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Articles 1  30 of 49
FullText Articles in Physics
Helium TuneOut Wavelength: Gauge Invariance And Retardation Corrections, Gordon W. F. Drake, Jacob Gabriel Manalo, PeiPei Zhang, Kenneth George Herbert Baldwin
Helium TuneOut Wavelength: Gauge Invariance And Retardation Corrections, Gordon W. F. Drake, Jacob Gabriel Manalo, PeiPei Zhang, Kenneth George Herbert Baldwin
Physics Publications
The problem of calculating the tuneout wavelength for an atom interacting with a plane electromagnetic wave is formulated as a zero in the Rayleigh scattering cross section, rather than a zero in the dynamic polarizability. Retardation (finite wavelength) corrections are discussed in the velocity gauge, and possible gauge transformations to a length form are investigated. For the special case of Sstates, it is shown that a pure length form exists for the leading p_{xz} retardation correction, even though one does not exist in general. The results of highprecision calculations in Hylleraas coordinates are presented for the tuneout wavelength of ...
Inactivation Of Myeloma Cancer Cells By Helium And Argon Plasma Jets: The Effect Comparison And The Key Reactive Species, Zeyu Chen, Qingjie Cui, Chen Chen, Dehui Xu, Dingxin Liu, H. L. Chen, Michael G. Kong
Inactivation Of Myeloma Cancer Cells By Helium And Argon Plasma Jets: The Effect Comparison And The Key Reactive Species, Zeyu Chen, Qingjie Cui, Chen Chen, Dehui Xu, Dingxin Liu, H. L. Chen, Michael G. Kong
Bioelectrics Publications
In plasma cancer therapy, the inactivation of cancer cells under plasma treatment is closely related to the reactive oxygen and nitrogen species (RONS) induced by plasmas. Quantitative study on the plasmainduced RONS that related to cancer cells apoptosis is critical for advancing the research of plasma cancer therapy. In this paper, the effects of several reactive species on the inactivation of LP1 myeloma cancer cells are comparatively studied with variable working gas composition, surrounding gas composition, and discharge power. The results show that helium plasma jet has a higher cell inactivation efficiency than argon plasma jet under the same discharge ...
Theory Of Noncontact Friction For AtomSurface Interactions, Ulrich D. Jentschura, M. Janke, Maarten F M De Kieviet
Theory Of Noncontact Friction For AtomSurface Interactions, Ulrich D. Jentschura, M. Janke, Maarten F M De Kieviet
Physics Faculty Research & Creative Works
The noncontact (van der Waals) friction is an interesting physical effect, which has been the subject of controversial scientific discussion. The direct friction term due to the thermal fluctuations of the electromagnetic field leads to a friction force proportional to 1/Z^{5} (where Z is the atomwall distance). The backaction friction term takes into account the feedback of thermal fluctuations of the atomic dipole moment onto the motion of the atom and scales as 1/Z^{8}. We investigate noncontact friction effects for the interactions of hydrogen, groundstate helium, and metastable helium atoms with αquartz (SiO_{2}), gold (Au ...
Comparison Between Electropositive And Electronegative Cold AtmosphericPressure Plasmas: A Modelling Study, Ding X. Liu, Jia F. Li, Ai J. Yang, Xiao H. Wang, Ming Z. Rong, Michael G. Kong
Comparison Between Electropositive And Electronegative Cold AtmosphericPressure Plasmas: A Modelling Study, Ding X. Liu, Jia F. Li, Ai J. Yang, Xiao H. Wang, Ming Z. Rong, Michael G. Kong
Bioelectrics Publications
Cold atmosphericpressure He + N_{2} and He + O_{2} plasmas are chosen as the representatives for electropositive and electronegative plasmas, of which the discharge characteristics are studied and then compared to each other by fluid models. As the increase of the impurity (N_{2} or O_{2}) fraction from 0 to 10%, for He + N_{2} plasmas the electron density and ion density increase, the spatiotemporal distributions of electron density, ion density, electron temperature and electron generation rate change a little. On contrast, for He + O_{2 }plasmas the electron density decreases, the ion density first increases and then decreases ...
