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Sample records for electron impact ionization

  1. Electron impact ionization of glycolaldehyde

    NASA Astrophysics Data System (ADS)

    Ptasinska, Sylwia; Denifl, Stephan; Scheier, Paul; Märk, Tilmann D.

    2005-05-01

    Positive ion formation upon electron impact ionization of the monomeric and dimeric form of glycolaldehyde is studied with high electron energy resolution. In the effusive neutral beam of evaporated monomeric glycolaldehyde some ions with a mass larger than the monomer indicate the presence of weakly bound neutral dimers. The yield of all ions that originate from the electron impact ionization of these neutral dimers exhibit a strong temperature dependence that can be interpreted as being due to the formation of dimers via three body collisions and thermal decomposition of the dimeric form back into monomers at higher temperatures. Ion efficiency curves are measured and analyzed for the 10 most abundant product cations of monomeric glycolaldehyde. The appearance energies of the parent ion signals of the monomer and dimer of glycolaldehyde (10.2 and 9.51 eV, respectively) are lower than the appearance energy of the parent cation of the more complex sugar deoxyribose that was recently determined to be 10.51 eV.

  2. Electron-Impact Ionization Cross Section Database

    National Institute of Standards and Technology Data Gateway

    SRD 107 Electron-Impact Ionization Cross Section Database (Web, free access)   This is a database primarily of total ionization cross sections of molecules by electron impact. The database also includes cross sections for a small number of atoms and energy distributions of ejected electrons for H, He, and H2. The cross sections were calculated using the Binary-Encounter-Bethe (BEB) model, which combines the Mott cross section with the high-incident energy behavior of the Bethe cross section. Selected experimental data are included.

  3. Electron-impact double ionization of magnesium

    SciTech Connect

    Ford, M.J.; El-Marji, B.; Doering, J.P.; Moore, J.H.; Coplan, M.A.; Cooper, J.W.

    1998-01-01

    Electron-impact double-ionization cross sections differential in the angles of the two ejected electrons have been measured at impact energies of 422 and 1052 eV. The energies of the ejected electrons were fixed at 100 eV each. The cross sections are very different at the two incident energies. At 1052 eV the ejected electrons are preferentially found in the forward direction with respect to the incident beam. At 422 eV they are found in the forward and backward directions with approximately equal probability. The 422-eV cross sections are largest when the incident-electron and ejected-electron momentum vectors lie in a common plane. The observations are discussed in the context of several models for double ionization. {copyright} {ital 1998} {ital The American Physical Society}

  4. Electron-Impact Ionization and Dissociative Ionization of Biomolecules

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Chaban, Galina M.; Dateo, Christopher E.

    2006-01-01

    It is well recognized that secondary electrons play an important role in radiation damage to humans. Particularly important is the damage of DNA by electrons, potentially leading to mutagenesis. Molecular-level study of electron interaction with DNA provides information on the damage pathways and dominant mechanisms. Our study of electron-impact ionization of DNA fragments uses the improved binary-encounter dipole model and covers DNA bases, sugar phosphate backbone, and nucleotides. An additivity principle is observed. For example, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3(sup prime)- and C5 (sup prime)-deoxyribose-phospate cross sections, differing by less than 5%. Investigation of tandem double lesion initiated by electron-impact dissociative ionization of guanine, followed by proton reaction with the cytosine in the Watson-Crick pair, is currently being studied to see if tandem double lesion can be initiated by electron impact. Up to now only OH-induced tandem double lesion has been studied.

  5. Dissociative Ionization of Benzene by Electron Impact

    NASA Technical Reports Server (NTRS)

    Huo, Winifred; Dateo, Christopher; Kwak, Dochan (Technical Monitor)

    2002-01-01

    We report a theoretical study of the dissociative ionization (DI) of benzene from the low-lying ionization channels. Our approach makes use of the fact that electron motion is much faster than nuclear motion and DI is treated as a two-step process. The first step is electron-impact ionization resulting in an ion with the same nuclear geometry as the neutral molecule. In the second step the nuclei relax from the initial geometry and undergo unimolecular dissociation. For the ionization process we use the improved binary-encounter dipole (iBED) model. For the unimolecular dissociation step, we study the steepest descent reaction path to the minimum of the ion potential energy surface. The path is used to analyze the probability of unimolecular dissociation and to determine the product distributions. Our analysis of the dissociation products and the thresholds of the productions are compared with the result dissociative photoionization measurements of Feng et al. The partial oscillator strengths from Feng et al. are then used in the iBED cross section calculations.

  6. Ionization of glycerin molecule by electron impact

    NASA Astrophysics Data System (ADS)

    Zavilopulo, A. N.; Shpenik, O. B.; Markush, P. P.; Kontrosh, E. E.

    2015-07-01

    The methods and results of studying the yield of positive ions produced due to direct and dissociative electron impact ionization of the glycerin molecule are described. The experiment is carried out using two independent setups, namely, a setup with a monopole mass spectrometer employing the method of crossing electron and molecular beams and a setup with a hypocycloidal electron spectrometer with the gas-filled cell. The mass spectra of the glycerin molecule are studied in the range of mass numbers of 10-95 amu at various temperatures. The energy dependences of the effective cross sections of the glycerin molecular ions produced by a monoenergetic electron beam are obtained and analyzed; using these dependences, the appearance energies of fragment ions are determined. The dynamics of the glycerin molecule fragment ions formation is investigated in the temperature range of 300-340 K.

  7. Electron-impact ionization of W27 +

    NASA Astrophysics Data System (ADS)

    Pindzola, M. S.; Loch, S. D.

    2016-06-01

    Electron-impact ionization cross sections for W27 + are calculated using a semirelativistic configuration-average distorted-wave (CADW) method. Calculations for direct ionization, excitation autoionization, and branching ratios are compared with recent calculations by Jonauskas et al. [Phys. Rev. A 91, 012715 (2015), 10.1103/PhysRevA.91.012715], who used fully relativistic subconfiguration-average distorted-wave (SCADW) and level-to-level distorted-wave (LLDW) methods. Reasonable agreement is found between the CADW and the recent LLDW calculations for direct ionization of the 4 l (l =0 -1 ,3 ) subshells, but not the 4 d subshell, and between the CADW and recent SCADW-LLDW calculations for excitation autoionization of the 4 l (l =0 -2 ) subshells. Reasonable agreement is also found between the CADW and the recent SCADW calculations, including branching ratios, but both differ from the recent LLDW calculations. Additional CADW calculations are made for excitation autoionization, including branching ratios involving the important 3 l (l =1 -2 ) subshells, not examined by Jonauskas et al. [Phys. Rev. A 91, 012715 (2015), 10.1103/PhysRevA.91.012715].

  8. Electron-Impact Ionization of Methane

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Dateo, Christopher E.; Kwak, Dochan (Technical Monitor)

    2001-01-01

    We report a study of the total ionization of CH_4 by electron impact and its dissociative ionization from the ^2T_2 channel. The calculation of the total ionization cross section uses the improved Binary-Encounter-Dipole model (iBED).(W. A Huo, Phys. Rev. A (submitted for publication).) The dipole Born cross section in the model is expressed in terms of a three-term representation and the optical oscillator strengths are taken from Backx and Van der Wiel.(C. Backx and M. J. Van der Wiel, I Phys. B 18) 3020 (1975). The nuclear dynamics for the dissociation of the ^2T_2 channel is studied using the statistical model. A search of the potential energy surface of the ^2T_2 state of CH_4^+ shows two minima, of C_2v and C_3v symmetries, in agreement with earlier calculations. ((a) K. Takeshita, J. Chem. Phys. 86), 329 (1987). (b) R. F. Frey and E. R. Davidson, J. Chem. Phys. 88, 1775 (1988). The dissociation of the CH_4^+ to CH_3^+ + H goes through a saddle point. Comparison with recent experimental data will be presented and the role of Jahn-Teller effect discussed.

  9. Single ionization of helium by electron impact

    SciTech Connect

    Bray, I.; Fursa, D. V.; Kadyrov, A. S.; Stelbovics, A. T.

    2010-06-15

    We suggest that the problem of single ionization of helium by electron impact, leaving the ion in the ground state, has been solved theoretically for the full range of kinematics and collision geometries of practical interest. Following the emphasis on the study of out-of-plane geometries where the cross sections are very small [Schulz et al., Nature 422, 48 (2003)], we find that the convergent close-coupling calculations, in either a frozen- or a multicore treatment of the target, are in excellent agreement with the available measurements. Curiously, some systematic discrepancies are identified for some in-plane cases where the cross sections are an order of magnitude larger. Further measurements are required to resolve these discrepancies. If subsequent measurements confirm the present calculations, then we would have a strong case that the problem has been solved.

  10. Dissociative Ionization of Pyridine by Electron Impact

    NASA Technical Reports Server (NTRS)

    Dateo, Christopher; Huo, Winifred; Kwak, Dochan (Technical Monitor)

    2002-01-01

    In order to understand the damage of biomolecules by electrons, a process important in radiation damage, we undertake a study of the dissociative ionization (DI) of pyridine (C5H5N) from the low-lying ionization channels. The methodology used is the same as in the benzene study. While no experimental DI data are available, we compare the dissociation products from our calculations with the dissociative photoionization measurements of Tixier et al. using dipole (e, e(+) ion) coincidence spectroscopy. Comparisons with the DI of benzene is also made so as to understand the difference in DI between a heterocyclic and an aromatic molecule.

  11. Influence of renormalization shielding on the electron-impact ionization process in dense partially ionized plasmas

    SciTech Connect

    Song, Mi-Young; Yoon, Jung-Sik; Jung, Young-Dae

    2015-04-15

    The renormalization shielding effects on the electron-impact ionization of hydrogen atom are investigated in dense partially ionized plasmas. The effective projectile-target interaction Hamiltonian and the semiclassical trajectory method are employed to obtain the transition amplitude as well as the ionization probability as functions of the impact parameter, the collision energy, and the renormalization parameter. It is found that the renormalization shielding effect suppresses the transition amplitude for the electron-impact ionization process in dense partially ionized plasmas. It is also found that the renormalization effect suppresses the differential ionization cross section in the peak impact parameter region. In addition, it is found that the influence of renormalization shielding on the ionization cross section decreases with an increase of the relative collision energy. The variations of the renormalization shielding effects on the electron-impact ionization cross section are also discussed.

  12. Threshold law for electron-atom impact ionization

    NASA Technical Reports Server (NTRS)

    Temkin, A.

    1982-01-01

    A derivation of the explicit form of the threshold law for electron impact ionization of atoms is presented, based on the Coulomb-dipole theory. The important generalization is made of using a dipole function whose moment is the dipole moment formed by an inner electron and the nucleus. The result is a modulated quasi-linear law for the yield of positive ions which applies to positron-atom impact ionization.

  13. Electron-impact ionization of Se2+ and Se3+

    NASA Astrophysics Data System (ADS)

    Pindzola, M. S.; Loch, S. D.

    2016-06-01

    Electron-impact ionization cross sections for Se2+ and Se3+ are calculated using a semi-relativistic configuration-average distorted-wave (CADW) method. Good agreement between the CADW calculations and recent experimental measurements are found for the single ionization of Se2+ from threshold to 500 eV and for the double ionization of Se2+ from threshold to 225 eV. Good agreement between the CADW calculations and recent experimental measurements are also found for the single ionization of Se3+ from threshold to 200 eV and for the double ionization of Se3+ near the peak of the cross section at 350 eV. Disagreements at other incident electron energies may be due to the complexity of the ionization pathways for low charged Se atomic ions, the various theoretical approximations, and the difficulty in measuring relatively small double ionization events.

  14. Electron impact multiple ionization cross sections of heavy ions

    NASA Astrophysics Data System (ADS)

    Zeng, Jiaolong; Liu, Pengfei; Dai, Jiayu; Yuan, Jianmin

    2014-05-01

    Cross sections of electron impact ionization are important in modeling both astrophysical and laboratory plasmas. For heavy ions, accurate determination of this microscopic physical quantity is difficult due to the complex atomic structure. At high incident electron energy, inner-shell excitation and ionization processes can occur, which will result in complicated decay including Auger and radiative decay processes. For deep inner-shell excitation and ionization, cascaded Auger processes are very likely. Under conditions of collisional ionization equilibrium, the balance of electron-ion recombination and electron impact single ionization determines the charge state distribution (CSD). Accurate CSD, which in turn determined by accurate cross sections, is very important in a wide regime of spectroscopic diagnostics to infer the physical conditions of plasmas such as the electron temperature, electron density, and elemental abundance. As an illustrative example, the cross sections from the ground configuration of Sn13+ in forming Sn13+, -Sn16+ are reported in detail. The contributions from the electron impact excitation, electron impact ionization and resonant excitation processes are included.

  15. Electron-Impact Total Ionization Cross Sections of Hydrocarbon Ions

    PubMed Central

    Irikura, Karl K.; Kim, Yong-Ki; Ali, M. A.

    2002-01-01

    The Binary-Encounter-Bethe (BEB) model for electron-impact total ionization cross sections has been applied to CH2+, CH3+, CH4+, C2H2+, C2H4+, C2H6+ and H3O+. The cross sections for the hydrocarbon ions are needed for modeling cool plasmas in fusion devices. No experimental data are available for direct comparison. Molecular constants to generate total ionization cross sections at arbitrary incident electron energies using the BEB formula are presented. A recent experimental result on the ionization of H3O+ is found to be almost 1/20 of the present theory at the cross section peak.

  16. Electron impact ionization of cycloalkanes, aldehydes, and ketones

    SciTech Connect

    Gupta, Dhanoj; Antony, Bobby

    2014-08-07

    The theoretical calculations of electron impact total ionization cross section for cycloalkane, aldehyde, and ketone group molecules are undertaken from ionization threshold to 2 keV. The present calculations are based on the spherical complex optical potential formalism and complex scattering potential ionization contribution method. The results of most of the targets studied compare fairly well with the recent measurements, wherever available and the cross sections for many targets are predicted for the first time. The correlation between the peak of ionization cross sections with number of target electrons and target parameters is also reported. It was found that the cross sections at their maximum depend linearly with the number of target electrons and with other target parameters, confirming the consistency of the values reported here.

  17. Electron impact ionization of Ar/sup 8 +/

    SciTech Connect

    Defrance, P.; Rachafi, S.; Jureta, J.; Meyer, F.; Chantrenne, S.

    1986-01-01

    Absolute electron impact ionization cross-sections have been measured for the Neon-like Ar/sup 8 +/ in the energy range from below the threshold for the metastable state to 2500 eV. No contribution of metastable states is observed. The results are well reproduced by the Distorted Wave Born Approximation. 12 refs., 1 fig.

  18. Electron-impact ionization of hydrogenlike ions in QED theory

    SciTech Connect

    Sun, H.-L.; Chang, J.-C.; Hsiao, J.-T.; Lin, S.-F.; Huang, K.-N.

    2010-04-15

    Relativistic cross sections for electron-impact ionization including quantum electrodynamic effects are studied for hydrogenlike ions in the two-potential formalism. Results are compared with other theoretical calculations and experimental data. Effects of the transverse-photon interaction as well as vacuum polarization potential between charges are analyzed. Systematic behaviors along the H-isoelectronic sequence are summarized.

  19. Ionization of the glycerin molecule by the electron impact

    NASA Astrophysics Data System (ADS)

    Zavilopulo, A. N.; Shpenik, O. B.; Markush, P. P.; Kontrosh, E. E.

    2014-10-01

    The paper describes experimental method for and presents the results of studying positive ion yields produced due to direct and dissociative electron-impact ionization of the glycerin molecule. The mass spectra of the glycerin molecule are studied in the range of mass numbers of 10-95 amu at different temperatures. The energy dependences of the ionization efficiency cross sections of the glycerin molecule ions produced by a monoenergetic electron beam are analyzed; using these dependences, the appearance energies of fragment ions are determined. The dynamics of fragment ion formation is investigated in the temperature range of 300-340 K.

  20. Electron impact ionization and multiphoton ionization of doped superfluid helium droplets: A comparison

    NASA Astrophysics Data System (ADS)

    He, Yunteng; Zhang, Jie; Kong, Wei

    2016-02-01

    We compare characteristics of electron impact ionization (EI) and multiphoton ionization (MPI) of doped superfluid helium droplets using the same droplet source. Selected dopant ion fragments from the two ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different ionization mechanisms. While EI directly ionizes helium atoms in a droplet therefore has higher yields for bigger droplets (within a limited size range), MPI is insensitive to the helium in a droplet and is only dependent on the number of dopant molecules. The optimal timing of the ionization pulse also varies with the doping pressure, implying a velocity slip among different sized droplets. Calculations of the doping statistics and ionization probabilities qualitatively agree with the experimental data. Our results offer a word of caution in interpreting the pressure and timing dependence of superfluid helium droplets, and we also devise a scheme in achieving a high degree of doping while limiting the contribution of dopant clusters.

  1. Electron impact ionization and multiphoton ionization of doped superfluid helium droplets: A comparison.

    PubMed

    He, Yunteng; Zhang, Jie; Kong, Wei

    2016-02-28

    We compare characteristics of electron impact ionization (EI) and multiphoton ionization (MPI) of doped superfluid helium droplets using the same droplet source. Selected dopant ion fragments from the two ionization schemes demonstrate different dependence on the doping pressure, which could be attributed to the different ionization mechanisms. While EI directly ionizes helium atoms in a droplet therefore has higher yields for bigger droplets (within a limited size range), MPI is insensitive to the helium in a droplet and is only dependent on the number of dopant molecules. The optimal timing of the ionization pulse also varies with the doping pressure, implying a velocity slip among different sized droplets. Calculations of the doping statistics and ionization probabilities qualitatively agree with the experimental data. Our results offer a word of caution in interpreting the pressure and timing dependence of superfluid helium droplets, and we also devise a scheme in achieving a high degree of doping while limiting the contribution of dopant clusters. PMID:26931697

  2. Fragmentation of the POPOP molecule by electron-impact ionization

    NASA Astrophysics Data System (ADS)

    Romanova, L. G.; Zavilopulo, A. N.; Shpenik, O. B.; Kukhto, A. V.; Agafonova, A. S.

    2008-07-01

    Single and dissociative ionizations of the POPOP molecule by electron impact in the gas phase are studied using mass spectroscopy. Fragmentation pathways of the molecule are proposed taking into account the common system of conjugated π-electrons and heteroatoms in the POPOP molecule. The appearance thresholds for certain fragments of the molecule are determined based on experimentally measured ionization cross sections as functions of the ionizing electron energy. An ion with m/z = 144 [C9H6ON]+ that is complementary to a fragment with m/z = 220 [C13H10ON]+ (present in the NIST mass spectrum database) is found for the first time in the mass spectrum of POPOP. Its appearance threshold is determined (Eap = 9.48 eV).

  3. Electron-Impact Ionization of Mg

    NASA Technical Reports Server (NTRS)

    Boivin, R. F.; Srivastava, S. K.

    1997-01-01

    A pulsed crossed beam technique is used to measure inonization cross-sections of metallic atoms. Relative values of cross-sections of single, double and triple inonization of magnesium have been successfully measured with good accuracy over the o-700 eV range. Absolute values of cross sections have been obtained by normalization to a theoretical value at high electron energy. Results are compared to previously published values and, for single inonization in particular, a comparison with theoretical cross-extions is perfomed.

  4. Electron-Impact Ionization Measurements Important for Solar Physics

    NASA Astrophysics Data System (ADS)

    Bannister, M. E.

    2004-05-01

    Electron impact ionization (EII) is the dominant ionization mechanism in the solar chromosphere, transition region, and corona. Analyzing spectra from this region of the sun requires accurate ionization balance calculations for plasmas in collisional ionization equilibrium as well as plasmas under conditions of non-equilibrium ionization. Here we report on a series of laboratory measurements of EII that are now underway at the ORNL Multicharged Ion Research Facility for selected ions in the heliumlike, berylliumlike, and oxygenlike isoelectronic sequences. We have found significant errors and uncertainties in the EII data for these isoelectronic sequences, primarily due to uncertainty in the fraction of metastable ions encountered in prior measurements. By determining the metastable ion fractions independent of the ionization experiments, our measurements will provide new EII data for both ground-state and metastable ions with uncertainties of 15% or less. This material is based upon work supported by NASA under Award No. NNH04AA151 issued through the Sun-Earth Connection Division's Solar & Heliospheric Physics Supporting Research and Technology Program and by the U.S. Department of Energy under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.

  5. Electron-impact dissociation and ionization of NO+ ions

    NASA Astrophysics Data System (ADS)

    Belic, D. S.; Urbain, X.; Cherkani-Hassani, H.; Defrance, P.

    2016-07-01

    Absolute cross sections for electron-impact ionization and dissociation of NO+ ions are reported. Simple ionization to NO2+ ion and production of singly charged N+ and O+ and doubly charged N2+ and O2+ fragments have been investigated. The animated electron-ion crossed-beam method is applied in the energy range from the respective thresholds up to 2.5 keV. The maximum of the simple ionization cross section is found to be (3.49 ± 0.07) × 10‑17 cm2 at 135 eV. The total cross sections for N+ and O+ fragments at the maximum are found to be (13.9 ± 1.0) × 10‑17 cm2 and (14.0 ± 1.4) × 10‑17 cm2, respectively, both at an energy of 85 eV. By performing careful magnetic field scans of the detected signal, contributions of dissociative excitation and dissociative ionization to N+ and O+ production are determined separately. The cross sections for asymmetric dissociative ionization to N2+ and O2+ are found to be over one order of magnitude smaller. Distributions of the kinetic energy release to the fragments are determined for all dissociation processes.

  6. Electron impact ionization of highly charged lithiumlike ions

    SciTech Connect

    Wong, K L

    1992-10-01

    Electron impact ionization cross sections can provide valuable information about the charge-state and power balance of highly charged ions in laboratory and astrophysical plasmas. In the present work, a novel technique based on x-ray measurements has been used to infer the ionization cross section of highly charged lithiumlike ions on the Livermore electron beam ion trap. In particular, a correspondence is established between an observed x ray and an ionization event. The measurements are made at one energy corresponding to approximately 2.3 times the threshold energy for ionization of lithiumlike ions. The technique is applied to the transition metals between Z=22 (titanium, Ti[sup 19+]) and Z=26 (iron, Fe[sup 23+]) and to Z=56 (barium, Ba[sup 53+]). The results for the transition metals, which have an estimated 17-33% uncertainty, are in good overall agreement with a relativistic distorted-wave calculation. However, less good agreement is found for barium, which has a larger uncertainty. Methods for properly accounting for the polarization in the x-ray intensities and for inferring the charge-state abundances from x-ray observations, which were developed for the ionization measurements, as well as an x-ray model that assists in the proper interpretation of the data are also presented.

  7. Measurements of Electron-Impact Ionization Relevant for Astrophysics

    NASA Astrophysics Data System (ADS)

    Bannister, M. E.

    2005-05-01

    For many cosmic plasmas, such as are formed in supernova remnants, stellar coronae, the interstellar medium (ISM), the intracluster medium in clusters of galaxies, and elliptical galaxies, electron impact ionization (EII) is the dominant ionization mechanism. Spectroscopic data produced by an array of past, present, and future satellite spectroscopic observatories are being used to address many fundamental questions in astrophysics. Analyzing the collected spectra from electron-ionized plasmas, however, requires accurate ionization balance calculations for plasmas in collisional ionization equilibrium (CIE) as well as plasmas under conditions of non-equilibrium ionization (NEI). Therefore accurate EII data are needed for ions found in these astrophysical environments. Here we report on recent laboratory measurements of EII at the ORNL Multicharged Ion Research Facility for selected ions in the berylliumlike isoelectronic sequence. These results are compared with state-of-the-art non-perturbative calculations for these ions. This systematic investigation of EII will continue with measurements on heliumlike and oxygenlike ions. For these isoelectronic sequences there appear to be significant errors and uncertainties in the EII data, primarily due to uncertainty in the fraction of metastable ions encountered in prior measurements. By determining the metastable ion fractions independent of the ionization experiments, our measurements will provide new EII data with uncertainties of 15% or less. This material is based upon work supported by NASA under Award Nos. NNH04AA151 and NNH04AA72I and by the U.S. Department of Energy under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.

  8. Electron-impact ionization measurements for use in astrophysics

    NASA Astrophysics Data System (ADS)

    Bannister, Mark E.

    2006-05-01

    Spectroscopic data produced by an array of past, present, and future satellite and space observatories are being used to address many fundamental questions in astrophysics. Analyzing the collected spectra from electron-ionized plasmas, however, requires accurate ionization balance calculations for plasmas in collisional ionization equilibrium (CIE) as well as plasmas under conditions of non-equilibrium ionization (NEI). Therefore accurate electron-impact ionization (EII) data are needed for ions found in many cosmic plasmas where EII is the dominant ionization mechanism, such as supernova remnants, stellar coronae, the interstellar medium (ISM), the intracluster medium in clusters of galaxies, and elliptical galaxies. Here we report on a program of laboratory measurements of EII for ions in the berylliumlike isoelectronic sequence at the ORNL Multicharged Ion Research Facility. These results are compared with state-of-the-art non-perturbative calculations. Our studies also focus on measurements of EII for heliumlike and oxygenlike ions. For these three isoelectronic sequences there appear to be significant errors and uncertainties in the EII data used in astrophysics, primarily due to uncertainty in the fraction of metastable ions encountered in prior measurements. By determining the metastable ion fractions independently of the ionization experiments, our measurements will provide new EII data with total uncertainties of 15% or less. This material is based upon work supported by NASA under Award Nos. NNH04AA151 and NNH04AA72I and by the U.S. Department of Energy under Contract No. DE-AC05-00OR22725 with UT-Battelle, LLC.

  9. Electron Impact Ionization of C_2F_6

    NASA Astrophysics Data System (ADS)

    Iga, Ione; Pereira Sanches, Ivana; Srivastava, Santosh Kumar

    2001-10-01

    Besides CF_4, perfluoroethane, C_2F_6, is also one of the fluorocarbon compounds most frequently used in plasma processing applications. Consequently, the knowledge of the ionization properties of C_2F6 is clearly of interest in order to model the plasma-chemical reactions. Nevertheless, only few partial ionization-cross-section measurements [1,2] for this molecule were reported in the literature. Also, the energy range covered in these studies was very limited (below 120 eV). Recently, we have studied these properties. More specifically, partial ionization cross sections (PICS) for the fragments: C^+, F^+, CF^+, CF_2^+, CF_3^+ and C_2F_5^+, produced by electron impact on C_2F_6, were measured in a single-collision condition from near ionization threshold to 1000 eV. In addition, total ionization cross sections (TICS) are also obtained by summing up the PICS's. The comparison of our measured PICS and derived TICS with available data [1-4] will be presented during the Conference. [1] H. U. Poll, J. Meischner, Contrib. Plasma Phys. 27 (1987) 359. [2] C. Q. Jiao, A Garscadden, P. D. Haaland, Chem. Phys. Lett. 310 (1999) 52. [3] H. Nishimura, W. M. Huo, M. A Ali and Y -K. Kim, J. Chem. Phys. 110 (1999) 3811. [4] L. G. Christophorou and J. K. Olthoff, J. Phys. Chem. Ref. Data 27 (1998) 1 and references therein.

  10. Electron-impact ionization of helium with large energy transfer

    SciTech Connect

    Bray, I.; Fursa, D. V.; Stelbovics, A. T.

    2006-09-15

    We consider the recently measured case of 730 eV electron-impact ionization of the ground state of helium with 205 and 500 eV coplanar outgoing electrons by Catoire et al. [J. Phys. B 39, 2827 (2006)]. These measurements, which are on a relative scale, show some unexpected structure and variation from the second-order distorted-wave Born approximation R-matrix and Brauner-Briggs-Klar theories. Using the convergent close-coupling method we provide an improved agreement with experiment, but some discrepancies still remain.

  11. Low-energy electron-impact ionization of helium

    SciTech Connect

    Schow, E.; Hazlett, K.; Childers, J. G.; Medina, C.; Vitug, G.; Khakoo, M. A.; Bray, I.; Fursa, D. V.

    2005-12-15

    Normalized doubly differential cross sections for the electron-impact ionization of helium at low energies are presented. The data are taken at the incident electron energies of 26.3, 28.3, 30.3, 32.5, 34.3, 36.5, and 40.7 eV and for scattering angles of 10 deg. -130 deg. The measurements involve the use of the moveable target method developed at California State University Fullerton to accurately determine the continuum background in the energy-loss spectra. Normalization of experimental data is made on a relative scale to well-established experimental differential cross sections for excitation of the n=2 manifold of helium and then on an absolute scale to the well-established total ionization cross sections of Shah et al. [J. Phys. B 21, 2751 (1988)]. Comparisons are made with available experimental data and the results of the convergent close-coupling theory.

  12. Cross Sections for Inner-Shell Ionization by Electron Impact

    SciTech Connect

    Llovet, Xavier; Powell, Cedric J.; Salvat, Francesc; Jablonski, Aleksander

    2014-03-15

    An analysis is presented of measured and calculated cross sections for inner-shell ionization by electron impact. We describe the essentials of classical and semiclassical models and of quantum approximations for computing ionization cross sections. The emphasis is on the recent formulation of the distorted-wave Born approximation by Bote and Salvat [Phys. Rev. A 77, 042701 (2008)] that has been used to generate an extensive database of cross sections for the ionization of the K shell and the L and M subshells of all elements from hydrogen to einsteinium (Z = 1 to Z = 99) by electrons and positrons with kinetic energies up to 1 GeV. We describe a systematic method for evaluating cross sections for emission of x rays and Auger electrons based on atomic transition probabilities from the Evaluated Atomic Data Library of Perkins et al. [Lawrence Livermore National Laboratory, UCRL-ID-50400, 1991]. We made an extensive comparison of measured K-shell, L-subshell, and M-subshell ionization cross sections and of Lα x-ray production cross sections with the corresponding calculated cross sections. We identified elements for which there were at least three (for K shells) or two (for L and M subshells) mutually consistent sets of cross-section measurements and for which the cross sections varied with energy as expected by theory. The overall average root-mean-square deviation between the measured and calculated cross sections was 10.9% and the overall average deviation was −2.5%. This degree of agreement between measured and calculated ionization and x-ray production cross sections was considered to be very satisfactory given the difficulties of these measurements.

  13. Semirelativistic model for ionization of atomic hydrogen by electron impact

    SciTech Connect

    Attaourti, Y.; Taj, S.; Manaut, B.

    2005-06-15

    We present a semirelativistic model for the description of the ionization process of atomic hydrogen by electron impact in the first Born approximation by using the Darwin wave function to describe the bound state of atomic hydrogen and the Sommerfeld-Maue wave function to describe the ejected electron. This model, accurate to first order in Z/c in the relativistic correction, shows that, even at low kinetic energies of the incident electron, spin effects are small but not negligible. These effects become noticeable with increasing incident electron energies. All analytical calculations are exact and our semirelativistic results are compared with the results obtained in the nonrelativistic Coulomb Born approximation both for the coplanar asymmetric and the binary coplanar geometries.

  14. Electron-impact ionization of Li2 and Li2+

    NASA Astrophysics Data System (ADS)

    Pindzola, M. S.; Robicheaux, F.; Ballance, C. P.; Colgan, J.

    2008-10-01

    Electron-impact ionization cross sections for Li2 and Li2+ are calculated using a configuration-average distorted-wave method. Bound orbitals for the molecule and its ions are calculated using a single-configuration self-consistent-field method based on a linear combination of Slater-type orbitals. The bound orbitals are transformed onto a two-dimensional lattice (r,θ) , which is variable in the radial coordinate and constant in the angular coordinate, from which Hartree with local exchange potentials are constructed. The single-particle Schrödinger equation is then solved for continuum distorted waves with S -matrix boundary conditions. Total ionization cross sections for Li2 at an equilibrium internuclear separation of R=5.0a.u. and for Li2+ at an equilibrium internuclear separation of R=5.9a.u. are presented.

  15. Electron-impact Ionization Of Li2 And Li+2

    SciTech Connect

    Colgan, James P

    2008-01-01

    Electron-impact ionization cross sections for Li{sub 2} and Li{sup +}{sub 2} are calculated using a configuration-average distorted-wave method. Bound orbitals for the molecule and its ions are calculated using a single configuration self-consistent field method based on a linear combination of Slater-type orbitals. The bound orbitals are transformed onto a two-dimensional lattice ({tau}, {theta}), which is variable in the radial coordinate and constant in the angular coordinate, from which Hartree with local exchange potentials are constructed. The single particle Schrodinger equation is then solved for continuum distorted-waves with S-matrix boundary conditions. Total ionization cross sections for Li{sub 2} at an equilibrium internuclear separation of R = 5.0 and for Li{sup +}{sub 2} at an equilibrium internuclear separation of R = 5.9 are presented.

  16. Electron- and photon-impact ionization of furfural

    SciTech Connect

    Jones, D. B.; Ali, E.; Madison, D. H. E-mail: madison@mst.edu; Nixon, K. L.; Limão-Vieira, P. E-mail: madison@mst.edu; Hubin-Franskin, M.-J.; Delwiche, J.; Ning, C. G.; Colgan, J.; Murray, A. J.; and others

    2015-11-14

    The He(I) photoelectron spectrum of furfural has been investigated, with its vibrational structure assigned for the first time. The ground and excited ionized states are assigned through ab initio calculations performed at the outer-valence Green’s function level. Triple differential cross sections (TDCSs) for electron-impact ionization of the unresolved combination of the 4a″  +  21a′ highest and next-highest occupied molecular orbitals have also been obtained. Experimental TDCSs are recorded in a combination of asymmetric coplanar and doubly symmetric coplanar kinematics. The experimental TDCSs are compared to theoretical calculations, obtained within a molecular 3-body distorted wave framework that employed either an orientation average or proper TDCS average. The proper average calculations suggest that they may resolve some of the discrepancies regarding the angular distributions of the TDCS, when compared to calculations employing the orbital average.

  17. Electron- and photon-impact ionization of furfural

    NASA Astrophysics Data System (ADS)

    Jones, D. B.; Ali, E.; Nixon, K. L.; Limão-Vieira, P.; Hubin-Franskin, M.-J.; Delwiche, J.; Ning, C. G.; Colgan, J.; Murray, A. J.; Madison, D. H.; Brunger, M. J.

    2015-11-01

    The He(i) photoelectron spectrum of furfural has been investigated, with its vibrational structure assigned for the first time. The ground and excited ionized states are assigned through ab initio calculations performed at the outer-valence Green's function level. Triple differential cross sections (TDCSs) for electron-impact ionization of the unresolved combination of the 4a″ + 21a' highest and next-highest occupied molecular orbitals have also been obtained. Experimental TDCSs are recorded in a combination of asymmetric coplanar and doubly symmetric coplanar kinematics. The experimental TDCSs are compared to theoretical calculations, obtained within a molecular 3-body distorted wave framework that employed either an orientation average or proper TDCS average. The proper average calculations suggest that they may resolve some of the discrepancies regarding the angular distributions of the TDCS, when compared to calculations employing the orbital average.

  18. Electron-impact-ionization cross section for the hydrogen atom

    NASA Astrophysics Data System (ADS)

    Hu, W.; Fang, D.; Wang, Y.; Yang, F.

    1994-02-01

    A distorted-wave Born exchange approximation was used to calculate the cross section for electron-impact ionization of the hydrogen atoms. Both the integral and energy-differential cross section were calculated. The results were compared with the latest experimental data and other theoretical calculations. Comparison shows that the calculations agree with differential cross-section measurements in general. For integral cross sections the calculation shows a better agreement with an earlier measurement [M.B. Shah, D. S. Elliott, and H. B. Gilbody, J. Phys. B 20, 3501 (1987)] in which the cross sections are normalized to the first Born approximation.

  19. Absolute electron-impact total ionization cross sections of chlorofluoromethanes

    NASA Astrophysics Data System (ADS)

    Martínez, Roberto; Sierra, Borja; Redondo, Carolina; Rayo, María N. Sánchez; Castaño, Fernando

    2004-12-01

    An experimental study is reported on the electron-impact total ionization cross sections (TICSs) of CCl4, CCl3F, CCl2F2, and CClF3 molecules. The kinetic energy of the colliding electrons was in the 10-85 eV range. TICSs were obtained as the sum of the partial ionization cross sections of all fragment ions, measured and identified in a linear double focusing time-of-flight mass spectrometer. The resulting TICS profiles—as a function of the electron-impact energy—have been compared both with those computed by ab initio and (semi)empirical methods and with the available experimental data. The computational methods used include the binary-encounter-Bethe (BEB) modified to include atoms with principal quantum numbers n⩾3, the Deutsch and Märk (DM) formalism, and the modified additivity rule (MAR). It is concluded that both modified BEB and DM methods fit the experimental TICS for (CF4), CClF3, CCl2F2, CCl3F, and CCl4 to a high accuracy, in contrast with the poor accord of the MAR method. A discussion on the factors influencing the discrepancies of the fittings is presented.

  20. Glow discharge electron impact ionization source for miniature mass spectrometers.

    PubMed

    Gao, Liang; Song, Qingyu; Noll, Robert J; Duncan, Jason; Cooks, R Graham; Ouyang, Zheng

    2007-05-01

    A glow discharge electron impact ionization (GDEI) source was developed for operation using air as the support gas. An alternative to the use of thermoemission from a resistively heated filament electron source for miniature mass spectrometers, the GDEI source is shown to have advantages of long lifetime under high-pressure operation and low power consumption. The GDEI source was characterized using our laboratory's handheld mass spectrometer, the Mini 10. The effects of the discharge voltage and pressure were investigated. Design considerations are illustrated with calculations. Performance is demonstrated in a set of experimental tests. The results show that the low power requirements, mechanical ruggedness, and quality of the data produced using the small glow discharge ion source make it well-suited for use with a portable handheld mass spectrometer. PMID:17441220

  1. Electron impact ionization of 5- and 6-chlorouracil: appearance energies

    NASA Astrophysics Data System (ADS)

    Denifl, S.; Ptasinska, S.; Gstir, B.; Scheier, P.; Märk, T. D.

