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Evolution of Rydberg states in half-cycle pulses: Classical, semiclassical, and quantum dynamics

Description: We summarize recent theoretical advances in the description of the evolution of Rydberg atoms subject to ultrashort pulses extending only a fraction of an optical cycle. We have performed classical. semiclassical and full quantum calculations in order to delineate the classical-quantum correspondence for impulsively perturbed atomic systems. We observe classical and quantum (or semiclassical) oscillations in excitation and ionization which depend on the initial state of atoms and on the strength of the perturbation. These predictions can be experimentally tested. 4 figs.
Date: December 31, 1994
Creator: Burgdoerfer, J. & Reinhold, C.
Partner: UNT Libraries Government Documents Department

Creating and probing coherent atomic states

Description: The authors present a brief review of recent experimental and theoretical time resolved studies of the evolution of atomic wavepackets. In particular, wavepackets comprising a superposition of very-high-lying Rydberg states which are created either using a short half-cycle pulse (HCP) or by rapid application of a DC field. The properties of the wavepackets are probed using a second HCP that is applied following a variable time delay and ionizes a fraction of the atoms, much like a passing-by ion in atomic collisions.
Date: June 1, 1997
Creator: Reinhold, C.O.; Burgdoerfer, J.; Frey, M.T. & Dunning, F.B.
Partner: UNT Libraries Government Documents Department

Resonance enhanced multiphoton and single-photon ionization of molecules and molecular fragments. Final report, May 1993--April 1997

Description: Resonance enhanced multiphoton ionization (REMPI) utilizes pulsed laser radiation to prepare a molecule in an excited state via absorption of one or more photons and to subsequently ionize that level before it decays. A remarkable feature of REMPI is that the very narrow bandwidth of laser radiation makes it possible to select a specific rotational level in the initial (ground) state and to prepare the excited state of interest in a single rotational level. Thus, by suitable choice of the excitation step, it is possible to selectively ionize a species that may be present. The key objective of the effort is to carry out quantitative studies of REMPI of molecules and molecular fragments, as well as of single-photon ionization of these species by coherent VUV radiation, in order to provide a robust description of significant spectral features of interest in related experiments and needed insight into the underlying dynamics of these spectra. A major focus of the effort is joint theoretical and experimental studies of these ion rotational distributions which are being widely studied by the zero-kinetic-energy (ZEKE) technique. This technique, which is based on the detection of photoelectrons resulting from pulsed-field ionization of very high Rydberg states lying just below an ion threshold, makes it possible to obtain cation distributions with subwavenumber resolution. The unprecedented resolution of this ZEKE technique is opening up entirely new vistas in studies of photoionization dynamics, ion spectroscopy, and state-selected ion-molecule reactions. Emerging applications built on the ultra-high resolution of this technique include its use for accurate determination of thermochemically important ionization energies, for characterization of ion rovibrational level structure of large organic molecules, of elemental clusters, and of weakly bound molecular complexes, for probing reactive fragments, and for pump-probe photoelectron studies of wavepacket dynamics. This surge of experimental activity in ultra-high resolution studies ...
Date: September 1, 1998
Creator: McKoy, V.
Partner: UNT Libraries Government Documents Department

Resonance enhanced multiphoton ionization spectra of molecules and molecular fragments. Annual technical report

Description: Resonance Enhanced Multiphoton Ionization (REMPI) utilizes pulsed laser radiation to prepare a molecule in an excited state via absorption of one or more photons and to subsequently ionize that state before it can decay. A remarkable feature of REMPI, and one that is very basic to many of its applications and uses, is that the very narrow bandwidth of the {open_quotes}pump{close_quotes} laser makes it possible to select a specific vibrational and rotational level in the initial state and to prepare the excited state of interest in a single vibrational and rotational level. Thus, by suitable choice of the photon pump transition, it is possible to selectively ionize a species of interest without ionizing any other species that might be present. This feature makes REMPI one of the most powerful tools for ultrasensitive detection of species. With REMPI it is also possible to study the photoionization dynamics of a single rotational level of an excited electronic state. Such state-resolved studies can certainly be expected to provide significant insight into the underlying dynamics of molecular photoionization.
Date: July 1, 1997
Partner: UNT Libraries Government Documents Department

