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Full-Text Articles in Physical Sciences and Mathematics

Differential Cross Sections For The Ionization Of Oriented H₂ Molecules By Electron Impact, James Colgan, Michael S. Pindzola, Francis J. Robicheaux, Christian V. Kaiser, Andrew James Murray, Don H. Madison Dec 2008

Differential Cross Sections For The Ionization Of Oriented H₂ Molecules By Electron Impact, James Colgan, Michael S. Pindzola, Francis J. Robicheaux, Christian V. Kaiser, Andrew James Murray, Don H. Madison

Physics Faculty Research & Creative Works

A nonperturbative close-coupling technique is used to calculate differential cross sections for the electron-impact ionization of H2 at an energy of 35.4 eV. Our approach allows cross sections for any orientation of the molecule with respect to the incident electron beam to be analyzed. New features in the resulting cross sections are found compared with the case where the molecular orientation is averaged, and also with cross sections for He at equivalent electron kinematics. When averaged over all possible molecular orientations, good agreement is found with recent experimental results.


Built-In Electric Field Assisted Spin Injection In Cr And Mn Δ-Layer Doped Aln/Gan(0001) Heterostructures From First Principles, X. Y. Cui, Julia E. Medvedeva, B. Delley, C. Stampfl, Arthur J. Freeman Dec 2008

Built-In Electric Field Assisted Spin Injection In Cr And Mn Δ-Layer Doped Aln/Gan(0001) Heterostructures From First Principles, X. Y. Cui, Julia E. Medvedeva, B. Delley, C. Stampfl, Arthur J. Freeman

Physics Faculty Research & Creative Works

Highly spin-polarized diluted ferromagnetic semiconductors are expected to be widely used as ideal spin injectors. Here, extensive first-principles density-functional theory calculations have been performed to investigate the feasibility of using Cr- and Mn-doped wurtzite polar AlN/GaN(0001) heterostructures, with the aim to realize the appealing half-metallic character and, hence, efficient electrical spin injection. To overcome the formation of detrimental embedded clusters, we propose digital delta-layer doping perpendicular to the growth direction so as to realize enhanced performance at room temperature. The formation energy, electronic and magnetic properties, and the degree of spin polarization for both neutral and charged valence ...


Interference Effects Due To Projectile Target Nucleus Scattering In Single Ionization Of H₂ By 75-Kev Proton Impact, Jason S. Alexander, Aaron C. Laforge, Ahmad Hasan, Z. S. Machavariani, M. F. Ciappina, R. D. Rivarola, Don H. Madison, Michael Schulz Dec 2008

Interference Effects Due To Projectile Target Nucleus Scattering In Single Ionization Of H₂ By 75-Kev Proton Impact, Jason S. Alexander, Aaron C. Laforge, Ahmad Hasan, Z. S. Machavariani, M. F. Ciappina, R. D. Rivarola, Don H. Madison, Michael Schulz

Physics Faculty Research & Creative Works

Doubly differential cross sections (DDCSs) for single ionization of molecular hydrogen by 75-keV proton impact have been measured and calculated as a function of the projectile scattering angle and energy loss. Interference structures are observed in the scattering angular dependence of the DDCSs, which disappear, however, at electron speeds near the projectile speed. The comparison to our calculations shows that the projectile-target nucleus interaction plays a central role. Furthermore, our data suggest that for a given scattering angle, ionization favors well-defined molecular orientations.


Spin- And Fine-Structure-Resolved Ionization Of Krypton, S. Bellm, J. Lower, R. P. Mceachran, E. Weigold, Ciarán Ryan-Anderson, Don H. Madison Dec 2008

Spin- And Fine-Structure-Resolved Ionization Of Krypton, S. Bellm, J. Lower, R. P. Mceachran, E. Weigold, Ciarán Ryan-Anderson, Don H. Madison

Physics Faculty Research & Creative Works

The influence of exchange, correlation, and relativistic effects in the ionization of heavy-target atoms can be sensitively probed by kinematically complete studies involving spin-polarized electrons, in particular when the fine structure of the residual ion is resolved. We present spin asymmetries, triple differential cross sections, and branching ratios for the ionization, by 127.5-eV and 114.3-eV electrons, of ground-state krypton atoms leading to the Kr+ 4s 2S1/2, 4p5 2P1/2, and 4p5 2P3/2 states. In order to untangle contributions from different physical effects, the experimental results are compared to those from distorted-wave Born approximation calculations (non- and ...