    2004-03-01

    Electron impact ionization of the gas phase modified DNA/RNA bases 5- and 6-ClU was studied using a crossed electron/neutral beams technique in combination with a quadrupole mass spectrometer. 5- and 6-ClU belong to the class of halouracils which are used in radiation therapy to increase the effect of ionizing radiation to tumours, when they are incorporated into cancer tissue. Besides determining the mass spectra for both molecules at the electron energy of 70 eV, the ionization efficiency curves for each parent ion and the most abundant fragment ions were measured near the threshold and the corresponding appearance energies (AEs) were derived using an iterative, non-linear least square fitting procedure using the Marquart-Levenberg algorithm based on the Wannier threshold law. The most abundant cations observed in mass spectra have a threshold value of AE ((C3H2ClNO)+/5-ClU)=11.12+/-0.03 eV and AE ((C3H2NO)+/6-ClU)=12.06+/-0.03 eV. The present AE value for the parent ion of 5-ClU AE((5-ClU)+/5-ClU)=9.38+/-0.05 eV is in fair agreement with previous calculations at the B3LYP level of theory. The AE((6-ClU)+/6-ClU)=9.71+/-0.05 eV is 0.33 eV higher than that for 5-ClU.

  2. Single electron impact ionization of the methane molecule

    NASA Astrophysics Data System (ADS)

    Bouamoud, Mammar; Sahlaoui, Mohammed; Benmansour, Nour El Houda; Atomic and Molecular Collisions Team

    2014-10-01

    Triply differential cross sections (TDCS) results of electron-impact ionization of the inner 2a1 molecular orbital of CH4 are presented in the framework of the Second Born Approximation and compared with the experimental data performed in coplanar asymmetric geometry. The cross sections are averaged on the random orientations of the molecular target for accurate comparison with experiments and are compared also with the theoretical calculations of the Three Coulomb wave (3CW) model. Our results are in good agreement with experiments and 3CW results in the binary peak. In contrast the Second Born Approximation yields a significant higher values compared to the 3CW results for the recoil peak and seems to describe suitably the recoil region where higher order effects can occur with the participation of the recoiling ion in the collision process.

  3. Relativistic model of secondary-electron energy spectra in electron-impact ionization

    SciTech Connect

    Miller, J.H. ); Manson, S.T. )

    1991-10-01

    A relativistic model for differential electron-impact-ionization cross sections that allows the energy spectrum of secondary electrons to be calculated over a wide range of primary-electron energies is presented. The semiempirical method requires only experimental total ionization cross sections and optical oscillator strengths for the target species of interest, but other information, if available, can be incorporated to make the formulation still more accurate. Results for ionization of helium indicate that the lower limit on primary-electron energy for application of the model is about 100 eV. The simple analytic form of the model facilitates investigation of the regions of the secondary-electron energy spectrum where relativistic effects are important.

  4. Electron impact ionization of Io's sodium emission cloud

    NASA Technical Reports Server (NTRS)

    Carlson, R. W.; Matson, D. L.; Johnson, T. V.

    1975-01-01

    The geometry of the sodium cloud associated with Io (Jupiter I) indicates that the lifetime of the neutral sodium atoms is an order of magnitude less than the photoionization lifetime. We suggest that ionization by thermal plasma electrons in the Jovian magnetosphere is the dominant Na loss process. Using plasma densities deduced from Pioneer 10 measurements, the lifetime and density distributions are calculated for Na and other species which may be present in the cloud around Io. Electron ionization of Na is found to be an order of magnitude faster than photoionization, in agreement with the lifetime deduced from Na cloud observations.

  5. Electron impact ionization cross sections of beryllium-tungsten clusters*

    NASA Astrophysics Data System (ADS)

    Sukuba, Ivan; Kaiser, Alexander; Huber, Stefan E.; Urban, Jan; Probst, Michael

    2016-01-01

    We report calculated electron impact ionization cross sections (EICSs) of beryllium-tungsten clusters, BenW with n = 1,...,12, from the ionization threshold to 10 keV using the Deutsch-Märk (DM) and the binary-encounter-Bethe (BEB) formalisms. The positions of the maxima of DM and BEB cross sections are mostly close to each other. The DM cross sections are more sensitive with respect to the cluster size. For the clusters smaller than Be4W they yield smaller cross sections than BEB and vice versa larger cross sections than BEB for clusters larger than Be6W. The maximum cross section values for the singlet-spin groundstate clusters range from 7.0 × 10-16 cm2 at 28 eV (BeW) to 54.2 × 10-16 cm2 at 43 eV (Be12W) for the DM cross sections and from 13.5 × 10-16 cm2 at 43 eV (BeW) to 38.9 × 10-16 cm2 at 43 eV (Be12W) for the BEB cross sections. Differences of the EICSs in different isomers and between singlet and triplet states are also explored. Both the DM and BEB cross sections could be fitted perfectly to a simple expression used in modeling and simulation codes in the framework of nuclear fusion research. Contribution to the Topical Issue "Atomic Cluster Collisions (7th International Symposium)", edited by Gerardo Delgado Barrio, Andrey Solov'Yov, Pablo Villarreal, Rita Prosmiti.Supplementary material in the form of one pdf file available from the Journal web page at http://dx.doi.org/10.1140/epjd/e2015-60583-7

  6. An experimental investigation of the dissociative ionization process of argon cluster ions induced by electron impact

    NASA Astrophysics Data System (ADS)

    Zhang, P.; Ma, X.; Yan, S.; Xu, S.; Zhang, S.; Zhu, X.; Li, B.; Feng, W.; Qian, D.; Zhang, R.; Guo, D.; Wen, W.; Zhang, D.; Yang, J.; Zhao, D.; Liu, H.

    2014-04-01

    Utilizing the Cold Target Recoil Ions Momentum Spectrometer (COLTRIMS), dissociative ionization of argon cluster was experimentally investigated by electron impact. The recoil ions produced both in the pure ionization process and the dissociative ionization channels are measured with collision energies from 100 and 1000 eV. The ratios of the dimer ions from pure ionization (Ar2P+) and the dimer ions from small cluster dissociation (Ar+2D) to the atomic argon ion (Ar+) in different stagnation pressures were obtained.

  7. Electron-impact ionization and electron attachment cross sections of radicals important in transient gaseous discharges

    NASA Technical Reports Server (NTRS)

    Lee, Long C.; Srivastava, Santosh K.

    1990-01-01

    Electron-impact ionization and electron attachment cross sections of radicals and excited molecules were measured using an apparatus that consists of an electron beam, a molecular beam and a laser beam. The information obtained is needed for the pulse power applications in the areas of high power gaseous discharge switches, high energy lasers, particle beam experiments, and electromagnetic pulse systems. The basic data needed for the development of optically-controlled discharge switches were also investigated. Transient current pulses induced by laser irradiation of discharge media were observed and applied for the study of electron-molecule reaction kinetics in gaseous discharges.

  8. Ionization yield in xenon due to electron impact

    NASA Astrophysics Data System (ADS)

    Dayashankar

    1982-04-01

    The ionization yield in xenon for complete energy degradation of electrons with initial energy up to 1 keV has been calculated by solving the generalized Fowler equation. The expression for the energy spectrum of secondary electrons from the O shell was obtained by using the empirical scaling functions to weight the Williams-Weizsäcker cross section for glancing collisions and the Mott cross section for knock-on collisions. The total ionization and excitation cross sections were taken from the recent evaluation reported by De Heer et al. Contributions from the inner-shell ionization and the Auger process were explicitly taken into account. The results are expressed in terms of the quantity W, the mean energy required to produce an ion pair. The W value is found to decrease with increasing incident energy, finally approaching a constant value of 23.1 eV for electrons with an energy above 200 eV. The results are generally in good agreement with the available experimental work.

  9. Electron-impact multiple ionization of Ne, Ar, Kr and Xe

    NASA Astrophysics Data System (ADS)

    Montanari, C. C.; Miraglia, J. E.

    2014-05-01

    This work describes the multiple ionization cross sections of rare gases by electron-impact. We pay special attention to the high energy region (0.1-10 keV) where the direct ionization is a minor contribution and the post-collisional electron emission dominates the final target charge state. We report here electron-impact single to sextuple ionization cross sections and total ionization cross sections including direct and post-collisional processes, even in the total values. We use the continuum distorted wave and the first Born approximations adapted to describe light-particle impact, i.e. energy, mass and trajectory corrections are incorporated, the latter by considering the electron-target potential and by using the Abel transformation. Auger-type post-collisional contributions are included in the multinomial expansion through experimental branching ratios after single ionization events. Tabulations of these experimental branching ratios for all the orbitals of the four targets are included. Present results are compared with the large amount of electron-impact experimental data available. We have obtained a good description of the multiple-ionization measurements at high energies, where the post-collisional ionization dominates. At intermediate energies, our theoretical results show the correct tendency, with the electron-impact ionization cross sections being far below the proton-impact ones.

  10. Hydrocarbon rate coefficients for proton and electron impact ionization, dissociation, and recombination in a hydrogen plasma.

    SciTech Connect

    Alman, D.A.; Brooks, J.N.; Ruzic, D.N.; Wang, Z.

    1999-07-21

    We estimate cross sections and rate coefficients for proton and electron impact ionization, dissociation, and recombination of neutral and ionized hydrocarbon molecules and fragments of the form C{sub x}H{sub y}{sup k}, x = 1-3, y = 1-6, k = 0,1 in a thermalized hydrogen-electron plasma.

  11. Excitation and ionization of highly charged ions by electron impact

    SciTech Connect

    Sampson, D.H.

    1989-11-15

    Two approaches for very rapid calculation of atomic data for high temperature plasma modeling have been developed. The first uses hydrogenic basis states and has been developed and applied in many papers discussed in previous progress reports. Hence, it is only briefly discussed here. The second is a very rapid, yet accurate, fully relativistic approach that has been developed over the past two or three years. It is described in more detail. Recently it has been applied to large scale production of atomic data. Specifically, it has been used to calculate relativistic distorted wave collision strengths and oscillator strengths for the following: all transitions from the ground level to the n=3 and 4 excited levels in the 71 Neon-like ions with nuclear charge number Z in the range 22 {le} Z {le} 92; all transitions among the 2s{sub {1/2}}, 2p{sub {1/2}} and 2p{sub 3/2} levels and from them to all nlj levels with n=3,4 and 5 in the 85 Li-like ions with 8 {le} Z {le} 92; all transitions among the 3s{sub {1/2}}, 3p{sub 3/2}, 3d{sub 3/2} and 3d{sub 5/2} levels and from them to all nlj levels with n=4 and 5 in the 71 Na-like ions with 22 {le} Z {le} 92; and all transitions among 4s{sub {1/2}}, 4p{sub {1/2}}, 4p{sub 3/2}, 4d{sub 3/2}, 4d{sub 5/2}, 4f{sub 5/2} and 4f{sub 7/2} levels and from them to all nlj levels with n=5 in the 33 Cu-like ions with 60 {le} Z {le} 92. Also the program has been extended to give cross-sections for excitation to specific magnetic sublevels of the target ion by an electron beam and very recently it has been extended to give relativistic distorted wave cross sections for ionization of highly charged ions by electron impact.

  12. Electron-impact ionization of interstellar hydrogen and helium at interplanetary shocks

    SciTech Connect

    Isenberg, P.A.; Feldman, W.C.

    1995-04-15

    The authors investigate the ionization of interstellar hydrogen and helium due to electron impact by shock-heated electrons. Taking the electron distributions measured at four interplanetary shocks at 1 AU, they show that the electrons in the downstream region of strong shocks can ionize interstellar atoms at rates matching or exceeding the nominal photoionization or charge-exchange rates. They suggest that this process may explain some puzzling observations of interstellar pickup ions made by the Ulysses spacecraft. 17 refs.

  13. Electron Impact Ionization and Dissociative Ionization of C2H2

    NASA Technical Reports Server (NTRS)

    Srivastava, S. K.

    1995-01-01

    By utilizing a crossed electron beam collision geometry, a combination of time-of-flight (TOF) and quadrupole mass spectrometers, and the relative flow technique1 normalized values of cross sections and appearance energies (AP) were obtained for the formation of singly and multiply ionized species resulting from the ionization and dissociation of C2H2. Details ont he apparatus and technique have been published previously.2,3.

  14. Fragmentation patterns of {alpha}-phenylcinnamic acid derivatives upon electron impact ionization; a computational approach

    SciTech Connect

    Palinko, I.; Tasi, G.; Toeroek, B.

    1995-04-01

    Secondary transformations such as fragmentation and rearrangement reacting are computed for {proportional_to}-phenylcinnamic acid derivations upon electron impact ionization. (AIP) {copyright}{ital 1995 American Institute of Physics}

  15. Electron impact ionization rates for interstellar H and He atoms near interplanetary shocks: Ulysses observations

    SciTech Connect

    Feldman, W.C.; Phillips, J.L.; Gosling, J.T.; Isenberg, P.A.

    1996-07-01

    Solar wind plasma data measured during the near-ecliptic phase of the Ulysses mission between October, 1990 and January, 1993 were studied to determine the relative importance of electron-impact ionization to the total ionization rates of interstellar hydrogen and helium atoms. During times of quiet flow conditions electron-impact ionization rates were found to be generally low, of the order of 1{percent} of the total ionization rates. However, just downstream of the strongest CME- and CIR-driven shock waves encountered by Ulysses, the electron impact-ionization rate at times was more than 10{percent} that of the charge-exchange rate for hydrogen and more than 100{percent} that of the photoionization rate for helium. {copyright} {ital 1996 American Institute of Physics.}

  16. Measurement of L-shell electron-impact ionization cross sections for highly charged uranium ions

    SciTech Connect

    Stoehlker, T.; Kraemer, A. |; Elliott, S.R.; Marrs, R.E.; Scofield, J.H.

    1997-10-01

    L-shell electron-impact ionization cross sections for highly charged uranium ions from fluorinelike U{sup 83+} through lithiumlike U{sup 89+} have been measured at 45-, 60-, and 75-keV electron energy. The cross sections were obtained from x-ray measurements of the equilibrium ionization balance in an electron beam ion trap. The measured cross sections agree with recent relativistic distorted wave calculations. {copyright} {ital 1997} {ital The American Physical Society}

  17. Measurement of electron-impact ionization cross sections for hydrogenlike high-Z ions

    SciTech Connect

    Marrs, R.E.; Elliott, S.R.; Scofield, J.H.

    1997-08-01

    Electron-impact ionization cross sections have been measured for the hydrogenlike ions of molybdenum, dysprosium, gold, and bismuth at selected electron energies between 1.3 and 3.9 times threshold. The cross sections were obtained from x-ray measurements of the equilibrium ionization balance in an electron beam ion trap. The measured cross sections agree with recent relativistic distorted-wave calculations that include both the Moeller interaction and exchange. {copyright} {ital 1997} {ital The American Physical Society}

  18. Simple ionization of atomic and diatomic lithium by electron impact

    NASA Astrophysics Data System (ADS)

    Joulakian, B.; Boudali, F.; Najjari, B.

    2002-01-01

    The e,2e reaction of atomic and diatomic lithium is studied. In the atomic case, the problem is treated as a four electron system for which the conservation of the total spin produces a variety of exchange terms whose importance in the determination of the transition matrix element of the ionization process is studied systematically in a very large domain of incidence energy (50 eV to 5 keV) by applying in the small and intermediate energy domain an asymptotically exact distorted wave procedure. In the diatomic case, a model potential is employed for the K shell electrons and the problem is treated as a vertical transition from the lowest vibrational and rotational level of the fundamental electronic state 1Σg of Li2 to the fundamental 2Σg state of Li2+. The comparison with experimental and recent theoretical results shows that the use of an all electron procedure improves the agreement with the experimental results.

  19. Parametrization of electron impact ionization cross sections for CO, CO2, NH3 and SO2

    NASA Technical Reports Server (NTRS)

    Srivastava, Santosh K.; Nguyen, Hung P.

    1987-01-01

    The electron impact ionization and dissociative ionization cross section data of CO, CO2, CH4, NH3, and SO2, measured in the laboratory, were parameterized utilizing an empirical formula based on the Born approximation. For this purpose an chi squared minimization technique was employed which provided an excellent fit to the experimental data.

  20. Relativistic effects on giant resonances in electron-impact double ionization

    SciTech Connect

    Pindzola, M.S.

    1987-06-01

    The electron-impact double-ionization cross section for Fr/sup +/ is calculated in the distorted-wave Born approximation. A giant resonance in the 5d subshell ionization-autoionization contribution to the cross section is found to be quite sensitive to changes in the double-well potential caused by relativistic effects on bound-state wave functions.

  1. Electron impact ionization rates for interstellar neutral H and He atoms near interplanetary shocks: Ulysses observations

    NASA Technical Reports Server (NTRS)

    Feldman, W. C.; Phillips, J. L.; Gosling, J. T.; Isenberg, P. A.

    1995-01-01

    During average solar wind flow conditions at 1 AU, ionization rates of interstellar neutrals that penetrate into the inner heliosphere are dominated by charge exchange with solar wind protons for H atoms, and by photoionization for He atoms. During occurrences of strong, coronal mass ejection (CME)-driven interplanetary shock waves near 1 AU, electron impact ionization can make substantial, if not dominating, contributions to interstellar neutral ionization rates in the regions downstream of the shocks. However, electron impact ionization is expected to be relatively less important with increasing heliocentric distance because of the decrease in electron temperature. Ulysses encountered many CME-driven shocks during its journey to and beyond Jupiter, and in addition, encountered a number of strong corotating interaction region (CIR) shocks. These shocks generally occur only beyond approximately 2 AU. Many of the CIR shocks were very strong rivalling the Earth's bow shock in electron heating. We have compared electron impact ionization rates calculated from electron velocity distributions measured downstream from CIR shocks using the Ulysses SWOOPS experiment to charge-exchange rates calculated from measured proton number fluxes and the photoionization rate estimated from an assumed solar photon spectrum typical of solar maximum conditions. We find that, although normally the ratio of electron-impact ionization rates to charge-exchange (for H) and to photoionization (for He) rates amounts to only about one and a few tens of percent, respectively, downstream of some of the stronger CIR shocks they amount to more than 10% and greater than 100%, respectively.

  2. Electron Impact Ionization Cross Sections and Rate Coefficients for Single Carbon Freon Molecules

    NASA Astrophysics Data System (ADS)

    Pal, Satyendra; Kumar, Neeraj

    2015-09-01

    Single carbon Freon molecules or chlorofluorocarbons (CFCs) are important industrial material with wide-ranging applications as refrigerant, aerosol propellant and semiconductor etchant, etc. The large-scale industrial consumption is of particular environmental concern because of its potential for ozone destruction in the stratosphere. In the present work, we have extended and generalized the modified Jain-Khare (JK) semi-empirical formalism for the evaluation of the total ionization cross sections corresponding to the formation of the cations in the electron impact ionization of molecules to the electron impact ionization of single carbon freon molecules, viz. CFCl3, CF2Cl2 and CF3Cl. The integral partial and the total ionization cross sections as function of incident electron energy are evaluated in the energy range varying from ionization threshold to 1000 eV. In absence of available differential cross sections, the corresponding derived partial and total ionization cross sections revealed a reasonably good agreement with the experimental and theoretical data, wherever available. In addition to the differential and integral ionization cross sections, we have also calculated the ionization rate coefficients using the evaluated partial ionization cross sections and the Maxwell-Boltzmann distribution as a function of electron temperature/energy. The work is supported by DST, New Delhi, India.

  3. Doubly differential measurements for multiple ionization of argon by electron impact: Comparison with positron impact and photoionization

    SciTech Connect

    Santos, A.C.F.; Hasan, A.; Yates, T.; DuBois, R.D.

    2003-05-01

    Doubly differential cross sections for single and multiple ionization of Ar have been measured for 500, 750, and 1000 eV electron impact. The cross sections were measured as a function of projectile energy loss and scattering angle. The energy loss range was 0-85% of the initial projectile energy and scattering angles were between {+-}22 deg. The data were put on an absolute scale by normalizing to total ionization cross sections available in the literature and found to be in good agreement with the absolute electron impact cross sections from DuBois and Rudd. For 750 eV impact, a comparison was made between the present electron impact data and positron impact data obtained using the same experimental conditions. The same energy dependence and yields for single ionization were found for both electron and positron impact. On the other hand, the double- and triple-ionization yields are smaller for positron impact as compared to electron impact. Comparisons with photoionization data showed that for outer shell ionization the fractions of double and triple ionization of argon by photon impact are in quite good agreement with the present electron impact data.

  4. Relativistic electronic dressing in laser-assisted ionization of atomic hydrogen by electron impact

    SciTech Connect

    Attaourti, Y.; Taj, S.

    2004-06-01

    Within the framework of the coplanar binary geometry where it is justified to use plane wave solutions for the study of the (e,2e) reaction and in the presence of a circularly polarized laser field, we introduce as a first step the Dirac-Volkov plane wave Born approximation 1 where we take into account only the relativistic dressing of the incident and scattered electrons. Then, we introduce the Dirac-Volkov plane wave Born approximation 2 where we take totally into account the relativistic dressing of the incident, scattered, and ejected electrons. We then compare the corresponding triple differential cross sections for laser-assisted ionization of atomic hydrogen by electron impact both for the nonrelativistic and the relativistic regime.

  5. Electron-impact ionization of multicharged ions at ORNL: 1985--1992

    SciTech Connect

    Gregory, D.C.; Bannister, M.E.

    1994-07-01

    Absolute cross sections are presented in graphs and tables for single ionization of forty-one ions, multiple ionization of four ions, and for dissociation and ionization of two molecular ions by electron impact. This memo is the third in a series of manuscripts summarizing previously published as well as unpublished ionization cross section measurements at ORNL; contents of the two previous memos are also referenced in this work. All work tabulated in this memo involved ion beams generated in the ORNL-ECR ion source and utilized the ORNL electron-ion crossed beams apparatus. Target ions range from atomic number Z = 8 (oxygen) to Z = 92 (uranium) in initial charge states from +1 to +16. Electron impact energies typically range from threshold to 1500 eV.

  6. Observation of two-center interference effects for electron impact ionization of N2

    NASA Astrophysics Data System (ADS)

    Chaluvadi, Hari; Nur Ozer, Zehra; Dogan, Mevlut; Ning, Chuangang; Colgan, James; Madison, Don

    2015-08-01

    In 1966, Cohen and Fano (1966 Phys. Rev. 150 30) suggested that one should be able to observe the equivalent of Young’s double slit interference if the double slits were replaced by a diatomic molecule. This suggestion inspired many experimental and theoretical studies searching for double slit interference effects both for photon and particle ionization of diatomic molecules. These effects turned out to be so small for particle ionization that this work proceeded slowly and evidence for interference effects were only found by looking at cross section ratios. Most of the early particle work concentrated on double differential cross sections for heavy particle scattering and the first evidence for two-center interference for electron-impact triple differential cross section (TDCS) did not appear until 2006 for ionization of H2. Subsequent work has now firmly established that two-center interference effects can be seen in the TDCS for electron-impact ionization of H2. However, in spite of several experimental and theoretical studies, similar effects have not been found for electron-impact ionization of N2. Here we report the first evidence for two-center interference for electron-impact ionization of N2.

  7. Impact ionization in N-polar AlGaN/GaN high electron mobility transistors

    SciTech Connect

    Killat, N. E-mail: Martin.Kuball@bristol.ac.uk; Uren, M. J.; Kuball, M. E-mail: Martin.Kuball@bristol.ac.uk; Keller, S.; Kolluri, S.; Mishra, U. K.

    2014-08-11

    The existence of impact ionization as one of the open questions for GaN device reliability was studied in N-polar AlGaN/GaN high electron mobility transistors. Electroluminescence (EL) imaging and spectroscopy from underneath the device gate contact revealed the presence of hot electrons in excess of the GaN bandgap energy even at moderate on-state bias conditions, enabling impact ionization with hole currents up to several hundreds of pA/mm. The detection of high energy luminescence from hot electrons demonstrates that EL analysis is a highly sensitive tool to study degradation mechanisms in GaN devices.

  8. Electron-impact ionization of helium for equal-energy-sharing kinematics

    SciTech Connect

    Stelbovics, A.T.; Bray, I.; Fursa, D.V.; Bartschat, K.

    2005-05-15

    The close-coupling approach to electron-helium single ionization is analyzed and several ways of defining the scattering amplitudes are determined, for both equal- and unequal-energy outgoing electrons. Nevertheless, the various definitions all lead to the same cross section. The convergent close-coupling (CCC) method with Laguerre (CCC-L) and box-based (CCC-B) target functions is applied to calculate electron-impact ionization of helium for the cases where the two outgoing electrons have equal energy. Excellent absolute agreement with experiment is obtained for all available cases of comparison.

  9. Angular distribution of Auger electrons due to 3d-shell impact ionization of krypton

    NASA Technical Reports Server (NTRS)

    Omidvar, K.

    1977-01-01

    Cross sections for electron impact ionization of krypton due to ejection of a 3d-shell electron have been calculated using screened hydrogenic and Hartree-Slater wavefunctions for the target atom. While the total ionization cross sections in the two approximations are within 10% of each other, the Auger electron angular distribution, related to cross sections for specific magnetic quantum numbers of the 3d electrons, are widely different in the two approximations. The angular distribution due to the Hartree-Slater approximation is in excellent agreement with measurement. The physical reason for the discrepancies in the two approximations is explained.

  10. Electron impact ionization in plasma technologies; studies on atomic boron and BN molecule

    NASA Astrophysics Data System (ADS)

    Joshi, Foram M.; Joshipura, K. N.; Chaudhari, Asha S.

    2016-05-01

    Electron impact ionization plays important role in plasma technologies. Relevant cross sections on atomic boron are required to understand the erosion processes in fusion experiments. Boronization of plasma exposed surfaces of tokomaks has proved to be an effective way to produce very pure fusion plasmas. This paper reports comprehensive theoretical investigations on electron scattering with atomic Boron and Boron Nitride in solid phases. Presently we determine total ionization cross-section Qion and the summed-electronic excitation cross section ΣQexc in a standard quantum mechanical formalism called SCOP and CSP-ic methods. Our calculated cross sections are examined as functions of incident electron energy along with available comparisons.

  11. Propensity for distinguishing two free electrons with equal energies in electron-impact ionization of helium

    NASA Astrophysics Data System (ADS)

    Ren, Xueguang; Senftleben, Arne; Pflüger, Thomas; Bartschat, Klaus; Zatsarinny, Oleg; Berakdar, Jamal; Colgan, James; Pindzola, Michael S.; Bray, Igor; Fursa, Dmitry V.; Dorn, Alexander

    2015-11-01

    We report a combined experimental and theoretical study on the electron-impact ionization of helium at E0=70.6 eV and equal energy sharing of the two outgoing electrons (E1=E2=23 eV ), where a double-peak or dip structure in the binary region of the triple differential cross section is observed. The experimental cross sections are compared with results from convergent close-coupling (CCC), B -spline R-matrix-with-pseudostates (BSR), and time-dependent close-coupling (TDCC) calculations, as well as predictions from the dynamic screening three-Coulomb (DS3C) theory. Excellent agreement is obtained between experiment and the nonperturbative CCC, BSR, and TDCC theories, and good agreement is also found for the DS3C model. The data are further analyzed regarding contributions in particular coupling schemes for the spins of either the two outgoing electrons or one of the outgoing electrons and the 1 s electron remaining in the residual ion. While both coupling schemes can be used to explain the observed double-peak structure in the cross section, the second one allows for the isolation of the exchange contribution between the incident projectile and the target. For different observation angles of the two outgoing electrons, we interpret the results as a propensity for distinguishing these two electrons—one being more likely the incident projectile and the other one being more likely ejected from the target.

  12. Electron Impact Ionization Cross Sections in Rb and Cs.

    NASA Astrophysics Data System (ADS)

    Reddish, T. J.; Lukomski, M.; Sutton, S.; Kedzierski, W.; McConkey, J. W.; Bartschat, K.; Bartlett, P. L.; Stelbovics, A. T.; Bray, I.

    2006-05-01

    We present a new atom trapping technique for determining absolute, total ionisation cross sections (TICS) out of an excited atom. The novel feature of this method is in utilizing Doppler cooling of neutral atoms to determine ionisation cross sections. This fluorescence-monitoring experiment, which is a variant of the `trap loss' technique, has enabled us to obtain the experimental electron impact ionisation cross sections out of the Cs 6^2P3/2 excited state between 7 - 400 eV. New CCC, R-Matrix with Pseudo-States (RMPS), and Born approximation single ionisation cross sections (SICS) are also presented for both the ground and excited states of Cs and Rb, and compared with the available experimental data. The comparison of the results reveals the importance of the autoionisation and multiple ionisation contributions to the TICS. The autoionisation contribution appears to be substantial for ionisation out of the Cs 6^2P and Rb 5^2P excited states; ˜ 3-4 larger than the direct ionisation contribution predicted by CCC at ˜ 30-50 eV. This surprising result shows the importance of multi-electron processes in determining the ionisation cross sections of heavy alkali atoms.

  13. Electron Impact Ionization of SOx, NOx and H2 SO4 - The Aerosol Relevance

    NASA Astrophysics Data System (ADS)

    Vaishnav, B. G.; Patel, U. R.; Joshipura, K. N.; Pandya, S. H.

    2016-05-01

    This paper reports our theoretical studies on electron impact ionization of reactive molecules SOx, NOx (x = 1-3) and H2 SO4, at incident energies from threshold to 2000 eV. Motivation for this work derives from the relevance of these molecules in connection with atmospheric aerosols analysis through mass spectrometric studies and quantification of mass concentrations amongst the aerosol species. The ionization efficiency of a molecule is directly proportional to ionization cross section, which represents the efficiency on a per-molecule basis. Study of electron impact ionization cross sections of molecules, like H2 SO4, versus number of electrons in the molecule can lead to information about mass concentrations of aerosol species. We have employed in this work, the well-known spherical complex potential formalism (SCOP), which provides total elastic as well as inelastic cross sections, wherein the latter includes ionization cross sections. We have developed a method to extract ionization cross section from calculated inelastic cross section by introducing a ratio function, in a semi-empirical formalism known as CSP-ic method. For SOx and NOx targets single-centre scattering calculations are performed, while for H2 SO4, the additivity rule augmented with overlap or screening corrections, has been employed. The calculated cross sections are examined as functions of incident electron energy along with comparisons (theoretical or experimental) as available.

  14. Use of the Bethe equation for inner-shell ionization by electron impact

    NASA Astrophysics Data System (ADS)

    Powell, Cedric J.; Llovet, Xavier; Salvat, Francesc

    2016-05-01

    We analyzed calculated cross sections for K-, L-, and M-shell ionization by electron impact to determine the energy ranges over which these cross sections are consistent with the Bethe equation for inner-shell ionization. Our analysis was performed with K-shell ionization cross sections for 26 elements, with L-shell ionization cross sections for seven elements, L3-subshell ionization cross sections for Xe, and M-shell ionization cross sections for three elements. The validity (or otherwise) of the Bethe equation could be checked with Fano plots based on a linearized form of the Bethe equation. Our Fano plots, which display theoretical cross sections and available measured cross sections, reveal two linear regions as predicted by de Heer and Inokuti [in Electron Impact Ionization, edited by T. D. Märk and G. H. Dunn, (Springer-Verlag, Vienna, 1985), Chap. 7, pp. 232-276]. For each region, we made linear fits and determined values of the two element-specific Bethe parameters. We found systematic variations of these parameters with atomic number for both the low- and the high-energy linear regions of the Fano plots. We also determined the energy ranges over which the Bethe equation can be used.

  15. Accuracy of Theoretical Calculations for Electron-Impact Ionization of atoms and Molecules

    NASA Astrophysics Data System (ADS)

    Madison, Don

    2015-09-01

    In the last two decades, there have been several close-coupling approaches developed which can accurately calculate the triply differential cross sections for electron impact ionization of effective one and two electron atoms. The agreement between experiment and theory is not particularly good for more complicated atoms and molecules. Very recently, a B-spline R-matrix with pseudostates (BSRPS) approach was used to investigate low energy electron impact ionization of neon and very good agreement with experiment was found. The perturbative 3-body distorted wave (3DW) approach which includes the exact final state electron-electron interaction (post collision interaction - PCI) gave comparably good agreement with experiment. For ionization of molecules, there have been numerous studies of high-energy electron impact. These studies are called EMS (Electron Momentum Spectroscopy) and they were very valuable in determining the accuracy of molecular wavefunctions since the measured cross sections were proportional to the momentum space molecular wavefunction. More recently, lower energy collisions have started to be measured and these cross sections are much more difficult for theory since the detailed kinematics of the experiment become important. So far, the only close coupling calculation reported for ionization of molecules is the time-dependent close-coupling calculation (TDCC) which has been developed for ionization of H2 and it yields relative good agreement with experiment. Again the molecular 3-body distorted wave (M3DW) gave equally good agreement with experiment. For polyatomic molecules, the only theory available is the M3DW. In this talk, I will show the current status of agreement between experiment and theory for low and intermediate energy single ionization of atoms and molecules. Work supported by the NSF and XSEDE.

  16. Spectroscopic investigations of L-shell ionization in heavy elements by electron impact

    NASA Astrophysics Data System (ADS)

    Rahangdale, H. V.; Mitra, D.; Das, P. K.; De, S.; Guerra, M.; Santos, J. P.; Saha, S.

    2016-05-01

    The absolute L subshell specific electron impact ionization cross sections near the ionization threshold (16 < E < 45 keV) of lead and thorium are obtained from the measured L X-ray production cross sections. Monte Carlo simulation is done to account for the effect of the backscattered electrons, and the final experimental results are compared with calculations performed using distorted wave Born approximation and the modified relativistic binary encounter Bethe model. The sensitivity of the results on the atomic parameters is explored. Observed agreements and discrepancies between the experimental results and theoretical estimates, and their dependence on the specific atomic parameters are reported.

  17. Investigation of Ionization and Dissociation Processes Produced by Electron Impact on Molecules.

    NASA Astrophysics Data System (ADS)

    Ma, Ce.

    1990-01-01

    Absolute electron impact partial ionization cross sections for Ar and CF_4 were measured by use of a newly built pulsed electron beam time-of-flight apparatus for incident electron energies from thresholds to 500 eV. The apparatus employed consisted of a low energy electron gun, 40 mm diameter ion extraction gold screens, time-of-flight drift tubes, micro-channel plate detectors and fast time to digital electronics. A pulsed electron beam was obtained by pulsing the control grid of the electron gun. Both beam - beam experiments and beam - constant gas target pressure experiments were carried out to determine the absolute partial ionization cross sections for Ar ^{+}, Ar^{2+ }, Ar^{3+} from an argon gas target, and for CF_sp {3}{+}, CF_sp {2}{+}, CF_sp {3}{2+}, CF^ {+}, CF_sp{2} {2+}, F^{+}, C^{+} from a CF _4 gas target. By charge weighted summing of the partial ionization cross sections, the total ionization cross sections of Ar and CF_4 were obtained. The total neutral dissociation cross section for CF_4 was inferred from the total ionization cross section and the total dissociation cross section. Also, a new method for determining absolute total electron scattering cross sections with corrections for forward scattering was developed. The electron beam current was measured as function of gas target pressure and the scattering path length. The total electron scattering cross section obtained from the new model is as much as 6% larger than the cross section derived from the traditional Beer's law for Ar at an incident electron energy of 300 eV. This method is capable of yielding reliable total cross section up to 10 keV. Finally, a study of the secondary electron emission as a function of ejection angle and ejection energy for CO, the doubly differential cross section (DDCS), is presented.

  18. Model for the charge-transfer probability in helium nanodroplets following electron-impact ionization

    SciTech Connect

    Ellis, Andrew M.; Yang Shengfu

    2007-09-15

    A theoretical model has been developed to describe the probability of charge transfer from helium cations to dopant molecules inside helium nanodroplets following electron-impact ionization. The location of the initial charge site inside helium nanodroplets subject to electron impact has been investigated and is found to play an important role in understanding the ionization of dopants inside helium droplets. The model is consistent with a charge migration process in small helium droplets that is strongly directed by intermolecular forces originating from the dopant, whereas for large droplets (tens of thousands of helium atoms and larger) the charge migration increasingly takes on the character of a random walk. This suggests a clear droplet size limit for the use of electron-impact mass spectrometry for detecting molecules in helium droplets.

  19. Electron-ejection cross sections in electron- and ion impact ionization: ab initio and semiempirical calculations

    SciTech Connect

    Manson, S.T.; Miller, J.H.

    1987-01-01

    Ab initio calculations of single and double differential cross sections for ionization by fast, charged particles within the framework of the Born approximation are presented. In addition, a semi-empirical method based on the asymptotic Bethe-Born expansion is also discussed. Both are applied to ionization of helium by electrons and protons in an effort to assess their accuracy and validity. Agreement with experiment is quite good. The implications for other targets is discussed.

  20. Electron-impact ionization cross sections out of the ground and excited states of cesium

    SciTech Connect

    Lukomski, M.; Sutton, S.; Kedzierski, W.; Reddish, T. J.; Bartschat, K.; Bartlett, P. L.; Bray, I.; Stelbovics, A. T.; McConkey, J. W.

    2006-09-15

    An atom trapping technique for determining absolute, total ionization cross sections (TICS) out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the 'trap loss' technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs state between 7 eV and 400 eV. CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region (<11 eV) where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.

  1. STORAGE RING CROSS SECTION MEASUREMENTS FOR ELECTRON IMPACT IONIZATION OF Fe{sup 12+} FORMING Fe{sup 13+} AND Fe{sup 14+}

    SciTech Connect

    Hahn, M.; Novotny, O.; Savin, D. W.; Grieser, M.; Krantz, C.; Repnow, R.; Wolf, A.; Lestinsky, M.; Mueller, A.; Schippers, S.

    2011-07-10

    We report electron impact ionization cross section measurements for electron impact single ionization of Fe{sup 12+} forming Fe{sup 13+} and electron impact double ionization of Fe{sup 12+} forming Fe{sup 14+}. These are the first electron impact ionization data for any Si-like ion uncontaminated by an unknown metastable fraction. Recent distorted wave calculations agree with our single ionization results to within {approx}15%. Double ionization is dominated by inner shell ionization of a 2l electron resulting in autoionization of a second electron as the inner shell hole is filled.