Fully Differential Cross Section For Four Body Charge Transfer Process, Ujjal Chowdhury, Allison L. Harris, Jerry Peacher, Don H. Madison
Fully Differential Cross Section For Four Body Charge Transfer Process, Ujjal Chowdhury, Allison L. Harris, Jerry Peacher, Don H. Madison
Physics Faculty Research & Creative Works
Recently experimental fully differential cross sections (FDCS) have been reported for double capture in proton helium collisions which disagree with existing theoretical calculations by two orders of magnitude. We introduce here a theoretical model for charge transfer processes which is fully quantum mechanical and takes all post collision interactions (PCI) between the particles into account exactly. The results of this model are in much better agreement with experimental data.
Four Body Charge Transfer Process In Proton Helium Collision, Ujjal Chowdhury, Allison L. Harris, Jerry Peacher, Don H. Madison
Four Body Charge Transfer Process In Proton Helium Collision, Ujjal Chowdhury, Allison L. Harris, Jerry Peacher, Don H. Madison
Physics Faculty Research & Creative Works
Recent advancements in experimental techniques now allow for the study of fully differential cross sections for 4body collisions. Theoretical fully differential cross sections will be presented and compared with absolute experimental data for transferexcitation in protonhelium collisions. The role of different scattering mechanism will be discussed.
Strongly Enhanced Backward Emission Of Electrons In Transfer And Ionization, Michael Schulz, Xincheng Wang, M. Gundmundsson, Katharina R. Schneider, Aditya H. Kelkar, Alexander B. Voitkiv, B. Najjari, Markus S. Schoffler, Lothar Ph H H Schmidt, Reinhard Dorner, Joachim Hermann Ullrich, Robert Moshammer, Daniel Fischer
Strongly Enhanced Backward Emission Of Electrons In Transfer And Ionization, Michael Schulz, Xincheng Wang, M. Gundmundsson, Katharina R. Schneider, Aditya H. Kelkar, Alexander B. Voitkiv, B. Najjari, Markus S. Schoffler, Lothar Ph H H Schmidt, Reinhard Dorner, Joachim Hermann Ullrich, Robert Moshammer, Daniel Fischer
Physics Faculty Research & Creative Works
We studied threedimensional angular distributions and longitudinal momentum spectra of electrons ejected in transfer plus ionization (TI), i.e., the ejection of one and the capture of a second target electron, for ionhelium collisions. We observe a pronounced structure strongly focused opposite to the projectile beam direction, which we associate with a new correlated TI mechanism proposed recently. This process contributes significantly to the total cross sections over a broad range of perturbations η, even at η as large as 0.5, where uncorrelated TI mechanisms were thought to be dominant.
Double Ionization Of Helium By HighlyChargedIon Impact Analyzed Within The FrozenCorrelation Approximation, Marcelo F. Ciappina, Tom Kirchner, Michael Schulz
Double Ionization Of Helium By HighlyChargedIon Impact Analyzed Within The FrozenCorrelation Approximation, Marcelo F. Ciappina, Tom Kirchner, Michael Schulz
Physics Faculty Research & Creative Works
We apply the frozencorrelation approximation (FCA) to analyze double ionization of helium by energetic highly charged ions. In this model the double ionization amplitude is represented in terms of single ionization amplitudes, which we evaluate within the continuum distorted waveeikonal initial state (CDWEIS) approach. Correlation effects are incorporated in the initial and final states, but are neglected during the time the collision process takes place. We implement the FCA using the Monte Carlo event generator technique, which allows us to generate theoretical event files and to compare theory and experiment using the same analysis tools. The comparison with previous theoretical ...
Relativistic ReducedMass And Recoil Corrections To Vacuum Polarization In Muonic Hydrogen, Muonic Deuterium, And Muonic Helium Ions, Ulrich D. Jentschura
Relativistic ReducedMass And Recoil Corrections To Vacuum Polarization In Muonic Hydrogen, Muonic Deuterium, And Muonic Helium Ions, Ulrich D. Jentschura
Physics Faculty Research & Creative Works
The reducedmass dependence of relativistic and radiative effects in simple muonic bound systems is investigated. The spindependent nuclear recoil correction of order (Zα)^{4}μ^{3}/m^{2}_{N} is evaluated for muonic hydrogen and deuterium and muonic helium ions (μ is the reduced mass and m_{N} is the nuclear mass). Relativistic corrections to vacuum polarization of order α(Zα)^{4}μ are calculated, with a full account of the reducedmass dependence. The results shift theoretical predictions. The radiativerecoil correction to vacuum polarization of order α(Zα)^{5}ln^{2}(Zα) μ^{2}/m_{N} is obtained in leading ...