Retrieving Photorecombination Cross Sections Of Atoms From High-Order Harmonic Spectra, Shinichiro Minemoto, Toshihito Umegaki, Yuichiro Oguchi, Toru Morishita, Anh-Thu Le, Shinichi Watanabe, Hirofumi Sakai Dec 2008

Retrieving Photorecombination Cross Sections Of Atoms From High-Order Harmonic Spectra, Shinichiro Minemoto, Toshihito Umegaki, Yuichiro Oguchi, Toru Morishita, Anh-Thu Le, Shinichi Watanabe, Hirofumi Sakai

Physics Faculty Research & Creative Works

We observe high-order harmonic spectra generated from a thin atomic medium, Ar, Kr, and Xe, by intense 800-nm and 1300-nm femtosecond pulses. A clear signature of a single-atom response is observed in the harmonic spectra. Especially in the case of Ar, a Cooper minimum, reflecting the electronic structure of the atom, is observed in the harmonic spectra. We successfully extract the photorecombination cross sections of the atoms in the field-free condition with the help of an accurate recolliding electron wave packet. The present protocol paves the way for exploring ultrafast imaging of molecular dynamics with attosecond resolution.


New (E,2e) Studies Of Atomic And Molecular Targets, E. M. Staicu-Casagrande, A. Naja, A. Lahmam-Bennani, A. S. Kheifets, Don H. Madison, B. Joulakian Nov 2008

New (E,2e) Studies Of Atomic And Molecular Targets, E. M. Staicu-Casagrande, A. Naja, A. Lahmam-Bennani, A. S. Kheifets, Don H. Madison, B. Joulakian

Physics Faculty Research & Creative Works

We report new coplanar (e,2e) measurements characterised by large energy transfer and close to minimum momentum transfer from the projectile to the target. Ionisation of the two-electron targets He and H2 is investigated under these particular kinematics. The experimental data are compared with the predictions of the most elaborate theoretical models. The obtained good agreement motivated us to extend our research to the case of more complex targets such as Ar. Comparison with the most elaborate models in the case of multi-electron targets is excellent. Destructive and constructive interference effects in the case of H2 are observed ...


Laser Channeling Of Bethe-Heitler Pairs, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel Nov 2008

Laser Channeling Of Bethe-Heitler Pairs, Erik Lotstedt, Ulrich D. Jentschura, Christoph H. Keitel

Physics Faculty Research & Creative Works

Electron-positron pair creation is analyzed for an arrangement involving three external fields: a high-frequency gamma photon, the Coulomb field of a nucleus, and a strong laser wave. The frequency of the incoming gamma photon is assumed to be larger than the threshold for pair production in the absence of a laser, and the peak electric field of the laser is assumed to be much weaker than Schwinger's critical field. The total number of pairs produced is found to be essentially unchanged by the laser field, while the differential cross section is drastically modified. We show that the laser can ...


Revisiting Unitarity Corrections For Electromagnetic Processes In Collisions Of Relativistic Nuclei, Ulrich D. Jentschura, Kai Hencken, Valery G. Serbo Nov 2008

Revisiting Unitarity Corrections For Electromagnetic Processes In Collisions Of Relativistic Nuclei, Ulrich D. Jentschura, Kai Hencken, Valery G. Serbo

Physics Faculty Research & Creative Works

Unitarity corrections to several electromagnetic processes in collisions of relativistic heavy nuclei are considered. They are due to the unitarity requirement for the S-matrix and correspond to the exchange of a light-by-light scattering block between colliding nuclei. We obtain improved results for the corrections to e+ e- and μ+ μ- pair production as well as new results for unitarity corrections to the production of photons via virtual Compton and virtual Delbrück scattering. These corrections can be numerically large; e.g., the μ+ μ- pair production cross section is reduced by about 50% and nuclear bremsstrahlung by about 15 ÷ 20%.


