as well as the general prospects for further development of this type of lattice treatment.
Date: September 1, 1994
Creator: Schulz, D. R.
Partner: UNT Libraries Government Documents Department

Current status and future perspectives of electron interactions with molecules, clusters, surfaces, and interfaces [Workshop on Fundamental challenges in electron-driven chemistry; Workshop on Electron-driven processes: Scientific challenges and technological opportunities]

Description: This report is based largely on presentations and discussions at two workshops and contributions from workshop participants. The workshop on Fundamental Challenges in Electron-Driven Chemistry was held in Berkeley, October 9-10, 1998, and addressed questions regarding theory, computation, and simulation. The workshop on Electron-Driven Processes: Scientific Challenges and Technological Opportunities was held at Stevens Institute of Technology, March 16-17, 2000, and focused largely on experiments. Electron-molecule and electron-atom collisions initiate and drive almost all the relevant chemical processes associated with radiation chemistry, environmental chemistry, stability of waste repositories, plasma-enhanced chemical vapor deposition, plasma processing of materials for microelectronic devices and other applications, and novel light sources for research purposes (e.g. excimer lamps in the extreme ultraviolet) and in everyday lighting applications. The life sciences are a rapidly advancing field where the important role of electron-driven processes is only now beginning to be recognized. Many of the applications of electron-initiated chemical processes require results in the near term. A large-scale, multidisciplinary and collaborative effort should be mounted to solve these problems in a timely way so that their solution will have the needed impact on the urgent questions of understanding the physico-chemical processes initiated and driven by electron interactions.
Date: September 1, 2000
Creator: Becker, Kurt H.; McCurdy, C. William; Orlando, Thomas M. & Rescigno, Thomas N.
Partner: UNT Libraries Government Documents Department

Time-dependent, lattice approach to atomic collisions

Description: Recent progress in developing and applying methods of direct numerical solution of atomic collision problems is described. Various forms of the three-body problem are used to illustrate these techniques. Specifically, the process of ionization in proton-, antiproton-, and electron-impact of atomic hydrogen is considered in applications ranging in computational intensity from collisions simulated in two spatial dimensions to treatment of the three-dimensional, fully correlated two-electron Schroedinger equation. These examples demonstrate the utility and feasibility of treating strongly interacting atomic systems through time-dependent, lattice approaches.
Date: December 1995
Creator: Schultz, D. R.
Partner: UNT Libraries Government Documents Department

Quasi-free ({ital e,e`p}) reactions: the first look from CEBAF

Description: Coincidence cross sections for ({ital e,e{sup `}p}) quasi-elastic scattering were measured at CEBAF with high statistical precision for C, Fe, and Au targets for 0.6 {lt} Q{sup 2} {lt} 3.3 GeV{sup 2}. {ital E{sub m}} and {ital P{sub m}} distributions obtained from a preliminary analysis are in reasonable agreement with prior data from SLAC, The preliminary results are compared with a PWIA calculation to determine the nuclear transparency as a function of Q{sup 2} and A. A. Rosenbluth analysis to extract the longitudinal and transverse cross sections from these data is anticipated.
Date: November 1, 1996
Creator: Abbott, D.; Amatuoni, T. & Armstrong, C.
Partner: UNT Libraries Government Documents Department

Relevant ion time scales for electron impact processes of atoms in dense plasmas

Description: In this paper a new model for treating collisional atomic processes has been presented. This model simultaneously and self-consistently treats electron and ion processes. For transitions frequencies above the ion plasma frequency, it is argued that little ion motion occurs although the interaction is still strong; the ion microfield perturbs the atom. The electron impact processes may still be described by a DSF between levels of the perturbed atoms, suggesting the name Microfield Stochastic Model (MSM) for this method. Future work will be directed towards refining some of the approximations used here for application to realistic systems.
Date: December 31, 1997
Creator: Murillo, M.S.
Partner: UNT Libraries Government Documents Department

Generation of metastable rare-gas beams and studies of electron-metastable collision processes. Final technical report, January 1, 1990--September 30, 1991

Description: The basic goals of this research effort of designing, developing, and testing a high-flux, high-purity metastable rare-gas beam source suitable for measurements of electron-collisions have been achieved. Here the authors briefly describe the status of this effort. This effort will be pursued with support from other sources of funding and results of this subsequent effort will be made available to Los Alamos National Laboratory. On the theoretical side they have extended their procedure for calculating the cross sections for electron impact excitation of molecules to determine these cross sections for collisions with metastable states of molecules. As a relevant application they have studied the differential and integral cross sections for the a {sup 1}{Delta}{sub g} {yields} b {sup 1}{Sigma}{sub g}{sup +} transition in O{sub 2} for which measurements (R.I. Hall and S. Trajmar, J. Phys. B 8, L293 (1975)) were available at a single energy (4.5 eV). The agreement between the calculated and measured values of these cross sections is encouraging and support the large value reported experimentally.
Date: December 31, 1993
Creator: McKoy, V. & Trajmar, S.
Partner: UNT Libraries Government Documents Department

Generalized oscillator strengths. Progress report, July 1, 1973--July 1, 1974

Description: Progress is described on research under Contract AT(11-1)3247 and research still to be completed in the period July 1, 1973 to July 1, 1974. The research objectives defined in the original proposal were closely followed. The principal accomplishments during the period were: The introduction of a computer controlled counting system with provision for automatic control and operation of the electron spectrometer currently in use. Electron scattering with excitation of singlet-triplet transitions for helium was studied during the year both to acquire information on collision cross sections and to test a general theory of the abnormally high cross sections for forward scattering found for certain types of transitions. A theoretically predicted minimum in the cross section (at zero scattering angle) was found in a study over the range 100 to 500 eV of the 1/sup 1/S yields 2/sup 3/S transition of helium. Abnormally high cross sections for singlet-triplet transitions at high kinetic energy are predicted when the orbital term symbol is unchanged on excitation. As a test of the theory the X/sup 1/ SIGMA /sup +/ yields b/sup 3/ SIGMA /su p +/ transition in CO was looked for and found at THETA = 0 deg at both 200 and 300 eV thus confirming the theory. New electron scattering studies on both CO and CO/sub 2/ are described. A new method for the calculation of singlet-triplet energy differences from generalized oscillator strengths is described. (auth)
Date: January 1, 1974
Creator: Lassettre, Edwin N.
Partner: UNT Libraries Government Documents Department