Spectroscopic and Physical Effects of Highly Polar Groups

Description: Since the development of the understanding that the electron distribution within a molecule is chiefly responsible for its properties and behavior, factors influencing this charge distribution have been of interest to scientists. The chemical reactivity of a molecule, the physical properties, and to a large extent, structure and geometry, are all functions of the electron distribution. This study examines the issue of electronic structure from two points of view, each of them focussing on a specific component within the molecules studied. In the present work, the effects of the highly polar carbonyl group on spectroscopic parameters and physical behavior are investigated. An additional area of study is the effect of fluorine substitution on the energy levels of some halogenated ethylenes. The specific parameters examined are the ionization potentials, the absorption frequencies, and the energies of a class of excited states known as molecular Rydberg states. It was during the study of these halogenated ethylenes that the observations leading to the carbonyl compound investigations were made, so that the two areas examined are connected both experimentally and chemically.
Date: December 1981
Creator: Schander, Judith Turner
Partner: UNT Libraries

2001 Gordon Research Conference on Photoions, Photoionization and Photodetachment. Final progress report [agenda and attendees list]

Description: The Gordon Research Conference on Photoions, Photoionization and Photodetachment was held at Williams College, Williamstown, Massachusetts, July 8-13, 2001. The 72 conference attendees represented the spectrum of endeavor in this field, coming from academia, industry, and government laboratories, and including US and foreign scientists, senior researchers, young investigators, and students. Emphasis was placed on current unpublished research and discussion of the future target areas in this field. There was a conscious effort to stimulate discussion about the key issues in the field today. Time for formal presentations was limited. Sessions included the following topics: Vibrational structure, Time resolved studies: nuclear wavepackets, Valence photoionization, Clusters and networks, Resonance structures and decay mechanisms, Ultrafast photoionization, Threshold photoionization, Molecule fixed properties, and Collisional phenomena.
Date: July 13, 2001
Creator: Johnson, Mark
Partner: UNT Libraries Government Documents Department

Resonance enhanced multiphoton ionization spectra of molecules and molecular fragments. Technical report, January 1990--December 1990

Description: The objective of our effort is to carry out theoretical studies of resonance enhanced multiphoton ionization processes in molecules and molecular fragments. These studies are designed to provide a quantitatively robust analysis and prediction of key spectral features of interest in several ongoing experimental studies and applications of this technique.
Date: July 1, 1997
Partner: UNT Libraries Government Documents Department

Studying Atomic Dynamics with Designer Pulses

Description: We present a brief review of recent experimental and theoretical progress on the dynamics of Rydberg atoms using short half cycle pulses. We discuss new possibilities in coherent control and non-linear dynamics of atoms which have lately become possible using various superpositions of such pulses.
Date: September 1, 1997
Creator: Reinhold, C. O.; Burgdorfer, J.; Frey, M. T. & Dunning, F. B.
Partner: UNT Libraries Government Documents Department

Resonant multiphoton ionization spectra of molecules and molecular fragments. Technical report, October 1987--September 1988

Description: The objective of our research under this contract is to carry out studies of resonant enhanced multiphoton ionization (REMPI) processes in molecules. In the (n + 1) - REMPI process of interest an atom or molecule in a specific initial state absorbs n photons making a transition to an intermediate state from which it is subsequently ionized by absorption of an additional photon. A remarkable feature of resonant enhanced multiphoton ionization is that the narrow bandwidth radiation of lasers makes it possible (i) to select a specific rovibrational level in the initial state of a molecule or fragment, (ii) to resonantly pump this level up to a selected rotational-vibrational level of an excited electronic state, and (iii) to subsequently photoionize the state that has been resonantly excited. The extreme state-selectivity and sensitivity make REMPI both a tool with several practical applications and an important technique for probing the photoionization dynamics of vibrationally and electronically excited states. Some significant applications of this technique include its use for state-specific detection of species and diagnostics in combustion and chemical etching media and plasmas, (ii) for state-specific generation of molecular ions for use in ion-molecule reaction studies, and (iii) as a probe of photofragmentation and gas-surface scattering including alignment and orientation effects in these processes.
Date: July 1, 1997
Partner: UNT Libraries Government Documents Department