Reexamining Blackbody Shifts For Hydrogenlike Ions, Ulrich D. Jentschura, Martin K. Haas Oct 2008

Reexamining Blackbody Shifts For Hydrogenlike Ions, Ulrich D. Jentschura, Martin K. Haas

Physics Faculty Research & Creative Works

We investigate blackbody-induced energy shifts for low-lying levels of atomic systems, with a special emphasis on transitions used in current and planned high-precision experiments on atomic hydrogen and ionized helium. Fine-structure- and Lamb-shift-induced blackbody shifts are found to increase with the square of the nuclear charge number, whereas blackbody shifts due to virtual transitions decrease with increasing nuclear charge as the fourth power of the nuclear charge. We also investigate the decay width acquired by the ground state of atomic hydrogen, due to interaction with blackbody photons. The corresponding width is due to an instability against excitation to higher excited ...


Simulations Of Baryon Acoustic Oscillations - I. Growth Of Large-Scale Density Fluctuations, Ryuichi Takahashi, Naoki Yoshida, Shun Saito, For Full List Of Authors, See Publisher's Website. Oct 2008

Simulations Of Baryon Acoustic Oscillations - I. Growth Of Large-Scale Density Fluctuations, Ryuichi Takahashi, Naoki Yoshida, Shun Saito, For Full List Of Authors, See Publisher's Website.

Physics Faculty Research & Creative Works

We critically examine how well the evolution of large-scale density perturbations is followed in cosmological N-body simulations. We first run a large volume simulation and perform a mode-by-mode analysis in three-dimensional Fourier space. We show that the growth of large-scale fluctuations significantly deviates from linear-theory predictions. The deviations are caused by non-linear coupling with a small number of modes at largest scales owing to finiteness of the simulation volume. We then develop an analytic model based on second-order perturbation theory to quantify the effect. Our model accurately reproduces the simulation results. For a single realization, the second-order effect appears typically ...


Absolute Cross Sections For The Ionization-Excitation Of Helium By Electron Impact, S. Bellm, J. Lower, E. Weigold, I. Bray, D. V. Fursa, K. Bartschat, Don H. Madison, Allison L. Harris Sep 2008

Absolute Cross Sections For The Ionization-Excitation Of Helium By Electron Impact, S. Bellm, J. Lower, E. Weigold, I. Bray, D. V. Fursa, K. Bartschat, Don H. Madison, Allison L. Harris

Physics Faculty Research & Creative Works

In a recent publication we presented detailed experimental and theoretical results for the electron-impact-induced ionization of ground-state helium atoms. The purpose of that work was to refine theoretical approaches and provide further insight into the Coulomb four-body problem. Cross section ratios were presented for transitions leading to excited states, relative to those leading to the ground state, of the helium ion. We now build on that study by presenting individual relative triple-differential ionization cross sections (TDCSs) for an additional body of experimental data measured at lower values of scattered-electron energies. This has been facilitated through the development of new electron-gun ...


Extraction Of The Species-Dependent Dipole Amplitude And Phase From High-Order Harmonic Spectra In Rare-Gas Atoms, Anh-Thu Le, Toru Morishita, C. D. Lin Aug 2008

Extraction Of The Species-Dependent Dipole Amplitude And Phase From High-Order Harmonic Spectra In Rare-Gas Atoms, Anh-Thu Le, Toru Morishita, C. D. Lin

Physics Faculty Research & Creative Works

Based on high-order harmonic generation (HHG) spectra obtained from solving the time-dependent Schrödinger equation for atoms, we established quantitatively that the HHG yield can be expressed as the product of a returning electron wave packet and photorecombination cross sections, and the shape of the returning wave packet is shown to be largely independent of the species. By comparing the HHG spectra generated from different targets under identical laser pulses, accurate structural information, including the phase of the recombination amplitude, can be retrieved. This result opens up the possibility of studying the target structure of complex systems, including their time evolution ...