BlackbodyRadiation Correction To The Polarizability Of Helium, Mariusz Puchalski, Ulrich D. Jentschura, Peter J. Mohr
BlackbodyRadiation Correction To The Polarizability Of Helium, Mariusz Puchalski, Ulrich D. Jentschura, Peter J. Mohr
Physics Faculty Research & Creative Works
The correction to the polarizability of helium due to blackbody radiation is calculated near room temperature. A precise theoretical determination of the blackbody radiation correction to the polarizability of helium is essential for dielectric gas thermometry and for the determination of the Boltzmann constant. We find that the correction, for not too high temperature, is roughly proportional to a modified hyperpolarizability (twocolor hyperpolarizability), which is different from the ordinary hyperpolarizability of helium. Our explicit calculations provide a definite numerical result for the effect and indicate that the effect of blackbody radiation can be excluded as a limiting factor for dielectric ...
Reaction Dynamics In Double Ionization Of Helium By Electron Impact, Marcelo F. Ciappina, Michael Schulz, Tom Kirchner
Reaction Dynamics In Double Ionization Of Helium By Electron Impact, Marcelo F. Ciappina, Michael Schulz, Tom Kirchner
Physics Faculty Research & Creative Works
We present theoretical fully differential cross sections (FDCS) for double ionization of helium by 500 eV and 2 keV electron impact. Contributions from various reaction mechanisms to the FDCS were calculated separately and compared to experimental data. Our theoretical methods are based on the first Born approximation. Higherorder effects are incorporated using the Monte Carlo event generator technique. Earlier, we successfully applied this approach to double ionization by ion impact, and in the work reported here it is extended to electron impact. We demonstrate that at 500 eV impact energy, double ionization is dominated by higherorder mechanisms. Even at 2 ...
Theoretical Fully Differential Cross Sections For DoubleChargeTransfer Collisions, Allison L. Harris, Jerry Peacher, Don H. Madison
Theoretical Fully Differential Cross Sections For DoubleChargeTransfer Collisions, Allison L. Harris, Jerry Peacher, Don H. Madison
Physics Faculty Research & Creative Works
We present a fourbody model for double charge transfer, called the fourbody doublecapture model. This model explicitly treats all four particles in the collision, and we apply it here to fully differential cross sections (FDCSs) for proton+helium collisions. The effects of initial and finalstate electron correlations are studied, as well as the role of the projectilenucleus interaction. We also present results for proton+helium single capture, as well as singlecapture:doublecapture ratios of FDCSs.
Comment On "Coincidence Studies Of He Ionized By C⁶⁺, Au²⁴⁺, And Au⁵³⁺", Michael Schulz, Robert Moshammer, Daniel Fischer, Joachim Hermann Ullrich
Comment On "Coincidence Studies Of He Ionized By C⁶⁺, Au²⁴⁺, And Au⁵³⁺", Michael Schulz, Robert Moshammer, Daniel Fischer, Joachim Hermann Ullrich
Physics Faculty Research & Creative Works
In a recent article, McGovern [Phys. Rev. APLRAAN1050294710.1103/PhysRevA. 81.042704 81, 042704 (2010)] suggested that the normalization of our measured fully differential cross section for ionization of helium by Au^{53+} needs to be checked. In this comment we confirm that the normalization of the published data is correct. Furthermore, we point out that, for a conclusive comparison between experiment and theory, an accurate inclusion of the experimental resolution using correct experimental parameters in the calculation is important.
FourBody Charge Transfer Processes In Heavy Particle Collisions, Allison L. Harris, Jerry Peacher, Michael Schulz, Don H. Madison
FourBody Charge Transfer Processes In Heavy Particle Collisions, Allison L. Harris, Jerry Peacher, Michael Schulz, Don H. Madison
Physics Faculty Research & Creative Works
Fully differential cross sections (FDCS) for proton + helium single capture and transferexcitation collisions are presented using the FourBody TransferExcitation (4BTE) model. This is a first order perturbative model that allows for any twoparticle interaction to be studied. For single capture, the effect of the projectilenuclear term in the perturbation is examined. It is shown that inclusion of this term results in an unphysical minimum in the FDCS, but is required to correctly predict the magnitude of the experimental results. For transferexcitation, the role of electron correlation in the target helium atom is studied, and shown to be unimportant in the ...