  2. Strong nonlinear electron multiplication without impact ionization in dielectric nanoparticles embedded in optical materials

    SciTech Connect

    Duchateau, Guillaume

    2013-02-15

    The interaction of a dielectric nano-particle or nano-defect, embedded in the bulk of an optical material, with an intense and short laser pulse is addressed. Due to the finite size of the target and the possible large production of electrons in the conduction band, large electric field enhancement or surintensity may be induced inside the particle. Since ionization rates also depend on the instantaneous electric field, a strong time-dependent connection between electron production and surintensity may take place. Such a connection is shown to possibly lead to a nonlinear temporal increase in the free electron density relevant from an avalanche process, called optical avalanche, similar to the one induced by electron impact ionization. However, the present build-up in the electron density clearly exhibits more nonlinear features than traditional collisional avalanche, which is shown to induce an exponential growth of the density: when the optical avalanche is engaged, the temporal electron evolution exhibits an explosive behavior. That leads to a nanometric plasma at solid density whose subsequent laser heating may lead locally to matter under extreme conditions. Furthermore, we show that the defect induces a change in the ionization mechanism in the course of interaction: a transition from multiphoton to tunnel ionization may take place.

  3. Measurements of the electron-impact double-to-single ionization ratio using trapped lithium

    NASA Astrophysics Data System (ADS)

    Huang, M.-T.; Zhang, L.; Hasegawa, S.; Southworth, S. H.; Young, L.

    2002-07-01

    The Li2+ to Li+ production cross-section ratio of ground-state atomic Li by electron-impact ionization has been measured for electron energies ranging from 200 eV to 1500 eV. The measurements were done using a pulsed, ion imaging time-of-flight spectrometer with Li atoms confined in a magneto-optical trap. The ratios are more accurate than the single earlier result for the Li2+ to Li+ ratios, a composite of two absolute measurements, and are systematically lower. Both experiments show similar energy dependences that disagree with the trend predicted by a semiempirical formulation. These measurements provide a benchmark for theoretical studies of electron-impact double ionization.

  4. Vibrational overtone spectroscopy of H/sub 2/O (4. gamma. /sub OH/) using energy-selective electron impact ionization

    SciTech Connect

    Hayden, C.C.; Penn, S.M.; Carlson, K.J.; Crim, F.F.

    1988-03-24

    The authors describe a new method for obtaining vibrational overtone spectra of polyatomic molecules in supersonic expansions that uses low-energy electrons to ionize the vibrationally excited molecules. Measuring the excitation spectrum of water in the region of the third overtone of the OH stretching vibration (4..sigma../sub OH/) demonstrates the technique. The ionization process is probably not direct but may occur by electron impact excitation to vibrationally and electronically excited states from which the neutral molecule is subsequently ionizes

  5. Electron-impact ionization of the K-shells of Heavy Atoms

    NASA Astrophysics Data System (ADS)

    Pindzola, M. S.

    2016-05-01

    Fully-relativistic subconfiguration-average distorted-wave (SCADW) calculations are made for the electron-impact ionization of the K-shells of heavy atoms. One set of calculations only include the two-body electrostatic interaction, while the other set includes the full two-body retarded electromagnetic interaction. The SCADW retarded electromagnetic calculations are found to be in good agreement with recent measurements made at the Institute for Physics at the University of Sao Paulo, Brazil for Au and Bi atoms. Calculations and measurements will also be presented for the K-shell ionization of the Ta atom. Work supported in part by Grants from NSF and DOE.

  6. Electron-impact ionization of the Se2+ and Se3+ atomic ions

    NASA Astrophysics Data System (ADS)

    Loch, S. D.; Pindzola, M. S.

    2016-05-01

    Semi-relativistic configuration-average distorted-wave (CADW) calculations are made for the electron-impact ionization of the Se2+ and Se3+ atomic ions. The CADW calculations are found to be in reasonable agreement with recent measurements made at the Multicharged Ion Research Facility at the University of Nevada in Reno. The CADW calculations for configurations near ionization thresholds are checked against level to level distorted-wave (LLDW) calculations. Work supported in part by Grants from NASA, NSF, and DOE.

  7. Evidence of strong projectile-target-core interaction in single ionization of neon by electron impact

    SciTech Connect

    Yan, S.; Zhang, P.; Xu, S.; Ma, X.; Zhang, S. F.; Zhu, X. L.; Feng, W. T.; Liu, H. P.

    2010-11-15

    The momentum distributions of recoil ions were measured in the single ionization of neon by electron impact at incident energies between 80 and 2300 eV. It was found that there are a noticeable number of recoil ions carrying large momenta, and the relative contributions of these ions becomes more pronounced with the further decrease of incident electron energy. These observed behaviors indicate that there is a strong projectile-target-core interaction in the single-ionization reaction. By comparing our results with those of electron-neon elastic scattering, we concluded that the elastic scattering of the projectile electron on the target core plays an important role at low and intermediate collision energies.

  8. Dissociative simple ionization of two active electron diatomic systems by fast electron impact

    NASA Astrophysics Data System (ADS)

    Lahmidi, N.; Joulakian, B.

    2005-01-01

    The dissociative (e, 2e) ionization of diatomic hydrogen and lithium by fast electrons is studied theoretically as a vertical transition from the lowest vibrational and rotational level of the fundamental electronic state 1Σ+g of H2 (and Li2) to the first dissociative 2Σu state of H2+ (and Li2+). After verification of the perturbative procedure in the non-dissociative case, for which experimental and theoretical results exist, the variation of the multiply differential cross section of the dissociative ionization is studied in a variety of situations to show the particularities of this process and motivate actually realizable complete experiments, which can detect the scattered and ejected electrons in coincidence with the bare detached nucleus. Our results show that the dynamically well understood behaviour in the case of simple (e, 2e) ionization breaks down in the dissociative case, because of the increasing influence of the electron-electron correlation of the two target electrons.

  9. Excitation and ionization of outer shells in Rb by electron impact

    NASA Astrophysics Data System (ADS)

    Roman, V.; Kupliauskienė, A.; Borovik, A.

    2015-10-01

    The relativistic distorted-wave and binary-encounter-dipole approximations were employed for calculating the electron-impact single ionization cross sections of the 5s, 4p6, 4s2, 3d10 shells and 4p6 excitation cross section for Rb atom taking into account both configuration interaction and relativistic effects. The capabilities of the most used theoretical approaches in describing the single ionization of Rb atom were considered by comparing the present and other available calculated data with the experimental total ionization and total direct single ionization cross sections over the electron-impact energy range from the 5s threshold to 600 eV. The best agreement within experimental uncertainty was obtained by using the non-relativistic binary-encounter-dipole approximation included in the LANL Atomic Physics Codes package. At present none of the used approximations (plane-wave Born or relativistic distorted wave) can satisfactorily describe the experimental excitation-autoionization cross section in rubidium because the efficient formation of the 4p6 core-excited negative-ion rubidium states at near-threshold impact energies is ignored in calculations.

  10. Differential studies and projectile charge effects in ionization of molecular nitrogen by positron and electron impact

    NASA Astrophysics Data System (ADS)

    de Lucio, O. G.; DuBois, R. D.

    2016-03-01

    Singly, doubly, and triply differential information, obtained from coincidence measurements, are presented for 250-eV positron- and electron-impact ionization of molecular nitrogen. Comparisons of these data as functions of energy loss, scattering, and emission angles illustrate differences associated with the sign of the projectile charge. Via a deconvolution and normalization procedure, the triply differential data are converted to absolute cross sections. By fitting the triply differential cross sections for single ionization with simple functions, the intensities, directions, and peak to background intensities of the binary peaks plus the ratio of recoil to binary interactions are compared for positron and electron impact. Formulas for the binary and recoil intensities plus for the orientation of the binary peak as a function of momentum transfer are extracted from the data. Differences in the relative amount of fragmentation as a function of energy loss are also observed.

  11. Dissociative Ionization and Product Distributions of Benzene and Pyridine by Electron Impact

    NASA Technical Reports Server (NTRS)

    Dateo, Christopher E.; Huo, Winifred M.; Fletcher, Graham D.

    2003-01-01

    We report a theoretical study of the dissociative ionization (DI) and product distributions of benzene (C6H6) and pyridine (C5H5N) from their low-lying ionization channels. Our approach makes use of the fact that electronic motion is much faster than nuclear motion allowing DI to be treated as a two-step process. The first step is the electron-impact ionization resulting in an ion with the same nuclear geometry as the neutral molecule. In the second step, the nuclei relax from the initial geometry and undergo unimolecular dissociation. For the ionization process we use the improved binary-encounter dipole (iBED) model [W.M. Huo, Phys. Rev. A64,042719-I (2001)]. For the unimolecular dissociation, we use multiconfigurational self-consistent field (MCSCF) methods to determine the steepest descent pathways to the possible product channels. More accurate methods are then used to obtain better energetics of the paths which are used to determine unimolecular dissociation probabilities and product distributions. Our analysis of the dissociation products and the thresholds of their productions for benzene are compared with the recent dissociative photoionization meausurements of benzene by Feng et al. [R. Feng, G. Cooper, C.E. Brion, J. Electron Spectrosc. Relat. Phenom. 123,211 (2002)] and the dissociative photoionization measurements of pyridine by Tixier et al. [S. Tixier, G. Cooper, R. Feng, C.E. Brion, J. Electron Spectrosc. Relat. Phenom. 123,185 (2002)] using dipole (e,e+ion) coincidence spectroscopy.

  12. Electron-impact ionization of molecular hydrogen at 38 eV incident energy

    NASA Astrophysics Data System (ADS)

    Colgan, James; Ren, Xueguang; Dorn, Alexander; Pindzola, M. S.

    2016-05-01

    We report on recent measurements of the triple differential cross sections from electron-impact ionization of molecular hydrogen at an incident energy of 38 eV. Results are reported for various orientations of the target molecule, as well as various scattering angles and energy sharings of the outgoing electrons. The measurements are compared with calculations performed using a time-dependent close-coupling approach. Reasonable agreement is found between theory and measurement. We also compare and contrast our results to those obtained at higher incident electron energies, which were reported recently.

  13. Use of the Bethe Equation for Inner-Shell Ionization by Electron Impact

    PubMed Central

    Powell, Cedric J.; Llovet, Xavier; Salvat, Francesc

    2016-01-01

    We analyzed calculated cross sections for K-, L-, and M-shell ionization by electron impact to determine the energy ranges over which these cross sections are consistent with the Bethe equation for inner-shell ionization. Our analysis was performed with K-shell ionization cross sections for 26 elements, with L-shell ionization cross sections for seven elements, with L3-subshell ionization cross sections for Xe, and with M-shell ionization cross sections for three elements. The validity or otherwise of the Bethe equation could be checked with Fano plots based on a linearized form of the Bethe equation. Our Fano plots, which display theoretical cross sections and available measured cross sections, reveal two linear regions as predicted by de Heer and Inokuti. For each region, we made linear fits and determined values of the two element-specific Bethe parameters. We found systematic variations of these parameters with atomic number for both the low- and the high-energy linear regions of the Fano plots. We also determined the energy ranges over which the Bethe equation can be used. PMID:27546903

  14. Triple differential cross sections for the ionization of water by electron impact

    NASA Astrophysics Data System (ADS)

    Tóth, Istvan; Nagy, Ladislau; Campeanu, Radu I.

    2014-12-01

    Calculated triple differential cross sections are presented for the ionization of the 3a1 orbital of water by electron impact. The cross sections are determined for symmetric coplanar and non-coplanar geometrical arrangements. The obtained results show reasonable agreement with experimental data for both geometries. Contribution to the Topical Issue "Elementary Processes with Atoms and Molecules in Isolated and Aggregated States", edited by Friedrich Aumayr, Bratislav Marinkovic, Stefan Matejcik, John Tanis and Kurt H. Becker.

  15. Electron impact and chemical ionization mass spectral analysis of a volatile uranyl derivative

    SciTech Connect

    Reutter, D.J.; Hardy, D.R.

    1981-01-01

    Quadrupole mass spectral analysis of the volatile uranium ligand complex bis (1,1,1,5,5,5-hexafluoro-2,4-pentanedionato) dioxouranium-di-n-butyl sulfoxide is described utilizing electron impact (EI) and methane chemical ionization (CI) ion sources. All major ions are tentatively identified and the potential usefulness of this complex for determining uranium isotope /sup 235/U//sup 238/U abundance is demonstrated.

  16. Cross-section measurements for electron-impact ionization of atoms

    NASA Astrophysics Data System (ADS)

    Freund, Robert S.; Wetzel, Robert C.; Shul, Randy J.; Hayes, Todd R.

    1990-04-01

    Absolute electron-impact cross sections have been measured from 0 to 200 eV for single ionization of 16 atoms (Mg, Fe, Cu, Ag, Al, Si, Ge, Sn, Pb, P, As, Sb, Bi, S, Se, and Te) with an estimated accuracy of +/-10%. Combined with our recent measurements of He, Ne, Ar, Kr, Xe, F, Cl, Br, I, Ga, and In [Wetzel et al., Phys. Rev. A 35, 559 (1987); Hayes et al., ibid. 35, 578 (1987); Shul, Wetzel, and Freund, ibid. 39, 5588 (1989)], a set of 27 atomic single-ionization cross sections has now been measured with the same apparatus. In addition, cross sections are reported for double ionization of ten atoms and triple ionization of eight atoms. The measurements are made by crossing an electron beam with a 3-keV beam of neutral atoms, prepared by charge-transfer neutralization of a mass-selected ion beam. The critical measurement of absolute neutral beam flux is made with a calibrated pyroelectric crystal. The magnitudes of the single-ionization-peak cross sections decrease monotonically across rows of the periodic table from group IIIA (Al,Ga,In) to group VIIIA (Ar,Kr,Xe), varying much more than predicted by various empirical formulas and classical and quantum-mechanical theories.

  17. Analysis and simulation for a model of electron impact excitation/deexcitation and ionization/recombination

    SciTech Connect

    Yan, Bokai; Caflisch, Russel E.; Barekat, Farzin; Cambier, Jean-Luc

    2015-10-15

    This paper describes a kinetic model and a corresponding Monte Carlo simulation method for excitation/deexcitation and ionization/recombination by electron impact in a plasma free of external fields. The atoms and ions in the plasma are represented by continuum densities and the electrons by a particle distribution. A Boltzmann-type equation is formulated and a corresponding H-theorem is formally derived. An efficient Monte Carlo method is developed for an idealized analytic model of the excitation and ionization collision cross sections. To accelerate the simulation, the reduced rejection method and binary search method are used to overcome the singular rate in the recombination process. Numerical results are presented to demonstrate the efficiency of the method on spatially homogeneous problems. The evolution of the electron distribution function and atomic states is studied, revealing the possibility under certain circumstances of system relaxation towards stationary states that are not the equilibrium states, a potential non-ergodic behavior.

  18. Ion appearance energies at electron-impact dissociative ionization of sulfur hexafluoride molecule and its fragments

    NASA Astrophysics Data System (ADS)

    Demesh, Shandor Sh.; Remeta, Eugene Yu.

    2015-07-01

    Theoretical analysis of appearance energies for SF{/k +} ( k = 0- n) ion fragments of SF6 molecule as well as F+ and F{2/+} ions at electron-impact dissociative ionization of SF n ( n = 1-6) molecules is presented. Theoretical methods of GAMESS software package were used to calculate the total energies of neutral and charged molecular and atomic fragments. The dissociative ionization process is concluded to occur via repulsive highly-excited electronic states of the SF6 molecule and its fragments, due to which the observed appearance energies exceed the theoretical values. The electron binding energies on the molecular orbitals in the SF6 molecule are compared with the ion fragment appearance energies.

  19. Generalized Kolbenstvedt model for electron impact ionization of the K-, L- and M-shell ions

    NASA Astrophysics Data System (ADS)

    Haque, A. K. F.; Shahjahan, M.; Uddin, M. A.; Patoary, M. A. R.; Basak, A. K.; Saha, B. C.; Malik, F. B.

    2010-04-01

    The recently proposed generalized Kolbenstvedt model (GKLV) of Haque et al (2007 Eur. Phys. J. D 42 203), for the electron impact ionization (EII) of atoms, was applied to a wide range of K-, L- and M-shell electrons of ionic targets from threshold to 1 MeV incident energy. The set of species-independent parameters, two for each of the ionized orbits, is the same as that for neutral targets, and provides an excellent account of the EII cross-sectional data for 36 ions, including those belonging to Li, Be, B, C, N, O and Ne electronic sequences as well as those having 3s-, 3p- and 3d-configurations of the M-shell in a consistent manner. The performance of GKLV is found to be better than that of the modified version of the BELL model (Haque et al 2006 Phys. Rev. A 73 052703, Haque et al 2006 Phys. Scr. 74 377).

  20. A combination thermal dissociation/electron impact ionization source for RIB generation

    SciTech Connect

    Alton, G.D.; Cui, B.; Welton, R.F.

    1996-12-31

    The flourishing interest in radioactive ion beams (RIBs) with intensities adequate for astrophysics and nuclear physics research place a premium on targets that will swiftly release trace amounts of short lived radio-nuclei in the presence of bulk quantities of target material and ion sources that have the capability of efficiently ionizing the release products. Because of the low probability of simultaneously dissociating and efficiently ionizing the individual atomic constituents of molecules containing the element of interest with conventional, hot-cathode, electron-impact ion sources, the species of interest is often distributed in several mass channels in the form of molecular sideband beams and, consequently, the intensity is diluted. The authors have conceived an ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high efficiency characteristics of an electron impact ionization source to address these problems. If the concept proves to be a viable option, the source will be used as a complement to the electron beam plasma ion sources already in use at the HRIBF. The design features and principles of operation of the source are described in this article.

  1. Electron-impact ionization of helium: A comprehensive experiment benchmarks theory

    SciTech Connect

    Ren, X.; Pflueger, T.; Senftleben, A.; Xu, S.; Dorn, A.; Ullrich, J.; Bray, I.; Fursa, D.V.; Colgan, J.; Pindzola, M.S.

    2011-05-15

    Single ionization of helium by 70.6-eV electron impact is studied in a comprehensive experiment covering a major part of the entire collision kinematics and the full 4{pi} solid angle for the emitted electron. The absolutely normalized triple-differential experimental cross sections are compared with results from the convergent close-coupling (CCC) and the time-dependent close-coupling (TDCC) theories. Whereas excellent agreement with the TDCC prediction is only found for equal energy sharing, the CCC calculations are in excellent agreement with essentially all experimentally observed dynamical features, including the absolute magnitude of the cross sections.

  2. The energy distribution cross section in threshold electron-atom impact ionization

    NASA Technical Reports Server (NTRS)

    Temkin, A.

    1974-01-01

    The flatness of the energy differential cross section in impact ionization is derived analytically in the Wannier theory. However it is shown that the Wannier zone is confined to a region of the order E/5 is less than or equal to epsilon is less than or equal to 4E/5, where E is the available energy and epsilon is the energy of the electrons. By contrasting the known results of photoionization and photodetachment, one can cogently argue that in the complementary region where electrons share their energy very unequally the cross section rises to a value independent of E, and that this region determines the form of the threshold law.

  3. Scaling law for total electron-impact ionization cross sections of Li-like ions

    SciTech Connect

    Ancarani, L.U.; Hervieux, P.-A.

    2005-09-15

    Experimental total cross sections for direct electron-impact ionization of the valence electron of several Li-like ions are seen to follow a new ab initio scaling law which is inspired by a Coulomb-Born model and the frozen-core Hartree-Fock approximation. The predictive character of this scaling law should be very useful to experimentalists and can be used to complete data tables needed for plasma or astrophysical studies. A single-parameter fit of the best available experimental data, once scaled, provides us with a single formula, for moderately charged Li-like ions, which is more accurate than Lotz semiempirical formula.

  4. Fragment appearance energies in dissociative ionization of a sulfur hexafluoride molecule by electron impact

    NASA Astrophysics Data System (ADS)

    Demesh, Sh. Sh.; Zavilopulo, A. N.; Shpenik, O. B.; Remeta, E. Yu.

    2015-06-01

    Theoretical analysis of the fragment appearance energies corresponding to possible channels of formation of SF{/k +} fragments in dissociative ionization of the SF6 molecule by an electron impact is carried out. The total energies of neutral and ion molecular and atomic fragments are calculated using the theoretical methods of the GAMESS program complex. It is concluded that apart from dissociative ionization via autoionizing repulsive electronic states of the SF6 molecule, the excitation channels for SF{/k +} fragments and F2 molecules play a significant role, which leads to higher values of the observed fragment appearance energy as compared to theoretical values. The dependence of the energy corresponding to the formation of SF{/k +} c fragments on the number k of fluorine atoms is considered.

  5. Total Electron-Impact Ionization Cross-Sections of CFx and NFx (x = 1 - 3)

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Tarnovsky, Vladimir; Becker, Kurt H.; Kwak, Dochan (Technical Monitor)

    2001-01-01

    The discrepancy between experimental and theoretical total electron-impact ionization cross sections for a group of fluorides, CFx, and NFx, (x = 1 - 3), is attributed to the inadequacies in previous theoretical models. Cross-sections calculated using a recently developed siBED (simulation Binary-Encounter-Dipole) model that takes into account the shielding of the long-range dipole potential between the scattering electron and target are in agreement with experimentation. The present study also carefully reanalyzed the previously reported experimental data to account for the possibility of incomplete collection of fragment ions and the presence of ion-pair formation channels. For NF3, our experimental and theoretical cross-sections compare well with the total ionization cross-sections recently reported by Haaland et al. in the region below dication formation.

  6. Electron Impact Ionization: A New Parameterization for 100 eV to 1 MeV Electrons

    NASA Technical Reports Server (NTRS)

    Fang, Xiaohua; Randall, Cora E.; Lummerzheim, Dirk; Solomon, Stanley C.; Mills, Michael J.; Marsh, Daniel; Jackman, Charles H.; Wang, Wenbin; Lu, Gang

    2008-01-01

    Low, medium and high energy electrons can penetrate to the thermosphere (90-400 km; 55-240 miles) and mesosphere (50-90 km; 30-55 miles). These precipitating electrons ionize that region of the atmosphere, creating positively charged atoms and molecules and knocking off other negatively charged electrons. The precipitating electrons also create nitrogen-containing compounds along with other constituents. Since the electron precipitation amounts change within minutes, it is necessary to have a rapid method of computing the ionization and production of nitrogen-containing compounds for inclusion in computationally-demanding global models. A new methodology has been developed, which has parameterized a more detailed model computation of the ionizing impact of precipitating electrons over the very large range of 100 eV up to 1,000,000 eV. This new parameterization method is more accurate than a previous parameterization scheme, when compared with the more detailed model computation. Global models at the National Center for Atmospheric Research will use this new parameterization method in the near future.

  7. Energy and angle differential cross sections for the electron-impact double ionization of helium

    SciTech Connect

    Colgan, James P; Pindzola, M S; Robicheaux, F

    2008-01-01

    Energy and angle differential cross sections for the electron-impact double ionization of helium are calculated using a non-perturbative time-dependent close-coupling method. Collision probabilities are found by projection of a time evolved nine dimensional coordinate space wave function onto fully antisymmetric products of spatial and spin functions representing three outgoing Coulomb waves. At an incident energy of 106 eV, we present double energy differential cross sections and pentuple energy and angle differential cross sections. The pentuple energy and angle differential cross sections are found to be in relative agreement with the shapes observed in recent (e,3e) reaction microscope experiments. Integration of the differential cross sections over all energies and angles yields a total ionization cross section that is also in reasonable agreement with absolute crossed-beams experiments.

  8. Storage Ring Cross Section Measurements for Electron Impact Ionization of Fe7+

    NASA Astrophysics Data System (ADS)

    Hahn, M.; Becker, A.; Bernhardt, D.; Grieser, M.; Krantz, C.; Lestinsky, M.; Müller, A.; Novotný, O.; Repnow, R.; Schippers, S.; Spruck, K.; Wolf, A.; Savin, D. W.

    2015-11-01

    We have measured electron impact ionization for Fe7+ from the ionization threshold up to 1200 eV. The measurements were performed using the TSR heavy ion storage ring. The ions were stored long enough prior to measurements to remove most metastables, resulting in a beam of 94% ground-level ions. Comparing with the previously recommended atomic data, we find that the Arnaud & Raymond cross section is up to about 40% larger than our measurement, with the largest discrepancies below about 400 eV. The cross section of Dere agrees to within 10%, which is about the magnitude of the experimental uncertainties. The remaining discrepancies between our measurement and the Dere calculations are likely due to shortcomings in the theoretical treatment of the excitation-autoionization contribution.

  9. Storage ring cross section measurements for electron impact ionization of Fe8+

    NASA Astrophysics Data System (ADS)

    Hahn, M.; Becker, A.; Bernhardt, D.; Grieser, M.; Krantz, C.; Lestinsky, M.; Müller, A.; Novotný, O.; Pindzola, M. S.; Repnow, R.; Schippers, S.; Spruck, K.; Wolf, A.; Savin, D. W.

    2016-04-01

    We have measured electron impact ionization (EII) for Fe8+ forming Fe9+ from below the ionization threshold to 1200 eV. These measurements were carried out at the TSR heavy ion storage ring. The objective of using a storage ring is to store the ion beam initially so that metastable levels decay, thereby allowing for measurements on a well-defined ground-level ion beam. In this case, however, some metastable levels were too long lived to be removed. We discuss several methods for quantifying the metastable fraction, which we estimate to be ∼30%–40%. Although metastables remain problematic, the present storage ring work improves upon other experimental geometries by limiting the metastable contamination to only a few long-lived excited levels. We discuss some future prospects for obtaining improved measurements of Fe8+ and other ions with long-lived metastable levels.

  10. Single electron ionization of NH3 and CH4 by swift proton impact

    NASA Astrophysics Data System (ADS)

    Tachino, C. A.; Monti, J. M.; Fojón, O. A.; Champion, C.; Rivarola, R. D.

    2015-01-01

    Single ionization from ammonia and methane molecules by impact of protons is analysed. Double differential cross sections are calculated, within the post- and prior-versions of the continuum distorted wave-eikonal initial state (CDW-EIS) model, considering two different representations of the initial bound state of the active electron. A comparison between both set of results shows a very little sensitivity of the double differential cross sections to the initial state representation in the case of ammonia molecules. On the other hand, discrepancies are found when CH4 molecular target is considered, showing that in this case the description of the corresponding molecular orbitals influences the cross section calculations.

  11. Electron-impact dissociative double ionization of N2 and CO: Dependence of transition probability on impact energy

    NASA Astrophysics Data System (ADS)

    Pandey, A.; Kumar, P.; Banerjee, S. B.; Subramanian, K. P.; Bapat, B.

    2016-04-01

    We present an experimental and computational analysis of dissociative double ionization of N2 and CO molecules under electron impact. Experiments are performed at three energies, viz. 1, 3, and 5 keV, in order to observe the effect of impact energy on the dissociative ionization kinematics. We compare the kinetic energy release (KER) distributions of the charge symmetric dissociation channels of N22 + and CO2 + at these impact energies. An approximately linear trend between the transition energy and the expected KER values is inferred on the basis of the calculated potential energy curves of the dications. Experimentally, the normalized differential KER cross sections for these channels show an increasing trend in the low KER range and a decreasing trend in the high KER range as the electron-impact energy is increased. This observation indicates that the transition probability for excitation to different molecular ion states is not only a function of energy difference between the ground and excited states, but also a complicated function of the impact energy. In addition, nature of the observed trend in the differential KER cross sections differs significantly from their differential transition probability, which are calculated using inelastic collision model for fast-electron-impact case.

  12. Monte Carlo calculation of electron initiated impact ionization in bulk zinc-blende and wurtzite GaN

    NASA Astrophysics Data System (ADS)

    Kolník, Ján; Oǧuzman, Ismail H.; Brennan, Kevin F.; Wang, Rongping; Ruden, P. Paul

    1997-01-01

    Calculations of the high-field electronic transport properties of bulk zinc-blende and wurtzite phase gallium nitride are presented focusing particularly on the electron initiated impact ionization rate. The calculations are performed using ensemble Monte Carlo simulations, which include the full details of the band structure derived from an empirical pseudopotential method. The model also includes the numerically generated electron impact ionization transition rate, calculated based on the pseudopotential band structures for both crystallographic phases. The electron initiated impact ionization coefficients are calculated as a function of the applied electric field. The electron distribution is found to be cooler and the ionization coefficients are calculated to be lower in the wurtzite phase as compared to zinc-blende gallium nitride at compatable electric-field strengths. The higher electron energies and the resulting larger impact ionization coefficients in zinc-blende gallium nitride are believed to result from the combined effects of a lower density of states and phonon scattering rate for energies near and below 3 eV above the conduction-band minimum, and a somewhat higher ionization transition rate compared to the wurtzite phase. The nature of the impact ionization threshold in both phases of gallium nitride is predicted to be soft. Although there is considerable uncertainty in the knowledge of the scattering rates and the band structure at high energies which lead to uncertainty in the Monte Carlo calculations, the results presented provide a first estimate of what the electron initiated impact ionization rate in GaN can be expected to be.

  13. Theoretical and Experimental Triple Differential Cross Sections for Electron Impact Ionization of SF6

    NASA Astrophysics Data System (ADS)

    Chaluvadi, Hari; Nixon, Kate; Murray, Andrew; Ning, Chuangang; Colgan, James; Madison, Don

    2014-10-01

    Experimental and theoretical Triply Differential Cross Sections (TDCS) will be presented for electron-impact ionization of sulfur hexafluoride (SF6) for the molecular orbital 1t1g. M3DW (molecular 3-body distorted wave) results will be compared with experiment for coplanar geometry and for perpendicular plane geometry (a plane which is perpendicular to the incident beam direction). In both cases, the final state electron energies and observation angles are symmetric and the final state electron energies range from 5 eV to 40 eV. It will be shown that there is a large difference between using the OAMO (orientation averaged molecular orbital) approximation and the proper average over all orientations and also that the proper averaged results are in much better agreement with experiment. Work supported by NSF under Grant Number PHY-1068237. Computational work was performed with Institutional resources made available through Los Alamos National Laboratory.

  14. Electrochemical Etching and Characterization of Sharp Field Emission Points for Electron Impact Ionization.

    PubMed

    Van Well, Tyler L; Redshaw, Matthew; Gamage, Nadeesha D; Kandegedara, R M Eranjan B

    2016-01-01

    A new variation of the drop-off method for fabricating field emission points by electrochemically etching tungsten rods in a NaOH solution is described. The results of studies in which the etching current and the molarity of the NaOH solution used in the etching process were varied are presented. The investigation of the geometry of the tips, by imaging them with a scanning electron microscope, and by operating them in field emission mode is also described. The field emission tips produced are intended to be used as an electron beam source for ion production via electron impact ionization of background gas or vapor in Penning trap mass spectrometry applications. PMID:27500824

  15. Triple Differential Cross Sections for Ionization of Laser-Aligned Mg Atoms by electron impact

    NASA Astrophysics Data System (ADS)

    Amami, Sadek; Madison, Don; Nixon, Kate; Murray, Andrew

    2013-09-01

    3DW (3-body distorted wave) triple differential cross sections have been calculated for electron impact ionization of magnesium atoms aligned by lasers. Calculations have been performed for the kinematics of the experiment performed by Kate Nixon and Andrew Murray at Manchester, England [K. L. Nixon and A. J. Murray 2011 Phys. Rev. Lett. 106, 123201]. An incident projectile was produced with energy of 41.91eV, scattered and ejected electrons were detected with equal energies (E1 =E2 =20eV), the scattered projectile was detected at a fixed angle of 30deg, and the ejected electrons were detected at angles ranging between 0circ; - 180circ; . The theoretical 3DW results will be compared with the experimental data. This work is supported by the US National Science Foundation under Grant.No.PHY-1068237.

  16. Relativistic calculations of cross sections for ionization of U90+ and U91+ ions by electron impact

    NASA Astrophysics Data System (ADS)

    Fontes, Christopher J.; Sampson, Douglas H.; Zhang, Hong Lin

    1995-01-01

    Relativistic distorted-wave calculations have been made of the cross sections for electron-impact ionization of U90+ and U91+ ions with the generalized Breit interaction included between bound and free electrons. Good agreement is obtained with recent electron-beam ion-trap experiments [R. E. Marrs, S. R. Elliott, and D. A. Knapp, Phys. Rev. Lett. 72, 4082 (1994)].

  17. A vortex line for K-shell ionization of a carbon atom by electron impact

    NASA Astrophysics Data System (ADS)

    Ward, S. J.; Macek, J. H.

    2014-10-01

    We obtained using the Coulomb-Born approximation a deep minimum in the TDCS for K-shell ionization of a carbon atom by electron impact for the electron ejected in the scattering plane. The minimum is obtained for the kinematics of the energy of incident electron Ei = 1801.2 eV, the scattering angle θf = 4°, the energy of the ejected electron Ek = 5 . 5 eV, and the angle for the ejected electron θk = 239°. This minimum is due to a vortex in the velocity field. At the position of the vortex, the nodal lines of Re [ T ] and Im [ T ] intersect. We decomposed the CB1 T-matrix into its multipole components for the kinematics of a vortex, taking the z'-axis parallel to the direction of the momentum transfer vector. The m = +/- 1 dipole components are necessary to obtain a vortex. We also considered the electron to be ejected out of the scattering plane and obtained the positions of the vortex for different values of the y-component of momentum of the ejected electron, ky. We constructed the vortex line for the kinematics of Ei = 1801.2 eV and θf = 4°. S.J.W. and J.H.M. acknowledge support from NSF under Grant No. PHYS- 0968638 and from D.O.E. under Grant Number DE-FG02-02ER15283, respectively.

  18. Electron-impact ionization of P-like ions forming Si-like ions

    SciTech Connect

    Kwon, D.-H.; Savin, D. W.

    2014-03-20

    We have calculated electron-impact ionization (EII) for P-like systems from P to Zn{sup 15+} forming Si-like ions. The work was performed using the flexible atomic code (FAC) which is based on a distorted-wave approximation. All 3ℓ → nℓ' (n = 3-35) excitation-autoionization (EA) channels near the 3p direct ionization threshold and 2ℓ → nℓ' (n = 3-10) EA channels at the higher energies are included. Close attention has been paid to the detailed branching ratios. Our calculated total EII cross sections are compared both with previous FAC calculations, which omitted many of these EA channels, and with the available experimental results. Moreover, for Fe{sup 11+}, we find that part of the remaining discrepancies between our calculations and recent measurements can be accounted for by the inclusion of the resonant excitation double autoionization process. Lastly, at the temperatures where each ion is predicted to peak in abundances in collisional ionization equilibrium, the Maxwellian rate coefficients derived from our calculations differ by 50%-7% from the previous FAC rate coefficients, with the difference decreasing with increasing charge.

  19. Comparison of experimental and theoretical electron-impact-ionization triple-differential cross sections for ethane

    NASA Astrophysics Data System (ADS)

    Ali, Esam; Nixon, Kate; Murray, Andrew; Ning, Chuangang; Colgan, James; Madison, Don

    2015-10-01

    We have recently examined electron-impact ionization of molecules that have one large atom at the center, surrounded by H nuclei (H2O , N H3 , C H4 ). All of these molecules have ten electrons; however, they vary in their molecular symmetry. We found that the triple-differential cross sections (TDCSs) for the highest occupied molecular orbitals (HOMOs) were similar, as was the character of the HOMO orbitals which had a p -type "peanut" shape. In this work, we examine ethane (C2H6 ) which is a molecule that has two large atoms surrounded by H nuclei, so that its HOMO has a double-peanut shape. The experiment was performed using a coplanar symmetric geometry (equal final-state energies and angles). We find the TDCS for ethane is similar to the single-center molecules at higher energies, and is similar to a diatomic molecule at lower energies.

  20. Impact ionization in the base of a hot-electron AlSb/InAs bipolar transistor

    NASA Technical Reports Server (NTRS)

    Vengurlekar, Arvind S.; Capasso, Federico; Chiu, T. Heng

    1990-01-01

    The operation of a new AlSb/InAs heterojunction bipolar transistor is studied. The electrons are injected into a p-InAs base across the AlSb/InAs heterojunction. The conduction-band discontinuity at this heterojunction is sufficiently large so that energy of the electrons injected into InAs exceeds the threshold for generating electron-hole pairs by impact ionization. The observed incremental common base current at zero collector-base bias decreases and becomes negative as the emitter current is increased, thus providing direct evidence for impact ionization entirely by band-edge discontinuities.

  1. Deep minimum in the triple differential cross sections for the electron-impact ionization of He

    NASA Astrophysics Data System (ADS)

    Colgan, James; Feagin, James; Pindzola, Michael

    2012-06-01

    We further explore the unusual deep minimum found in the triple differential cross sections for the electron-impact ionization of helium. This feature has been observed experimentally more than 15 years ago [1] and confirmed via close-coupling calculations [2]. A recent study [3] identified the minimum with a vortex in the two-electron continuum, and an analytic expansion of the electron pair about the vortex has recently been derived [4]. The imaging theorem [3] is invoked to compute the TDCS from the radial wavefunctions propagated in time via solution of the time-dependent Schr"odinger equation for the electron helium system. This allows us to more easily visualize the portion of the wavefunction that contributes to the TDCS at the specific ejected electron angles where the deep minimum is observed. Interesting features in the radial wavefunction as a function of time are found, which appear to be consistent with the prediction [3] that a vortex in the two-electron wavefunction is responsible for the observed deep minimum. [1] A. J. Murray and F. H. Read, J. Phys. B 26, L359 (1993). [2] J. Colgan et al, J. Phys. B. 42, 171001 2009. [3] J. H. Macek, et al, Phys. Rev. Letts. 104, 033201 (2010). [4] J. M. F Feagin, J. Phys. B 44, 011001 (2011).

  2. Calculation of electron-impact ionization using the J-matrix method

    SciTech Connect

    Konovalov, D. A.; Bray, I.

    2010-08-15

    The J-matrix approach to electron-atom scattering is applied to ionization processes. We consider the Temkin-Poet model of e-H ionization. Convergence issues are studied with greater detail than previously possible using other close-coupling methods. The numerical strengths of the technique are emphasized with the long-term goal of application to ionization-plus-excitation processes.

  3. Observation of interatomic Coulombic decay and electron-transfer-mediated decay in high-energy electron-impact ionization of Ar2

    NASA Astrophysics Data System (ADS)

    Yan, S.; Zhang, P.; Ma, X.; Xu, S.; Li, B.; Zhu, X. L.; Feng, W. T.; Zhang, S. F.; Zhao, D. M.; Zhang, R. T.; Guo, D. L.; Liu, H. P.