Ergoregion Instability Of Black Hole Mimickers, Paolo Pani, Vitor Cardoso, Mariano Cadoni, Marco Cavaglia Aug 2008

Ergoregion Instability Of Black Hole Mimickers, Paolo Pani, Vitor Cardoso, Mariano Cadoni, Marco Cavaglia

Physics Faculty Research & Creative Works

Ultra-compact, horizonless objects such as gravastars, boson stars, wormholes and superspinars can mimick most of the properties of black holes. Here we show that these "black hole mimickers" will most likely develop a strong ergoregion instability when rapidly spinning. Instability timescales range between ∼ 10-5s and ∼ weeks depending on the object, its mass and its angular momentum. For a wide range of parameters the instability is truly effective. This provides a strong indication that astrophysical ultra-compact objects with large rotation are black holes.


Evidence Of Wave-Particle Duality For Single Fast Hydrogen Atoms, Henning T. Schmidt, Daniel Fischer, Zoltan Berenyi, C. Lewis Cocke, M. Gudmundsson, Nicole Haag, Henrik A B Johansson, Anders Kallberg, Sergey B. Levin, Peter Reinhed, Ulf Sassenberg, Reinhold S. Schuch, Ansgar Simonsson, Kristian Stochkel, Henrik Cederquist Aug 2008

Evidence Of Wave-Particle Duality For Single Fast Hydrogen Atoms, Henning T. Schmidt, Daniel Fischer, Zoltan Berenyi, C. Lewis Cocke, M. Gudmundsson, Nicole Haag, Henrik A B Johansson, Anders Kallberg, Sergey B. Levin, Peter Reinhed, Ulf Sassenberg, Reinhold S. Schuch, Ansgar Simonsson, Kristian Stochkel, Henrik Cederquist

Physics Faculty Research & Creative Works

We report the direct observation of interference effects in a Young's double-slit experiment where the interfering waves are two spatially separated components of the de Broglie wave of single 1.3 MeV hydrogen atoms formed close to either target nucleus in H++H2 electron-transfer collisions. Quantum interference strongly influences the results even though the hydrogen atoms have a de Broglie wavelength, λdB, as small as 25 fm.


The Evolution Of Ga And As Core Levels In The Formation Of Fe/Gaas (001): A High Resolution Soft X-Ray Photoelectron Spectroscopic Study, Tiehan H. Shen, Denis Greig, Mark Hopkinson, George Daniel Waddill, Jamie D. W. Thompson, James R. Neal, Simon A. Morton, James G. Tobin, Jim A. D. Matthew Jul 2008

The Evolution Of Ga And As Core Levels In The Formation Of Fe/Gaas (001): A High Resolution Soft X-Ray Photoelectron Spectroscopic Study, Tiehan H. Shen, Denis Greig, Mark Hopkinson, George Daniel Waddill, Jamie D. W. Thompson, James R. Neal, Simon A. Morton, James G. Tobin, Jim A. D. Matthew

Physics Faculty Research & Creative Works

A high resolution soft x-ray photoelectron spectroscopic study of Ga and as 3d core levels has been conducted for Fe/GaAs (001) as a function of Fe thickness. This work has provided unambiguous evidence of substrate disrupting chemical reactions induced by the Fe overlayer—a quantitative analysis of the acquired spectra indicates significantly differing behavior of Ga and as during Fe growth, and our observations have been compared with existing theoretical models. Our results demonstrate that the outdiffusing Ga and as remain largely confined to the interface region, forming a thin intermixed layer. Whereas at low coverages Fe has little ...


Relation Between Channel And Spatial Mesoscopic Correlations In Volume-Disordered Waveguides, Alexey Yamilov Jul 2008

Relation Between Channel And Spatial Mesoscopic Correlations In Volume-Disordered Waveguides, Alexey Yamilov

Physics Faculty Research & Creative Works

We investigate the relationship between channel and spatial mesoscopic correlations in volume-disordered waveguides. We emphasize the importance of the surface escape function, which describes the distribution of transmitted flux among different channels, and we derive expressions for spatial field and intensity correlation functions directly from the channel ones.