Atomic physics in strong fields. Final report, September 15, 1990--August 15, 1997

Description: In this final report the author presents a summary of recent research accomplishments. In this grant period (FY90--97), some 36 papers have been published. [See Part 4 for a list of publications]. Significant progress has been made in several areas, both in the development of new theoretical and computational methods, their applications to experimental observations, and in the prediction of some novel new high-intensity phenomena. More detailed discussions on individual research project can be found in previous DOE annual reports and in published articles. Summaries are given of recent research accomplishments in the following areas: (1) time evolution and multiphoton ionization of Rydberg wavepacket in microwave fields; (2) multiphoton detachment of H{sup {minus}}; (3) multiphoton and above-threshold ionization in two-color fields; (4) multiphoton above-threshold ionization by intense laser pulses; and (5) laser-induced chemical bond softening and hardening of H{sub 2}{sup +}, and D{sub 2}{sup +} in intense laser fields.
Date: December 1, 1997
Creator: Chu, S. I.
Partner: UNT Libraries Government Documents Department

The reaction dynamics of alkali dimer molecules and electronically excited alkali atoms with simple molecules

Description: This dissertation presents the results from the crossed molecular beam studies on the dynamics of bimolecular collisions in the gas phase. The primary subjects include the interactions of alkali dimer molecules with simple molecules, and the inelastic scattering of electronically excited alkali atoms with O{sub 2}. The reaction of the sodium dimers with oxygen molecules is described in Chapter 2. Two reaction pathways were observed for this four-center molecule-molecule reaction, i.e. the formations of NaO{sub 2} + Na and NaO + NaO. NaO{sub 2} products exhibit a very anisotropic angular distribution, indicating a direct spectator stripping mechanism for this reaction channel. The NaO formation follows the bond breaking of O{sub 2}, which is likely a result of a charge transfer from Na{sub 2} to the excited state orbital of O{sub 2}{sup {minus}}. The scattering of sodium dimers from ammonium and methanol produced novel molecules, NaNH{sub 3} and Na(CH{sub 3}OH), respectively. These experimental observations, as well as the discussions on the reaction dynamics and the chemical bonding within these molecules, will be presented in Chapter 3. The lower limits for the bond dissociation energies of these molecules are also obtained. Finally, Chapter 4 describes the energy transfer between oxygen molecules and electronically excited sodium atoms.
Date: December 1, 1995
Creator: Hou, H.
Partner: UNT Libraries Government Documents Department

Pressure Effects on Electric Field Spectra of Molecular Rydberg States

Description: Electric field studies, electrochromism, were used to obtain excited-state data for analogous divalent sulfur compounds. The sulfides investigated were dimethyl sulfide and small cyclic sulfides including the three to six member ring compounds. The excited-state dipole moments and polarizabilities are reported for the first s, p, and d Rydberg absorption bands which occur in the near vacuum ultraviolet region from 230 to 170 nm. The excited-state data are interpreted in terms of the particular excited-state (s, p, or d) for the molecules and the bending differences due to the presence of the ring and the number of atoms in the ring. The next section describes the use of electrochromism to investigate the pressure effect of argon, carbon tetrafluoride and sulfur hexafluoride on the spectra for molecular Rydberg states.
Date: December 1982
Creator: Altenloh, Daniel Dean
Partner: UNT Libraries