    2013-10-01

    We measured the kinetic energy distributions of the fragment ions of doubly and quadruply ionized argon dimers using 3000 eV electron impact. For the dissociation of (Ar2)2+, the peak that indicates radiative charge transfer is observed, where the outer-shell ionization (dominant in highly charged ion collision) and the inner-shell ionization (preferential in x-ray experiments) have approximately equal contributions. For the dissociation of (Ar2)4+, the interatomic Coulombic decay and electron-transfer-mediated decay are first observed in the electron-impact process.

  4. Theoretical and Experimental Triple Differential Cross Sections for Electron Impact Ionization of Methane

    NASA Astrophysics Data System (ADS)

    Ch, Haari; Xu, Shenyue; Ning, Chuangang; Madison, Don; Ren, Xueguang; Pflueger, Thomas; Senftleben, Arne; Dorn, Alexander; Ullrich, Joachim

    2011-05-01

    Triple differential cross sections have been calculated and measured for 54 eV electron-impact ionization of the highest occupied molecular orbital (HOMO) 1t2 state of methane (CH4). Results will be presented both for the scattering plane and a plane in which the ejected electron is perpendicular to the incident beam direction. A systematic comparison between theoretical DWBA (distorted wave Born approximation), M3DW (molecular 3-body distorted wave), and experiment will be given for ejected electron energies ranging between 5 eV to 20 eV and scattered projectile angles ranging between 20 degrees and 55 degrees. In the perpendicular plane, better qualitative agreement between experiment and theory was found for the smaller projectile scattering angles and higher ejected electron energies. In the scattering plane on the other hand, agreement between theory and experiment tended to be better for the lower ejected electron energies. This work was supported by the National Science Foundation under Grant. No. PHY-0757749.

  5. Second-order Born approximation for the ionization of molecules by electron and positron impact

    SciTech Connect

    Dal Cappello, C.; Rezkallah, Z.; Houamer, S.; Charpentier, I.; Hervieux, P. A.; Ruiz-Lopez, M. F.; Dey, R.; Roy, A. C.

    2011-09-15

    Second-order Born approximation is applied to study the ionization of molecules. The initial and final states are described by single-center wave functions. For the initial state a Gaussian wave function is used while for the ejected electron it is a distorted wave. Results of the present model are compared with recent (e,2e) experiments on the water molecule. Preliminary results are also presented for the ionization of the thymine molecule by electrons and positrons.

  6. Experimental and Theoretical Fully differential cross sections for electron impact ionization of phenol molecules

    NASA Astrophysics Data System (ADS)

    Ali, Esam; Jones, D.; Silva, G.; Chiari, L.; Neves, R.; Lopes, M.; Brunger, M.; Ning, C.; Madison, D.

    2014-10-01

    Experimental and theoretical Fully Differential Cross Sections (FDCS) are presented for 250 eV electron impact ionization of the highest and next highest occupied molecular orbitals (HOMO and NHOMO). Theoretical results are compared with experiment for in plane scattering with projectile scattering angles of 5°, 10°, and 15°. Different theoretical models are examined - the molecular 3 body distorted wave (M3DW), and the distorted wave Born approximation (DWBA), with the effects of the post collision interaction (PCI) treated either exactly or with the Ward-Macek approximations. These approximations show good agreement with experimental data for binary peaks. However, for the recoil peak region, experiment finds a noticeable peak while theory predicts no peak. No recoil peak suggests no (or very weak) nuclear scattering, so we have investigated the importance of nuclear scattering by moving the nuclei closer to the center of mass. Work supported by NSF and the XSEDE.

  7. A (e,2e +ion) study of low-energy electron-impact ionization of THF

    NASA Astrophysics Data System (ADS)

    Ali, Esam; Ren, Xueguang; Ning, Chuangang; Dorn, Alexander; Madison, Don

    2015-09-01

    We have investigated the Fully Differential Cross Sections (FDCS) for electron impact induced ionization of THF (C4H8O) by low-energy (Eo = 26 eV) for three different orbital states of the highest, next highest, and next-next highest occupied molecular orbitals (HOMO, NHOMO, and Next NHOMO). Theoretical results are compared with experiment for in plane scattering with projectile scattering angles of 15°, 25°, 35°, and 50°. Different theoretical models are examined - the molecular 3 body distorted wave (M3DW), and the distorted wave Born approximation (DWBA), with the effects of the post collision interaction (PCI) treated either exactly or with the Ward-Macek approximations. This work is supported by the US National Science Foundation under Grant No. PHY-1068237 and XSEDE resources provided by the Texas Advanced Computing Center (Grant No. TG-MCA07S029).

  8. Electron-impact excitation and ionization cross sections for ground state and excited helium atoms

    SciTech Connect

    Ralchenko, Yu. Janev, R.K.; Kato, T.; Fursa, D.V.; Bray, I.; Heer, F.J. de

    2008-07-15

    Comprehensive and critically assessed cross sections for the electron-impact excitation and ionization of ground state and excited helium atoms are presented. All states (atomic terms) with n{<=}4 are treated individually, while the states with n{>=}5 are considered degenerate. For the processes involving transitions to and from n{>=}5 levels, suitable cross section scaling relations are presented. For a large number of transitions, from both ground and excited states, convergent close coupling calculations were performed to achieve a high accuracy of the data. The evaluated/recommended cross section data are presented by analytic fit functions, which preserve the correct asymptotic behavior of the cross sections. The cross sections are also displayed in graphical form.

  9. S-model calculations for high-energy-electron-impact double ionization of helium

    NASA Astrophysics Data System (ADS)

    Gasaneo, G.; Mitnik, D. M.; Randazzo, J. M.; Ancarani, L. U.; Colavecchia, F. D.

    2013-04-01

    In this paper the double ionization of helium by high-energy electron impact is studied. The corresponding four-body Schrödinger equation is transformed into a set of driven equations containing successive orders in the projectile-target interaction. The transition amplitude obtained from the asymptotic limit of the first-order solution is shown to be equivalent to the familiar first Born approximation. The first-order driven equation is solved within a generalized Sturmian approach for an S-wave (e,3e) model process with high incident energy and small momentum transfer corresponding to published measurements. Two independent numerical implementations, one using spherical and the other hyperspherical coordinates, yield mutual agreement. From our ab initio solution, the transition amplitude is extracted, and single differential cross sections are calculated and could be taken as benchmark values to test other numerical methods in a previously unexplored energy domain.

  10. Ionization cross sections and rate coefficients for CFCl3 molecule by electron impact

    NASA Astrophysics Data System (ADS)

    Pal, Satyendra; Kumar, Neeraj

    2013-09-01

    Chlorofluorocarbons (CFCs) or freons are important industrial material with wide-ranging applications as refrigerant, aerosol propellant and semiconductor etchant, etc. The large-scale industrial consumption is of particular environmental concern because of its potential for ozone destruction in the stratosphere. The present work reports the calculations for differential cross sections as a function of secondary/ ejected electron energy and the scattering angle in the ionization of CFCl3 by electron collision leading to the production of various cations viz. CCl3+,CFCl2+,CCl2+,CFCl+, CCl+, Cl+, CF+, F+, and C+ through direct and dissociative ionization processes at a fixed incident electron energy of 200 eV. A modified Jain-Khare semi-empirical formalism based on oscillator strength has been employed. To the best of our knowledge, no experimental and/or theoretical data is available for comparison of the present results for differential cross sections. The corresponding derived integral cross sections in terms of the partial ionization cross sections corresponding to these cations, in the energy range varying from ionization threshold to 1000 eV, revealed a reasonably good agreement with the experimental and theoretical data, wherever available. In addition to the differential and integral ionization cross sections, we have also calculated the ionization rate coefficients using the evaluated partial ionization cross sections and the Maxwell-Boltzmann distribution as a function of electron energy.

  11. Molecular Data for a Biochemical Model of DNA Radiation Damage: Electron Impact Ionization and Dissociative Ionization of DNA Bases and Sugar-Phosphate Backbone

    NASA Technical Reports Server (NTRS)

    Dateo, Christopher E.; Fletcher, Graham D.

    2004-01-01

    As part of the database for building up a biochemical model of DNA radiation damage, electron impact ionization cross sections of sugar-phosphate backbone and DNA bases have been calculated using the improved binary-encounter dipole (iBED) model. It is found that the total ionization cross sections of C3'- and C5'-deoxyribose-phospate, two conformers of the sugar-phosphate backbone, are close to each other. Furthermore, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3'- and C5'-deoxyribose-phospate cross sections, differing by less than 10%. Of the four DNA bases, the ionization cross section of guanine is the largest, then in decreasing order, adenine, thymine, and cytosine. The order is in accordance with the known propensity of oxidation of the bases by ionizing radiation. Dissociative ionization (DI), a process that both ionizes and dissociates a molecule, is investigated for cytosine. The DI cross section for the formation of H and (cytosine-Hl)(+), with the cytosine ion losing H at the 1 position, is also reported. The threshold of this process is calculated to be 17.1 eV. Detailed analysis of ionization products such as in DI is important to trace the sequential steps in the biochemical process of DNA damage.

  12. Electron-impact excitation and ionization of W3+ for the determination of tungsten influx in a fusion plasma

    NASA Astrophysics Data System (ADS)

    Ballance, C. P.; Loch, S. D.; Pindzola, M. S.; Griffin, D. C.

    2013-03-01

    Tungsten will be employed as a plasma facing material in the ITER fusion reactor under construction in Cadarache, France; therefore, there is a significant need for accurate electron-impact excitation and ionization data for the ions of tungsten. We report on the results of extensive calculations of ionization and excitation for W3+ that are intended to provide the atomic data needed for the determination of impurity influx diagnostics of tungsten in several existing tokamak reactors. The electron-impact excitation rate coefficients for this study were determined using the relativistic R-matrix method. The contribution to direct electron-impact ionization was determined using the distorted-wave approximation, the accuracy of which was verified by an R-matrix with pseudo states calculation. Contributions to total ionization from excitation autoionization were also generated from the relativistic R-matrix method. These results were then employed to calculate values of ionization per emitted photon, or SXB ratios, for four carefully selected spectral lines; these data will allow the determination of impurity influx from tungsten facing surfaces. For the range of densities of importance in the edge region of a tokamak reactor, these SXB ratios are found to be nearly independent of electron density but vary significantly with electron temperature.

  13. Evaluation of the computational methods for electron-impact total ionization cross sections: Fluoromethanes as benchmarks

    NASA Astrophysics Data System (ADS)

    Torres, I.; Martínez, R.; Sánchez Rayo, M. N.; Castaño, F.

    2001-09-01

    The experimental electron-impact total ionization cross sections (TICSs, ICSs) of CF4, CHF3, CH2F2, and CH3F fluoromethanes reported so far and a new set of data obtained with a linear double focusing time-of-flight mass spectrometer have been compared with the ab initio and (semi)empirical based ICS available methods. TICSs computational methods include: two approximations of the binary-encounter dipole (BED) referred to hereafter as Kim (Kim-BEB) and Khare (Khare-BEB) methods, the Deutsch and Märk (DM) formalism, also requiring atomic and molecular ab initio information, the modified additivity rule (MAR), and the Harland and Vallance (HV) methods, both based on semiempirical or empirical correlations. The molecular ab initio information required by the Kim, Khare, and DM methods has been computed at a variety of quantum chemistry levels, with and without electron correlation and a comprehensive series of basis sets. The general conclusions are summarized as follows: the Kim method yields TICS in excellent agreement with the experimental method; the Khare method provides TICS very close to that of Kim at low electron-impact energies (<100 eV), but their Mott and Bethe contributions are noticeably different; in the Kim and Khare approximations the electron correlation methods improve the fittings to the experimental profiles in contrast with the large basis sets, that leads to poorer results; the DM formalism yields TICS profiles with shapes similar to the experimental and the BEB methods, but consistently lower and with the profiles maxima shifted towards lower incident electron energies; the MAR method supplies very good ICS profiles, between those of BEB and DM methods; finally, the empirical HV method provides rather poor fittings concomitant with the simplicity and the few empirical parameters used.

  14. Exchange distortion and postcollision interaction for intermediate-energy electron-impact ionization of argon

    SciTech Connect

    Prideaux, A.; Madison, D.H.; Bartschat, K.

    2005-09-15

    Measurements of fully differential cross sections for electron impact ionization of atoms have been performed for over 30 years. However, only within the last ten years has agreement between experiment and theory been achieved for ionization of hydrogen and helium. For the heavier inert gases, reasonably good agreement between experiment and theory has only been achieved for high incident energies while serious discrepancies are common for intermediate and low incident energies. It is believed that a major source of the problem stems from an improper/inadequate treatment of exchange distortion (ED) and the effects of post-collision interactions (PCIs). In this paper, two different methods for including ED are examined--one based upon the R matrix (close-coupling) approach and one originating from the single-configuration Hartree-Fock approach. In general, these two methods predict significant, but different, ED effects. The importance of PCI is studied by including the final-state Coulomb interaction directly in the final-state wave function. This procedure guarantees that PCI effects will be included to all orders of perturbation theory. For intermediate energies, PCI is an important effect and leads to an overall improvement in the agreement between experiment and theory.

  15. Optical potential approach to the electron-atom impact ionization threshold problem

    NASA Technical Reports Server (NTRS)

    Temkin, A.; Hahn, Y.

    1973-01-01

    The problem of the threshold law for electron-atom impact ionization is reconsidered as an extrapolation of inelastic cross sections through the ionization threshold. The cross sections are evaluated from a distorted wave matrix element, the final state of which describes the scattering from the Nth excited state of the target atom. The actual calculation is carried for the e-H system, and a model is introduced which is shown to preserve the essential properties of the problem while at the same time reducing the dimensionability of the Schrodinger equation. Nevertheless, the scattering equation is still very complex. It is dominated by the optical potential which is expanded in terms of eigen-spectrum of QHQ. It is shown by actual calculation that the lower eigenvalues of this spectrum descend below the relevant inelastic thresholds; it follows rigorously that the optical potential contains repulsive terms. Analytical solutions of the final state wave function are obtained with several approximations of the optical potential.

  16. Exchange distortion and postcollision interaction for intermediate-energy electron-impact ionization of argon

    NASA Astrophysics Data System (ADS)

    Prideaux, A.; Madison, D. H.; Bartschat, K.

    2005-09-01

    Measurements of fully differential cross sections for electron impact ionization of atoms have been performed for over 30 years. However, only within the last ten years has agreement between experiment and theory been achieved for ionization of hydrogen and helium. For the heavier inert gases, reasonably good agreement between experiment and theory has only been achieved for high incident energies while serious discrepancies are common for intermediate and low incident energies. It is believed that a major source of the problem stems from an improper/inadequate treatment of exchange distortion (ED) and the effects of post-collision interactions (PCIs). In this paper, two different methods for including ED are examined—one based upon the R matrix (close-coupling) approach and one originating from the single-configuration Hartree-Fock approach. In general, these two methods predict significant, but different, ED effects. The importance of PCI is studied by including the final-state Coulomb interaction directly in the final-state wave function. This procedure guarantees that PCI effects will be included to all orders of perturbation theory. For intermediate energies, PCI is an important effect and leads to an overall improvement in the agreement between experiment and theory.

  17. Cross sections of electron capture and electron capture ionization versus the impact parameter in collisions of a proton with multielectron atoms

    NASA Astrophysics Data System (ADS)

    Afrosimov, V. V.; Basalaev, A. A.; Ogurtsov, G. N.; Panov, M. N.

    2014-05-01

    The absolute differential cross sections of scattering of hydrogen atoms resulting from an electron capture and an electron capture ionization are measured for collisions of 4.5- and 11-keV protons with argon and xenon atoms. The range of scattering angles is 0°-2°. From the scattering differential cross section found experimentally, the probabilities of single-electron capture and electron capture ionization as a function of the impact parameter are calculated. The dependences of the incident particle scattering angle on the impact parameter (deviation function) for interactions with Ar and Xe atoms are calculated in terms of classical mechanics using the Moliére—Yukawa potential to describe the interaction of atomic particles. Analysis is given to the probabilities of electron capture and electron capture ionization versus the impact parameter and to the distribution of the electron density on different electron shells in a target atom versus a distance to the core. It is concluded that only electrons from the outer shell of the target atom are involved in the process of electron capture ionization. The cross section of electron capture ionization is calculated in the proton energy range 5-20 keV.

  18. STORAGE RING CROSS-SECTION MEASUREMENTS FOR ELECTRON IMPACT SINGLE AND DOUBLE IONIZATION OF Fe{sup 9+} AND SINGLE IONIZATION OF Fe{sup 10+}

    SciTech Connect

    Hahn, M.; Novotny, O.; Savin, D. W.; Becker, A.; Grieser, M.; Krantz, C.; Wolf, A.; Lestinsky, M.; Repnow, R.; Mueller, A.; Schippers, S.; Spruck, K.

    2012-11-20

    We have measured electron impact ionization from the ground state of Fe{sup 9+} and Fe{sup 10+} over the relative electron-ion collision energy ranges 200-1900 eV and 250-1800 eV, respectively. The ions were confined in an ion storage ring long enough for essentially all metastable levels to radiatively relax to the ground state. For single ionization, we find a number of discrepancies between the existing theoretical cross sections and our results. The calculations appear to neglect some excitation-autoionization (EA) channels, particularly from n = 3 to n' excitations, which are important near threshold, and those from n = 2 {yields} 3 excitations, which contribute at about 650 eV. Conversely, at higher energies the calculations appear to overestimate the importance of EA channels due to excitation into levels where n {>=} 4. The resulting experimental rate coefficients agree with the most recent theory for Fe{sup 9+} to within 16% and for Fe{sup 10+} to within 19% at temperatures where these ions are predicted to form in collisional ionization equilibrium. We have also measured double ionization of Fe{sup 9+} forming Fe{sup 11+} in the energy range 450-3000 eV and found that although there is an appreciable cross section for direct double ionization, the dominant mechanism appears to be through direct ionization of an inner shell electron producing an excited state that subsequently stabilizes through autoionization.

  19. Flow injection of liquid samples to a mass spectrometer with ionization under vacuum conditions: a combined ion source for single-photon and electron impact ionization.

    PubMed

    Schepler, Claudia; Sklorz, Martin; Passig, Johannes; Famiglini, Giorgio; Cappiello, Achille; Zimmermann, Ralf

    2013-09-01

    Electrospray ionization (ESI), atmospheric pressure chemical ionization (APCI), and atmospheric pressure photo-ionization (APPI) are the most important techniques for the ionization of liquid samples. However, working under atmospheric pressure conditions, all these techniques involve some chemical rather than purely physical processes, and therefore, side reactions often yield to matrix-dependent ionization efficiencies. Here, a system is presented that combines both soft single-photon ionization (SPI) and hard 70 eV electron impact ionization (EI) of dissolved compounds under vacuum conditions. A quadrupole mass spectrometer was modified to enable direct EI, a technique developed by Cappiello et al. to obtain library-searchable EI mass spectra as well as soft SPI mass spectra of sample solutions. An electron beam-pumped rare gas excimer lamp working at 126 nm was used as well as a focusable vacuum UV light source for single-photon ionization. Both techniques, EI and SPI, were applied successfully for flow injection experiments providing library-matchable EI fragment mass spectra and soft SPI mass spectra, showing dominant signals for the molecular ion. Four model compounds were analyzed: hexadecane, propofol, chlorpropham, and eugenol, with detection limits in the picomolar range. This novel combination of EI and SPI promises great analytical benefits, thanks to the possibility of combining database alignment for EI data and molecular mass information provided by SPI. Possible applications for the presented ionization technology system are a matrix-effect-free detection and a rapid screening of different complex mixtures without time-consuming sample preparation or separation techniques (e.g., for analysis of reaction solutions in combinatorial chemistry) or a switchable hard (EI) and soft (SPI) MS method as detection step for liquid chromatography. PMID:23812882

  20. Numerical study of the wave-vector dependence of the electron interband impact ionization rate in bulk GaAs

    NASA Technical Reports Server (NTRS)

    Wang, Yang; Brennan, Kevin F.

    1994-01-01

    Ensemble Monte Carlo calculations of the electron interband impact ionization rate in bulk GaAs are presented using a wave-vector (k)-dependent formulation of the ionization transition rate. The transition rate is evaluated through the use of numerically generated wavefunctions determined via a k-p calculation within the first two conduction bands at numerous points within a finely spaced three-dimensional grid in k space. The transition rate is determined to be greatest for states within the second conduction band. Is is found that the interband impact ionization transition rate in bulk GaAs is best characterized as having an exceedingly soft threshold energy. As a consequence, the dead space, defined as the distance over which the ionization probability for a given carrier is assumed to be zero, is estimated to be much larger than that estimated using a harder threshold. These results have importance in the design of the multiquantum-well avalanche photodiodes.

  1. Numerical Study of the Wave-Vector Dependence of the Electron Interband Impact Ionization Rate in Bulk GaAs

    NASA Technical Reports Server (NTRS)

    Wang, Yang; Brennan, Kevin F.

    1994-01-01

    Ensemble Monte Carlo calculations of the electron interband impact ionization rate in bulk GaAs are presented using a wave-vector (k)-dependent formulation of the ionization transition rate. The transition rate is evaluated through use of numerically generated wavefunctions determined via a k-p calculation within the first two conduction bonds at numerous points within a finely spaced three-dimensional grid in k space. The transition rate is determined to be greatest for states within the second conduction band. It is found that the interband impact ionization transition rate in bulk GaAs is best characterized as having an exceedingly "soft" threshold energy. As a consequence, the dead space, defined as the distance over which the ionization probability for a given carrier is assumed to be zero, is estimated to be-much larger than that estimated using a "harder" threshold. These results have importance in the design of multiquantum-well avalanche photodiodes.

  2. Impact of electron ionization on the generation of high-order harmonics from molecules

    SciTech Connect

    Brener, S.; Moiseyev, N.; Ivanov, M. V.

    2003-08-01

    When the laser frequency is tuned to be equal to the molecular electronic excitation, high-order harmonics are generated due to the electronic dipole transitions between the corresponding two potential-energy surfaces (PES). A natural, often taken, choice is the PES of the field-free molecular system. In this special choice the ionization phenomenon is not considered. Only the effect of the dissociation is considered. The method we developed enables one to remain within the framework of the 2-PES approximation and yet to include also the ionization effect in the calculations of molecular high-order harmonic generation spectra. In this approach the coupling between the electronic and nuclear motions is taken into consideration by using coupled complex adiabatic PES. As an illustrative numerical example, we calculated the high harmonic generation (HHG) spectra of H{sub 2}{sup +} in a 730-nm laser with the intensity of 8.77x10{sup 13} W/cm{sup 2}. The inclusion of the ionization in our approach not only enables the electrons to tunnel through the effective static potential barrier, but also apply an asymmetric force which accelerates the electron before ionization takes place. Therefore, indirectly the inclusion of the ionization by the laser field may lead eventually to an enhanced HHG spectra in comparison with the calculated one when the ''natural'' choice of the field-free 2PES is taken.

  3. Gridded electron reversal ionizer

    NASA Technical Reports Server (NTRS)

    Chutjian, Ara (Inventor)

    1993-01-01

    A gridded electron reversal ionizer forms a three dimensional cloud of zero or near-zero energy electrons in a cavity within a filament structure surrounding a central electrode having holes through which the sample gas, at reduced pressure, enters an elongated reversal volume. The resultant negative ion stream is applied to a mass analyzer. The reduced electron and ion space-charge limitations of this configuration enhances detection sensitivity for material to be detected by electron attachment, such as narcotic and explosive vapors. Positive ions may be generated by generating electrons having a higher energy, sufficient to ionize the target gas and pulsing the grid negative to stop the electron flow and pulsing the extraction aperture positive to draw out the positive ions.

  4. A Universal model for electron impact ionization of K, L and M-shells.

    NASA Astrophysics Data System (ADS)

    Bary Malik, Fazley; Haque, A. K. F.; Uddin, M. A.; Basak, A. K.; Saha, B. C.; Karim, K. R.

    2007-06-01

    A modified version of the original Kolbenstvedt model, which has its roots in quantum electrodynamical description of electron-electron scattering, will be presented. This modified model describes reasonably well cross sections of K-shell ionization of H, He, Li, C, N, O, Mg, Si, P and S, L-shell ionization of Ag, Sn, Ba, Ho, Ta, Au, Pb, Bi and U, M-shell ionization of Pb, Bi and U, from threshold to a few GeV incident energy. The same model with slight modification to account for the ionic charge is also applicable to ionic targets such as Ne^8+, Mo^41+, U^82+ from threshold to a few MeV incident energy. Experimentally observed increase of the cross section at high energies seems to be a consequence of the Møller interaction between two interacting electrons.

  5. Electron impact fragmentation of adenine: partial ionization cross sections for positive fragments

    NASA Astrophysics Data System (ADS)

    van der Burgt, Peter J. M.; Finnegan, Sinead; Eden, Samuel

    2015-07-01

    Using computer-controlled data acquisition we have measured mass spectra of positive ions for electron impact on adenine, with electron energies up to 100 eV. Ion yield curves for 50 ions have been obtained and normalized by comparing their sum to the average of calculated total ionization cross sections. Appearance energies have been determined for 37 ions; for 20 ions for the first time. All appearance energies are consistent with the fragmentation pathways identified in the literature. Second onset energies have been determined for 12 fragment ions (for 11 ions for the first time), indicating the occurrence of more than one fragmentation process e.g. for 39 u (C2HN+) and 70 u (C2H4N3+). Matching ion yield shapes (118-120 u, 107-108 u, 91-92 u, and 54-56 u) provide new evidence supporting closely related fragmentation pathways and are attributed to hydrogen rearrangement immediately preceding the fragmentation. We present the first measurement of the ion yield curve of the doubly charged parent ion (67.5 u), with an appearance energy of 23.5 ± 1.0 eV. Contribution to the Topical Issue "COST Action Nano-IBCT: Nano-scale Processes Behind Ion-Beam Cancer Therapy", edited by Andrey Solov'yov, Nigel Mason, Gustavo García, Eugene Surdutovich.

  6. Importance of the recoil contribution in Two Step 2 mechanism for the electron impact double ionization process

    NASA Astrophysics Data System (ADS)

    Li, C.; Staicu Casagrande, E. M.; Lahmam-Bennani, A.

    2014-04-01

    The second order, Two-Step-2 (TS2) mechanism for electron impact double ionization (DI) of various targets at intermediate incident energy is investigated based on a kinematical analysis which assumes the DI to result from two successive (e,2e) single ionization (SI) events. The results show that under the present kinematics, the inclusion of the recoil scattering in each of these (e,2e)-SI steps (in previous studies only the binary scattering was considered) allows a more detailed understanding of the various peaks observed in the experimental angular distributions of the ejected electrons in both (e,3-1e) and (e,3e) experiments.

  7. Ionization By Impact Electrons in Solids: Electron Mean Free Path Fitted Over A Wide Energy Range

    SciTech Connect

    Ziaja, B; London, R A; Hajdu, J

    2005-06-09

    We propose a simple formula for fitting the electron mean free paths in solids both at high and at low electron energies. The free-electron-gas approximation used for predicting electron mean free paths is no longer valid at low energies (E < 50 eV), as the band structure effects become significant at those energies. Therefore we include the results of the band structure calculations in our fit. Finally, we apply the fit to 9 elements and 2 compounds.

  8. Direct evidence of two interatomic relaxation mechanisms in argon dimers ionized by electron impact

    PubMed Central

    Ren, Xueguang; Jabbour Al Maalouf, Elias; Dorn, Alexander; Denifl, Stephan

    2016-01-01

    In weakly bound systems like liquids and clusters electronically excited states can relax in inter-particle reactions via the interplay of electronic and nuclear dynamics. Here we report on the identification of two prominent examples, interatomic Coulombic decay (ICD) and radiative charge transfer (RCT), which are induced in argon dimers by electron collisions. After initial ionization of one dimer constituent ICD and RCT lead to the ionization of its neighbour either by energy transfer to or by electron transfer from the neighbour, respectively. By full quintuple-coincidence measurements, we unambiguously identify ICD and RCT, and trace the relaxation dynamics as function of the collisional excited state energies. Such interatomic processes multiply the number of electrons and shift their energies down to the critical 1–10 eV range, which can efficiently cause chemical degradation of biomolecules. Therefore, the observed relaxation channels might contribute to cause efficient radiation damage in biological systems. PMID:27000407

  9. On a source of electron impact ionization in Io's upstream atmosphere

    NASA Astrophysics Data System (ADS)

    Shaposhnikov, V. E.; Zaitsev, V. V.; Rucker, H. O.; Litvinenko, G. V.; Konovalenko, A. A.

    2013-09-01

    A mechanism for the ionization of Io's atmosphere due to the moon's motion through the Jovian magnetic field is considered. Attention is paid to the important role of charge separation in the upstream part of Io's ionosphere and accumulation of electrons and positive ions on the low and top ionospheric boundaries which results in (a) the creation of longitudinal component (with respect to the Jovian magnetic field lines) of polarization electric field, (b) the driving of Bounemann plasma turbulence, and (c) the heating of electrons and the ionization of neutrals. Estimations show that the proposed mechanism can essentially heat the electrons and increase the electron density. The increase with the plasma density and the electron temperature can result in an ionospheric plasma distribution and overcomes the difficulty with generation of the most bright part of UV emission of the Io's equatorial spots.

  10. Small-signal modeling with direct parameter extraction for impact ionization effect in high-electron-mobility transistors

    SciTech Connect

    Guan, He; Lv, Hongliang; Guo, Hui Zhang, Yuming

    2015-11-21

    Impact ionization affects the radio-frequency (RF) behavior of high-electron-mobility transistors (HEMTs), which have narrow-bandgap semiconductor channels, and this necessitates complex parameter extraction procedures for HEMT modeling. In this paper, an enhanced small-signal equivalent circuit model is developed to investigate the impact ionization, and an improved method is presented in detail for direct extraction of intrinsic parameters using two-step measurements in low-frequency and high-frequency regimes. The practicability of the enhanced model and the proposed direct parameter extraction method are verified by comparing the simulated S-parameters with published experimental data from an InAs/AlSb HEMT operating over a wide frequency range. The results demonstrate that the enhanced model with optimal intrinsic parameter values that were obtained by the direct extraction approach can effectively characterize the effects of impact ionization on the RF performance of HEMTs.

  11. Electron impact ionization in the Martian atmosphere: Interplay between scattering and crustal magnetic field effects

    NASA Astrophysics Data System (ADS)

    Lillis, Robert J.; Fang, Xiaohua

    2015-07-01

    Precipitating electrons are typically the dominant source of energy input into Mars' nighttime upper atmosphere, with consequences for atmospheric and ionospheric structure, composition, chemistry, and electrodynamics. Mars' spatially heterogeneous crustal magnetic fields affect the fluxes of precipitating electrons, via both the magnetic mirror force and Gauss' law of conservation of magnetic flux. We use a kinetic electron transport model to examine ionization rate profiles that result from the combination of these magnetic effects and elastic and inelastic scattering by atmospheric neutrals. Specifically, we calculate ionization rates as a function of altitude, crustal magnetic field strength, and the initial energy and pitch angle of the precipitating electrons, covering the relevant ranges of these parameters. Several complex behaviors are exhibited, including bifurcating ionization peaks with distinct characteristics and energy-dependent and crustal field strength-dependent increases in ionization with decreasing pitch angle. Elucidating such behavior is important for understanding the effect of Mars' unique crustal fields on the Mars upper atmosphere and ionosphere, both to predict the consequences of measured electron precipitation and to enable, for the first time, downward coupling of global plasma models with thermosphere-ionosphere models.

  12. Ionization cross-sections for the production of positive ions from H2O by electron impact

    NASA Technical Reports Server (NTRS)

    Rao, M. V. V. S.; Iga, I.; Srivastava, S. K.

    1995-01-01

    Water is present in the atmospheres of 6 of the 9 planets. Cross section values for the direct and partial ionization of H2O by electron impact have been measured and compared with previously published data. The present measurements have been carried out from thresholds to 1 KeV by utilizing a crossed electron beam and molecular beam collision geometry and an improved ion extraction technique.

  13. The study of ionization by electron impact of a substance simulating spent nuclear fuel components

    NASA Astrophysics Data System (ADS)

    Antonov, N. N.; Bochkarev, E. I.; Gavrikov, A. V.; Samokhin, A. A.; Smirnov, V. P.

    2015-11-01

    Plasma sources of model substances are necessary to solve problems associated with development of the spent nuclear fuel (SNF) plasma separation method. Lead was chosen to simulate kinetic and dynamic properties of the heavy SNF components. In this paper we present the results of a study of a lead vapor discharge with a lead concentration of 1012-1013 cm-3. Ionization was carried out by an electron beam (with energy of up to 500 eV per electron) inside a centimeter gap between planar electrodes. The discharge was numerically modeled using the hydrodynamic and single-particle approximation. Current-voltage characteristics and single ionization efficiency were obtained as functions of the vapors concentration and thermoelectric current. An ion current of hundreds of microamperes at the ionization efficiency near tenths of a percent was experimentally obtained. These results are in good agreement with our model.

  14. Electron-impact ionization of benzoic acid, nicotinic acid and their n-butyl esters

    NASA Astrophysics Data System (ADS)

    Opitz, Joachim

    2007-08-01

    Electron-impact ionization mass spectra, the decay of metastable ions, ionization and appearance energies and bond energies, as dissociation energies, are reported for the title compounds. An ionization energy of 9.47 eV was obtained for benzoic acid, 9.43 eV for benzoic acid n-butyl ester, 9.61 eV for nicotinic acid and 9.97 eV for nicotinic acid n-butyl ester. Molecular ions of both butyl esters show two common main fragmentation pathways: the first process is a McLafferty rearrangement, characterized by the transfer of one H-atom from the aliphatic ester chain, which leads to the ions of either the organic acid or 1-butene. From their appearance energies and known thermodynamic data, gas-phase formation enthalpies () of the parent n-butyl esters are calculated. Values of for benzoic acid n-butyl ester and for nicotinic acid n-butyl ester were obtained. The second process is characterized by the transfer of two H-atoms from the ester chain leading to a protonated form of the corresponding organic acids and C4H7 radicals. Good evidence is provided for the formation of methylallyl radicals. Appearance energies are used to calculate a proton affinity (PA) for benzoic acid. The obtained value of PA = (8.73 ± 0.3) eV, corresponding to a protonation of the carbonyl group, is in close corroboration with published data (PA = 8.51 eV). Activation energies for the intermediate H-transfers were found to be insignificant. This methodic gateway is applied to the system of nicotinic acid and its butyl ester. Adopting the formation of a methylallyl radical, the obtained proton affinity of nicotinic acid, PA = 8.58 eV, is very near to the published data of benzoic acid. An alternative fragmentation mechanism leading to a value of PA [approximate] 9.5 eV (typical for a protonation of the pyridine-nitrogen) is very unlikely. It is concluded that this transfer of two H-atoms from the ester chain is controlled by a charge switching between the carboxylic oxygen atoms which leads to

  15. Influence of Electron-Impact Multiple Ionization on Equilibrium and Dynamic Charge State Distributions: A Case Study Using Iron

    NASA Astrophysics Data System (ADS)

    Hahn, M.; Savin, D. W.

    2015-02-01

    We describe the influence of electron-impact multiple ionization (EIMI) on the ionization balance of collisionally ionized plasmas. Previous ionization balance calculations have largely neglected EIMI. Here, EIMI cross-section data are incorporated into calculations of both equilibrium and non-equilibrium charge-state distributions (CSDs). For equilibrium CSDs, we find that EIMI has only a small effect and can usually be ignored. However, for non-equilibrium plasmas the influence of EIMI can be important. In particular, we find that for plasmas in which the temperature oscillates there are significant differences in the CSD when including versus neglecting EIMI. These results have implications for modeling and spectroscopy of impulsively heated plasmas, such as nanoflare heating of the solar corona.

  16. Electron-impact ionization cross sections out of the ground and 6P2 excited states of cesium

    NASA Astrophysics Data System (ADS)

    Łukomski, M.; Sutton, S.; Kedzierski, W.; Reddish, T. J.; Bartschat, K.; Bartlett, P. L.; Bray, I.; Stelbovics, A. T.; McConkey, J. W.

    2006-09-01

    An atom trapping technique for determining absolute, total ionization cross sections (TICS) out of an excited atom is presented. The unique feature of our method is in utilizing Doppler cooling of neutral atoms to determine ionization cross sections. This fluorescence-monitoring experiment, which is a variant of the “trap loss” technique, has enabled us to obtain the experimental electron impact ionization cross sections out of the Cs 6P3/22 state between 7eV and 400eV . CCC, RMPS, and Born theoretical results are also presented for both the ground and excited states of cesium and rubidium. In the low energy region (<11eV) where best agreement between these excited state measurements and theory might be expected, a discrepancy of approximately a factor of five is observed. Above this energy there are significant contributions to the TICS from both autoionization and multiple ionization.

  17. INFLUENCE OF ELECTRON-IMPACT MULTIPLE IONIZATION ON EQUILIBRIUM AND DYNAMIC CHARGE STATE DISTRIBUTIONS: A CASE STUDY USING IRON

    SciTech Connect

    Hahn, M.; Savin, D. W.

    2015-02-10

    We describe the influence of electron-impact multiple ionization (EIMI) on the ionization balance of collisionally ionized plasmas. Previous ionization balance calculations have largely neglected EIMI. Here, EIMI cross-section data are incorporated into calculations of both equilibrium and non-equilibrium charge-state distributions (CSDs). For equilibrium CSDs, we find that EIMI has only a small effect and can usually be ignored. However, for non-equilibrium plasmas the influence of EIMI can be important. In particular, we find that for plasmas in which the temperature oscillates there are significant differences in the CSD when including versus neglecting EIMI. These results have implications for modeling and spectroscopy of impulsively heated plasmas, such as nanoflare heating of the solar corona.

  18. Role of elastic projectile-electron scattering in double ionization of helium by fast proton impact

    NASA Astrophysics Data System (ADS)

    Schulz, M.; Ciappina, M. F.; Kirchner, T.; Fischer, D.; Moshammer, R.; Ullrich, J.

    2009-04-01

    We present a systematic study of atomic four-body fragmentation dynamics. To this end we have measured a variety of multiple differential double ionization cross sections for 6 MeV p+He collisions. The data are compared to a first-order calculation with correlated electrons and to a simulation representing a second-order process, with some experimental results seemingly in favor of the first, others in agreement with the second approach. This apparent conflict can be resolved by accounting for elastic scattering between the projectile and one electron already promoted to the continuum through electron-electron correlation in the first-order process.