Signature Of Ericson Fluctuations In Helium Inelastic Scattering Cross Sections Near The Double Ionization Threshold, Junliang Xu, Anh-Thu Le, Toru Morishita, C. D. Lin Jul 2008

Signature Of Ericson Fluctuations In Helium Inelastic Scattering Cross Sections Near The Double Ionization Threshold, Junliang Xu, Anh-Thu Le, Toru Morishita, C. D. Lin

Physics Faculty Research & Creative Works

We calculated the inelastic electron impact excitation cross sections of He⁺ by electrons for a model helium atom to examine the onset of the signature of quantum chaotic scattering in this simple system. We find Ericson fluctuations (EF) in the calculated inelastic scattering cross sections only when the impact energies lie within about 0.21 eV below the double ionization threshold. We also discuss the stringent requirements and the proper methods for analyzing the inelastic scattering cross sections in order to observe EF experimentally.


Double Ionization Of Helium By Ion Impact Analyzed Using Four-Body Dalitz Plots, M. F. Ciappina, Michael Schulz, T. Kirchner, Daniel Fischer, R. Moshammer, J. D. Ullrich Jun 2008

Double Ionization Of Helium By Ion Impact Analyzed Using Four-Body Dalitz Plots, M. F. Ciappina, Michael Schulz, T. Kirchner, Daniel Fischer, R. Moshammer, J. D. Ullrich

Physics Faculty Research & Creative Works

We have performed experimental and theoretical studies of double ionization of helium by 6 MeV proton impact using a recently developed tool, four-particle Dalitz plots [Schulz et al., J. Phys. B 22, 3091 (2007)] which enable the representation of multiple differential cross sections as a function of all four fragments in a single spectrum without loss of any part of the total cross section. As a result, the relative importance of the various interactions between the fragments can be studied in great detail. Comparisons of experimental data with theoretical first-order calculations and simulations for the higher-order (TS-2) process show that ...


Ergoregion Instability Of Ultracompact Astrophysical Objects, Vitor Cardoso, Paolo Pani, Mariano Cadoni, Marco Cavaglia Jun 2008

Ergoregion Instability Of Ultracompact Astrophysical Objects, Vitor Cardoso, Paolo Pani, Mariano Cadoni, Marco Cavaglia

Physics Faculty Research & Creative Works

Most of the properties of black holes can be mimicked by horizonless compact objects such as gravastars and boson stars. We show that these ultracompact objects develop a strong ergoregion instability when rapidly spinning. Instability time scales can be of the order of 0.1 seconds to 1 week for objects with mass M=1-106M⊙ and angular momentum J > 0.4M2. This provides a strong indication that ultracompact objects with large rotation are black holes. Explosive events due to ergoregion instability have a well-defined gravitational-wave signature. These events could be detected by next-generation gravitational-wave detectors such as ...


Space-Based Gravitational-Wave Detectors Can Determine The Thermal History Of The Early Universe, Kazunori Nakayama, Shun Saito, Yudai Suwa, Jun'ichi Yokoyama Jun 2008

Space-Based Gravitational-Wave Detectors Can Determine The Thermal History Of The Early Universe, Kazunori Nakayama, Shun Saito, Yudai Suwa, Jun'ichi Yokoyama

Physics Faculty Research & Creative Works

It is shown that space-based gravitational-wave detectors such as DECIGO and/or the Big Bang Observer will provide us with invaluable information on the cosmic thermal history after inflation, and they will be able to determine the reheat temperature TR provided that it lies in the range preferred by the cosmological gravitino problem, TR ~ 105-9 GeV. Therefore it is strongly desired that they will be put into practice as soon as possible.


Random-Walk Access Times On Partially Disordered Complex Networks: An Effective Medium Theory, Julian Candia, V. M. Kenkre, Paul Ernest Parris Jun 2008

Random-Walk Access Times On Partially Disordered Complex Networks: An Effective Medium Theory, Julian Candia, V. M. Kenkre, Paul Ernest Parris

Physics Faculty Research & Creative Works

An analytic effective medium theory is constructed to study the mean access times for random walks on hybrid disordered structures formed by embedding complex networks into regular lattices, considering transition rates F that are different for steps across lattice bonds from the rates f across network shortcuts. The theory is developed for structures with arbitrary shortcut distributions and applied to a class of partially disordered traversal enhanced networks in which shortcuts of fixed length are distributed randomly with finite probability. Numerical simulations are found to be in excellent agreement with predictions of the effective medium theory on all aspects addressed ...