Zero Temperature Hope Calculations

Description: The primary purpose of the HOPE code is to calculate opacities over a wide temperature and density range. It can also produce equation of state (EOS) data. Since the experimental data at the high temperature region are scarce, comparisons of predictions with the ample zero temperature data provide a valuable physics check of the code. In this report we show a selected few examples across the periodic table. Below we give a brief general information about the physics of the HOPE code. The HOPE code is an ''average atom'' (AA) Dirac-Slater self-consistent code. The AA label in the case of finite temperature means that the one-electron levels are populated according to the Fermi statistics, at zero temperature it means that the ''aufbau'' principle works, i.e. no a priory electronic configuration is set, although it can be done. As such, it is a one-particle model (any Hartree-Fock model is a one particle model). The code is an ''ion-sphere'' model, meaning that the atom under investigation is neutral within the ion-sphere radius. Furthermore, the boundary conditions for the bound states are also set at the ion-sphere radius, which distinguishes the code from the INFERNO, OPAL and STA codes. Once the self-consistent AA state is obtained, the code proceeds to generate many-electron configurations and proceeds to calculate photoabsorption in the ''detailed configuration accounting'' (DCA) scheme. However, this last feature is meaningless at zero temperature. There is one important feature in the HOPE code which should be noted; any self-consistent model is self-consistent in the space of the occupied orbitals. The unoccupied orbitals, where electrons are lifted via photoexcitation, are unphysical. The rigorous way to deal with that problem is to carry out complete self-consistent calculations both in the initial and final states connecting photoexcitations, an enormous computational task. The Amaldi correction is an ...
Date: July 26, 2002
Creator: Rozsnyai, Balazs F.
Partner: UNT Libraries Government Documents Department

Theoretical atomic collision physics. Progress report, July 1, 1991--June 30, 1992

Description: The current focus of the research is low-energy (collision v<<bound v{sub e}) inelastic collisions for selected systems that possess the characteristic that many intermediate states are strongly coupled, such as can occur in classes of excited-atom (including Rydberg atom) collisions with atoms, molecules and positive and negative ions: (1) We are interested in the dependence of various differential and total cross sections on the angular momentum of the initial excited state and on the alignment of the initial electron charge distribution (for non-spherical initially excited states). (2) We wish to understand how characteristics of the classical trajectories (in CTMC calculations), e.g. multiple encounters, quasi-periodicity, chaos, relate to characteristics of the probability (scattering) amplitudes obtained from semiclassical (quantum mechanical) treatments. (3) In particular, in order to investigate a range of ``interaction regimes,`` we have proposed to study low-Rydberg-atom collisions with: ions and polar molecules (long range interaction); non-polar molecules and atoms (short-range interaction); as well as electron-attaching atoms/molecules (transient electron capture possible). (4) We plan to look for observable signatures of possibly novel intracollisional interference effects and quasi-vibrational resonance effects that may occur in low-Rydberg collisions.
Date: March 9, 1992
Creator: Lane, N. F.
Partner: UNT Libraries Government Documents Department

The role of high Rydberg states in the generation of negative ions in negative-ion discharges

Description: The generation of substantial yields of H{sup {minus}} ions in a laser excited H{sub 2} gas has been reported by Pinnaduwage and Christoforu. These H{sup {minus}} yields have been attributed to (2 + 1) REMP photoexcitation processes leading to dissociative attachment of doubly-excited or superexcited states (SES), or dissociative attachment of high Rydberg product states. The new feature of these experiments is the implied large dissociative attachment rates, of order 10{sup {minus}6} cm{sup 3} sec{sup {minus}1}, values that are orders-of-magnitude larger than the dissociative attachment of the vibrationally excited levels of the ground electronic state. While these laser excitations are not directly applicable to a hydrogen negative-ion discharge, the implication of large dissociative attachment rates to the high Rydberg states may affect both the total negative-ion density and the interpretation of discharge performance. Within the discharge energetic electrons will collisionally excite the higher Rydberg states, and the relative contribution of the dissociative attachment of these states when compared with the dissociative attachment to the ground state vibrational levels, is the topic of this paper.
Date: November 28, 1995
Creator: Hiskes, J.R.
Partner: UNT Libraries Government Documents Department