Systematic Analysis Of DoubleIonization Dynamics Based On FourBody Dalitz Plots, Daniel Fischer, Michael Schulz, Katharina R. Schneider, Marcelo F. Ciappina, Tom Kirchner, Aditya H. Kelkar, S. Hagman, Manfred Grieser, Kai Uwe Kuhnel, Robert Moshammer, Joachim Hermann Ullrich
Systematic Analysis Of DoubleIonization Dynamics Based On FourBody Dalitz Plots, Daniel Fischer, Michael Schulz, Katharina R. Schneider, Marcelo F. Ciappina, Tom Kirchner, Aditya H. Kelkar, S. Hagman, Manfred Grieser, Kai Uwe Kuhnel, Robert Moshammer, Joachim Hermann Ullrich
Physics Faculty Research & Creative Works
We report on an experimental and theoretical systematic study of double ionization of helium by ion impact in terms of fourparticle Dalitz plots. Several collision systems covering abroad range of perturbation parameters η (projectile charge to speed ratio) were investigated. With increasing η we observe a systematic trend from features, characteristic to correlated doubleionization mechanisms, to signatures of higherorder processes not requiring electronelectron correlations [the mechanism called "twosteptwo projectileelectron interaction" (TS2)]. The data for the largest η can qualitatively be amazingly well described by a simple model only including the TS2 mechanism.
FourBody Model For Transfer Excitation, Allison L. Harris, Jerry Peacher, Don H. Madison, James Colgan
FourBody Model For Transfer Excitation, Allison L. Harris, Jerry Peacher, Don H. Madison, James Colgan
Physics Faculty Research & Creative Works
We present here a fourbody model for transferexcitation collisions, which we call the fourbody transferexcitation (4BTE) model. Each twobody interaction is explicitly included in the 4BTE model, allowing us to study the effects of individual twobody interactions. We apply our model to fully differential cross sections for proton+helium collisions, and study the effect of the incident projectileatom interaction, the scattered projectileion interaction, the projectilenuclear interaction, and electron correlation within the target atom.
Feasibility Of Coherent Xuv Spectroscopy On The 1s2s Transition In Singly Ionized Helium, Maximilian Herrmann, Martin K. Haas, Ulrich D. Jentschura, Franz Kottmann, Dietrich Leibfried, Guido Saathoff, Christoph Gohle, Akira Ozawa, V. Batteiger, S. Knunz, Nikolai N. Kolachevsky, H. A. Schussler, Theodor Wolfgang Hansch, Th H. Udem
Feasibility Of Coherent Xuv Spectroscopy On The 1s2s Transition In Singly Ionized Helium, Maximilian Herrmann, Martin K. Haas, Ulrich D. Jentschura, Franz Kottmann, Dietrich Leibfried, Guido Saathoff, Christoph Gohle, Akira Ozawa, V. Batteiger, S. Knunz, Nikolai N. Kolachevsky, H. A. Schussler, Theodor Wolfgang Hansch, Th H. Udem
Physics Faculty Research & Creative Works
The 1S2S twophoton transition in singly ionized helium is a highly interesting candidate for precision tests of boundstate quantum electrodynamics (QED). With the recent advent of extreme ultraviolet frequency combs, highly coherent quasicontinuouswave light sources at 61 nm have become available, and precision spectroscopy of this transition now comes into reach for the first time. We discuss quantitatively the feasibility of such an experiment by analyzing excitation and ionization rates, propose an experimental scheme, and explore the potential for QED tests.
Differential Cross Sections For The Ionization Of Oriented H_{2} Molecules By Electron Impact, James Colgan, Michael S. Pindzola, Francis J. Robicheaux, Christian V. Kaiser, Andrew James Murray, Don H. Madison
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 closecoupling technique is used to calculate differential cross sections for the electronimpact ionization of H_{2} 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.
Reexamining Blackbody Shifts For Hydrogenlike Ions, Ulrich D. Jentschura, Martin K. Haas
Reexamining Blackbody Shifts For Hydrogenlike Ions, Ulrich D. Jentschura, Martin K. Haas
Physics Faculty Research & Creative Works
We investigate blackbodyinduced energy shifts for lowlying levels of atomic systems, with a special emphasis on transitions used in current and planned highprecision experiments on atomic hydrogen and ionized helium. Finestructure and Lambshiftinduced 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 ...