Theory Of Smeared Quantum Phase Transitions, Jose A. Hoyos, Thomas Vojta Jun 2008

Theory Of Smeared Quantum Phase Transitions, Jose A. Hoyos, Thomas Vojta

Physics Faculty Research & Creative Works

We present an analytical strong-disorder renormalization group theory of the quantum phase transition in the dissipative random transverse-field Ising chain. For Ohmic dissipation, we solve the renormalization flow equations analytically, yielding asymptotically exact results for the low-temperature properties of the system. We find that the interplay between quantum fluctuations and Ohmic dissipation destroys the quantum critical point by smearing. We also determine the phase diagram and the behavior of observables in the vicinity of the smeared quantum phase transition.


Retrieval Of Electron-Atom Scattering Cross Sections From Laser-Induced Electron Rescattering Of Atomic Negative Ions In Intense Laser Fields, Xiaoxin Zhou, Zhangjin Chen, Toru Morishita, Anh-Thu Le, C. D. Lin May 2008

Retrieval Of Electron-Atom Scattering Cross Sections From Laser-Induced Electron Rescattering Of Atomic Negative Ions In Intense Laser Fields, Xiaoxin Zhou, Zhangjin Chen, Toru Morishita, Anh-Thu Le, C. D. Lin

Physics Faculty Research & Creative Works

We investigated the two-dimensional electron momentum distributions of atomic negative ions in an intense laser field by solving the time-dependent Schrödinger equation (TDSE) and using the first- and second-order strong-field approximations (SFAs). We showed that photoelectron energy spectra and low-energy photoelectron momentum distributions predicted from SFAs are in reasonable agreement with the solutions from the TDSE. More importantly, we showed that accurate electron-atom elastic scattering cross sections can be retrieved directly from high-energy electron momentum spectra of atomic negative ions in the laser field. This opens up the possibility of measuring electron-atom and electron-molecule scattering cross sections from the photodetachment ...


Impact Of Massive Neutrinos On The Nonlinear Matter Power Spectrum, Shun Saito, Masahiro Takada, Atsushi Taruya May 2008

Impact Of Massive Neutrinos On The Nonlinear Matter Power Spectrum, Shun Saito, Masahiro Takada, Atsushi Taruya

Physics Faculty Research & Creative Works

We present the first attempt to analytically study the nonlinear matter power spectrum for a mixed dark matter model containing neutrinos of total mass ~0.1eV, based on cosmological perturbation theory. The suppression in the power spectrum amplitudes due to massive neutrinos is enhanced in the weakly nonlinear regime. We demonstrate that, thanks to this enhanced effect, the use of such a nonlinear model may enable a precision of σ(mν,tot) ~ 0. 07eV in constraining the total neutrino mass for the planned galaxy redshift survey, a factor of 2 improvement compared to the linear regime.


Fundamental Constants And Tests Of Theory In Rydberg States Of Hydrogenlike Ions, Ulrich D. Jentschura, Peter J. Mohr, Joseph Tan, Benedikt J. Wundt Apr 2008

Fundamental Constants And Tests Of Theory In Rydberg States Of Hydrogenlike Ions, Ulrich D. Jentschura, Peter J. Mohr, Joseph Tan, Benedikt J. Wundt

Physics Faculty Research & Creative Works

A comparison of precision frequency measurements to quantum electrodynamics (QED) predictions for Rydberg states of hydrogenlike ions can yield information on values of fundamental constants and test theory. With the results of a calculation of a key QED contribution reported here, the uncertainty in the theory of the energy levels is reduced to a level where such a comparison can yield an improved value of the Rydberg constant.


Electron Self-Energy In The Presence Of A Magnetic Field: Hyperfine Splitting And G Factor, Vladimir A. Yerokhin, Ulrich D. Jentschura Apr 2008

Electron Self-Energy In The Presence Of A Magnetic Field: Hyperfine Splitting And G Factor, Vladimir A. Yerokhin, Ulrich D. Jentschura

Physics Faculty Research & Creative Works

A high-precision numerical calculation is reported for the self-energy correction to the hyperfine splitting and to the bound-electron g factor in hydrogenlike ions with low nuclear charge numbers. The binding nuclear Coulomb field is treated to all orders, and the nonperturbative remainder beyond the known Zα-expansion coefficients is determined. For the 3He+ ion, the nonperturbative remainder yields a contribution of -450Hz to the normalized difference of the 1S and 2S hyperfine-structure intervals, to be compared with the experimental uncertainty of 71 Hz and with the theoretical error of 50 Hz due to other contributions. In the case of the ...