Resonance enhanced multiphoton and single-photon ionization of molecules and molecular fragments. Annual technical report, May 1, 1994--April 30, 1995

Description: The overall objective of this work is to carry out quantitative theoretical studies of these laser-driven ionization processes in molecules so as to provide both a robust description of key spectral features of interest in applications and related experiments and needed insight into these spectra. A major focus of this effort is combined theoretical-experimental studies of molecular ion spectra which are being widely studied by the zero-kinetic-energy (ZEKE) technique. This ZEKE technique, which is base3d on pulsed-field ionization (PFI) of very high Rydberg states, makes it possible to obtain ion distributions with sub-wavenumber resolution and is clearly opening up entirely new vistas in studies of molecular ionization. Some highlights of the progress include: (1) The author has extended the theoretical formulation and computational procedures used in these studies of molecular ionization spectra to general polyatomic systems; (2) He has completed combined theoretical-experimental studies of the molecular ion distributions for photoionization of H{sub 2}S, H{sub 2}CO, and CH{sub 3} by coherent VUV radiation; (3) He has carried out the first calculations of the molecular ion rotational distributions for electronically excited states of NO{sup +} (a {sup 3}{Sigma}{sup +}) and CO{sup +} (A {sup 2}{Pi}); (4) he has also completed calculations of the ion rotational distributions for laser ionization of the small prototypical radicals OH, NH, and CH; and (5) Extensions of the studies of molecular photoionization processes of interest here to large polyatomic molecules are computationally quite demanding. These computational demands arise primarily from complexities associated with the quantum mechanical equations which must be solved to obtain the photoelectron wavefunctions required in these studies. To meet these computational needs the author is currently developing strategies for carrying out these calculations on massively parallel computers such as the Intel Paragon and Cray T3D.
Date: December 31, 1995
Creator: McKoy, V.
Partner: UNT Libraries Government Documents Department

Amplitude modulation of atomic wave functions. Final report

Description: The major theoretical advance has been to show that one can modulate Rydberg wave functions using either of two methods: (1) the amplitude modulation technique which depends on autoionization to deplete part of the wave function, or (2) a phase modulation method, which uses a change in the core potential to create a localized phase shift in the wave function. Essentially, these two methods can both be seen as using the core potential to change the Rydberg wave function, using the imaginary part of the potential to do amplitude modulation, or using the real part of the potential to do phase modulation. This work will be published as the authors acquire experimental results which show the differences between the two methods. One of the results of this theoretical study is that the initial proposal to study Barium 6snd states had a significant flaw. Neither the autoionization time, nor the quantum defect shifts are very large in these cases. This means that the modulation is relatively small. This shows itself primarily in the difficulty of seeing significant population redistribution into different 6snd states. The authors intend to correct this in the next funding cycle either: (a) by using the more quickly decaying Ba 6pnf states to modulate 6snd states, or (b) by using Sr 5 snd states, as outlined in this report. Their first, low power experiments are complete. These experiments have used two pulses to do a temporal version of the Ramsey separated oscillatory fields excitation. The two pulses are generated by passing the single pulse through a Michelson-Morley interferometer, which is computer controlled to sweep one arm through 2.5 {micro}m in steps of 10 nm. The second pulse`s excitation interferes with that of the first pulse, and so the total excitation has a sinusoidal variation (with a time period ...
Date: November 1, 1998
Partner: UNT Libraries Government Documents Department

High-resolution energy-selected study of the reaction NH3+ -> NH2 ++H: Accurate thermo chemistry for the NH2/NH2+ and NH3/NH3 + systems