  19. Experimental and Theoretical Fully differential cross sections for electron impact ionization of furfuryl molecules

    NASA Astrophysics Data System (ADS)

    Ali, Esam; Jones, Darryl; Nixon, Kate; Ning, Chuangang; Brunger, Michael; Murray, Andrew; Madison, Don

    2015-09-01

    Experimental and theoretical Fully Differential Cross Sections (FDCS) are presented for 250 eV electron impact ionization of the highest and next highest occupied molecular orbitals (HOMO and NHOMO). Theoretical results are compared with experiment for in plane scattering with projectile scattering angles of 5°, 10°, and 15°. Different theoretical models are examined - the molecular 3 body distorted wave (M3DW), and the distorted wave Born approximation (DWBA), with the effects of the post collision interaction (PCI) treated either exactly or with the Ward-Macek approximations. These approximations show good agreement with experimental data for binary peaks. However, for the recoil peak region, experiment finds a noticeable peak while theory predicts no peak. No recoil peak suggests no (or very weak) nuclear scattering, so we have investigated the importance of nuclear scattering by moving the nuclei closer to the center of mass. This work is supported by the US National Science Foundation under Grant No. PHY-1068237 and XSEDE resources provided by the Texas Advanced Computing Center (Grant No. TG-MCA07S029).

  20. Production of metastable Ar[sup +] ions by electron-impact ionization of Ar measured by translational-energy spectroscopy

    SciTech Connect

    Kamber, E.Y. ); Enos, C.S.; Brenton, A.G. )

    1993-07-01

    The translational-energy-spectroscopy technique has been used to measure the apparent ionization-excitation functions for the metastable states 3 [sup 4]D, 3[ital d] [sup 4]F, 3[ital d] [sup 2]F, and 3[ital d][prime] [sup 2][ital F] of an Ar[sup +] ion beam extracted from an electron-impact ion source. The initial states were identified from the measured energy loss in the translational-energy spectra for single-electron stripping from ground-state and metastable Ar[sup +] ions in collisions with O[sub 2]. This technique provides an alternative method of selectivity in the study of electron-impact ionization and excitation processes.

  1. Isomer and Fluorination Effects among Fluorine Substituted Hydrocarbon C3/C4 Molecules in Electron Impact Ionization

    NASA Astrophysics Data System (ADS)

    Patel, U. R.; Joshipura, K. N.

    2015-05-01

    Electron collision processes are very important in both man-made and natural plasmas, for determining the energy balances and transport properties of electrons. Electron -molecule scattering leading to ionization represents one of the most fundamental processes in collision physics. In the gas phase, the total efficiency of the process is described by the absolute total electron impact ionization cross section. Carbon based materials are some of the widely used materials for a divertor plate and magnetically confined fusion devices. In the ``ITER,'' it is very important for steady state operation to have an estimate of the lifetime of carbon plasma facing components. Apart from fusion plasma relevance, the present theoretical study is very important in modeling and controlling other electron assisted processes in many areas. Hydrocarbons play an important role for plasma diagnostics as impurities in the Tokamak fusion divertor, as seed gases for the production of radicals and ions in low temperature plasma processing. Fluorine substituted hydrocarbons (perfluorocarbons) are important as reactants in plasma assisted fabrication processes. In the present work, we have calculated total ionization cross sections Qion for C3/C4 Hydrocarbon isomers by electron impact, and comparisons are made mutually to observe isomer effect. Comparisons are also made by substituting H atom by F atom and revealing fluorination effect. The present calculations are quite significant owing to the lack of experimental data, with just an isolated previous theoretical work in some cases.

  2. Plasma effect on fast-electron-impact-ionization from 2p state of hydrogen-like ions

    SciTech Connect

    Qi, Y. Y.; Ning, L. N.; Wang, J. G.; Qu, Y. Z.

    2013-12-15

    Plasma effects on the high-energy electron-impact ionization process from 2p orbital of Hydrogen-like ions embedded in weakly coupled plasmas are investigated in the first Born approximation. The plasma screening of the Coulomb interaction between charged particles is represented by the Debye Hückel model. The screening of Coulomb interactions decreases the ionization energies and varies the wave functions for not only the bound orbital but also the continuum; the number of the summation for the angular-momentum states in the generalized oscillator strength densities is reduced with the plasma screening stronger when the ratio of ε/I{sub 2p} (I{sub 2p} is the ionization energy of 2p state and ε is the energy of the continuum electron) is kept, and then the contribution from the lower-angular-momentum states dominates the generalized oscillator strength densities, so the threshold phenomenon in the generalized oscillator strength densities and the double differential cross sections are remarkable: The accessional minima, the outstanding enhancement, and the resonance peaks emerge a certain energy region, whose energy position and width are related to the vicinity between δ and the critical value δ{sub nl}{sup c}, corresponding to the special plasma condition when the bound state |nl just enters the continuum; the multiple virtual-state enhancement and the multiple shape resonances in a certain energy domain also appear in the single differential cross section whenever the plasma screening parameter passes through a critical value δ{sub nl}{sup c}, which is similar to the photo-ionization process but different from it, where the dipole transition only happens, but multi-pole transition will occur in the electron-impact ionization process, so its multiple virtual-state enhancements and the multiple shape resonances appear more frequently than the photo-ionization process.

  3. Double ionization of single oriented water molecules by electron impact: Second-order Born description

    SciTech Connect

    Dal Cappello, C.; Champion, C.; Kada, I.; Mansouri, A.

    2011-06-15

    The double ionization of isolated water molecules fixed in space is investigated within a theoretical approach based on the second-order Born approximation. Electron angular distributions have been studied for specific kinematical conditions. The three usual mechanisms, the shake-off and the two two-step mechanisms, have been identified. A significant contribution of the two-step mechanism is clearly visible for some particular kinematics.

  4. Absolute effective cross sections of ionization of adenine and guanine molecules by electron impact

    NASA Astrophysics Data System (ADS)

    Shafranyosh, I. I.; Svida, Yu. Yu.; Sukhoviya, M. I.; Shafranyosh, M. I.; Minaev, B. F.; Baryshnikov, G. V.; Minaeva, V. A.

    2015-10-01

    Effective cross sections of the formation of positive ions of nitrous nucleic acids of adenine and guanine are determined by the crossed electron and molecular beam method in the energy interval from the threshold to 200 eV. It is found that the maximal value of the total cross section of adenine ionization is attained at an energy of 90 eV and is equal to (2.8 ± 0.6) × 10-15 cm2. The maximal value of the total cross section of guanine ionization is equal to (3.2 ± 0.7) × 10-15 cm2 and is observed at an energy of 88 eV. The energy ionization thresholds are determined, which amount to (8.8 ± 0.2) eV for adenine and to (8.3 ± 0.2) eV for guanine. The adenine and guanine mass spectra are measured. The absolute values of partial ionization cross sections of adenine and guanine molecules are determined.

  5. Calculation of intermediate-energy electron-impact ionization of molecular hydrogen and nitrogen using the paraxial approximation

    SciTech Connect

    Serov, Vladislav V.

    2011-12-15

    We have implemented the paraxial approximation followed by the time-dependent Hartree-Fock method with a frozen core for the single impact ionization of atoms and two-atomic molecules. It reduces the original scattering problem to the solution of a five-dimensional time-dependent Schroedinger equation. Using this method, we calculated the multifold differential cross section of the impact single ionization of the helium atom, the hydrogen molecule, and the nitrogen molecule from the impact of intermediate-energy electrons. Our results for He and H{sub 2} are quite close to the experimental data. Surprisingly, for N{sub 2} the agreement is good for the paraxial approximation combined with first Born approximation but worse for pure paraxial approximation, apparently because of the insufficiency of the frozen-core approximation.

  6. An electron impact and chemical ionization study of some diethyl dicarboxylates

    NASA Astrophysics Data System (ADS)

    Harrison, Alex G.; Malat, Jan

    1997-11-01

    The electron ionization and Bronsted acid chemical ionization mass spectra of the diethyl esters of succinic acid, methylmalonic acid, glutaric acid, ethylmalonic acid and dimethylmalonic acid have been determined. The major primary fragmentation reaction of the molecular ion in the electron ionization mass spectra is by loss of OC2H5 while the MH+ ions fragment by loss of C2H5OH to form the same fragment ion. Using isotopic labelling (diethyl-d5 esters) and metastable ion studies, it is shown that the [M---OC2H5]+ ions formed from diethyl succinate and diethyl glutarate have ethyl-cationated cyclic anhydride structures which fragment further by elimination of C2H4 to form the protonated anhydride. For the remaining esters the [M---OC2H5]+ ions have an acylium ion structure and fragment primarily by elimination of CO to form, initially, substituted [alpha]-carboethoxy carbenium ions although there is significant rearrangement to protonated ethyl esters of olefinic acids prior to further fragmentation.

  7. Experimental and theoretical double differential cross sections for electron impact ionization of methane.

    PubMed

    Yavuz, Murat; Ozer, Zehra Nur; Ulu, Melike; Champion, Christophe; Dogan, Mevlut

    2016-04-28

    Experimental and theoretical double differential cross sections (DDCSs) for electron-induced ionization of methane (CH4) are here reported for primary energies ranging from 50 eV to 350 eV and ejection angles between 25° and 130°. Experimental DDCSs are compared with theoretical predictions performed within the first Born approximation Coulomb wave. In this model, the initial molecular state is described by using single center wave functions, the incident (scattered) electron being described by a plane wave, while a Coulomb wave function is used for modeling the secondary ejected electron. A fairly good agreement may be observed between theory and experiment with nevertheless an expected systematic overestimation of the theory at low-ejection energies (<50 eV). PMID:27131548

  8. Influence of electron impact ionization on the termination shock: model case studies

    SciTech Connect

    Soloviev, V.Y.; Schwadron, N.A.; McComas, D.J.

    2004-09-15

    We include a latitudinally localized increase in ionization and subsequent mass loading in a 2.5-dimensional magneto-hydrodynamic case study to analyze its impact on the magnetic field, the flow field geometry, and the TS location. The localized additional mass loading leads to deflection of the flow and weakens the TS. We suggest the possibility that Voyager 1 may have been inside such a region during the recent {approx} 6 month period in 2002 when Voyager 1 observed energetic particle signatures consistent with a TS crossing, but only moderate changes in the magnetic field intensity and ACR spectrum.

  9. Relativistic calculations of excitation and ionization of highly charged ions by electron impact. Final technical report

    SciTech Connect

    Sampson, D.H.

    1992-04-15

    Our rapid relativistic atomic structure program and relativistic distorted-wave programs for excitation and ionization of highly charged ions were further improved. The generalized Briet interaction and other QED corrections were added to the atomic structure program, and the speed of the distorted-wave excitation program was increased by over an order of magnitude over what it was when our initial large-scale relativistic calculations of excitation of Ne-like ions were made. The improved programs were then used to calculate collision strengths for 330 transitions in F-like ions with 22 {le} Z {le} 92 and 248 transitions in Ni-like ions with 60 {le} Z {le} 92. We expanded the relativistic collision program to include an option to use atomic structure data by the well-known multi-configuration Dirac-Fock (MCDF) program of Grant and A coworkers. This was used in calculating collision strengths for the 45 {Delta}n = 0 transitions with n=2 in Be-like ions with 8 {le} Z {le} 92. This relativistic collision strength program was also extended to include an option to include the generalized Breis interaction in the scattering matrix elements and the importance of this for He-like, He-like and Li-like ions with Z = 26, 54 and 92 was studied. The factorization method was applied to ionization. Regardless of the complexity of the ion the ionization cross sections could be written as a sum of the products of a readily calculated coefficient that depends only on ion properties and a hydrogen-like cross section. Work was also done on excitation and ionization by directive and, in some cases spin-polarized electrons, which is of interest for some EBIT experiments and the study of solar flares. We also used our extensive collision strength results to test the

  10. Relativistic calculations of excitation and ionization of highly charged ions by electron impact

    SciTech Connect

    Sampson, D.H.

    1992-04-15

    Our rapid relativistic atomic structure program and relativistic distorted-wave programs for excitation and ionization of highly charged ions were further improved. The generalized Briet interaction and other QED corrections were added to the atomic structure program, and the speed of the distorted-wave excitation program was increased by over an order of magnitude over what it was when our initial large-scale relativistic calculations of excitation of Ne-like ions were made. The improved programs were then used to calculate collision strengths for 330 transitions in F-like ions with 22 [le] Z [le] 92 and 248 transitions in Ni-like ions with 60 [le] Z [le] 92. We expanded the relativistic collision program to include an option to use atomic structure data by the well-known multi-configuration Dirac-Fock (MCDF) program of Grant and A coworkers. This was used in calculating collision strengths for the 45 [Delta]n = 0 transitions with n=2 in Be-like ions with 8 [le] Z [le] 92. This relativistic collision strength program was also extended to include an option to include the generalized Breis interaction in the scattering matrix elements and the importance of this for He-like, He-like and Li-like ions with Z = 26, 54 and 92 was studied. The factorization method was applied to ionization. Regardless of the complexity of the ion the ionization cross sections could be written as a sum of the products of a readily calculated coefficient that depends only on ion properties and a hydrogen-like cross section. Work was also done on excitation and ionization by directive and, in some cases spin-polarized electrons, which is of interest for some EBIT experiments and the study of solar flares. We also used our extensive collision strength results to test the

  11. Effect of a vortex in the triply differential cross section for electron-impact K -shell ionization of carbon

    NASA Astrophysics Data System (ADS)

    Ward, S. J.; Macek, J. H.

    2014-12-01

    Vortices are an inherent property of the velocity fields of complex, time-dependent, Schrödinger wave functions ψ occurring where both the real and the imaginary parts of ψ vanish. They have been known since the early work of Dirac on magnetic monopoles and have frequently been studied theoretically. The possibility of observing them by exploiting an "imaging theorem" that relates atomic wave functions to measured electron momentum distributions has recently been proposed. Using the Coulomb-Born approximation, we examine ionization of a K -shell electron of a model carbon atom by fast electron impact. For an incident electron energy of 1801.2 eV and a scattering angle of 4∘, we find a vortex in the velocity field associated with a zero in the ionization T -matrix element and hence in the triply differential cross section, and we obtain a segment of the vortex line. Angular momentum transfer is essential to produce the vortex in the velocity field and the corresponding zero in the ionization T -matrix element and in the triply differential cross section.

  12. CORRIGENDUM: Corrections to the following three papers pertaining to electron impact ionization efficiency curves calculated using the BEB model for molecules containing third and fourth row atoms

    NASA Astrophysics Data System (ADS)

    Vallance, Claire; Harland, Peter W.

    2005-04-01

    Absolute electron impact ionization cross sections for CH3X, where X = H, F, Cl, Br, and I Claire Vallance et al 1997 J. Phys. B: At. Mol. Opt. Phys. 30 2465 2475 Absolute electron-impact ionization cross sections for a range of C1 to C5 chlorocarbons James E Hudson et al 2001 J. Phys. B: At. Mol. Opt. Phys. 34 3025 3039 Absolute electron impact ionization cross-sections for CO, CO2, OCS and CS2 James E Hudson et al 2004 J. Phys. B: At. Mol. Opt. Phys. 37 445 455 We have recently re-examined some published binary-encounter Bethe (BEB) calculations on the electron impact ionization cross sections for halogenated hydrocarbons and sulfur-containing molecules, and found a discrepancy with our earlier results. Please see the PDF file for full details.

  13. Electron-impact excitation and ionization of atomic boron at low and intermediate energies

    NASA Astrophysics Data System (ADS)

    Wang, Kedong; Zatsarinny, Oleg; Bartschat, Klaus

    2016-05-01

    We present a comprehensive study of electron collisions with boron atoms by using the B -spline R -matrix method for electron energies ranging from threshold to 100 eV. Elastic, excitation, and ionization cross sections were obtained for all transitions between the lowest 11 states of boron. A multiconfiguration Hartree-Fock method with nonorthogonal term-dependent orbitals was employed to generate accurate wave functions for the target states. Close-coupling expansions including 13, 51, and 999 physical and pseudo-target states of boron were used to check the sensitivity of the results to changes in the theoretical model. The cross-section dataset obtained from the large-scale calculations is expected to be sufficiently accurate and comprehensive for most current modeling applications involving neutral boron.

  14. Experimental and theoretical triple-differential cross sections for tetrahydrofuran ionized by low-energy 26-eV-electron impact

    NASA Astrophysics Data System (ADS)

    Ali, Esam; Ren, XueGuang; Dorn, Alexander; Ning, Chuangang; Colgan, James; Madison, Don

    2016-06-01

    We report an experimental and theoretical study of low-energy electron-impact ionization of tetrahydrofuran, which is a molecule of biological interest. The experiments were performed using an advanced reaction microscope specially built for electron-impact ionization studies. The theoretical calculations were performed within the molecular three-body distorted-wave model. Reasonably good agreement is found between experiment and theory.

  15. Dissociative-ionization cross sections for 12-keV-electron impact on CO{sub 2}

    SciTech Connect

    Bhatt, Pragya; Singh, Raj; Yadav, Namita; Shanker, R.

    2011-10-15

    The dissociative ionization of a CO{sub 2} molecule is studied at an electron energy of 12 keV using the multiple ion coincidence imaging technique. The absolute partial ionization cross sections and the precursor-specific absolute partial ionization cross sections of resulting fragment ions are obtained and reported. It is found that {approx}75% of single ionization, 22% of double ionization, and {approx}2% of triple ionization of the parent molecule contribute to the total fragment ion yield; quadruple ionization of CO{sub 2} is found to make a negligibly small contribution. Furthermore, the absolute partial ionization cross sections for ion-pair and ion-triple formation are measured for nine dissociative ionization channels of up to a quadruply ionized CO{sub 2} molecule. In addition, the branching ratios for single-ion, ion-pair, and ion-triple formation are also determined.

  16. Monte Carlo study of electron initiated impact ionization in bulk zincblende and wurtzite phase ZnS

    NASA Astrophysics Data System (ADS)

    Bellotti, E.; Brennan, K. F.; Wang, R.; Ruden, P. P.

    1998-05-01

    This paper presents a theoretical study of the high field electronic transport properties of the cubic and hexagonal phases of zinc sulfide (ZnS) using an ensemble Monte Carlo method. Essential features of the model are the inclusion of realistic energy band structures calculated from a local pseudopotential method and numerically calculated impact ionization transition rates. The polar optical phonon scattering rate has also been computed numerically from the band structure. The relevant transport quantities have been computed for field values between 100 kV/cm and 2 MV/cm. On the basis of these calculations it is predicted that the electron distribution is cooler and the average energy lower in the wurtzite phase than in the zincblende phase over the entire field range examined. The difference in average energy between the two phases becomes pronounced for field magnitudes above 1 MV/cm while it is smaller in the field range between 700 kV/cm and 1 MV/cm. As a result, the ionization coefficients are expected to be higher in the zincblende phase than in the wurtzite phase. This can be attributed to differences in the density of states between the two polytypes. The quantum yield has also been computed. It is found that even though the threshold for impact ionization is relatively hard in both polytypes, the threshold for the wurtzite phase is harder than the threshold for the zincblende phase.

  17. Electron ionization cross-section calculations for liquid water at high impact energies

    NASA Astrophysics Data System (ADS)

    Bousis, C.; Emfietzoglou, D.; Hadjidoukas, P.; Nikjoo, H.; Pathak, A.

    2008-04-01

    Cross-sections for the ionization of liquid water is perhaps the most essential set of data needed for modeling electron transport in biological matter. The complexity of ab initio calculations for any multi-electron target has led to largely heuristic semi-empirical models which take advantage elements of the Bethe, dielectric and binary collision theories. In this work we present various theoretical models for calculating total ionization cross-sections (TICSs) for liquid water over the 10 keV-1 MeV electron energy range. In particular, we extend our recent dielectric model calculations for liquid water to relativistic energies using both the appropriate kinematic corrections and the transverse part. Comparisons are made with widely used atomic and molecular TICS models such as those of Khare and co-workers, Kim-Rudd, Deutsch-Märk, Vriens and Gryzinski. The required dipole oscillator strength was provided by our recent optical-data model which is based on the latest experimental data for liquid water. The TICSs computed by the above models differ by up to 40% from the dielectric results. The best agreement (to within ∼10%) was obtained by Khare's original model and an approximate form of Gryzinski's model. In contrast, the binary-encounter-dipole (BED) models of both Kim-Rudd and Khare and co-workers resulted in ∼10-20% higher TICS values, while discrepancies increased to ∼30-40% when their simpler binary-encounter-Bethe (BEB) versions were used. Finally, we discuss to what extent the accuracy of the TICS is indicative of the reliability of the underlying differential cross-sections.

  18. Deep minimum in the Coulomb-Born TDCS for inner-shell ionization of carbon by electron impact

    NASA Astrophysics Data System (ADS)

    Ward, S. J.; Macek, J. H.

    2013-09-01

    Recently, a minimum in the TDCS of electron impact ionization of helium has been explained in terms of a vortex. We have determined the kinematics to obtain a deep minimum due to a vortex in the TDCS for K shell ionization of carbon by electron impact using the Coulomb-Born (CB1) approximation. The deep minimum occurs at an angle of the ejected electron of 239° for an incident energy of 1801 . 2 eV , a scattering angle of 4°, and energy of the ejected electron of 5 . 5 eV . At the angle of the minimum, both the real and imaginary parts of the T-matrix are zero. The integral of the velocity field around a closed path encircling the vortex position is 2 π. Following the treatment of Ref., we decomposed both the Born (B1) and the CB1 T-matrix into their multipole components. The l = 1 , m = +/- 1 CB1 multipole components are important in determining the shape of the CB1 angular distribution. S. J. W. and J. H. M. acknowledge support from NSF under grant no. PHYS-0968638 and from D.O.E. under grant number DE-FG02-02ER15283, respectively.

  19. Electron-impact total ionization cross sections of DNA sugar-phosphate backbone and an additivity principle

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Dateo, Christopher E.

    2005-01-01

    The improved binary-encounter dipole (iBED) model [W.M. Huo, Phys. Rev. A64, 042719-1 (2001)l is used to study the total ionization cross sections of the DNA sugar-phosphate backbone by electron impact. Calculations using neutral fragments found that the total ionization cross sections of C3' - and C5', -deoxyribose-phospate, two conformers of the sugar-phosphate backbone, are close to each other. Furthermore, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3' - and C5" -deoxyribose-phospate cross sections, differing by less than 10%. The result implies that certain properties of the-DNA, like the total singly ionization cross section, are localized properties and a building-up or additivity principle may apply. This allows us to obtain accurate properties of larger molecular systems built up from the results of smaller subsystem fragments. Calculations are underway using a negatively charged sugar-phosphate backbone with a metal counter-ion.

  20. Near-threshold electron-impact doubly differential cross sections for the ionization of argon and krypton

    SciTech Connect

    Yates, Brent R.; Khakoo, Murtadha A.

    2011-04-15

    We present normalized doubly differential cross sections (DDCS's) for the near-threshold, electron-impact single ionization of argon and krypton, similar to those taken earlier for Ne and Xe [Yates et al., J. Phys. B 42, 095206 (2009)]. The Ar measurements were taken at incident energies of 17, 18, 20, and 30 eV while the Kr measurements were taken at 15, 16, 17.5, and 20 eV. The DDCS scattering angles range from 15 deg. to 120 deg. The differential data are initially normalized to available experimental cross sections for excitation of the ground np{sup 6} to the np{sup 5}(n+1)s excited states of the noble gas and, after integration, to well-established experimental total ionization cross sections of Rapp and Englander-Golden [J. Chem. Phys. 43, 1464 (1965)].

  1. STORAGE RING MEASUREMENT OF ELECTRON IMPACT IONIZATION FOR Mg{sup 7+} FORMING Mg{sup 8+}

    SciTech Connect

    Hahn, M.; Lestinsky, M.; Novotny, O.; Savin, D. W.; Bernhardt, D.; Mueller, A.; Schippers, S.; Wolf, A.

    2010-04-01

    We report electron impact ionization cross section measurements for Mg{sup 7+} forming Mg{sup 8+} at center of mass energies from approximately 200 eV to 2000 eV. The experimental work was performed using the heavy-ion storage ring TSR located at the Max-Planck-Institut fuer Kernphysik in Heidelberg, Germany. We find good agreement with distorted wave calculations using both the GIPPER code of the Los Alamos Atomic Physics Code suite and using the Flexible Atomic Code.

  2. Time-dependent close-coupling studies of the electron-impact ionization of excited-state helium

    SciTech Connect

    Colgan, J.; Pindzola, M. S.

    2002-12-01

    The time-dependent close-coupling theory is applied to the study of the electron-impact ionization of helium from the excited (1s2s) configuration. Calculations are made in an effort to resolve the discrepancy between theoretical calculations and existing experimental measurements for this cross section. We find good agreement with the existing convergent close-coupling calculations of Bray and Fursa [J. Phys. B 28, L197 (1995)], but are in substantial disagreement with the experimental measurements of this quantity by Dixon et al. [J. Phys. B 9, 2617 (1976)].

  3. Highly Charged Ions from Laser-Cluster Interactions: Local-Field-Enhanced Impact Ionization and Frustrated Electron-Ion Recombination

    SciTech Connect

    Fennel, Thomas; Ramunno, Lora; Brabec, Thomas

    2007-12-07

    Our molecular dynamics analysis of Xe{sub 147-5083} clusters identifies two mechanisms that contribute to the yet unexplained observation of extremely highly charged ions in intense laser cluster experiments. First, electron impact ionization is enhanced by the local cluster electric field, increasing the highest charge states by up to 40%; a corresponding theoretical method is developed. Second, electron-ion recombination after the laser pulse is frustrated by acceleration electric fields typically used in ion detectors. This increases the highest charge states by up to 90%, as compared to the usual assumption of total recombination of all cluster-bound electrons. Both effects together augment the highest charge states by up to 120%, in reasonable agreement with experiments.

  4. Electron-impact excitation and ionization of atomic boron at low and intermediate energies

    NASA Astrophysics Data System (ADS)

    Wang, Kedong; Zatsarinny, Oleg; Bartschat, Klaus

    2016-05-01

    We present a comprehensive study of electron collisions with neutral boron atoms. The calculations were performed with the B-Spline R-matrix (close-coupling) method, by employing a parallelized version of the associated computer code. Elastic, excitation, and ionization cross sections were obtained for all transitions involving the lowest 11 states of boron, for incident electron energies ranging from threshold to 100 eV. A multiconfiguration Hartree-Fock method with nonorthogonal term-dependent orbitals was used to generate accurate wave functions for the target states. Close-coupling expansions including 13, 51, and 999 physical and pseudo states were set up to check the sensitivity of the predictions to variations in the theoretical model. The cross-section dataset generated in this work is expected to be the most accurate one available today and should be sufficiently comprehensive for most modeling applications involving neutral boron. Work supported by the China Scholarship Council and the United States National Science Foundation under Grants PHY-1403245 and PHY-1520970, and by the XSEDE allocation PHY-090031.

  5. Following electron impact excitations of single Os, Pt, Hg, Pb and Po atom L subshells ionization cross section calculations by using Lotz's equation

    NASA Astrophysics Data System (ADS)

    Aydinol, M.; Aydeniz, D.

    2016-03-01

    L shell ionization cross section and Li subshells ionization cross sections of Os, Pt, Hg, Pb, Po atoms calculated. For each atom, ten different electron impacty energy values Eoi used. Calculations carried out by using nonrelativistic Lotz equation in Matlab. Ionization cross section values obtained for Eoi values in the energy range of ELi ≤Eoi≤4ELi for each atom. Starting allmost from Eoi = ELi (i = 1,2,3) values of the each subshell ionization threshold energy, ionization cross section are increasing rapidly with Eoi. For a fixed Eoi = 3. ELi values, while Z increases from Z = 76 to Z = 84, ionization cross section are decrease. These results help to understand some results which obtained from other electron-sigle atom impact studies on σLi subshells.

  6. The second Born approximation for the double ionization of N2 by electron impact

    NASA Astrophysics Data System (ADS)

    Lamy, P.; Dal Cappello, C.; Charpentier, I.; Ruiz-Lopez, M. F.; Hervieux, P. A.

    2016-07-01

    In their (e,3e) and (e,3-1e) experiments of the double ionization (DI) of the outermost orbital of N2, Li et al (2012 J. Phys. B: At. Mol. Opt. Phys. 45 135201) recently showed that the process is largely dominated by a two-step-2 mechanism, which is a double interaction of the incident electron with the target. From a theoretical point of view, this should entail the use of the second Born approximation. In the past, very few theoretical calculations had been carried out this way because it requires a difficult numerical triple integration. We propose here to take into account the second Born approximation for the DI of N2 by using the closure approximation. The initial state is described by a single-center wave function derived from the usual multi-center wave function obtained in the self-consistent-field Hartree–Fock method using the linear combination of atomic orbitals-molecular orbital (LCAO-MO) approximation. The final state describes the interaction between each of the ejected electrons and the target by a Coulomb wave and the interaction between the two ejected electrons with the use of the Gamow factor. We calculate differential cross sections using the same kinematic conditions as Li et al (intermediate incident energy about 600 eV) for (e,3e) and (e,3-1e) DI of N2. The results show that the model does not allow a shift of the variation of the four-fold differential cross section near the momentum transfer to be obtained nor its opposite when we include the contribution given by the second Born approximation, as in (e,3-1e) experiments.

  7. Ionization and electron-capture cross sections for single- and multiple-electron removal from H2O by Li3 + impact

    NASA Astrophysics Data System (ADS)

    Luna, H.; Wolff, W.; Montenegro, E. C.; Tavares, André C.; Lüdde, H. J.; Schenk, G.; Horbatsch, M.; Kirchner, T.

    2016-05-01

    In this work, we report experimental and theoretical ionization and electron-capture cross sections for single-, double- and triple-electron removal from H2O by Li3 + impact at energies ranging from 0.75 to 5.8 MeV. The experiment was carried out by selecting both the final charge state of the projectile and the ejected fragments in coincidence to obtain cross sections associated with ionization and electron-capture channels. The ionic fragments and the emitted electrons produced under single-collision conditions were collected by a time-of-flight spectrometer with single-hit (e.g., OH++H0 ) and double-hit events (e.g., OH++H+ ) properly discriminated. For the one- and two-electron removal cases, the calculations based on the basis generator method for orbital propagation agree well with the experiment for most of the collision channels studied. Auger-electron emission after vacancy production in the inner 2 a1 orbital of H2O is shown to have a substantial effect on the final charge-state distributions over the entire impact-energy interval.

  8. Effect of the Mo/ller interaction on electron-impact ionization of high-Z hydrogenlike ions

    NASA Astrophysics Data System (ADS)

    Moores, D. L.; Reed, K. J.

    1995-01-01

    We have investigated the effects of the Mo/ller interaction in relativistic distorted-wave calculations of cross sections for electron-impact ionization of high-Z hydrogenlike ions. We found that the Mo/ller interaction significantly increases the cross section for hydrogenlike uranium, and brings our calculated results into very good agreement with experimental results reported by Marrs, Elliott, and Knapp [Phys. Rev. Lett. 72, 4082 (1994)]. We found similar increases in the cross sections for other hydrogenlike ions. Our results also show that these effects become important at much lower collision energy than previously reported [D. L. Moores and M. S. Pindzola, Phys. Rev. A 41, 3603 (1990)]. With the Mo/ller interaction included, our cross sections for these ions are in good agreement with preliminary results obtained in recent experiments on the electron-beam ion trap (EBIT).

  9. Effect of the Moller interaction on electron-impact ionization of high-[ital Z] hydrogenlike ions

    SciTech Connect

    Moores, D.L. ); Reed, K.J. )

    1995-01-01

    We have investigated the effects of the Moller interaction in relativistic distorted-wave calculations of cross sections for electron-impact ionization of high-[ital Z] hydrogenlike ions. We found that the Moller interaction significantly increases the cross section for hydrogenlike uranium, and brings our calculated results into very good agreement with experimental results reported by Marrs, Elliott, and Knapp [Phys. Rev. Lett. [bold 72], 4082 (1994)]. We found similar increases in the cross sections for other hydrogenlike ions. Our results also show that these effects become important at much lower collision energy than previously reported [D. L. Moores and M. S. Pindzola, Phys. Rev. A [bold 41], 3603 (1990)]. With the Moller interaction included, our cross sections for these ions are in good agreement with preliminary results obtained in recent experiments on the electron-beam ion trap (EBIT).

  10. Effect of fluoro substitution on the fragmentation of the K-shell excited/ionized pyridine studied by electron impact.

    PubMed

    Sakai, Masamichi; Okada, Kazumasa

    2011-07-01

    Fragmentation of the pyridine ring followed by K-shell excitation/ionization has been studied with 2-fluoropyridine (2FPy) by electron impact. Ab initio molecular orbital (MO) calculations were also carried out to investigate the electronic states correlating with specific fragment ions. The fragment ions are produced characteristically at the N 1s edge, while the spectra observed at the F 1s and C 1s edges exhibit a small difference from that at the valence ionization. The production of the C(4)H(2)(+), C(4)H(3)(+) and C(4)H(2)F(+) ions indicates that the cleavage of the N-C6 and C2-C3 bonds or the N-C2 and C5-C6 bonds is likely to occur after the N 1s excitation/ionization. Ab initio MO calculations indicate that the former fission is likely to proceed through the n(N)(1)π(2)(1)π(3)(2) and n(N)(0)π(2)(2)π(3)(2) excited states of the parent molecular dication. On the other hand, the breakage of the N-C2 and C4-C5 bonds, which specifically proceeds at the N 1s edge for 2-methylpyridine, does not occur for 2FPy. The present calculation reveals that the products of this channel are unstable by the electronegativity of fluorine and that the relative energy of the Auger-final states of 2FPy is lowered by the reorganization and electron correlation effects. PMID:21744416

  11. Effect of initial-state target polarization on the single ionization of helium by 1-keV electron impact

    NASA Astrophysics Data System (ADS)

    Sun, Shi-Yan; Ma, Xiao-Yan; Li, Xia; Miao, Xiang-Yang; Jia, Xiang-Fu

    2012-07-01

    We report new results of triple differential cross sections for the single ionization of helium by 1-KeV electron impact at the ejection energy of 10 eV. Investigations have been made for both the perpendicular plane and the plane perpendicular to the momentum transfer geometries. The present calculation is based on the three-Coulomb wave function. Here we have also incorporated the effect of target polarization in the initial state. A comparison is made between the present calculation with the results of other theoretical methods and a recent experiment [Dürr M, Dimopoulou C, Najjari B, Dorn A, Bartschat K, Bray I, Fursa D V, Chen Z, Madison D H and Ullrich J 2008 Phys. Rev. A 77 032717]. At an impact energy of 1 KeV, the target polarization is found to induce a substantial change of the cross section for the ionization process. We observe that the effect of target polarization plays a dominant role in deciding the shape of triple differential cross sections.

  12. Symmetry properties of the S matrix in a fully relativistic distorted-wave treatment of electron-impact ionization

    SciTech Connect

    Pyper, N. C.; Kampp, Marco; Whelan, Colm T.

    2005-05-15

    The symmetry properties of the S matrix in a fully relativistic distorted-wave treatment of electron-impact ionization are investigated. It is shown that the square modulus of the scattering matrix element in which the spin states of all four electrons are determined is not invariant under the reversal of the direction of alignment of all spins. The largest of two contributions to this noninvariance originates from the relativistic modifications of the continuum wave functions induced by the distorting potential of the target atom. A second smaller contribution is manifested on reducing the eight-dimensional matrix elements of the QED covariant propagator to purely spatial two-electron integrals. The triple differential cross section (TDCS) exhibits a spin asymmetry unless the entire scattering process occurs in a single plane. There will be a difference in the TDCS between an (e,2e) event in which the initial beam is polarized parallel or antiparallel with respect to the beam direction even if the target is unpolarized and the final spin states are not determined. The TDCS will remain unchanged if, in addition to reversal of the direction of spin alignment, one appropriate momentum component of one of the two outgoing electrons is reversed.

  13. Use of Relativistic Effective Core Potentials in the Calculation of Electron-Impact Ionization Cross Sections

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Kim, Yong-Ki

    1999-01-01

    Based on the Binary-Encounter-Bethe (BEB) model, the advantage of using relativistic effective core potentials (RECP) in the calculation of total ionization cross sections of heavy atoms or molecules containing heavy atoms is discussed. Numerical examples for Ar, Kr, Xe, and WF6 are presented.

  14. Multiple ionization of helium and krypton by electron impact close to threshold: appearance energies and Wannier exponents

    NASA Astrophysics Data System (ADS)

    Denifl, S.; Gstir, B.; Hanel, G.; Feketeova, L.; Matejcik, S.; Becker, K.; Stamatovic, A.; Scheier, P.; Märk, T. D.

    2002-11-01

    We determined appearance energy (AE) values AE(Xn+/X) for the formation of singly (He+) and doubly charged (He2+) He ions and multiply charged Kr ions Krn+ up to n = 6 following electron impact on He and Kr atoms using a high-resolution electron impact ionization mass spectrometer. The data analysis employs an iterative, non-linear least-squares fitting routine, the Marquart-Levenberg algorithm, in conjunction with either a 2-function or a 3-function fit based on a power threshold law. This allows us to extract the relevant AEs and also the corresponding exponents for a Wannier-type power law from the measured near-threshold data. The values of the AEs determined in this work are compared with other available experimental and with spectroscopic AE values and the extracted exponents p are compared with other available experimental data and with the predictions of the various Wannier-type power law models. One observation is particularly noteworthy, namely the fact that none of the available experimental data seem to support the large values of 'p' predicted by the Wannier-Geltman and the generalized Wannier law for n > 3.

  15. Electron impact multiple ionization of neon, argon and xenon atoms close to threshold: appearance energies and Wannier exponents

    NASA Astrophysics Data System (ADS)

    Gstir, B.; Denifl, S.; Hanel, G.; Rümmele, M.; Fiegele, T.; Cicman, P.; Stano, M.; Matejcik, S.; Scheier, P.; Becker, K.; Stamatovic, A.; Märk, T. D.