Relativistic Calculation Of The Two-Photon Decay Rate Of Highly Excited Ionic States, Ulrich D. Jentschura, Andrey S. Surzhykov Apr 2008

Relativistic Calculation Of The Two-Photon Decay Rate Of Highly Excited Ionic States, Ulrich D. Jentschura, Andrey S. Surzhykov

Physics Faculty Research & Creative Works

Based on quantum electrodynamics, we reexamine the two-photon decay of one-electron atoms. Special attention is paid to the calculation of the (two-photon) total decay rates which can be viewed as the imaginary part of the two-loop self-energy. We argue that our approach can be easily applied to the cases with a virtual state having an intermediate energy between the initial and the final state of the decay process leading, thus, to the resonance peaks in the two-photon energy distribution. In order to illustrate our approach, we obtain fully relativistic results, resolved into electric and magnetic multipole components, for the two-photon ...


Large-Angle Electron Diffraction Structure In Laser-Induced Rescattering From Rare Gases, D. Ray, B. Ulrich, I. Bocharova, C. Maharjan, P. Ranitovic, B. Gramkow, M. Magrakvelidze, S. De, I. V. Litvinyuk, Anh-Thu Le, Toru Morishita, C. D. Lin, G. G. Paulus, C. L. Cocke Apr 2008

Large-Angle Electron Diffraction Structure In Laser-Induced Rescattering From Rare Gases, D. Ray, B. Ulrich, I. Bocharova, C. Maharjan, P. Ranitovic, B. Gramkow, M. Magrakvelidze, S. De, I. V. Litvinyuk, Anh-Thu Le, Toru Morishita, C. D. Lin, G. G. Paulus, C. L. Cocke

Physics Faculty Research & Creative Works

We have measured full momentum images of electrons rescattered from Xe, Kr, and Ar following the liberation of the electrons from these atoms by short, intense laser pulses. At high momenta the spectra show angular structure (diffraction) which is very target dependent and in good agreement with calculated differential cross sections for the scattering of free electrons from the corresponding ionic cores.


Alignment Of Heavy Few-Electron Ions Following Excitation By Relativistic Coulomb Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Alexandre Gumberidze, Stephan Fritzsche Apr 2008

Alignment Of Heavy Few-Electron Ions Following Excitation By Relativistic Coulomb Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Alexandre Gumberidze, Stephan Fritzsche

Physics Faculty Research & Creative Works

The Coulomb excitation of highly charged few-electron ions in relativistic collisions with protons and low- Z atoms is studied within the framework of first-order perturbation theory and the multiconfiguration Dirac-Fock method. Apart from the computation of the total excitation cross sections, a detailed theoretical analysis has been performed for the magnetic sublevel population of the residual ions. To describe this population, general expressions are derived for the alignment parameters of the excited states of the ions, taking into account the relativistic and many-electron effects. Calculations are performed for the K→L and K→M excitation of helium- and lithiumlike uranium ...


Structural Evolution Of Ammonia Borane For Hydrogen Storage, Jinbo Yang, Jagat Lamsal, Qingsheng Cai, William B. Yelon, William Joseph James Mar 2008

Structural Evolution Of Ammonia Borane For Hydrogen Storage, Jinbo Yang, Jagat Lamsal, Qingsheng Cai, William B. Yelon, William Joseph James

Physics Faculty Research & Creative Works

We have studied the crystal structure of fully deuterated BH3NH3 using powder neutron diffraction at different temperatures. It is evident that an order-disorder phase transition occurs around 225 K. At low temperature, the compound crystallizes in the orthorhombic structure with space group Pnm21 and gradually transforms to a high temperature tetragonal structure with space group I4 mm above 225 K. At 16 K, the BD3-ND3 unit stacks along the c axis with a tilt angle of about 16° between the N-B bond and the c axis. As the temperature is increased, the BD3-ND3 groups start to reorient along the c ...