Description: Employing the newly developed high-resolution pulsed field ionization-photoelectron (PFI-PE)-photoion coincidence (PFI-PEPICO) technique, we have examined the dissociation of energy-selected NH{sub 3}{sup +} to form NH{sub 2}{sup +} + H near its threshold. The breakdown curves for NH{sub 2}{sup +} and NH{sub 3}{sup +} thus obtained yield a value of 15.765 {+-} 0.001 eV for the 0 K dissociation threshold or appearance energy (AE) for NH{sub 2}{sup +} from NH{sub 3}. This value, together with the known ionization energy (IE=10.1864 {+-} 0.0001 eV) and 0 K bond dissociation energy (D{sub 0} = 4.6017 {+-} 0.0025 eV) for NH{sub 3}, allows the determination of the D{sub 0}(NH{sub 2}{sup +}-H) and IE(NH{sub 2}), which are 5.5786 {+-} 0.0010 and 11.1633 {+-} 0.0025 eV, respectively. Using the known 0 K heats of formation ({Delta}H{sup 0}{sub f0}) for NH{sub 3} and H and the AE(NH{sub 2}{sup +}), we obtain the {Delta}H{sup o}{sub f0}(NH{sub 2}{sup +}) = 302.60 {+-} 0.08 kcal/mol. The PFI-PE spectrum for NH{sub 3} exhibits a step-like feature at the 0 K AE(NH{sub 2}{sup +}), indicating that the dissociation of excited NH{sub 3} in high-n (n {ge} 100) Rydberg states at energies slightly above the dissociation threshold occurs on a time scale {le}10{sup -7} s. This step confirms the AE(NH{sub 2}{sup +}) value derived from the PFI-PEPICO measurements. Highly accurate energetic data with well-founded error limits, such as those obtained in the present and other studies using the PFI techniques, are expected to play an important role for the development of the next generation of ab initio quantum computation procedures. This experiment has stimulated a state-of-the-art ab initio quantum chemical calculation (Dixon et al., J. Chem. Phys., accepted). The comparison between theoretical predictions and the best experimental results for the NH{sub 2}/NH{sub 2}{sup +} and NH{sub 3}/NH{sub 3}{sup +} systems indicates that the ...
Date: March 1, 2001
Creator: Song, Y.; Qian, X.M.; Lau, K.C.; Ng, C.Y.; Liu, J.B. & Chen, W.W.
Partner: UNT Libraries Government Documents Department

Photoionization Dynamics in Pure Helium Droplets

Description: The photoionization and photoelectron spectroscopy of pure He droplets are investigated at photon energies between 24.6 eV (the ionization energy of He) and 28 eV. Time-of-flight mass spectra and photoelectron images were obtained at a series of molecular beam source temperatures and pressures to assess the effect of droplet size on the photoionization dynamics. At source temperatures below 16 K, the photoelectron images are dominated by fast electrons produced via direct ionization of He atoms, with a small contribution from very slow electrons with kinetic energies below 1 meV arising from an indirect mechanism. The fast photoelectrons have as much as 0.5 eV more kinetic energy than those from atomic He at the same photon energy. This result is interpreted and simulated within the context of a 'dimer model', in which one assumes vertical ionization from two nearest neighbor He atoms to the attractive region of the He2+ potential energy curve. Possible mechanism for the slow electrons, which were also seen at energies below IE(He), are discussed, including vibrational autoionizaton of Rydberg states comprising an electron weakly bound to the surface of a large HeN+ core.
Date: February 4, 2007
Creator: Peterka, Darcy S.; Kim, Jeong Hyun; Wang, Chia C.; Poisson,Lionel & Neumark, Daniel M.
Partner: UNT Libraries Government Documents Department

Resonance ionization spectroscopy of zirconium atoms

Description: We have examined the stepwise-resonant three-photon-ionization spectrum of neutral zirconium atoms using three separately-tunable pulsed visible dye lasers. Lifetimes of even-parity levels (measured with delayed-photoionization technique) range from 10 to 100 nsec. Direct ionization cross sections appear to be less than 10{sup {minus}17} cm{sup 2}; newly-detected autoionizing levels give peak ionization cross sections (inferred from saturation fluences) up to 10{sup {minus}15} cm{sup 2}. Members of Rydberg series converging to the 315 and 1323 cm{sup {minus}1} levels of Zr{sup +} were identified. ``Clumps`` of autoionizing levels are thought to be due to Rydberg-valence mixing.
Date: May 1, 1992
Creator: Page, R. H.; Dropinski, S. C.; Worden, E. F. Jr. & Stockdale, J. A. D.
Partner: UNT Libraries Government Documents Department