    2002-07-01

    We report the results of the experimental determination of the appearance energy values AE(Xn + /X) for the formation of multiply charged Ne, Ar and Xe ions up to n = 4 (Ne), n = 6 (Ar) and n = 8 (Xe) following electron impact on Ne, Ar and Xe atoms using a dedicated high-resolution electron impact ionization mass spectrometer. The data analysis uses the Marquart-Levenberg algorithm, which is an iterative, nonlinear least-squares-fitting routine, in conjunction with either a two-function or a three-function fit based on a power threshold law. This allows us to extract the relevant AEs and corresponding exponents for a Wannier-type power law from the measured near-threshold data. The values of the AEs determined in this work are compared with other available experimental and spectroscopic values of the AEs and the extracted exponents are compared with other available experimental data and with the predictions of the various Wannier-type power law models.

  16. Relativistic calculations of cross sections for ionization of U[sup 90+] and U[sup 91+] ions by electron impact

    SciTech Connect

    Fontes, C.J. ); Sampson, D.H.; Zhang, H.L. )

    1995-01-01

    Relativistic distorted-wave calculations have been made of the cross sections for electron-impact ionization of U[sup 90+] and U[sup 91+] ions with the generalized Breit interaction included between bound and free electrons. Good agreement is obtained with recent electron-beam ion-trap experiments [R. E. Marrs, S. R. Elliott, and D. A. Knapp, Phys. Rev. Lett. [bold 72], 4082 (1994)].

  17. Comparative analysis of dioxins and furans by electron impact, high-resolution mass spectrometry and by electron capture, negative ionization, low-resolution mass spectrometry

    SciTech Connect

    Koester, C.J.; Harless, R.L.; Hites, R.A.

    1990-01-01

    Electron impact, high resolution mass spectrometry (HRMS) is currently the method of choice for the analysis of polychlorinated dibenso-p-dioxins and dibenzofurans (PCDD/F) because of its ability to detect PCDD/F in the presence of interfering compounds, such as polychlorinated biphenyls (PCB), which cannot be resolved by low resolution methods. The PDCC/F analyses may also be performed using electron capture, negative ionization (ECNI) low resolution mass spectrometry, providing extensive sample preparation is done to remove interferences. Before ECNI low resolution mass spectrometry (MS) can be accepted as a routine method for PCDD/F analysis, it is necessary to show that results generated by this method are comparable to those obtained by HRMS. Known mixtures and unknown air samples were analyzed by electron impact HRMS (Finnigan MAT 90 system) and by ECNI low resolution MS (Hewlett Packard 5985B). Both instruments were fitted with a gas chromatographic inlet. The PCDD/F concentrations determined by the two techniques compare favorably, typically within 20%. The major difference between these two methods is that the ECNI low resolution method shows poor sensitivity in detecting 2,3,7,8-tetrachlorodioxin. However, ECNI MS offers the advantage of lower detection limits (50-100 fg) than electron impact HRMS (0.1 to 0.5 pg). These results suggest that ECNI low resolution MS can be a simple, low cost alternative to the common high resolution methods used for PCDD/F analysis.

  18. High-resolution (e, 2e + ion) study of electron-impact ionization and fragmentation of methane

    SciTech Connect

    Ren, Xueguang Pflüger, Thomas; Weyland, Marvin; Baek, Woon Yong; Rabus, Hans; Ullrich, Joachim; Dorn, Alexander

    2015-05-07

    The ionization and fragmentation of methane induced by low-energy (E{sub 0} = 66 eV) electron-impact is investigated using a reaction microscope. The momentum vectors of all three charged final state particles, two outgoing electrons, and one fragment ion, are detected in coincidence. Compared to the earlier study [Xu et al., J. Chem. Phys. 138, 134307 (2013)], considerable improvements to the instrumental mass and energy resolutions have been achieved. The fragment products CH{sub 4}{sup +}, CH{sub 3}{sup +}, CH{sub 2}{sup +}, CH{sup +}, and C{sup +} are clearly resolved. The binding energy resolution of ΔE = 2.0 eV is a factor of three better than in the earlier measurements. The fragmentation channels are investigated by measuring the ion kinetic energy distributions and the binding energy spectra. While being mostly in consistence with existing photoionization studies the results show differences including missing fragmentation channels and previously unseen channels.

  19. Lucky drift impact ionization in amorphous semiconductors

    NASA Astrophysics Data System (ADS)

    Kasap, Safa; Rowlands, J. A.; Baranovskii, S. D.; Tanioka, Kenkichi

    2004-08-01

    The review of avalanche multiplication experiments clearly confirms the existence of the impact ionization effect in this class of semiconductors. The semilogarithmic plot of the impact ionization coefficient (α) versus the reciprocal field (1/F) for holes in a-Se and electrons in a-Se and a-Si :H places the avalanche multiplication phenomena in amorphous semiconductors at much higher fields than those typically reported for crystalline semiconductors with comparable bandgaps. Furthermore, in contrast to well established concepts for crystalline semiconductors, the impact ionization coefficient in a-Se increases with increasing temperature. The McKenzie and Burt [S. McKenzie and M. G. Burt, J. Phys. C 19, 1959 (1986)] version of Ridley's lucky drift (LD) model [B. K. Ridley, J. Phys. C 16, 3373 (1988)] has been applied to impact ionization coefficient versus field data for holes and electrons in a-Se and electrons in a-Si :H. We have extracted the electron impact ionization coefficient versus field (αe vs F) data for a-Si :H from the multiplication versus F and photocurrent versus F data recently reported by M. Akiyama, M. Hanada, H. Takao, K. Sawada, and M. Ishida, Jpn. J. Appl. Phys.41, 2552 (2002). Provided that one accepts the basic assumption of the Ridley LD model that the momentum relaxation rate is faster than the energy relaxation rate, the model can satisfactorily account for impact ionization in amorphous semiconductors even with ionizing excitation across the bandgap, EI=Eg. If λ is the mean free path associated with momentum relaxing collisions and λE is the energy relaxation length associated with energy relaxing collisions, than the LD model requires λE>λ. The application of the LD model with energy and field independent λE to a-Se leads to ionization threshold energies EI that are quite small, less than Eg/2, and requires the possible but improbable ionization of localized states. By making λE=λE(E ,F) energy and field dependent, we were

  20. The threshold laws for electron-atom and positron-atom impact ionization

    NASA Technical Reports Server (NTRS)

    Temkin, A.

    1983-01-01

    The Coulomb-dipole theory is employed to derive a threshold law for the lowest energy needed for the separation of three particles from one another. The study focuses on an electron impinging on a neutral atom, and the dipole is formed between an inner electron and the nucleus. The analytical dependence of the transition matrix element on energy is reduced to lowest order to obtain the threshold law, with the inner electron providing a shield for the nucleus. Experimental results using the LAMPF accelerator to produce a high energy beam of H- ions, which are then exposed to an optical laser beam to detach the negative H- ion, are discussed. The threshold level is found to be confined to the region defined by the upper bound of the inverse square of the Coulomb-dipole region. Difficulties in exact experimental confirmation of the threshold are considered.

  1. Compact ultrafast orthogonal acceleration time-of-flight mass spectrometer for on-line gas analysis by electron impact ionization and soft single photon ionization using an electron beam pumped rare gas excimer lamp as VUV-light source.

    PubMed

    Mühlberger, F; Saraji-Bozorgzad, M; Gonin, M; Fuhrer, K; Zimmermann, R

    2007-11-01

    Orthogonal acceleration time-of-flight mass spectrometers (oaTOFMS), which are exhibiting a pulsed orthogonal extraction of ion bunches into the TOF mass analyzer from a continuous primary ion beam, are well-suited for continuous ionization methods such as electron impact ionization (EI). Recently an electron beam pumped rare gas excimer lamp (EBEL) was introduced, which emits intensive vacuum UV (VUV) radiation at, e.g., 126 nm (argon excimer) and is well suited as the light source for soft single photon ionization (SPI) of organic molecules. In this paper, a new compact oaTOFMS system which allows switching between SPI, using VUV-light from an EBEL-light source, and conventional EI is described. With the oaTOFMS system, EBEL-SPI and EI mass spectral transients can be recorded at very high repetition rates (up to 100 kHz), enabling high duty cycles and therefore good detection efficiencies. By using a transient recorder card with the capability to perform on-board accumulation of the oaTOF transients, final mass spectra with a dynamic range of 106 can be saved to the hard disk at a rate of 10 Hz. As it is possible to change the ionization modes (EI and SPI) rapidly, a comprehensive monitoring of complex gases with highly dynamic compositions, such as cigarette smoke, is possible. In this context, the EI based mass spectra address the bulk composition (compounds such as water, oxygen, carbon dioxide, etc. in the up to percentage concentration range) as well as some inorganic trace gases such as argon, sulfur dioxide, etc. down to the low ppm level. The EBEL-SPI mass spectra on the other hand are revealing the organic composition down to the lower ppb concentration range. PMID:17900147

  2. Calculation of the multifold differential cross section of the electron-impact ionization of molecular hydrogen by prolate spheroidal external complex scaling method with second Born corrections

    SciTech Connect

    Serov, Vladislav V.; Joulakian, Boghos B.

    2010-08-15

    We introduce the second Born dipole corrections in our recently developed ab initio procedure based on the driven Schroedinger equation formalism and the external scaling method for the determination of the multifold differential cross sections of the single and double ionization of molecular hydrogen by electron impact. To test our procedure, we first apply it to the excitation-ionization process of a He atom and compare the results to those of equivalent theoretical results, which are available. We then show that the introduction of the second Born correction including only dipole terms improves the agreement with the experimental results only in the case of the simple ionization. We think that the introduction of nondipole contributions in the second Born term which are not taken into account in the present work is necessary in the case of the double ionization process.

  3. Dissociation mechanisms of the Ar trimer induced by a third atom in high-energy electron-impact ionization

    NASA Astrophysics Data System (ADS)

    Yan, S.; Zhang, P.; Ma, X.; Xu, S.; Tian, S. X.; Li, B.; Zhu, X. L.; Feng, W. T.; Zhao, D. M.

    2014-06-01

    We experimentally studied the dissociation dynamics of a highly charged Ar3 cluster initiated by a high-energy electron. The dissociation patterns of the correlated ions from a two-body and a three-body Coulombic explosion (CE) of (Ar3)2+ suggest that predissociation alters the evolution of radiative charge transfer. The three-body CE in (Ar3)4+ and (Ar3)5+ is driven, after double ionization of one constituent Ar atom, by single ionization with a simultaneous interatomic Coulombic decay process.

  4. Some recent progress on the measurement of K-shell ionization cross-sections of atoms by electron impact: Application to Ti and Cr elements

    NASA Astrophysics Data System (ADS)

    An, Z.; Liu, M. T.; Fu, Y. C.; Luo, Z. M.; Tang, C. H.; Li, C. M.; Zhang, B. H.; Tang, Y. J.

    2003-07-01

    In this paper, we have taken some measures to improve the accuracy of our experimental data for K-shell ionization cross-sections by electron impact. These measures include (1) measurement of the thin target thickness with Rutherford backscattering spectroscopy and (2) detection efficiency calibration in the lower energy region using thick carbon target bremsstrahlung by electron impact and (3) electron reflection correction and electron mean track length correction based upon Monte Carlo method. These measures are applied to the measurement of K-shell ionization cross-sections of Ti and Cr elements from the threshold energies up to 26 keV. From the comparison with some theoretical models, empirical formulae and some previous experimental data, it is concluded that these measures taken in this paper are effective in the improvement of accuracy of experimental data. The present experimental data for Ti and Cr elements also clarify the discrepancies among some experimental data sets. In addition, these measures will also be very helpful in the measurement of K-shell ionization cross-sections for lower Z elements and in the measurement of L, M-shell ionization cross-sections for medium and higher Z elements.

  5. The double ionization of H{sub 2} by fast electron impact: Influence of the final state electron-electron correlation

    SciTech Connect

    Chuluunbaatar, O. Gusev, A. A.; Joulakian, B. B.

    2013-02-15

    We have determined fully differential cross sections of the (e, 3e) double ionization of H{sub 2} by employing correlated initial- and final-state wave functions. We have constructed for the description of the two slow ejected electrons a symmetrized product of a correlation function and two-center continuum wave functions, which fulfill the correct boundary conditions asymptotically up to the order O((kr){sup -2}). We have shown that the introduction of the correlated part of the final-state wave function improves the results on the (e, 3-1e) of H{sub 2}.

  6. LETTER TO THE EDITOR: The validity of classical trajectory and perturbative quantal methods for electron-impact ionization from excited states in H-like ions

    NASA Astrophysics Data System (ADS)

    Griffin, D. C.; Ballance, C. P.; Pindzola, M. S.; Robicheaux, F.; Loch, S. D.; Ludlow, J. A.; Witthoeft, M. C.; Colgan, J.; Fontes, C. J.; Schultz, D. R.

    2005-06-01

    To test the validity of classical trajectory and perturbative quantal methods for electron-impact ionization of H-like ions from excited states, we have performed advanced close-coupling calculations of ionization from excited states in H, Li2+ and B4+ using the R-matrix with pseudo states and the time-dependent close-coupling methods. Comparisons with our classical trajectory Monte Carlo (CTMC) and distorted-wave (DW) calculations show that the CTMC method is more accurate than the DW method for H, but does not improve with n and grows substantially worse with Z, while the DW method improves with Z and grows worse with n.

  7. Comparison of experimental and theoretical triple differential cross sections for the single ionization of C O2 (1 πg ) by electron impact

    NASA Astrophysics Data System (ADS)

    Ozer, Zehra N.; Ali, Esam; Dogan, Mevlut; Yavuz, Murat; Alwan, Osman; Naja, Adnan; Chuluunbaatar, Ochbadrakh; Joulakian, Boghos B.; Ning, Chuan-Gang; Colgan, James; Madison, Don

    2016-06-01

    Experimental and theoretical triple differential cross sections for intermediate-energy (250 eV) electron-impact single ionization of the CO2 are presented for three fixed projectile scattering angles. Results are presented for ionization of the outermost 1 πg molecular orbital of C O2 in a coplanar asymmetric geometry. The experimental data are compared to predictions from the three-center Coulomb continuum approximation for triatomic targets, and the molecular three-body distorted wave (M3DW) model. It is observed that while both theories are in reasonable qualitative agreement with experiment, the M3DW is in the best overall agreement with experiment.

  8. STORAGE RING CROSS SECTION MEASUREMENTS FOR ELECTRON IMPACT SINGLE AND DOUBLE IONIZATION OF Fe{sup 13+} AND SINGLE IONIZATION OF Fe{sup 16+} AND Fe{sup 17+}

    SciTech Connect

    Hahn, M.; Novotny, O.; Savin, D. W.; Becker, A.; Grieser, M.; Krantz, C.; Repnow, R.; Wolf, A.; Bernhardt, D.; Mueller, A.; Schippers, S.; Spruck, K.; Lestinsky, M.

    2013-04-10

    We report measurements of electron impact ionization for Fe{sup 13+}, Fe{sup 16+}, and Fe{sup 17+} over collision energies from below threshold to above 3000 eV. The ions were recirculated using an ion storage ring. Data were collected after a sufficiently long time that essentially all the ions had relaxed radiatively to their ground state. For single ionization of Fe{sup 13+}, we find that previous single pass experiments are more than 40% larger than our results. Compared to our work, the theoretical cross section recommended by Arnaud and Raymond is more than 30% larger, while that of Dere is about 20% greater. Much of the discrepancy with Dere is due to the theory overestimating the contribution of excitation-autoionization via n = 2 excitations. Double ionization of Fe{sup 13+} is dominated by direct ionization of an inner shell electron accompanied by autoionization of a second electron. Our results for single ionization of Fe{sup 16+} and Fe{sup 17+} agree with theoretical calculations to within the experimental uncertainties.

  9. Copper fine-structure K-shell electron impact ionization cross sections for fast-electron diagnostic in laser-solid experiments

    SciTech Connect

    Palmeri, P.; Quinet, P.; Batani, D.

    2015-03-15

    The K-shell electron impact ionization (EII) cross section, along with the K-shell fluorescence yield, is one of the key atomic parameters for fast-electron diagnostic in laser-solid experiments through the K-shell emission cross section. In addition, copper is a material that has been often used in those experiments because it has a maximum total K-shell emission yield. Furthermore, in a campaign dedicated to the modeling of the K lines of astrophysical interest (Palmeri et al., 2012), the K-shell fluorescence yields for the K-vacancy fine-structure atomic levels of all the copper isonuclear ions have been calculated. In this study, the K-shell EII cross sections connecting the ground and the metastable levels of the parent copper ions to the daughter ions K-vacancy levels considered in Palmeri et al. (2012) have been determined. The relativistic distorted-wave (DW) approximation implemented in the FAC atomic code has been used for the incident electron kinetic energies up to 10 times the K-shell threshold energies. Moreover, the resulting DW cross sections have been extrapolated at higher energies using the asymptotic form proposed by Davies et al. (2013)

  10. Copper fine-structure K-shell electron impact ionization cross sections for fast-electron diagnostic in laser-solid experiments

    NASA Astrophysics Data System (ADS)

    Palmeri, P.; Quinet, P.; Batani, D.

    2015-03-01

    The K-shell electron impact ionization (EII) cross section, along with the K-shell fluorescence yield, is one of the key atomic parameters for fast-electron diagnostic in laser-solid experiments through the K-shell emission cross section. In addition, copper is a material that has been often used in those experiments because it has a maximum total K-shell emission yield. Furthermore, in a campaign dedicated to the modeling of the K lines of astrophysical interest (Palmeri et al., 2012), the K-shell fluorescence yields for the K-vacancy fine-structure atomic levels of all the copper isonuclear ions have been calculated. In this study, the K-shell EII cross sections connecting the ground and the metastable levels of the parent copper ions to the daughter ions K-vacancy levels considered in Palmeri et al. (2012) have been determined. The relativistic distorted-wave (DW) approximation implemented in the FAC atomic code has been used for the incident electron kinetic energies up to 10 times the K-shell threshold energies. Moreover, the resulting DW cross sections have been extrapolated at higher energies using the asymptotic form proposed by Davies et al. (2013).

  11. Vanadium fine-structure K-shell electron impact ionization cross sections for fast-electron diagnostic in laser–solid experiments

    SciTech Connect

    Palmeri, P.; Quinet, P.; Batani, D.

    2015-09-15

    The K-shell electron impact ionization (EII) cross section, along with the K-shell fluorescence yield, is one of the key atomic parameters for fast-electron diagnostic in laser–solid experiments through the K-shell emission cross section. In addition, in a campaign dedicated to the modeling of the K lines of astrophysical interest (Palmeri et al. (2012)), the K-shell fluorescence yields for the K-vacancy fine-structure atomic levels of all the vanadium isonuclear ions have been calculated. In this study, the K-shell EII cross sections connecting the ground and the metastable levels of the parent vanadium ions to the daughter ions K-vacancy levels considered in Palmeri et al. (2012) have been determined. The relativistic distorted-wave (DW) approximation implemented in the FAC atomic code has been used for the incident electron kinetic energies up to 20 times the K-shell threshold energies. Moreover, the resulting DW cross sections have been extrapolated at higher energies using the asymptotic behavior of the modified relativistic binary encounter Bethe model (MRBEB) of Guerra et al. (2012) with the density-effect correction proposed by Davies et al. (2013)

  12. The Effect of the Residual Ion Potential on the Fully Differential Cross Section of Helium for Ionization by Electron Impact

    SciTech Connect

    Toth, A.; Nagy, L.

    2011-10-03

    We have carried out calculations for the fully differential cross section of the ionization of helium by electron projectiles. In order to study the effect of the residual ion potential, we employed three models, and tested them for the coplanar and perpendicular plane geometry. In spite of the simplicity of our models, the results for the coplanar case are in fair agreement with the available experimental data. The results for the perpendicular geometry need more improvement.

  13. Electron-impact ionization of laser-excited Ba-138 (... 5p6 6s 6p) and Ba-138 (... 5p6 6s 5d) atoms

    NASA Technical Reports Server (NTRS)

    Trajmar, S.; Nickel, J. C.; Antoni, T.

    1986-01-01

    Electron-impact ionization cross sections for laser-excited Ba-138 (... 5p6 6s 6p; 1P1, M = - 1) and cascade-populated Ba-138 (... 5p6 6s 5d; 1D + 3D) atoms were measured in the threshold to 10 eV energy range. The peak cross sections for the excited species are about a factor of 2 larger than that for ground-state Ba. In addition, it was demonstrated that ionization from individual magnetic substates of various hyperfine levels can be studied. The ionization cross sections in the case of Ba-138 (1P1) were found to be equal for the M = 0 and for the M = + or - 1 sublevels within the experimental error limit.

  14. Partial-ionization cross sections of a CO{sub 2} molecule due to impact of 10-26-keV electrons

    SciTech Connect

    Bhatt, Pragya; Singh, Raj; Yadav, Namita; Shanker, R.

    2010-10-15

    Experimental data on total- and partial-ionization cross sections of ionic fragments of CO{sub 2} molecule produced by impact of 10-26-keV electrons are obtained on a crossed-beam apparatus in our laboratory. An ejected electron-produced ion-coincidence technique is employed together with a time-of-flight mass spectrometer for analysis of the ions. The six ionic fragments, CO{sub 2}{sup +}, CO{sup +}, CO{sub 2}{sup 2+}, O{sup +}, C{sup +}, and C{sup 2+}, resulting from dissociative ionization of the CO{sub 2} molecule are observed and identified; their relative ionization cross sections and branching ratios are determined as a function of impact energy. The binary-encounter Bethe model is found to overestimate the experimental data for total-ionization cross sections of the observed ions. No other experimental or theoretical data exist in the investigated energy range to make a direct comparison with the present results.

  15. Molecular orientation effect on the differential cross sections for the electron-impact double ionization of oriented water molecules

    SciTech Connect

    Champion, C.; Dal Cappello, C.; Oubaziz, D.; Aouchiche, H.; Popov, Yu. V.

    2010-03-15

    Double ionization of isolated water molecules fixed in space is here investigated in a theoretical approach based on the first Born approximation. Secondary electron angular distributions are reported for particular (e,3e) kinematical conditions and compared in terms of shape and magnitude. Strong dependence of the fivefold differential cross sections on the molecular target orientation is clearly observed in (e,3-1e) as well as (e,3e) channels. Furthermore, for the major part of the kinematics considered, we identified the different mechanisms involved in the double ionization of water molecule, namely, the direct shake-off process as well as the two-step1 process. They are both discussed and analyzed with respect to the molecular target orientation.

  16. Kinematically complete study of low-energy electron-impact ionization of argon: Internormalized cross sections in three-dimensional kinematics

    NASA Astrophysics Data System (ADS)

    Ren, Xueguang; Amami, Sadek; Zatsarinny, Oleg; Pflüger, Thomas; Weyland, Marvin; Dorn, Alexander; Madison, Don; Bartschat, Klaus

    2016-06-01

    As a further test of advanced theoretical methods to describe electron-impact single-ionization processes in complex atomic targets, we extended our recent work on Ne (2 p ) ionization [X. Ren, S. Amami, O. Zatsarinny, T. Pflüger, M. Weyland, W. Y. Baek, H. Rabus, K. Bartschat, D. Madison, and A. Dorn, Phys. Rev. A 91, 032707 (2015), 10.1103/PhysRevA.91.032707] to Ar (3 p ) ionization at the relatively low incident energy of E0=66 eV. The experimental data were obtained with a reaction microscope, which can cover nearly the entire 4 π solid angle for the secondary electron emission. We present experimental data for detection angles of 10, 15, and 20∘ for the faster of the two outgoing electrons as a function of the detection angle of the secondary electron with energies of 3, 5, and 10 eV, respectively. Comparison with theoretical predictions from a B -spline R -matrix (BSR) with pseudostates approach and a three-body distorted-wave (3DW) approach, for detection of the secondary electron in three orthogonal planes as well as the entire solid angle, shows overall satisfactory agreement between experiment and the BSR results, whereas the 3DW approach faces difficulties in predicting some of the details of the angular distributions. These findings are different from our earlier work on Ne (2 p ), where both the BSR and 3DW approaches yielded comparable levels of agreement with the experimental data.

  17. Ag K-shell ionization by electron impact: New cross-section measurements between 50 and 100 keV and review of previous experimental data

    NASA Astrophysics Data System (ADS)

    Vanin, V. R.; Manso Guevara, M. V.; Maidana, N. L.; Martins, M. N.; Fernández-Varea, J. M.

    2016-02-01

    We report the measurement of Ag K-shell ionization cross-section by electron impact in the range 50-100 keV and review the experimental data found in the literature. The sample consisted in a thin film of Ag evaporated on a thin C backing. The x-ray spectra generated by electron bombardment in the São Paulo Microtron were observed with a planar HPGe detector. The ratios between characteristic and bremsstrahlung x-ray yields were transformed to ionization cross sections with the help of theoretical atomic-field bremsstrahlung cross sections. The measured cross sections are compared with existing experimental values and calculations based on the semi-relativistic distorted-wave Born approximation. According to our experiment, the ratio of Ag Kβ to Kα x-ray intensities is 0.2018(24).

  18. Cross sections for ionization of K, L and M shells of atoms by impact of electrons and positrons with energies up to 1 GeV: Analytical formulas

    NASA Astrophysics Data System (ADS)

    Bote, David; Salvat, Francesc; Jablonski, Aleksander; Powell, Cedric J.

    2009-11-01

    Analytical formulas are presented for the easy calculation of cross sections for ionization of K, L and M shells of neutral atoms by impact of electrons and positrons with kinetic energies up to 1 GeV. Each formula contains a number of parameters that are characteristic of the element, the active electron shell and the projectile particle. The values of these parameters were determined by fitting the cross section values in an extensive database that was calculated recently by means of a composite algorithm that combines the distorted-wave and plane-wave Born approximations. Tables of parameter values are given for all elements, from hydrogen (Z=1) to einsteinium (Z=99). The proposed analytical expressions yield ionization cross sections that agree with those in the numerical database to within about 1%, except for projectiles with near-threshold energies.

  19. Cross sections for ionization of K, L and M shells of atoms by impact of electrons and positrons with energies up to 1 GeV: Analytical formulas

    SciTech Connect

    Bote, David; Salvat, Francesc Jablonski, Aleksander

    2009-11-15

    Analytical formulas are presented for the easy calculation of cross sections for ionization of K, L and M shells of neutral atoms by impact of electrons and positrons with kinetic energies up to 1 GeV. Each formula contains a number of parameters that are characteristic of the element, the active electron shell and the projectile particle. The values of these parameters were determined by fitting the cross section values in an extensive database that was calculated recently by means of a composite algorithm that combines the distorted-wave and plane-wave Born approximations. Tables of parameter values are given for all elements, from hydrogen (Z=1) to einsteinium (Z=99). The proposed analytical expressions yield ionization cross sections that agree with those in the numerical database to within about 1%, except for projectiles with near-threshold energies.

  20. Measurements of absolute K-shell ionization cross sections and L-shell x-ray production cross sections of Ge by electron impact

    SciTech Connect

    Merlet, C.; Llovet, X.; Salvat, F.

    2004-03-01

    Results from measurements of absolute K-shell ionization cross sections and L{alpha} x-ray production cross sections of Ge by impact of electrons with kinetic energies ranging from the ionization threshold up to 40 keV are presented. The cross sections were obtained by measuring K{alpha} and L{alpha} x-ray intensities emitted from ultrathin Ge films deposited onto self-supporting carbon backing films. Recorded x-ray intensities were converted to absolute cross sections by using estimated values of the sample thicknesses, the number of incident electrons, and the detector efficiency. Experimental data are compared with the results of widely used simple analytical formulas, with calculated cross sections obtained from the plane-wave and distorted-wave Born approximations and with experimental data from the literature.

  1. Specific fragmentation of the K-shell excited/ionized pyridine derivatives studied by electron impact: 2-, 3- and 4-methylpyridine.

    PubMed

    Sakai, Masamichi; Okada, Kazumasa; Ohno, Keiichi; Tabayashi, Kiyohiko

    2010-03-01

    Fragmentation of the pyridine ring upon K-shell excitation/ionization has been studied with gaseous 2-, 3- and 4-methylpyridine by the electron-impact method. Ab initio molecular orbital (MO) calculations were also carried out to explore electronic states correlating with specific fragments. Some specific fragmentation channels were identified from the ionic fragments enhanced characteristically at the N 1s edge. Yields of the C(2)HN(+) and C(5)H(5)(+)/C(5)H(6)(+) ions show that the fission of the N-C2 and C4-C5/C5-C6 bonds of the ring is likely to occur after the N 1s excitation and ionization. Ab initio MO calculations for the 2-methylpyridine molecule indicate that the dissociation channels to produce these ions are only accessible through the excited states of the parent molecular dication, which can be formed by Auger decays after the N 1s ionization. Fragment ions via hydrogen rearrangement are produced as well, but the rearrangement is not a phenomenon specific to the K-shell excitation/ionization. PMID:20166104

  2. Large-scale B-spline R-matrix calculations of electron impact excitation and ionization processes in complex atoms

    NASA Astrophysics Data System (ADS)

    Zatsarinny, Oleg

    2013-09-01

    In recent years, the B-spline R-matrix (BSR) method has been applied to the treatment of a large number of atomic structure and electron-atom collision problems. Characteristic features of the BSR approach include the use of B-splines as a universal basis to describe the projectile electron inside the R-matrix box and the employment of term-dependent, and hence non-orthogonal, orbitals to construct the target states. The latter flexibility has proven to be of crucial importance for complex targets with several partially filled subshells. The published computer code has since been updated and extended to allow for a fully relativistic description at the level of the Dirac-Coulomb hamiltonian. Also, the systematic inclusion of a large number of pseudo-states in the close-coupling expansion has made it possible to extend the range of applicability from elastic and inelastic low-energy near-threshold phenomena to intermediate energies (up to several times the ionization threshold) and, in particular, to describe ionization processes as well. The basic ideas of the BSR approach will be reviewed, and its application will be illustrated for a variety of targets. Particular emphasis will be placed on systems of relevance for applications in gaseous electronics, such as the generation of complete datasets for electron collisions with the heavy noble gases Ne-Xe. Many of our data, which are needed for the description of transport processes in plasmas, are available through the LXCat database. This work was performed in collaboration with Klaus Bartschat. It is supported by the National Science Foundation under Grant No. PHY-1212450 and the XSEDE Allocation PHY-090031.

  3. Following electron impact excitations of Rn, Ra, Th, U and Pu single atom L sub-shells ionization cross section calculations by using Lotz's equation

    NASA Astrophysics Data System (ADS)

    Ayinol, M.; Aydeniz, D.

    2016-03-01

    L shell ionization cross section and Li subshells ionization cross sections of Rn, Ra, Th, U, Pu atoms calculated. For each of atoms, ten different electron impact energy values (Eo) are used. Calculations carried out by using Lotz equation in Matlab. First, calculations done for non-relativistic case by using non-relativistic Lotz equation then repeated with relativistic Lotz equation. σL total and σLi(i = 1,2,3) subshells ionisation cross section values obtained for Eo values in the energy range of ELi ionization threshold energy, σL total and σLi (i = 1,2,3) are increasing rapidly with Eo. For a fixed Eo = 3.ELi), while Z increases from 86electron-atom impact studies.

  4. Proton-impact ionization cross sections of adenine measured at 0.5 and 2.0 MeV by electron spectroscopy

    SciTech Connect

    Iriki, Y.; Kikuchi, Y.; Imai, M.; Itoh, A.

    2011-11-15

    Double-differential ionization cross sections (DDCSs) of vapor-phase adenine molecules (C{sub 5}H{sub 5}N{sub 5}) by 0.5- and 2.0-MeV proton impact have been measured by the electron spectroscopy method. Electrons ejected from adenine were analyzed by a 45 Degree-Sign parallel-plate electrostatic spectrometer over an energy range of 1.0-1000 eV at emission angles from 15 Degree-Sign to 165 Degree-Sign . Single-differential cross sections (SDCSs) and total ionization cross sections (TICSs) were also deduced. It was found from the Platzman plot, defined as SDCSs divided by the classical Rutherford knock-on cross sections per target electron, that the SDCSs at higher electron energies are proportional to the total number of valence electrons (50) of adenine, while those at low-energy electrons are highly enhanced due to dipole and higher-order interactions. The present results of TICS are in fairly good agreement with recent classical trajectory Monte Carlo calculations, and moreover, a simple analytical formula gives nearly equivalent cross sections in magnitude at the incident proton energies investigated.

  5. Proton-impact ionization cross sections of adenine measured at 0.5 and 2.0 MeV by electron spectroscopy

    NASA Astrophysics Data System (ADS)

    Iriki, Y.; Kikuchi, Y.; Imai, M.; Itoh, A.

    2011-11-01

    Double-differential ionization cross sections (DDCSs) of vapor-phase adenine molecules (C5H5N5) by 0.5- and 2.0-MeV proton impact have been measured by the electron spectroscopy method. Electrons ejected from adenine were analyzed by a 45∘ parallel-plate electrostatic spectrometer over an energy range of 1.0-1000 eV at emission angles from 15∘ to 165∘. Single-differential cross sections (SDCSs) and total ionization cross sections (TICSs) were also deduced. It was found from the Platzman plot, defined as SDCSs divided by the classical Rutherford knock-on cross sections per target electron, that the SDCSs at higher electron energies are proportional to the total number of valence electrons (50) of adenine, while those at low-energy electrons are highly enhanced due to dipole and higher-order interactions. The present results of TICS are in fairly good agreement with recent classical trajectory Monte Carlo calculations, and moreover, a simple analytical formula gives nearly equivalent cross sections in magnitude at the incident proton energies investigated.

  6. Kinematically complete study of low-energy electron-impact ionization of neon: Internormalized cross sections in three-dimensional kinematics

    NASA Astrophysics Data System (ADS)

    Ren, Xueguang; Amami, Sadek; Zatsarinny, Oleg; Pflüger, Thomas; Weyland, Marvin; Baek, Woon Yong; Rabus, Hans; Bartschat, Klaus; Madison, Don; Dorn, Alexander

    2015-03-01

    Low-energy (E0=65 eV ) electron-impact single ionization of Ne (2 p ) has been investigated to thoroughly test state-of-the-art theoretical approaches. The experimental data were measured using a reaction microscope, which can cover nearly the entire 4 π solid angle for the secondary electron emission energies ranging from 2 to 8 eV, and projectile scattering angles ranging from 8 .5∘ to 20 .0∘ . The experimental triple-differential cross sections are internormalized across all measured scattering angles and ejected energies. The experimental data are compared to predictions from a hybrid second-order distorted-wave Born plus R -matrix approach, the distorted-wave Born approximation with the inclusion of postcollision interaction (PCI), a three-body distorted-wave approach (3DW), and a B -spline R -matrix (BSR) with pseudostates approach. Excellent agreement is found between the experiment and predictions from the 3DW and BSR models, for both the angular dependence and the relative magnitude of the cross sections in the full three-dimensional parameter space. The importance of PCI effects is clearly visible in this low-energy electron-impact ionization process.

  7. Two-centre partial-wave calculations for the multiply differential cross section of the simple ionization of diatomic lithium Li2 by fast electron impact

    NASA Astrophysics Data System (ADS)

    Elboudali, F.; Joulakian, B.

    2001-12-01

    The (e, 2e) ionization of diatomic lithium Li2 by fast electrons is studied by applying, for the slow ejected electron, an asymptotically exact partial-wave description, which takes into account the diatomic nature of the problem. The ionization is considered as a vertical transition from the lowest vibrational and rotational level of the fundamental electronic state 1Σg+ of Li2 to the fundamental 2Σg+ state of Li2+. After verification of the procedure on the (e, 2e) ionization of diatomic hydrogen H2 for which experimental and theoretical results exist we present the particularities and favourable directions for Li2 targets.

  8. Ionization of xenon by electrons: Partial cross sections for single, double, and triple ionization

    SciTech Connect

    Mathur, D.; Badrinathan, C.

    1987-02-01

    High-sensitivity measurements of relative partial cross sections for single, double, and triple ionization of Xe by electron impact have been carried out in the energy region from threshold to 100 eV using a crossed-beam apparatus incorporating a quadrupole mass spectrometer. The weighted sum of the relative partial cross sections at 50 eV are normalized to the total ionization cross section of Rapp and Englander-Golden to yield absolute cross-section functions. Shapes of the partial cross sections for single and double ionization are difficult to account for within a single-particle picture. Comparison of the Xe/sup +/ data with 4d partial photoionization cross-section measurements indicates the important role played by many-body effects in describing electron-impact ionization of high-Z atoms.

  9. Electron-Impact Ionization of Multicharged Ions: Cross-Sections Data from Oak Ridge National Laboratory (ORNL) and the Controlled Fusion Atomic Data Center (CFADC)

    DOE Data Explorer

    This website presents experimental ionization cross sections measured using the Electron-Ion Crossed Beams apparatus in the Multicharged Ion Research Facility (MIRF) at the Physics Division of Oak Ridge National Laboratory (ORNL). The data are given in both graphical and tabular form along with the reference to the original publication of the experimental results. Also presented in the figures are theoretical cross sections supporting the experiments. For details of the theoretical work, refer to the original publication given for the particular experiment. These pages are based primarily on three technical memorandums issued by ORNL: 1(D. H. Crandall, R. A. Phaneuf, and D. C. Gregory, Electron Impact Ionization of Multicharged Ions, ORNL/TM-7020, Oak Ridge National Laboratory, 1979; 2) D. C. Gregory, D. H. Crandall, R. A. Phaneuf, A. M. Howald, G. H. Dunn, R. A. Also presented are more recent (1993-present) data, both published and unpublished. The data pages feature dynamic plotting, allowing the user to choose which sets of data to plot and zoom in on regions of interest within the plot. [Taken from http://www-cfadc.phy.ornl.gov/xbeam/index.html

  10. Vacuum ultraviolet studies of electron impact of helium: Excitation of He n P Rydberg series and ionization-excitation of He nl Rydberg series

    SciTech Connect

    Shemansky, D.E.; Hall, D.T.; Ajello, J.M.; Franklin, B.