Signature Of Ericson Fluctuations In Helium Inelastic Scattering Cross Sections Near The Double Ionization Threshold, Junliang Xu, AnhThu Le, Toru Morishita, C. D. Lin
Signature Of Ericson Fluctuations In Helium Inelastic Scattering Cross Sections Near The Double Ionization Threshold, Junliang Xu, AnhThu 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 FourBody Dalitz Plots, M. F. Ciappina, Michael Schulz, T. Kirchner, Daniel Fischer, R. Moshammer, J. D. Ullrich
Double Ionization Of Helium By Ion Impact Analyzed Using FourBody 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, fourparticle 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 firstorder calculations and simulations for the higherorder (TS2) process show that ...
Alignment Of Heavy FewElectron Ions Following Excitation By Relativistic Coulomb Collisions, Andrey S. Surzhykov, Ulrich D. Jentschura, Th H. Stohlker, Alexandre Gumberidze, Stephan Fritzsche
Alignment Of Heavy FewElectron 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 fewelectron ions in relativistic collisions with protons and low Z atoms is studied within the framework of firstorder perturbation theory and the multiconfiguration DiracFock 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 manyelectron effects. Calculations are performed for the K→L and K→M excitation of helium and lithiumlike uranium ...
Electron Density And Temperature Measurement Of An Atmospheric Pressure Plasma By Millimeter Wave Interferometer, Xinpei Lu, Mounir Laroussi
Electron Density And Temperature Measurement Of An Atmospheric Pressure Plasma By Millimeter Wave Interferometer, Xinpei Lu, Mounir Laroussi
Electrical & Computer Engineering Faculty Publications
In this paper, a 105 GHz millimeter wave interferometer system is used to measure the electron density and temperature of an atmospheric pressure helium plasma driven by submicrosecond pulses. The peak electron density and electronneutral collision frequency reach 8 X 10^{12} cm^{3} and 2.1 X 10^{12} s^{1}, respectively. According to the electronhelium collision cross section and the measured electronneutral collision frequency, the electron temperature of the plasma is estimated to reach a peak value of about 8.7 eV.
Projectile AngularDifferential Cross Sections For Transfer And Transfer Excitation In Proton Collisions With Helium, M. Zapukhlyak, T. Kirchner, Ahmad Hasan, B. Tooke, Michael Schulz
Projectile AngularDifferential Cross Sections For Transfer And Transfer Excitation In Proton Collisions With Helium, M. Zapukhlyak, T. Kirchner, Ahmad Hasan, B. Tooke, Michael Schulz
Physics Faculty Research & Creative Works
Projectile angulardifferential cross sections for singletransfer and transfer excitation have been calculated with the twocenter extension of the nonperturbative basis generator method for 5200 keV protonhelium collisions. The calculations are based on the independent electron model, and the eikonal approximation has been used to extract angulardifferential cross sections from impactparameterdependent transition amplitudes. The present results are compared with experimental and previous theoretical data where available. In particular, we consider the ratio of transfer excitation to single capture versus double excitation to single excitation at intermediate energies. An experimentally observed structure in this ratio at a scattering angle about 0.5 ...
TripleDifferential Cross Sections For Target Ionization With Simultaneous Projectile Detachment In 200Kev H⁻ + He Collisions, T. Ferger, Michael Schulz, Daniel Fischer, B. Najjari, R. Moshammer, J. D. Ullrich
TripleDifferential Cross Sections For Target Ionization With Simultaneous Projectile Detachment In 200Kev H⁻ + He Collisions, T. Ferger, Michael Schulz, Daniel Fischer, B. Najjari, R. Moshammer, J. D. Ullrich
Physics Faculty Research & Creative Works
We have performed a kinematically complete experiment for target ionization with simultaneous projectile detachment (TIPD) in 200keV H^{−} + He collisions. From the data we extracted tripledifferential cross sections (TDCSs) for each electron separately. These TDCSs closely resemble corresponding data for single ionization by chargedparticle impact. Surprisingly, the contributions from higherorder processes to TIPD, proceeding through two independent interactions of each electron with the core of the respective other collision partner, are found to be somewhat larger than the firstorder process proceeding through the electronelectron interaction.
Analysis Of Experimental Data For IonImpact Single Ionization Of Helium With Monte Carlo Event Generators Based On Quantum Theory, M. Dürr, B. Najjari, Michael Schulz, A. Dorn, R. Moshammer, A. B. Voitkiv, J. Ullrich
Analysis Of Experimental Data For IonImpact Single Ionization Of Helium With Monte Carlo Event Generators Based On Quantum Theory, M. Dürr, B. Najjari, Michael Schulz, A. Dorn, R. Moshammer, A. B. Voitkiv, J. Ullrich
Physics Faculty Research & Creative Works
Recent multiply differential experimental data taken with reaction microscopes severely challenge predictions of quantum mechanical fewbody models. Here, we report on a thorough analysis of all known possible experimental resolution effects and their influence on the extracted cross sections. Using a Monte Carlo event generator to simulate true events on the basis of quantum calculations allows us to consistently incorporate all aspects of the experimental resolution of the reaction microscope. We study the effect of the instrumental function in single ionization of helium by 3.6 MeV/u Au53+ and 100 MeV/u C6+ ions and find it to significantly ...