High resolution studies of atoms and small molecules

Description: High resolution, continuous wave lasers have been utilized successfully in studies of small molecules. Examples of two-photon excitation schemes and of multiple resonance excitation sequences will be discussed within the framework of the spectroscopy and dynamics of selected Rydberg states of nitric oxide. Initial results on the circular dichroism of angular distributions in photoelectron spectra of individual hyperfine states of cesium will also be discussed, but no data given.
Date: October 1, 1992
Creator: Bushaw, B. A.; Tonkyn, R. G. & Miller, R. J.
Partner: UNT Libraries Government Documents Department

Atomic physics in strong fields. Progress report

Description: This report discusses: Microwave Driven Multiphoton Excitation Dynamics in Rydberg Atoms; Nonadiabatic Geometric Phases of Multiphoton Transitions in Dissipative Systems and Spin-j Systems; and Nonperturbative Treatments of Atomic and Molecular Processes in Intense Laser Fields.
Date: April 1, 1992
Creator: Chu, Shih-I
Partner: UNT Libraries Government Documents Department

Dielectronic Recombination Theory

Description: A theory now in wide use for the calculation of dielectronic recombination cross sections ({sigma}{sup DR}) and rate coefficients ({alpha}{sup DR}) was one introduced originally by Feshbach for nuclear physics applications, and then later adapted for atomic scattering problems by Hahn. In the following, we briefly review this theory in a very general form, which allows one to account for the effects of overlapping and interacting resonances, as well as continuum-continuum coupling. An extension of our notation will then also allow for the inclusion of the effects of direct radiative recombination, along with a treatment of the interference between radiative and dielectronic recombination. Other approaches to the calculation of {sigma}{sup DR} have been described by Fano and by Seaton. We will not consider those theories here. Calculations of {alpha}{sup DR} have progressed considerably over the last 25 years, since the early work of Burgess. Advances in the reliability of theoretical predictions have also been promoted recently b a variety of direct laboratory measurements of {sigma}{sup DR}. While the measurements of {sigma}{sup DR} for {delta}n {ne} 0 excitations have tended to agree very well with calculations, the case of {delta}n = 0 has been much problematic. However, by invoking a mechanism originally proposed by Jacobs, which takes into account the effect of stray electric fields on high Rydberg states (HRS) participating in the DR process, new calculations have improved the agreement between theory and experiment for these cases. Nevertheless, certain discrepancies still remain.
Date: 1991
Creator: LaGattuta, K. J.
Partner: UNT Libraries Government Documents Department

Correlated charge-changing ion-atom collisions. Progress report, February 16, 1990--February 15, 1993

Description: This report summarizes the progress and accomplishments in accelerator atomic physics research supported by DOE grant DE-FG02-87ER13778 from February 16, 1990 through February 15, 1993. This work involves the experimental investigation of atomic interactions in collisions of charged projectiles with neutral targets or electrons, with particular emphasis on two-electron interactions and electron-correlation effects. The processes studied are of interest both from fundamental and applied points of view. In the latter case, results are obtained which are relevant to the understanding of laboratory and astrophysical plasmas, highly-excited (Rydberg) and continuum states of atoms and ions, atomic structure effects, the interaction of ions with surfaces, and the development of heavy-ion storage-rings. The results obtained have provided the basis for several M.A. thesis projects at Western Michigan and several Ph.D. dissertation projects are currently underway. Summaries of work completed and work in progress are given below in Section II. This research has resulted in 26 papers (in print and in press), 12 invited presentations at national and international meetings, and 28 contributed presentations as detailed in Section III.
Date: February 1, 1993
Creator: Tanis, J. A.
Partner: UNT Libraries Government Documents Department