    1985-09-15

    Laboratory measurements of the electron excitation cross sections of emission in the He Rydberg series (1sS S-1snp P) for n = 2,3,4 have been obtained. The cross sections were estimated by two methods: (1) analysis of calibrated laboratory spectra placed on an absolute scale using the H Ly dissociative excitation standard and (2) analysis of relative cross section data using a modified Born approximation. A new method has been developed for the application of the Bethe-Born approximation using experimental relative excitation functions that does not require extrapolation in a Fano plot in the determination of the absolute cross section. The two methods agree to within 3% for the 58.4 nm line when allowance is made for cascade transitions. We find the direct excitation cross sections at 200 eV for the n = 2,3,4 members of the published electron impact experimental measurements of the two electron process of ionization-excitation impact are generally in agreement, especially on the energy dependence of excitation functions, but show significant differences with theoretical calculations.

  11. Analysis of tert-butyldimethylsilyl derivatives in heavy gas oil from Brazilian naphthenic acids by gas chromatography coupled to mass spectrometry with electron impact ionization.

    PubMed

    Vaz de Campos, Maria Cecília; Oliveira, Eniz Conceição; Filho, Pedro José Sanches; Piatnicki, Clarisse Maria Sartori; Caramão, Elina Bastos

    2006-02-10

    Naphthenic acids, C(n)H(2n+Z)O(2), are a complex mixture of alkyl-substituted acyclic and cycle-aliphatic carboxylic acids. The content of naphthenic acids and their derivatives in crude oils is very small, which hinders their extraction from matrixes of wide and varied composition. In this work, liquid-liquid extraction, followed by solid phase extraction with an ion exchange resin (Amberlyst A-27) and ultrasound desorption were used to isolate the acid fraction from heavy gas oil of Marlim petroleum (Campos, Rio de Janeiro, Brazil). The analysis was accomplished through gas chromatography coupled to mass spectrometry with electron impact ionization, after derivatization with N-methyl-N-(tert-butyldimethylsilyl)trifluoracetamide (MTBDMSTFA). The results indicate the presence of carboxylic acids belonging to families of alicyclic and naphthenic compounds which contain up to four rings in the molecule. PMID:16439253

  12. Theoretical investigation of wave-vector-dependent analytical and numerical formulations of the interband impact-ionization transition rate for electrons in bulk silicon and GaAs

    NASA Technical Reports Server (NTRS)

    Kolnik, Jan; Wang, Yang; Oguzman, Ismail H.; Brennan, Kevin F.

    1994-01-01

    The electron interband impact-ionization rate for both silicon and gallium arsenide is calculated using an ensemble Monte Carlo simulation with the expressed purpose of comparing different formulations of the interband ionization transition rate. Specifically, three different treatments of the transition rate are examined: the traditional Keldysh formula, a new k-dependent analytical formulation first derived by W. Quade, E. Scholl, and M. Rudan (1993), and a more exact, numerical method of Y. Wang and K. F. Brennan (1994). Although the completely numerical formulation contains no adjustable parameters and as such provides a very reliable result, it is highly computationally intensive. Alternatively, the Keldysh formular, although inherently simple and computationally efficient, fails to include the k dependence as well as the details of the energy band structure. The k-dependent analytical formulation of Quade and co-workers overcomes the limitations of both of these models but at the expense of some new parameterization. It is found that the k-dependent analytical method of Quade and co-workers produces very similar results to those obtained with the completely numerical model for some quantities. Specifically, both models predict that the effective threshold for impact ionization in GaAs and silicon is quite soft, that the majority of ionization events originate from the second conduction band in both materials, and that the transition rate is k dependent. Therefore, it is concluded that the k-dependent analytical model can qualitatively reproduce results similar to those obtained with the numerical model yet with far greater computational efficiency. Nevertheless, there exist some important drawbacks to the k-dependent analytical model of Quade and co-workers: These are that it does not accurately reproduce the quantum yield data for bulk silicon, it requires determination of a new parameter, related physically to the overlap intergrals of the Bloch state which

  13. Electron-impact ionization mass-spectrometry of molecules and clusters in a pulsed helium droplet source

    NASA Astrophysics Data System (ADS)

    Yang, Shengfu; Brereton, Scott; Ellis, Andrew M.

    2006-03-01

    A pulsed helium droplet source has been developed and characterized. The nozzle geometry was found to be critical in allowing controlled tuning of helium nanodroplet size by variation of the stagnation pressure and temperature. The average droplet size scales according to a simple p,T scaling law, placing pulsed helium nanodroplet sources on a par with cw sources for the first time. Using this pulsed source, the ability of helium nanodroplets to impede ion fragmentation in electron impact mass spectrometry has been explored. A number of haloalkanes and C1--C6 alcohols were selected as the target species. The presence of helium alters the fragmentation patterns when compared with the gas phase, with some ion product channels being more strongly affected than others. Parent ion intensities are also enhanced by the helium for alcohols, but only for the two cyclic alcohols studied, cyclopentanol and cyclohexanol, is this effect large enough to transform the parent ion from a minor product (in the gas phase) into the most abundant ion in the helium droplet experiments. The results obtained are difficult to explain solely by rapid cooling of the excited parent ions by the surrounding superfluid helium, although this undoubtedly takes place. A second factor also seems to be involved, a cage effect which favors hydrogen atom loss over other fragmentation channels.

  14. An (e, 2e + ion) study of low-energy electron-impact ionization and fragmentation of tetrahydrofuran with high mass and energy resolutions

    SciTech Connect

    Ren, Xueguang Pflüger, Thomas; Weyland, Marvin; Baek, Woon Yoon; Rabus, Hans; Ullrich, Joachim; Dorn, Alexander

    2014-10-07

    We study the low-energy (E{sub 0} = 26 eV) electron-impact induced ionization and fragmentation of tetrahydrofuran using a reaction microscope. All three final-state charged particles, i.e., two outgoing electrons and one fragment ion, are detected in triple coincidence such that the momentum vectors and, consequently, the kinetic energies for charged reaction products are determined. The ionic fragments are clearly identified in the experiment with a mass resolution of 1 amu. The fragmentation pathways of tetrahydrofuran are investigated by measuring the ion kinetic energy spectra and the binding energy spectra where an energy resolution of 1.5 eV has been achieved using the recently developed photoemission electron source. Here, we will discuss the fragmentation reactions for the cations C{sub 4}H{sub 8}O{sup +}, C{sub 4}H{sub 7}O{sup +}, C{sub 2}H{sub 3}O{sup +}, C{sub 3}H{sub 6}{sup +}, C{sub 3}H{sub 5}{sup +}, C{sub 3}H{sub 3}{sup +}, CH{sub 3}O{sup +}, CHO{sup +}, and C{sub 2}H{sub 3}{sup +}.

  15. An (e, 2e + ion) study of low-energy electron-impact ionization and fragmentation of tetrahydrofuran with high mass and energy resolutions.

    PubMed

    Ren, Xueguang; Pflüger, Thomas; Weyland, Marvin; Baek, Woon Yoon; Rabus, Hans; Ullrich, Joachim; Dorn, Alexander

    2014-10-01

    We study the low-energy (E0 = 26 eV) electron-impact induced ionization and fragmentation of tetrahydrofuran using a reaction microscope. All three final-state charged particles, i.e., two outgoing electrons and one fragment ion, are detected in triple coincidence such that the momentum vectors and, consequently, the kinetic energies for charged reaction products are determined. The ionic fragments are clearly identified in the experiment with a mass resolution of 1 amu. The fragmentation pathways of tetrahydrofuran are investigated by measuring the ion kinetic energy spectra and the binding energy spectra where an energy resolution of 1.5 eV has been achieved using the recently developed photoemission electron source. Here, we will discuss the fragmentation reactions for the cations C4H8O(+), C4H7O(+), C2H3O(+), C3H6(+), C3H5(+), C3H3(+), CH3O(+), CHO(+), and C2H3(+). PMID:25296813

  16. Ionization of water by (20-150)-keV protons: Separation of direct-ionization and electron-capture processes

    SciTech Connect

    Gobet, F.; Eden, S.; Coupier, B.; Tabet, J.; Farizon, B.; Farizon, M.; Gaillard, M.J.; Carre, M.; Ouaskit, S.; Maerk, T. D.; Scheier, P.

    2004-12-01

    Mass analyzed product ions have been detected in coincidence with the projectile following the ionization of water by proton impact. Measurement of the projectile charge state postcollision enables the different ionization processes to be identified: direct ionization, single electron capture, and double electron capture. A complete set of partial and total absolute cross sections is reported for the direct ionization and electron capture processes initiated by proton collisions at 20-150 keV. The cross sections for the direct ionization of H{sub 2}O by proton impact are compared with previous electron impact results [Straub et al., J. Chem. Phys. 108, 109 (1998)].

  17. Multiple ionization of xenon by proton impact

    SciTech Connect

    Manson, S.T.; DuBois, R.D.

    1987-12-01

    An experimental and theoretical study of multiple ionization of xenon for 0.2- to 2.0-MeV proton impact was made. Absolute cross sections for producing xenon ions with charges from +1 to +3 were measured, and calculations of subshell cross sections were performed. Experiment and theory are consistent and indicate that multiple ionization of xenon by fast protons occurs via inner-shell ionization. This is in contrast to the lighter noble gases where direct multiple outer shell ionization can be predominant.

  18. Electron-impact ionization of neon at low projectile energy: an internormalized experiment and theory for a complex target.

    PubMed

    Pflüger, Thomas; Zatsarinny, Oleg; Bartschat, Klaus; Senftleben, Arne; Ren, Xueguang; Ullrich, Joachim; Dorn, Alexander

    2013-04-12

    As a fundamental test for state-of-the-art theoretical approaches, we have studied the single ionization (2p) of neon at a projectile energy of 100 eV. The experimental data were acquired using an advanced reaction microscope that benefits from high efficiency and a large solid-angle acceptance of almost 4π. We put special emphasis on the ability to measure internormalized triple-differential cross sections over a large part of the phase space. The data are compared to predictions from a second-order hybrid distorted-wave plus R-matrix model and a fully nonperturbative B-spline R-matrix (BSR) with pseudostates approach. For a target of this complexity and the low-energy regime, unprecedented agreement between experiment and the BSR model is found. This represents a significant step forward in the investigation of complex targets. PMID:25167263

  19. MH 2+ṡ ion production from protonated polypeptides by electron impact: observation and determination of ionization energies and a cross-section

    NASA Astrophysics Data System (ADS)

    Budnik, Bogdan A.; Zubarev, Roman A.

    2000-01-01

    Irradiation of gas-phase MH + ions of polypeptides up to MW 3493 by 11 to 70 eV electrons produced further ionization: MH ++e -→MH 2+·+2 e -, with ionization thresholds of 11.4±0.5 eV for [Arg-8]-vasopressin (MW 1084), 10.7±0.5 eV for substance P (MW 1347), 11.4±0.6 eV for renin substrate (MW 1759) and 10.6±0.4 eV for melittin (MW 2846). The ionization cross-section of vasopressin MH + ions was found to be (1.3±0.4)·10 -15 cm 2 for 20 eV electrons. The gas-phase MH 2+ṡ ions are rather stable at room temperature, with lifetimes of hundreds of seconds at 10 -10 Torr.

  20. Electron-impact double ionization of He by applying the Jacobi matrix approach to the Faddeev-Merkuriev equations

    SciTech Connect

    Mengoue, M. Silenou; Njock, M. G. Kwato; Piraux, B.; Popov, Yu. V.; Zaytsev, S. A.

    2011-05-15

    We apply the Jacobi matrix method to the Faddeev-Merkuriev differential equations in order to calculate the three-body wave function that describes the double continuum of an atomic two-electron system. This function is used to evaluate within the first-order Born approximation, the fully differential cross sections for (e,3e) processes in helium. The calculations are performed in the case of a coplanar geometry in which the incident electron is fast and both ejected electrons are slow. Quite unexpectedly, the results obtained by reducing our double-continuum wave function to its asymptotic expression are in satisfactory agreement with all the experimental data of Lahmam-Bennani et al.[A. Lahaman-Bennani et al., Phys. Rev. A 59, 3548 (1999); A. Kheifets et al., J. Phys. B 32, 5047 (1999).] without any need for renormalizing the data. When the full double-continuum wave function is used, the agreement of the results with the experimental data improves significantly. However, a detailed analysis of the calculations shows that full convergence in terms of the basis size is not reached. This point is discussed in detail.

  1. Oxygen ionization rates at Mars and Venus - Relative contributions of impact ionization and charge exchange

    NASA Technical Reports Server (NTRS)

    Zhang, M. H. G.; Luhmann, J. G.; Nagy, A. F.; Spreiter, J. R.; Stahara, S. S.

    1993-01-01

    Oxygen ion production rates above the ionopauses of Venus and Mars are calculated for photoionization, charge exchange, and solar wind electron impact ionization processes. The latter two require the use of the Spreiter and Stahara (1980) gas dynamic model to estimate magnetosheath velocities, densities, and temperatures. The results indicate that impact ionization is the dominant mechanism for the production of O(+) ions at both Venus and Mars. This finding might explain both the high ion escape rates measured by Phobos 2 and the greater mass loading rate inferred for Venus from the bow shock positions.

  2. Study of the angular distributions of X-rays emitted following L3 ionization of gold atoms by electron impact

    NASA Astrophysics Data System (ADS)

    Wright, I.; Sestric, G.; Ferguson, S.; Williams, S.

    2015-03-01

    Theoretical work suggests that when an atomic inner-shell vacancy with total angular momentum j greater than 1/2 is created by interaction with a photon or charged particle the vacancy will be aligned due to the magnetic sublevels of the ion having nonstatistical populations. The experiments we performed, testing this theory, involved measurements of the angular distributions of gold Lα, Lβ, and Ll X-rays at forward angles in the range 0 degrees to 25 degrees emitted after being bombarded with 15-keV electrons. After corrections for absorption of the characteristic X-rays within the gold target, our results suggest that the angular distributions of the Lα and Lβ X-rays are essentially isotropic, as no angular dependence was observed in our data outside of experimental uncertainties. However, the results of our experiments suggest that the angular distribution of the gold Ll X-rays may be weakly anisotropic.

  3. High-efficiency electron ionizer for a mass spectrometer array

    NASA Technical Reports Server (NTRS)

    Chutjian, Ara (Inventor); Darrach, Murray R. (Inventor); Orient, Otto J. (Inventor)

    2001-01-01

    The present invention provides an improved electron ionizer for use in a quadrupole mass spectrometer. The improved electron ionizer includes a repeller plate that ejects sample atoms or molecules, an ionizer chamber, a cathode that emits an electron beam into the ionizer chamber, an exit opening for excess electrons to escape, at least one shim plate to collimate said electron beam, extraction apertures, and a plurality of lens elements for focusing the extracted ions onto entrance apertures.

  4. Communication: Electron ionization of DNA bases.

    PubMed

    Rahman, M A; Krishnakumar, E

    2016-04-28

    No reliable experimental data exist for the partial and total electron ionization cross sections for DNA bases, which are very crucial for modeling radiation damage in genetic material of living cell. We have measured a complete set of absolute partial electron ionization cross sections up to 500 eV for DNA bases for the first time by using the relative flow technique. These partial cross sections are summed to obtain total ion cross sections for all the four bases and are compared with the existing theoretical calculations and the only set of measured absolute cross sections. Our measurements clearly resolve the existing discrepancy between the theoretical and experimental results, thereby providing for the first time reliable numbers for partial and total ion cross sections for these molecules. The results on fragmentation analysis of adenine supports the theory of its formation in space. PMID:27131520

  5. Communication: Electron ionization of DNA bases

    NASA Astrophysics Data System (ADS)

    Rahman, M. A.; Krishnakumar, E.

    2016-04-01

    No reliable experimental data exist for the partial and total electron ionization cross sections for DNA bases, which are very crucial for modeling radiation damage in genetic material of living cell. We have measured a complete set of absolute partial electron ionization cross sections up to 500 eV for DNA bases for the first time by using the relative flow technique. These partial cross sections are summed to obtain total ion cross sections for all the four bases and are compared with the existing theoretical calculations and the only set of measured absolute cross sections. Our measurements clearly resolve the existing discrepancy between the theoretical and experimental results, thereby providing for the first time reliable numbers for partial and total ion cross sections for these molecules. The results on fragmentation analysis of adenine supports the theory of its formation in space.

  6. Single ionization of helium by 730-eV electrons

    SciTech Connect

    Stevenson, M. A.; Lohmann, B.; Bray, I.; Fursa, D. V.; Stelbovics, A. T.

    2007-03-15

    We present fully differential measurements of 730-eV electron-impact single ionization of the ground state of helium with 205- or 100-eV outgoing electrons. Internormalized data are obtained for coplanar geometries with the fast electron detected at {theta}{sub A}=6 degree sign , 9 degree sign , and 12 degree sign . The data are compared, where possible, with the corresponding data of Catoire et al. [J. Phys. B 39, 2827 (2006)] and the convergent close-coupling theory. An improved agreement is found between the present measurements and the theory.

  7. Ionization of rubidium by 50-eV electrons

    SciTech Connect

    Haynes, M.A.; Lohmann, B.; Bray, I.; Bartschat, K.

    2004-04-01

    We report on a joint experimental and theoretical study of 50-eV electron-impact ionization of rubidium. Comparison of the experimental data with theoretical predictions from various models shows good qualitative agreement, as long as distortion and channel-coupling effects in the projectile-target interaction are accounted for. The remaining differences between experiment and theory indicate the need for further studies of this collision system.

  8. Electron- and proton-induced ionization of pyrimidine

    SciTech Connect

    Champion, Christophe; Quinto, Michele; Weck, Philippe F

    2015-03-27

    This present work describes a quantum-mechanically based model of the electron- and proton-induced ionization of isolated pyrimidine molecules. The impact energies range from the target ionization threshold up to ~1 keV for electrons and from 10 keV up to 10 MeV for protons. The cross-section calculations are performed within the 1st Born approximation in which the ejected electron is described by a Coulomb wave whereas the incident and the scattered projectiles are both described by plane waves. The pyrimidine target is described using the Gaussian 09 software package. Furthermore, our theoretical predictions obtained are in good agreement with experimental absolute total cross sections, while large discrepancies are observed between existing semi-empirical models and the present calculations.

  9. Electron- and proton-induced ionization of pyrimidine

    DOE PAGESBeta

    Champion, Christophe; Quinto, Michele; Weck, Philippe F

    2015-03-27

    This present work describes a quantum-mechanically based model of the electron- and proton-induced ionization of isolated pyrimidine molecules. The impact energies range from the target ionization threshold up to ~1 keV for electrons and from 10 keV up to 10 MeV for protons. The cross-section calculations are performed within the 1st Born approximation in which the ejected electron is described by a Coulomb wave whereas the incident and the scattered projectiles are both described by plane waves. The pyrimidine target is described using the Gaussian 09 software package. Furthermore, our theoretical predictions obtained are in good agreement with experimental absolutemore » total cross sections, while large discrepancies are observed between existing semi-empirical models and the present calculations.« less

  10. HF Accelerated Electron Fluxes, Spectra, and Ionization

    NASA Astrophysics Data System (ADS)

    Carlson, Herbert C.; Jensen, Joseph B.

    2015-10-01

    Wave particle interactions, an essential aspect of laboratory, terrestrial, and astrophysical plasmas, have been studied for decades by transmitting high power HF radio waves into Earth's weakly ionized space plasma, to use it as a laboratory without walls. Application to HF electron acceleration remains an active area of research (Gurevich in Usp Fizicheskikh Nauk 177(11):1145-1177, 2007) today. HF electron acceleration studies began when plasma line observations proved (Carlson et al. in J Atmos Terr Phys 44:1089-1100, 1982) that high power HF radio wave-excited processes accelerated electrons not to ~eV, but instead to -100 times thermal energy (10 s of eV), as a consequence of inelastic collision effects on electron transport. Gurevich et al (J Atmos Terr Phys 47:1057-1070, 1985) quantified the theory of this transport effect. Merging experiment with theory in plasma physics and aeronomy, enabled prediction (Carlson in Adv Space Res 13:1015-1024, 1993) of creating artificial ionospheres once ~GW HF effective radiated power could be achieved. Eventual confirmation of this prediction (Pedersen et al. in Geophys Res Lett 36:L18107, 2009; Pedersen et al. in Geophys Res Lett 37:L02106, 2010; Blagoveshchenskaya et al. in Ann Geophys 27:131-145, 2009) sparked renewed interest in optical inversion to estimate electron spectra in terrestrial (Hysell et al. in J Geophys Res Space Phys 119:2038-2045, 2014) and planetary (Simon et al. in Ann Geophys 29:187-195, 2011) atmospheres. Here we present our unpublished optical data, which combined with our modeling, lead to conclusions that should meaningfully improve future estimates of the spectrum of HF accelerated electron fluxes. Photometric imaging data can significantly improve detection of emissions near ionization threshold, and confirm depth of penetration of accelerated electrons many km below the excitation altitude. Comparing observed to modeled emission altitude shows future experiments need electron density profiles

  11. Energy differential cross sections for F9+-impact single and double ionization of He

    NASA Astrophysics Data System (ADS)

    Pindzola, M. S.; Lee, T. G.; Colgan, J.

    2015-07-01

    Time-dependent close-coupling methods are used to calculate energy differential cross sections for the single and double ionization of He by impact with F9+ ions at 4.0 MeV amu-1. Single ionization energy differential cross sections using both a one active electron method and a two active electron method are compared with recent experimental results. Double ionization energy differential cross sections using a two active electron method are presented to guide future experiments.

  12. CF3+ fragmentation by electron impact ionization of perfluoro-propyl-vinyl-ethers, C5F10O, in gas phase

    NASA Astrophysics Data System (ADS)

    Kondo, Yusuke; Ishikawa, Kenji; Hayashi, Toshio; Miyawaki, Yudai; Takeda, Keigo; Kondo, Hiroki; Sekine, Makoto; Hori, Masaru

    2015-04-01

    The gas phase fragmentations of perfluoro-propyl-vinyl ether (PPVE, C5F10O) are studied experimentally. Dominant fragmentations of PPVE are found to be the result of a dissociative ionization reaction, i.e., CF3+ via direct bond cleavage, and C2F3O- and C3F7O- via electron attachment. Regardless of the appearance energy of around 14.5 eV for the dissociative ionization of CF3+, the observed ion efficiency for the CF3+ ion was extremely large the order of 10-20 cm-2, compared with only 10-21 cm-2 for the other channels. PPVE characteristically generated CF3+ as the largest abundant ion are advantageous for use of feedstock gases in plasma etching processes.

  13. Massive cluster impact ionization of saccharides

    SciTech Connect

    Dookeran, N.N.; Todd, P.J.

    1995-12-31

    The authors studied the utility of ionizing saccharides by massive cluster impact (MCI), a form of secondary ionization wherein the primary ions are high molecular weight clusters. For a number of compounds and classes, MCI yields copious secondary ions without prior derivitization or the need to find a suitable matrix. In fact, MCI can be used for in situ ionization of some analytes directly from biologic tissue. For the simple sugars and disaccharides that were studied, the authors found that persistent ( e.g. > 2 h) positive and negative secondary ion emission could almost always be detected from pure samples. The authors characterized the secondary anions from a variety of saccharides by tandem mass spectrometry (MS/MS), and found the behavior of the MS/MS spectra to be consistent, sensible, diagnostic and invariant with the dose suffered by the sample.

  14. Vacuum ultraviolet studies of electron impact of helium Excitation of He n1P0 Rydberg series and ionization-excitation of He(+) nl Rydberg series

    NASA Technical Reports Server (NTRS)

    Shemansky, D. E.; Hall, D. T.; Ajello, J. M.; Franklin, B.

    1985-01-01

    The cross sections for the He I 1s2 1S-1snp 1P0 series have been measured using a relative flow method, with the absolute scale fixed by the H Ly-alpha dissociative excitation cross section standard. The results are compared with those obtained using a relative cross section data analysis by modified Born approximation, and good agreement is found. Cross sections for the ionization-excitation of the He II 121.51 nm and He II 164.04 nm transmissions have been measured, and the results strongly suggest that theoretical calculations of the reactions differ fundamentally from physical reality. The failure of the theory to describe experimental results stems from the neglect in the theory of electron correlation effects between the two orbital electrons.

  15. ECC study in positron impact ionization in molecular hydrogen

    NASA Astrophysics Data System (ADS)

    Campeanu, R. I.; Zohouri Haghian, N.

    2012-12-01

    The electron capture to the continuum phenomenon in positron impact ionization of molecular hydrogen is studied with the distorted wave Born approximation. Our theoretical model produces results which are in better agreement with the experiment than the more elaborate models of [J. Fiol, V.D. Rodriguez, R.O. Barrachina, J. Phys. B: At. Mol. Opt. Phys. 34, 933 (2001)] and [A. Benedek, R.I. Campeanu, J. Phys. B: At. Mol. Opt. Phys. 40, 1589 (2007)] previously employed in this study.

  16. Observation of impact ionization in vanadium dioxide

    NASA Astrophysics Data System (ADS)

    Holleman, Joshua; Bishop, Michael; Garcia, Carlos; Beekman, Christianne; Lee, Shinbuhm; Lee, Ho Nyung; Manousakis, Efstratios; McGill, Stephen

    Pump-probe optical spectroscopy was used to investigate the possibility of charge carrier multiplication by impact ionization in a 100 nm film of VO2 in the M1 insulating phase. The film was excited by pump pulses with energies above and below twice the band gap energy and observed with two different probe wavelengths. The transient reflectivities of the film were then compared. We observed an enhancement of the reflectivity for the higher energy pump pulses near zero delay compared to the reflectivity for the lower energy pump pulses for both probe wavelengths. Additionally, we identified and described multiple timescales within the charge dynamics. This experiment demonstrated that impact ionization acts as a carrier multiplication process in this prototypical strongly-correlated system. This work was supported by NSF DMR-1229217.

  17. Fundamental study of impact ionization plasma detector

    NASA Astrophysics Data System (ADS)

    Ohashi, H.; Muranaga, K.; Sasaki, S.; Nogami, K.; Shibata, H.

    Impact ionization plasma detectors are commonly used for cosmic dust research on board spacecraft. There seems to be no scientific background on their shape, area, and applied high voltage; they are determined empirically. To design a dust detector having large aperture and lightweight to collect dust effectively for the future mission, we are to study fundamental physics of dust impact ionization phenomena. To determine parameters of impact ionization, a simple detector is designed; metal target, two grids, with/without sidewall. Distance from target to grid, grid to grid, applied voltages are variable. Each electrode is connected to charge sensitive preamplifiers, signals are observed with a digital oscilloscope. Experiments using micro-particle accelerators are made at HIT, Univ. Tokyo in Japan, and at MPI-K in Germany. Time difference of two grid signals (plasma expansion velocity), and target signal rise time are determined from observed signals. Preliminary study shows, plasma expansion velocity is dependent on applied high voltage, not dependent on dust velocity. There is a clear correlation between dust particle velocity and target signal rise time. Sidewall effect is to be studied in the near future experiment.

  18. Differential cross sections for ionization of helium, neon, and argon by fast electrons

    SciTech Connect

    Miller, J.H.; Manson, S.T.

    1984-05-01

    Ionization cross sections, differential in the energy of secondary electrons, are presented for high-energy electrons incident on helium, neon, and argon. The results are based on Bethe's theory for inelastic scattering of fast charged particles using photoabsorption data and proton-impact differential ionization cross sections to determine the coefficients of this asymptotic expansion of the first Born approximation. The model cross sections are compared with experimental data for primary-electron energies between 100 and 5000 eV.

  19. Hot electron dominated rapid transverse ionization growth in liquid water.

    PubMed

    Brown, Michael S; Erickson, Thomas; Frische, Kyle; Roquemore, William M

    2011-06-20

    Pump/probe optical-transmission measurements are used to monitor in space and time the ionization of a liquid column of water following impact of an 800-nm, 45-fs pump pulse. The pump pulse strikes the 53-μm-diameter column normal to its axis with intensities up to 2 × 10(15) W/cm2. After the initial photoinization and for probe delay times < 500 fs, the neutral water surrounding the beam is rapidly ionized in the transverse direction, presumably by hot electrons with initial velocities of 0.55 times the speed of light (relativistic kinetic energy of ~100 keV). Such velocities are unusual for condensed-matter excitation at the stated laser intensities. PMID:21716461

  20. Simultaneous resonant enhanced multiphoton ionization and electron avalanche ionization in gas mixtures

    SciTech Connect

    Shneider, Mikhail N.; Zhang Zhili; Miles, Richard B.

    2008-07-15

    Resonant enhanced multiphoton ionization (REMPI) and electron avalanche ionization (EAI) are measured simultaneously in Ar:Xe mixtures at different partial pressures of mixture components. A simple theory for combined REMPI+EAI in gas mixture is developed. It is shown that the REMPI electrons seed the avalanche process, and thus the avalanche process amplifies the REMPI signal. Possible applications are discussed.

  1. Photodissociation of methyl iodide at 229. 4 nm: A determination of the fragment recoil anisotropy using energy-selective electron impact ionization and time-of-flight mass spectrometry

    SciTech Connect

    Penn, S.M.; Hayden, C.C.; Carlson Muyskens, K.J.; Crim, F.F.

    1988-09-01

    Energy-selective electron impact ionization of laser-produced photofragments together with time-of-flight mass spectrometry is a general and sensitive means of studying primary photodissociation processes. Low-energy electrons ionize photofragments without the production of background fragment ions from dissociative ionization of the parent molecules, and the time-of-flight mass spectral peak shapes provide direct information on the photofragment recoil anisotropy. In the first application of this combination of techniques, we have studied the photodissociation of methyl iodide at 229.4 nm, the short-wavelength end of the A band, in order to assess the contribution of transitions to the /sup 1/Q/sub 1/ state to the absorption profile. The results presented here show that I(/sup 2/P/sub 1//sub ///sub 2/) is the primary iodine--atom product and that the transition is largely parallel (..beta.. = (1.6 +- 0.1) for I(/sup 2/P/sub 1//sub ///sub 2/)) at 229.4 nm. These data together with previous photofragmentation results suggest that excitation to the /sup 3/Q/sub 0/ state dominates the entire A band absorption profile.

  2. Theoretical electron impact elastic, ionization and total cross sections for silicon hydrides, SiHx (x = 1, 2, 3, 4) and disilane, Si2H6 from threshold to 5 keV

    NASA Astrophysics Data System (ADS)

    Vinodkumar, M.; Limbachiya, C.; Korot, K.; Joshipura, K. N.

    2008-07-01

    In this article we report comprehensive calculations of total elastic (Qel), and total ionization cross sections, (Qion), on silicon hydrides SiHx (x = 1 4) and disilane, Si2H6 on electron impact at energies from circa threshold to 2000 eV and total (complete) cross sections (QT) up to 5 keV. Spherical complex optical potential (SCOP) formalism is employed to evaluate Qel and QT. Total ionization cross sections, Qion, are derived from total inelastic cross sections, Qinel, using our complex spherical potential ionization contribution (CSP-ic) method. Dependence of QT on the dipole polarizability of the target and incident energy is presented for these targets through analytical formula, using which calculation of QT is extended up to 5 keV. Comparison of QT for all these targets is carried out to present a general theoretical picture of collision processes and also to visualize the dependence of QT on the total number of electrons in the target and hence on the geometrical size of the target. Present calculations also provide information on the excitation processes of these targets. Present results are compared with available experimental and other theoretical data wherever available and overall good agreement is observed. There is probably no data for total elastic and total (complete) cross sections for SiHx (x = 2-3) in the present energy range and hence reported for the first time.

  3. Electron Ionization Mass Spectrum of Tellurium Hexafluoride

    SciTech Connect

    Clark, Richard A.; McNamara, Bruce K.; Barinaga, Charles J.; Peterson, James M.; Govind, Niranjan; Andersen, Amity; Abrecht, David G.; Schwantes, Jon M.; Ballou, Nathan E.

    2015-05-18

    The first electron ionization mass spectrum of tellurium hexafluoride (TeF6) is reported. The starting material was produced by direct fluorination of Te metal or TeO2 with nitrogen trifluoride. Formation of TeF6 was confirmed through cryogenic capture of the tellurium fluorination product and analysis through Raman spectroscopy. The eight natural abundance isotopes were observed for each of the set of fragment ions: TeF5+, TeF4+ TeF3+, TeF2+, TeF1+, and Te+, Te2+. A trend in increasing abundance was observed for the even fluoride bearing ions: TeF1+ < TeF3+ < TeF5+, and a decreasing abundance was observed for the even fragment series: Te(0)+ > TeF2+ > TeF4+ > TeF6+, with the molecular ion TeF6+ not observed at all. Density functional theory based electronic structure calculations were used to calculate optimized ground state geometries of these gas phase species and their relative stabilities explain the trends in the data and the lack of observed signal for TeF6+.

  4. Comment on ``Oxygen ionization rates at Mars and Venus: Relative contributions of impact ionization and charge exchange'' by M. H. Zhang, J. G. Luhmann, A. F. Nagy, J. R. Spreiter, and S. S. Stahara

    NASA Astrophysics Data System (ADS)

    Krymskii, A. M.; Breus, T. K.

    The accuracy of estimates of electron impact ionization which are based on the gasdynamic model of the solar wind interaction with Venus is discussed. Employing the hybrid simulations and in situ data on electron temperature or electron fluxes the electron impact ionization is reevaluated. The electron impact ionization rate estimated in this paper is typically 4-8 times less than the value derived from the gasdynamic model Zhang et al. [1993]. During solar maximum the photoionization rate is typically greater than the electron impact ionization rate.

  5. Solid-state impact-ionization multiplier

    NASA Astrophysics Data System (ADS)

    Lee, Hong-Wei

    This dissertation presents an innovative solid-state current amplifier based on impact-ionization. Unlike avalanche photodetectors which use the same amplification principle, this device can be integrated with any external current source. A discrete amplifier was built on a silicon surface using standard CMOS fabrication processes including lithography, oxidation, ion implantation, diffusion, chemical wet etching, metal deposition, annealing, and rapid thermal processing. Testing was performed by connecting the device to a silicon photodiode, indium-gallium-arsenide photodiodes, and a function generator to demonstrate its compatibility with arbitrary current sources. Current gains above 100 along with pre-amplified leakage currents of less than 10 nA were measured. This amplifier can also be cascaded to achieve very high gains similar to the photomultiplier tube but with much smaller size and no vacuum environment required. Testing was done by amplifying the output signal from an external silicon photodiode. Current gains over 600 were measured when two amplifying devices were cascaded. Additionally, the gain saturation phenomenon of the amplifier due to the space-charge effect is investigated. The measured gain saturation is observed to match very well with the theoretical based predictions. We also present a design rule for obtaining high current gain from the cascaded structure without experiencing gain saturation. Initial bandwidth of the SIM when connected to a silicon photodiode was measured to be about 300 kHz. As we replace the photodiode by a function generator, the bandwidth improved to 450 kHz which is the frequency limit of the system. These results were made on the first generation of SIM devices. We discovered that the space-charge resistance Rsc plays a significant role in determining frequency response. In future generations of the device, we can begin with optimizing the device geometry to reduce this resistance. Also, we can reduce the size of the

  6. Treatment of Electronic Energy Level Transition and Ionization Following the Particle-Based Chemistry Model

    NASA Technical Reports Server (NTRS)

    Liechty, Derek S.; Lewis, Mark

    2010-01-01

    A new method of treating electronic energy level transitions as well as linking ionization to electronic energy levels is proposed following the particle-based chemistry model of Bird. Although the use of electronic energy levels and ionization reactions in DSMC are not new ideas, the current method of selecting what level to transition to, how to reproduce transition rates, and the linking of the electronic energy levels to ionization are, to the author s knowledge, novel concepts. The resulting equilibrium temperatures are shown to remain constant, and the electronic energy level distributions are shown to reproduce the Boltzmann distribution. The electronic energy level transition rates and ionization rates due to electron impacts are shown to reproduce theoretical and measured rates. The rates due to heavy particle impacts, while not as favorable as the electron impact rates, compare favorably to values from the literature. Thus, these new extensions to the particle-based chemistry model of Bird provide an accurate method for predicting electronic energy level transition and ionization rates in gases.

  7. Electron- and proton-induced ionization of pyrimidine

    NASA Astrophysics Data System (ADS)

    Champion, Christophe; Quinto, Michele A.; Weck, Philippe F.

    2015-05-01

    The present work describes a quantum-mechanically based model of the electron- and proton-induced ionization of isolated pyrimidine molecules. The impact energies range from the target ionization threshold up to ~1 keV for electrons and from 10 keV up to 10 MeV for protons. The cross-section calculations are performed within the 1st Born approximation in which the ejected electron is described by a Coulomb wave whereas the incident and the scattered projectiles are both described by plane waves. The pyrimidine target is described using the Gaussian 09 software package. The theoretical predictions obtained are in good agreement with experimental absolute total cross sections, while large discrepancies are observed between existing semi-empirical models and the present calculations. Contribution to the Topical Issue "COST Action Nano-IBCT: Nano-scale Processes Behind Ion-Beam Cancer Therapy", edited by Andrey Solov'yov, Nigel Mason, Gustavo García, Eugene Surdutovich.

  8. Theory of steady-state plane tunneling-assisted impact ionization waves

    SciTech Connect

    Kyuregyan, A. S.

    2013-07-15

    The effect of band-to-band and trap-assisted tunneling on the properties of steady-state plane ionization waves in p{sup +}-n-n{sup +} structures is theoretically analyzed. It is shown that such tunneling-assisted impact ionization waves do not differ in a qualitative sense from ordinary impact ionization waves propagating due to the avalanche multiplication of uniformly distributed seed electrons and holes. The quantitative differences of tunneling-assisted impact ionization waves from impact ionization waves are reduced to a slightly different relation between the wave velocity u and the maximum field strength E{sub M} at the front. It is shown that disregarding impact ionization does not exclude the possibility of the existence of tunneling-assisted ionization waves; however, their structure radically changes, and their velocity strongly decreases for the same E{sub M}. A comparison of the dependences u(E{sub M}) for various ionization-wave types makes it possible to determine the conditions under which one of them is dominant. In conclusion, unresolved problems concerning the theory of tunneling-assisted impact ionization waves are discussed and the directions of further studies are outlined.

  9. Electron-impact spectroscopy

    NASA Technical Reports Server (NTRS)

    Trajmar, S.

    1990-01-01

    The methods of electron impact spectroscopy and cross section measurements are discussed and compared to optical spectroscopy. A brief summary of the status of this field and the available data is given.

  10. Angular distribution of Auger electrons due to 3d-shell ionization of krypton

    NASA Technical Reports Server (NTRS)

    Omidvar, K.