Ionization And IonizationExcitation Of Helium To The N=14 States Of He^{+} By Electron Impact, Susan M. Bellm, Julian C A Lower, Klaus Bartschat, Xiaoxu Guan, Daniel Weflen, Matthew S. Foster, Allison L. Harris, Don H. Madison
Ionization And IonizationExcitation Of Helium To The N=14 States Of He+ By Electron Impact, Susan M. Bellm, Julian C A Lower, Klaus Bartschat, Xiaoxu Guan, Daniel Weflen, Matthew S. Foster, Allison L. Harris, Don H. Madison
Physics Faculty Research & Creative Works
We present experimental and theoretical results for the electronimpactinduced ionization of groundstate helium atoms. Using a highsensitivity toroidal electron spectrometer, we measured crosssection ratios for transitions leading to the first three excited states of the residual helium ion relative to the transition leaving the ion in the ground state. Measurements were performed for both symmetric and asymmetricenergysharing kinematics. By presenting results as a ratio, a direct comparison can be made between theoretical and experimental predictions without recourse to normalization. The experimental data are compared to theoretical predictions employing various firstorder models and a secondorder hybrid distortedwave + convergent R matrix with ...
Effects Of The FinalState ElectronIon Interactions On The Fully Differential Cross Sections For HeavyParticleImpact Ionization Of Helium, Don H. Madison, Jerry Peacher, M. Foster, K. Bartschat, H. P. Saha, Allison L. Harris
Effects Of The FinalState ElectronIon Interactions On The Fully Differential Cross Sections For HeavyParticleImpact Ionization Of Helium, Don H. Madison, Jerry Peacher, M. Foster, K. Bartschat, H. P. Saha, Allison L. Harris
Physics Faculty Research & Creative Works
Threedimensional fully differential cross sections for heavyparticleimpact ionization of helium are examined. Previously, the threebody distortedwave (3DW) model has achieved good agreement with experiment in the scattering plane for small momentum transfers, but poor agreement for large momentum transfers. Poor agreement was also observed outside the scattering plane for all momentum transfers. In particular, the 3DW calculations predicted cross sections that were too small both perpendicular to the scattering plane and for large momentum transfers. The important unanswered question concerns the physical effects that cause the significant disagreement between experiment and theory. In previous works, the role of the projectileion ...
YoungType Interference In (E, 2e) Ionization Of H₂, D. S. MilneBrownlie, Matthew S. Foster, Junfang Gao, B. Lohmann, Don H. Madison
YoungType Interference In (E, 2e) Ionization Of H₂, D. S. MilneBrownlie, Matthew S. Foster, Junfang Gao, B. Lohmann, Don H. Madison
Physics Faculty Research & Creative Works
We have investigated the electron impact single ionization of the hydrogen molecule, with fully determined kinematics. The experimental and theoretical results are compared with He ionization under the same conditions. The results indicate that the ejected electron angular distribution for H_{2} is modified due to Youngtype interference between ionization amplitudes for scattering from the two centers in the hydrogen molecule. The observable result is a suppression of the backward scattering (recoil) peak compared with the binary peak.
Kinetic Correlation In PhotoDoubleIonization Processes: The HeIsoelectronic Sequence, Sebastian Otranto, C. R. Garibotti
Kinetic Correlation In PhotoDoubleIonization Processes: The HeIsoelectronic Sequence, Sebastian Otranto, C. R. Garibotti
Physics Faculty Research & Creative Works
Analytical models proposed to represent the twoelectron continuum are revisited. Main results obtained with these models are summarized. Recent studies of the photodoubleionization (PDI) of the Heisoelectronic sequence by means of the recently introduced SC3 model are shown and compared with the results predicted by classical and semiclassical Wannier approaches. By fitting the triply differential cross sections (TDCSs) with the usual dipolar Gaussian form we find that the width has a power dependence on excess energy with exponent 0.25 in the near threshold region and departs from this law with increasing energy