    1977-01-01

    Cross sections for electron impact ionization of krypton due to ejection of a 3rd shell electron have been calculated using screened hydrogenic and Hartree-Slater wave functions for target atom. While the total ionization cross sections in the two approximations are within 10% of each other, the Auger electron angular distribution, related to cross sections for specific magnetic quantum numbers of the 3rd electrons, is widely different in the two approximations. The angular distribution due to Hartree-Slater approximation is in excellent agreement with measurement. The physical reason for the discrepancies in the two approximations is explained.

  11. Determination of 5alpha-androst-16-en-3alpha-ol in truffle fermentation broth by solid-phase extraction coupled with gas chromatography-flame ionization detector/electron impact mass spectrometry.

    PubMed

    Wang, Guan; Li, Yuan-Yuan; Li, Dong-Sheng; Tang, Ya-Jie

    2008-07-15

    A novel method using solid-phase extraction coupled with gas chromatography and flame ionization detector (FID)/electron impact mass spectrometry (EIMS) was developed for the determination of 5alpha-androst-16-en-3alpha-ol (androstenol), a steroidal compound belonging to the group of musk odorous 16-androstenes, in truffle fermentation broth. Comparison studies between FID and EIMS indicated two detectors gave similar quantitative results. The highest androstenol concentration of 123.5 ng/mL was detected in Tuber indicum fermentation broth, while no androstenol was found in Tuber aestivum fermentation broth. For the first time, this work confirmed the existence of androstenol in the truffle fermentation broth, which suggested truffle fermentation is a promising alternative for androstenol production on a large scale. PMID:18585987

  12. Differential cross sections for ionization of water vapor by high-velocity bare ions and electrons

    SciTech Connect

    Miller, J.H.; Wilson, W.E.; Manson, S.T.; Rudd, M.E.

    1987-01-01

    A semiempirical model of single differential cross sections (SDCS) for ionization of water vapor by fast electrons and bare ions is presented. At low secondary-electron energy, the model is based on an asymptotic expansion of the first Born approximation with coefficients, that are independent of projectile properties, evaluated from experimental photoabsorption and proton-impact ionization data. As the secondary-electron energy increases, the model converges to a binary-encounter approximation. Comparisons with measured differential, total, and dissociative cross sections for ionization of water by fast electrons are used to test the model. For primary electrons with energy greater than about 500 eV, agreement with these data is generally within experimental uncertainty; however, some discrepancies of uncertain origin exist.

  13. Multielectron transitions resulting from interactions between target and projectile electrons in ionizing collisions

    SciTech Connect

    Manson, S.T. ); DuBois, R.D. )

    1992-12-01

    Interactions between target and projectile electrons leading to ionization of one of the collision partners and simultaneous excitation of the other are investigated for fast clothed-particle--clothed-particle collisions. For H-atom impact, the first Born approximation is used to demonstrate that the low-energy-electron emission is dominated by electron-electron rather than by electron-nucleus interaction processes. For a broad class of structured particle collision systems, the electron-electron interaction is shown to play an important, non-neglibible, role. Doubly differential cross sections for energetic H-He collisions illustrate this point.

  14. Electron-Atom Ionization Calculations using Propagating Exterior Complex Scaling

    NASA Astrophysics Data System (ADS)

    Bartlett, Philip

    2007-10-01

    The exterior complex scaling method (Science 286 (1999) 2474), pioneered by Rescigno, McCurdy and coworkers, provided highly accurate ab initio solutions for electron-hydrogen collisions by directly solving the time-independent Schr"odinger equation in coordinate space. An extension of this method, propagating exterior complex scaling (PECS), was developed by Bartlett and Stelbovics (J. Phys. B 37 (2004) L69, J. Phys. B 39 (2006) R379) and has been demonstrated to provide computationally efficient and accurate calculations of ionization and scattering cross sections over a large range of energies below, above and near the ionization threshold. An overview of the PECS method for three-body collisions and the computational advantages of its propagation and iterative coupling techniques will be presented along with results of: (1) near-threshold ionization of electron-hydrogen collisions and the Wannier threshold laws, (2) scattering cross section resonances below the ionization threshold, and (3) total and differential cross sections for electron collisions with excited targets and hydrogenic ions from low through to high energies. Recently, the PECS method has been extended to solve four-body collisions using time-independent methods in coordinate space and has initially been applied to the s-wave model for electron-helium collisions. A description of the extensions made to the PECS method to facilitate these significantly more computationally demanding calculations will be given, and results will be presented for elastic, single-excitation, double-excitation, single-ionization and double-ionization collisions.

  15. Electron ionization of open/closed chain isocarbonic molecules relevant in plasma processing: Theoretical cross sections

    SciTech Connect

    Patel, Umang R.; Joshipura, K. N.; Pandya, Siddharth H.; Kothari, Harshit N.

    2014-01-28

    In this paper, we report theoretical electron impact ionization cross sections from threshold to 2000 eV for isocarbonic open chain molecules C{sub 4}H{sub 6}, C{sub 4}H{sub 8}, C{sub 4}F{sub 6} including their isomers, and closed chain molecules c-C{sub 4}H{sub 8} and c-C{sub 4}F{sub 8}. Theoretical formalism employed presently, viz., Complex Scattering Potential-ionization contribution method has been used successfully for a variety of polyatomic molecules. The present ionization calculations are very important since results available for the studied targets are either scarce or none. Our work affords comparison of C{sub 4} containing hydrocarbon versus fluorocarbon molecules. Comparisons of the present ionization cross sections are made wherever possible, and new ionization data are also presented.

  16. Ionization by few-cycle pulses: Tracing the electron orbits

    SciTech Connect

    Milosevic, D.B.; Paulus, G.G.; Becker, W.

    2005-06-15

    High-order above-threshold ionization by few-cycle laser pulses is analyzed in terms of quantum orbits. For a given carrier-envelope phase, the number of contributing orbits and their ionization and rescattering times determine the shape of the angle-resolved spectrum in all detail. Conversely, analysis of a given spectrum reveals the carrier-envelope phase and the various interfering pathways from which the electron could choose.

  17. Calculation of total and ionization cross sections for electron scattering by primary benzene compounds

    NASA Astrophysics Data System (ADS)

    Singh, Suvam; Naghma, Rahla; Kaur, Jaspreet; Antony, Bobby

    2016-07-01

    The total and ionization cross sections for electron scattering by benzene, halobenzenes, toluene, aniline, and phenol are reported over a wide energy domain. The multi-scattering centre spherical complex optical potential method has been employed to find the total elastic and inelastic cross sections. The total ionization cross section is estimated from total inelastic cross section using the complex scattering potential-ionization contribution method. In the present article, the first theoretical calculations for electron impact total and ionization cross section have been performed for most of the targets having numerous practical applications. A reasonable agreement is obtained compared to existing experimental observations for all the targets reported here, especially for the total cross section.

  18. Calculation of total and ionization cross sections for electron scattering by primary benzene compounds.

    PubMed

    Singh, Suvam; Naghma, Rahla; Kaur, Jaspreet; Antony, Bobby

    2016-07-21

    The total and ionization cross sections for electron scattering by benzene, halobenzenes, toluene, aniline, and phenol are reported over a wide energy domain. The multi-scattering centre spherical complex optical potential method has been employed to find the total elastic and inelastic cross sections. The total ionization cross section is estimated from total inelastic cross section using the complex scattering potential-ionization contribution method. In the present article, the first theoretical calculations for electron impact total and ionization cross section have been performed for most of the targets having numerous practical applications. A reasonable agreement is obtained compared to existing experimental observations for all the targets reported here, especially for the total cross section. PMID:27448889

  19. Theory of hole initiated impact ionization in bulk zincblende and wurtzite GaN

    NASA Astrophysics Data System (ADS)

    Oǧuzman, Ismail H.; Bellotti, Enrico; Brennan, Kevin F.; Kolník, Ján; Wang, Rongping; Ruden, P. Paul

    1997-06-01

    In this article, the first calculations of hole initiated interband impact ionization in bulk zincblende and wurtzite phase GaN are presented. The calculations are made using an ensemble Monte Carlo simulation including the full details of all of the relevant valence bands, derived from an empirical pseudopotential approach, for each crystal type. The model also includes numerically generated hole initiated impact ionization transition rates, calculated based on the pseudopotential band structure. The calculations predict that both the average hole energies and ionization coefficients are substantially higher in the zincblende phase than in the wurtzite phase. This difference is attributed to the higher valence band effective masses and equivalently higher effective density of states found in the wurtzite polytype. Furthermore, the hole ionization coefficient is found to be comparable to the previously calculated electron ionization coefficient in zincblende GaN at an applied electric field strength of 3 MV/cm. In the wurtzite phase, the electron and hole impact ionization coefficients are predicted to be similar at high electric fields, but at lower fields, the hole ionization rate appears to be greater.

  20. Electron impact excitation coefficients for laboratory and astrophysical plasmas

    NASA Technical Reports Server (NTRS)

    Davis, J.; Kepple, P. C.; Blaha, M.

    1976-01-01

    Electron impact excitation rate coefficients have been obtained for a number of transitions in highly ionized ions of interest to astrophysical and laboratory plasmas. The calculations were done using the method of distorted waves. Results are presented for various transitions in highly ionized Ne, Na, Al, Si, A, Ca, Ni and Fe.

  1. Electron ionization and dissociation of aliphatic amino acids

    NASA Astrophysics Data System (ADS)

    Papp, P.; Shchukin, P.; Kočíšek, J.; Matejčík, Š.

    2012-09-01

    We present experimental and theoretical study of electron ionization and dissociative ionization to the gas phase amino acids valine, leucine, and isoleucine. A crossed electron/molecular beams technique equipped with quadrupole mass analyzer has been applied to measure mass spectra and ion efficiency curves for formation of particular ions. From experimental data the ionization energies of the molecules and the appearance energies of the fragment ions were determined. Ab initio calculations (Density Functional Theory and G3MP2 methods) were performed in order to calculate the fragmentation paths and interpret the experimental data. The experimental ionization energies of parent molecules [P]+ 8.91 ± 0.05, 8.85 ± 0.05, and 8.79 ± 0.05 eV and G3MP2 ionization energies (adiabatic) of 8.89, 8.88, and 8.81 eV were determined for valine, leucine, and isoleucine, respectively, as well as the experimental and theoretical threshold energies for dissociative ionization channels. The comparison of experimental data with calculations resulted in identification of the ions as well as the neutral fragments formed in the dissociative reactions. Around 15 mass/charge ratio fragments were identified from the mass spectra by comparison of experimental appearance energies with calculated reaction enthalpies for particular dissociative reactions.

  2. Ionization, electron attachment, and drift in CHF3.

    PubMed

    de Urquijo, J; Alvarez, I; Cisneros, C

    1999-10-01

    Using a pulsed Townsend technique, we have measured the effective ionization coefficient and the electron drift velocities in CHF(3). The density-normalized electric field intensity E/N ranged from 4 to 250 townsends (Td) (1 Td=10(-17) V cm(2)). The E/N value at which the effective ionization coefficient becomes zero was estimated to be 66 Td. For E/N<20 Td, the electron attachment coefficients are practically constant, and are compatible to within about +/-70% with previously measured values at thermal energies and above. PMID:11970373

  3. Multiple ionization of atomic targets by proton impact

    SciTech Connect

    Toburen, L.H.; DuBois, R.D.; Manson, S.T.

    1982-10-01

    We have combined experimental measurements of multiply charged ion production, doubly differential electron emission cross sections and Auger electron spectra produced in fast proton noble-gas collisions with theoretical inner and outer shell ionization cross sections in an effort to provide a consistent description of the ionization process. A detailed analysis is provided for 1-4 MeV proton ionization of krypton. Our measured relative yields of Kr/sup +2/ and Kr/sup +3/ ions are in approximate agreement with photoionization results of Krause and Carlson. If we assume nearly half of the 3d vacancies created in Kr are filled through multiple (3 dNNN) Auger transitions, the M-subshell ionization cross sections that we derive from our Auger electron spectra are in good agreement with theoretical calculations. The absolute yields of Kr/sup +2/ and Kr/sup +3/ are, however, a factor of 2 smaller than the calculated values.

  4. Two-electron ionization and stabilization beyond the dipole approximation

    SciTech Connect

    Staudt, Andreas; Keitel, Christoph H.

    2006-04-15

    A two-dimensional model atom is employed to study the ionization behavior of helium subjected to strong laser fields in the high-frequency regime. The evolution of the system is studied by means of numerical integration of the Schroedinger equation beyond the dipole approximation. Ionization probabilities of the two-electron atom in highly intense laser fields have been calculated for different pulse shapes. It is confirmed that the mutual repulsion between the two electrons as well as the length of the laser pulses significantly alter the ionization probabilities of the system. Nondipole effects are shown to lead to a considerable increase of the ionization probabilities. For certain laser pulse shapes, a regime of ionization suppression is investigated which exists in addition to two-electron stabilization. The applicability of our model scheme to the case of heliumlike systems is discussed, and it is shown that stabilization may also occur in these systems, and how it is altered in dependence of the nuclear charge.

  5. Observation of Impact Ionization of Shallow States in Sub-Kelvin, High-Purity Germanium

    NASA Astrophysics Data System (ADS)

    Phipps, A.; Sadoulet, B.; Sundqvist, K. M.

    2016-01-01

    We report on the observation of impact ionization processes involving shallow impurity states in a sub-Kelvin, high-purity n-type germanium detector similar to those used by direct detection dark matter experiments such as the Cryogenic Dark Matter Search. An optical fiber is used to generate packets of charge carriers near one surface of the detector. The charge carriers drift to the opposite surface by application of an electric field. The resulting drift current is measured by a high-speed charge amplifier. The onset of impact ionization for both electron and hole transport is clearly observed in the drift current as the applied electric field is increased above ≈ 5 V/cm. We present the effective charge collection efficiency and trapping length as a function of applied electric field for electrons and holes. We estimate the impact ionization cross section to be on the order of 5× 10^{-13} {cm}^2.

  6. Observation of Impact Ionization of Shallow States in Sub-Kelvin, High-Purity Germanium

    NASA Astrophysics Data System (ADS)

    Phipps, A.; Sadoulet, B.; Sundqvist, K. M.

    2016-07-01

    We report on the observation of impact ionization processes involving shallow impurity states in a sub-Kelvin, high-purity n-type germanium detector similar to those used by direct detection dark matter experiments such as the Cryogenic Dark Matter Search. An optical fiber is used to generate packets of charge carriers near one surface of the detector. The charge carriers drift to the opposite surface by application of an electric field. The resulting drift current is measured by a high-speed charge amplifier. The onset of impact ionization for both electron and hole transport is clearly observed in the drift current as the applied electric field is increased above ≈ 5 V/cm. We present the effective charge collection efficiency and trapping length as a function of applied electric field for electrons and holes. We estimate the impact ionization cross section to be on the order of 5× 10^{-13} mathrm {cm}^2.

  7. Observation of Impact Ionization of Shallow States in Sub-Kelvin, High-Purity Germanium

    NASA Astrophysics Data System (ADS)

    Phipps, A.; Sadoulet, B.; Sundqvist, K. M.

    2016-07-01

    We report on the observation of impact ionization processes involving shallow impurity states in a sub-Kelvin, high-purity n-type germanium detector similar to those used by direct detection dark matter experiments such as the Cryogenic Dark Matter Search. An optical fiber is used to generate packets of charge carriers near one surface of the detector. The charge carriers drift to the opposite surface by application of an electric field. The resulting drift current is measured by a high-speed charge amplifier. The onset of impact ionization for both electron and hole transport is clearly observed in the drift current as the applied electric field is increased above ≈ 5 V/cm. We present the effective charge collection efficiency and trapping length as a function of applied electric field for electrons and holes. We estimate the impact ionization cross section to be on the order of 5× 10^{-13} {cm}^2.

  8. Characteristics of tunneling and impact ionization in ZnS:Mn-based thin-film electroluminescent structures

    SciTech Connect

    Gurin, N. T. Sabitov, O. Yu.; Afanas'ev, A. M.

    2007-10-15

    A method for measuring the characteristics of tunneling and impact ionization in thin-film electroluminescent emitters is suggested. This method makes it possible to find time dependences of the space-charge layer thickness near the anode and the length of the impact ionization region, to determine more exactly the time dependence of the field in the potential barrier at the cathode interface, the maximum depth of the surface states from which electron tunneling occurs, the minimum thickness of the barrier, and the electron tunneling probability, as well as the impact ionization rate for the deep centers related to structural defects of the phosphor layer.

  9. Target electron ionization in Li2+-Li collisions: A multi-electron perspective

    NASA Astrophysics Data System (ADS)

    Śpiewanowski, M. D.; Gulyás, L.; Horbatsch, M.; Goullon, J.; Ferreira, N.; Hubele, R.; de Jesus, V. L. B.; Lindenblatt, H.; Schneider, K.; Schulz, M.; Schuricke, M.; Song, Z.; Zhang, S.; Fischer, D.; Kirchner, T.

    2015-04-01

    Target electron removal in Li2+-Li collisions at 2290 keV/amu is studied experimentally and theoretically for ground and excited lithium target configurations. It is shown that in outer-shell ionization a single-electron process plays the dominant part. However, the K-shell ionization results are more difficult to interpret. According to our calculations, the process is shown to be strongly single-particle like. On one hand, a high resemblance between theoretical single-particle ionization and exclusive inner-shell ionization is demonstrated, and contributions from multi-electron processes are found to be weak. On the other hand, it is indicated by the discrepancy between experimental and single-particle theoretical results that multi-electron processes involving ionization from the outer-shell may play a crucial role.

  10. Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization.

    PubMed

    Neustetter, M; Jabbour Al Maalouf, E; Limão-Vieira, P; Denifl, S

    2016-08-01

    Electron ionization of neat tungsten hexacarbonyl (W(CO)6) clusters has been investigated in a crossed electron-molecular beam experiment coupled with a mass spectrometer system. The molecule is used for nanofabrication processes through electron beam induced deposition and ion beam induced deposition techniques. Positive ion mass spectra of W(CO)6 clusters formed by electron ionization at 70 eV contain the ion series of the type W(CO)n (+) (0 ≤ n ≤ 6) and W2(CO)n (+) (0 ≤ n ≤ 12). In addition, a series of peaks are observed and have been assigned to WC(CO)n (+) (0 ≤ n ≤ 3) and W2C(CO)n (+) (0 ≤ n ≤ 10). A distinct change of relative fragment ion intensity can be observed for clusters compared to the single molecule. The characteristic fragmentation pattern obtained in the mass spectra can be explained by a sequential decay of the ionized organometallic, which is also supported by the study of the clusters when embedded in helium nanodroplets. In addition, appearance energies for the dissociative ionization channels for singly charged ions have been estimated from experimental ion efficiency curves. PMID:27497555

  11. Fragmentation pathways of tungsten hexacarbonyl clusters upon electron ionization

    NASA Astrophysics Data System (ADS)

    Neustetter, M.; Jabbour Al Maalouf, E.; Limão-Vieira, P.; Denifl, S.

    2016-08-01

    Electron ionization of neat tungsten hexacarbonyl (W(CO)6) clusters has been investigated in a crossed electron-molecular beam experiment coupled with a mass spectrometer system. The molecule is used for nanofabrication processes through electron beam induced deposition and ion beam induced deposition techniques. Positive ion mass spectra of W(CO)6 clusters formed by electron ionization at 70 eV contain the ion series of the type W(CO)n+ (0 ≤ n ≤ 6) and W2(CO)n+ (0 ≤ n ≤ 12). In addition, a series of peaks are observed and have been assigned to WC(CO)n+ (0 ≤ n ≤ 3) and W2C(CO)n+ (0 ≤ n ≤ 10). A distinct change of relative fragment ion intensity can be observed for clusters compared to the single molecule. The characteristic fragmentation pattern obtained in the mass spectra can be explained by a sequential decay of the ionized organometallic, which is also supported by the study of the clusters when embedded in helium nanodroplets. In addition, appearance energies for the dissociative ionization channels for singly charged ions have been estimated from experimental ion efficiency curves.

  12. Two-center approach to fully differential positron-impact ionization of hydrogen

    NASA Astrophysics Data System (ADS)

    Kadyrov, A. S.; Bailey, J. J.; Bray, I.; Stelbovics, A. T.

    2014-01-01

    The two-center approach to positron-impact ionization of atomic hydrogen is shown to follow from the exact post form of the breakup amplitude [Kadyrov, Bray, Mukhamedzhanov, and Stelbovics, Phys. Rev. Lett. 101, 230405 (2008), 10.1103/PhysRevLett.101.230405]. In such approaches distinct ionization amplitudes arise from each center for the same ionization process. The fully differential cross section for the positron-impact breakup of atomic hydrogen is calculated including direct ionization of the target and electron capture into the positronium continuum. We show that the coherent combination of the amplitudes leads to oscillations in the differential cross sections, whereas the incoherent combination does not. The latter has also the advantage of being consistent with the unitary close-coupling formalism.

  13. Interference in above-threshold-ionization electron distributions from molecules

    SciTech Connect

    Henkel, Jost; Lein, Manfred; Engel, Volker

    2011-05-15

    We present quantum-mechanical studies on above-threshold ionization of molecular ions in two and three dimensions. The momentum distributions show signatures of interfering emissions from the molecular centers. These structures deviate from a simple double-slit model that ignores the electron-ion interaction, but they are reproduced by an eikonal model. Such distortions of the interference pattern are partly responsible for the absence of clear interference patterns in the angle-integrated electron energy spectra.

  14. Improved atomic data for electron-transport predictions by the codes TIGER and TIGERP. I. Inner-shell ionization by electron collision

    SciTech Connect

    Peek, J.M.; Halbleib, J.A.

    1983-01-01

    The inner-shell ionization data for electron-target collisions now in use in the TIGER and TIGERP electron-transport codes are extracted and compared with other data for these processes. The TIGER cross sections for K-shell ionization by electron collisions are found to be seriously in error for large-Z targets and incident electron energies greater than 1 MeV. A series of TIGER and TIGERP runs were carried out with and without improved K-shell electron ionization cross section data replacing that now in use. The relative importance of electron-impact and photon ionization of the various subshells was also extracted from these runs. In general, photon ionization dominated in the examples studied so the sensitivity of many predicted properties to errors in the electron-impact subshell ionization data was not large. However, some differences were found and, as all possible applications were not covered in this study, it is recommended that these electron-impact data now in TIGER and TIGERP be replaced. Cross section data for the processes under study are reviewed and those that are most suitable for this application are identified. 19 references, 9 figures, 2 tables.

  15. Inelastic electron interaction (attachment/ionization) with deoxyribose

    NASA Astrophysics Data System (ADS)

    Ptasińska, S.; Denifl, S.; Scheier, P.; Märk, T. D.

    2004-05-01

    We have investigated experimentally the formation of anions and cations of deoxyribose sugar (C5H10O4) via inelastic electron interaction (attachment/ionization) using a monochromatic electron beam in combination with a quadrupole mass spectrometer. The ion yields were measured as a function of the incident electron energy between about 0 and 20 eV. As in the case of other biomolecules (nucleobases and amino acids), low energy electron attachment leads to destruction of the molecule via dissociative electron attachment reactions. In contrast to the previously investigated biomolecules dehydrogenation is not the predominant reaction channel for deoxyribose; the anion with the highest dissociative electron attachment (DEA) cross section of deoxyribose is formed by the release of neutral particles equal to two water molecules. Moreover, several of the DEA reactions proceed already with "zero energy" incident electrons. In addition, the fragmentation pattern of positively charged ions of deoxyribose also indicates strong decomposition of the molecule by incident electrons. For sugar the relative amount of fragment ions compared to that of the parent cation is about an order of magnitude larger than in the case of nucleobases. We determined an ionization energy value for C5H10O4+ of 10.51±0.11 eV, which is in good agreement with ab initio calculations. For the fragment ion C5H6O2+ we obtained a threshold energy lower than the ionization energy of the parent molecular ion. All of these results have important bearing for the question of what happens in exposure of living tissue to ionizing radiation. Energy deposition into irradiated cells produces electrons as the dominant secondary species. At an early time after irradiation these electrons exist as ballistic electrons with an initial energy distribution up to several tens of electron volts. It is just this energy regime for which we find in the present study rather characteristic differences in the outcome of electron

  16. Ionization-Induced Electron Trapping inUltrarelativistic Plasma Wakes

    SciTech Connect

    Oz, E.; Deng, S.; Katsouleas, T.; Muggli, P.; Barnes, C.D.; Blumenfeld, I.; Decker, F.J.; Emma, P.; Hogan, M.J.; Ischebeck, R.; Iverson, R.H.; Kirby, N.; Krejcik, P.; O'Connell, C.; Siemann, R.H.; Walz, D.; Auerbach, D.; Clayton, C.E.; Huang, C.; Johnson, D.K.; Joshi, C.; /UCLA

    2007-04-06

    The onset of trapping of electrons born inside a highly relativistic, 3D beam-driven plasma wake is investigated. Trapping occurs in the transition regions of a Li plasma confined by He gas. Li plasma electrons support the wake, and higher ionization potential He atoms are ionized as the beam is focused by Li ions and can be trapped. As the wake amplitude is increased, the onset of trapping is observed. Some electrons gain up to 7.6 GeV in a 30.5 cm plasma. The experimentally inferred trapping threshold is at a wake amplitude of 36 GV/m, in good agreement with an analytical model and PIC simulations.

  17. Positron impact ionization of atomic hydrogen

    SciTech Connect

    Acacia, P.; Campeanu, R.I.; Horbatsch, M.

    1993-05-01

    We will present integrated cross sections for ionization of atomic hydrogen by positrons. These have been calculated in a distorted-wave approximation using energy-dependent effective charges in the final channel as well as static and polarization potentials in the initial channel. We present two models for calculating the energy-dependent effective charges both of which produce results in good agreement with the recent experimental measurements of Spicher et al. This is in contrast to previous distorted-wave calculations which used fixed effective charges as well as classical trajectory calculations. Both of these latter methods produced results which were substantially below ours and the experimental data.

  18. Integral elastic, electronic-state, ionization, and total cross sections for electron scattering with furfural

    NASA Astrophysics Data System (ADS)

    Jones, D. B.; da Costa, R. F.; Varella, M. T. do N.; Bettega, M. H. F.; Lima, M. A. P.; Blanco, F.; García, G.; Brunger, M. J.

    2016-04-01

    We report absolute experimental integral cross sections (ICSs) for electron impact excitation of bands of electronic-states in furfural, for incident electron energies in the range 20-250 eV. Wherever possible, those results are compared to corresponding excitation cross sections in the structurally similar species furan, as previously reported by da Costa et al. [Phys. Rev. A 85, 062706 (2012)] and Regeta and Allan [Phys. Rev. A 91, 012707 (2015)]. Generally, very good agreement is found. In addition, ICSs calculated with our independent atom model (IAM) with screening corrected additivity rule (SCAR) formalism, extended to account for interference (I) terms that arise due to the multi-centre nature of the scattering problem, are also reported. The sum of those ICSs gives the IAM-SCAR+I total cross section for electron-furfural scattering. Where possible, those calculated IAM-SCAR+I ICS results are compared against corresponding results from the present measurements with an acceptable level of accord being obtained. Similarly, but only for the band I and band II excited electronic states, we also present results from our Schwinger multichannel method with pseudopotentials calculations. Those results are found to be in good qualitative accord with the present experimental ICSs. Finally, with a view to assembling a complete cross section data base for furfural, some binary-encounter-Bethe-level total ionization cross sections for this collision system are presented.

  19. Integral elastic, electronic-state, ionization, and total cross sections for electron scattering with furfural.

    PubMed

    Jones, D B; da Costa, R F; Varella, M T do N; Bettega, M H F; Lima, M A P; Blanco, F; García, G; Brunger, M J

    2016-04-14

    We report absolute experimental integral cross sections (ICSs) for electron impact excitation of bands of electronic-states in furfural, for incident electron energies in the range 20-250 eV. Wherever possible, those results are compared to corresponding excitation cross sections in the structurally similar species furan, as previously reported by da Costa et al. [Phys. Rev. A 85, 062706 (2012)] and Regeta and Allan [Phys. Rev. A 91, 012707 (2015)]. Generally, very good agreement is found. In addition, ICSs calculated with our independent atom model (IAM) with screening corrected additivity rule (SCAR) formalism, extended to account for interference (I) terms that arise due to the multi-centre nature of the scattering problem, are also reported. The sum of those ICSs gives the IAM-SCAR+I total cross section for electron-furfural scattering. Where possible, those calculated IAM-SCAR+I ICS results are compared against corresponding results from the present measurements with an acceptable level of accord being obtained. Similarly, but only for the band I and band II excited electronic states, we also present results from our Schwinger multichannel method with pseudopotentials calculations. Those results are found to be in good qualitative accord with the present experimental ICSs. Finally, with a view to assembling a complete cross section data base for furfural, some binary-encounter-Bethe-level total ionization cross sections for this collision system are presented. PMID:27083717

  20. Photo-triggering and secondary electron produced ionization in electric discharge ArF* excimer lasers

    NASA Astrophysics Data System (ADS)

    Xiong, Zhongmin; Kushner, Mark J.

    2011-10-01

    Electric discharge excimer lasers are sustained in multi-atmosphere attaching gas mixtures that are typically preionized to enable a reproducible, uniform glow, which maximizes optical quality and gain. This preionization is often accomplished using UV light produced by a corona discharge within the plasma cavity. To quantify the relationship between corona discharge properties and those of the laser discharge, the triggering of electron avalanche by preionizing UV light in an electric discharge-pumped ArF* excimer laser was numerically investigated using a two-dimensional model. The preionizing UV fluxes were generated by a corona-bar discharge driven by the same voltage pulse as the main discharge sustained in a multi-atmospheric Ne/Ar/Xe/F2 gas mixture. The resulting peak photo-electron density in the inter-electrode spacing is around 108 cm-3, and its distribution is biased toward the UV source. The preionization density increases with increasing dielectric constant and capacitance of the corona bar. The symmetry and uniformity of the discharge are, however, improved significantly once the main avalanche develops. In addition to bulk electron impact ionization, the ionization generated by sheath accelerated secondary electrons was found to be important in sustaining the discharge current at experimentally observed values. At peak current, the magnitude of the ionization by sheath accelerated electrons is comparable to that from bulk electron impact in the vicinity of the cathode.

  1. Dynamical orientation effects in atomic ionization by impact of protons and positrons

    NASA Astrophysics Data System (ADS)

    Fregenal, Daniel; Barrachina, Raúl; Bernardi, Guillermo; Suárez, Sergio; Fiol, Juan

    2011-10-01

    Recent results in ionization collisions with positrons and protons showed that just above the two-body threshold, for electron velocities close to the final projectile's velocity, the electron-projectile continuum dipole is narrowly oriented along the direction of motion of its centre-of-mass, with the negative charge pointing towards the residual target. Although a forward-backward asymmetry in the vicinity of the two-body threshold has been studied many year ago in ion impact ionization collisions, that was by far a much milder effect that left no fingerprint on the cusp position. Our results show that the phenomena is present for ionization by impact of both protons and positrons. In this communication, through measurements on H+ + He and calculations we analyze in detail this effect that can be linked to a dynamical alignment of the two-body subsystem in the continuum. Recent results in ionization collisions with positrons and protons showed that just above the two-body threshold, for electron velocities close to the final projectile's velocity, the electron-projectile continuum dipole is narrowly oriented along the direction of motion of its centre-of-mass, with the negative charge pointing towards the residual target. Although a forward-backward asymmetry in the vicinity of the two-body threshold has been studied many year ago in ion impact ionization collisions, that was by far a much milder effect that left no fingerprint on the cusp position. Our results show that the phenomena is present for ionization by impact of both protons and positrons. In this communication, through measurements on H+ + He and calculations we analyze in detail this effect that can be linked to a dynamical alignment of the two-body subsystem in the continuum. This work was partially supported by the Consejo Nacional de Investigaciones Cientificas y Tecnicas, Universidad Nacional de Cuyo and Fundacion Balseiro.

  2. Impact ionization across the conduction-band-edge discontinuity of quantum-well heterostructures

    NASA Technical Reports Server (NTRS)

    Chuang, S. L.; Hess, K.

    1986-01-01

    Impact ionization across the band-edge discontinuity of quantum-well heterostructures is studied theoretically. A heterolayer structure of alternating Al(x)Ga(1-x)As and GaAs layers is considered where the GaAs layers are heavily doped with donors. Thus a large number of electrons is confined to the quantum-well region. Incident electrons are heated up by applied electric fields and collide with the electrons confined in the well regions. Both the ionization rate as a function of the incident energy, and average ionization rates are computed. Device applications of such multiple quantum-well structures and the possibility of a complete analog to the conventional photomultiplier are discussed.

  3. Three component plasma electron distribution in the intermediate ionized coma of Comet Giacobini-Zinner

    NASA Astrophysics Data System (ADS)

    Zwickl, R. D.; Baker, D. N.; Bame, S. J.; Feldman, W. C.; Fuselier, S. A.; Huebner, W. F.; McComas, D. J.; Young, D. T.

    1986-04-01

    The observation of three distinct components of the electron distribution function measured in the intermediate ionized coma (IIC) and plasma tail of Comet Giacobini-Zinner is reported. It is believed that the cold component represents electrons produced close to the comet nucleus by ionization of cometary matter and subsequent cooling by Coulomb collisions. The second component also appears to be composed of electrons produced by photoionization of cometary neutrals, but sufficiently far from the nucleus that the distributions are largely unaffected by Coulomb interactions. The hot component is probably a population of electrons originating in the solar wind. Throughout the IIC, the electrostatic potential of the spacecraft was very low (less than 0.8 eV), implying that ICE generated very little impact-produced plasma during its passage.

  4. Reversal electron attachment ionizer for detection of trace species

    NASA Technical Reports Server (NTRS)

    Bernius, Mark T. (Inventor); Chutjian, Ara (Inventor)

    1990-01-01

    An in-line reversal electron, high-current ionizer capable of focusing a beam of electrons to a reversal region and executing a reversal of said electrons, such that the electrons possess zero kinetic energy at the point of reversal, may be used to produce both negative and positive ions. A sample gas is introduced at the point of electron reversal for low energy electron-(sample gas) molecule attachment with high efficiency. The attachment process produces negative ions from the sample gas, which includes species present in trace (minute) amounts. These ions are extracted efficiently and directed to a mass analyzer where they may be detected and identified. The generation and detection of positive ions is accomplished in a similar fashion with minimal adjustment to potentials applied to the apparatus.

  5. Multiplexed electronically programmable multimode ionization detector for chromatography

    DOEpatents

    Wise, M.B.; Buchanan, M.V.

    1988-05-19

    Method and apparatus for detecting and differentiating organic compounds based on their electron affinity. An electron capture detector cell (ECD) is operated in a plurality of multiplexed electronically programmable operating modes to alter the detector response during a single sampling cycle to acquire multiple simultaneous chromatograms corresponding to each of the different operating modes. The cell is held at a constant subatmospheric pressure while the electron collection bias voltage applied to the cell is modulated electronically to allow acquisition of multiple chromatograms for a single sample elution from a chromatograph representing three distinctly different response modes. A system is provided which automatically controls the programmed application of bias pulses at different intervals and/or amplitudes to switch the detector from an ionization mode to the electron capture mode and various degrees therebetween to provide an improved means of tuning an ECD for multimode detection and improved specificity. 6 figs.

  6. Implementation of the external complex scaling method in spheroidal coordinates: Impact ionization of molecular hydrogen

    SciTech Connect

    Serov, Vladislav V.; Joulakian, Boghos B.

    2009-12-15

    We develop an ab initio procedure based on the driven Schroedinger equation formalism and the external complex scaling method for the determination of the multifold differential cross sections of the single and double ionization of molecular hydrogen by single photon and fast electron impact. We take advantage of the separability of the two-center Schrodinger equation in prolate spheroidal coordinates in the numerical calculation of the two-electron two-center wave function of the initial and final states of the target. After having verified our procedure by reproducing existing confirmed triple differential cross sections of the (e,2e) ionization of H{sub 2}, we have extended our calculation to the double ionization of H{sub 2}. Our results on double photoionization agree with existing experimental results. We observe in the mean time a small difference with respect to the absolute results obtained by similar ab initio calculations using spherical bases. For the case of the double ionization by fast electron impact for which very few experimental results exist, our results confirm the existing disagreement between the theoretical results and the unique experimental one in the case of (e,3-1e). This we think makes it clear that for (e,3e) the introduction of the higher terms of the Born series for mean energy electron-impact regime is necessary.

  7. Target electron ionization in Li2+-Li collisions: A multi-electron perspective

    NASA Astrophysics Data System (ADS)

    Śpiewanowski, M. D.; Gulyás, L.; Horbatsch, M.; Kirchner, T.

    2015-05-01

    The recent development of the magneto-optical trap reaction-microscope has opened a new chapter for detailed investigations of charged-particle collisions from alkali atoms. It was shown that energy-differential cross sections for ionization from the outer-shell in O8+-Li collisions at 1500 keV/amu can be readily explained with the single-active-electron approximation. Understanding of K-shell ionization, however, requires incorporating many-electron effects. An ionization-excitation process was found to play an important role. We present a theoretical study of target electron removal in Li2+-Li collisions at 2290 keV/amu. The results indicate that in outer-shell ionization a single-electron process plays the dominant part. However, the K-shell ionization results are more difficult to interpret. On one hand, we find only weak contributions from multi-electron processes. On the other hand, a large discrepancy between experimental and single-particle theoretical results indicate that multi-electron processes involving ionization from the outer shell may be important for a complete understanding of the process. Work supported by NSERC, Canada and the Hungarian Scientific Research Fund.

  8. Multiple ionization of atomic targets by proton impact

    SciTech Connect

    Toburen, L.H.; DuBois, R.D.; Manson S.T.

    1983-04-01

    The authors have combined experimental measurements of multiply charged ion production, doubly differential electron emission cross sections and Auger electron spectra produced in fast-proton noble-gas collisions with theoretical inner and outer shell ionization cross sections in an effort to provide a unified description of the ionization process. A detailed analysis is provided for 1-4 MeV proton ionization of krypton. Measured relative yields of Kr/sup +2/ and Kr/sup +3/ ions are in approximate agreement with the photoionization results of Krause and Carlson. If it is assumed that nearly half of the 3d vacancies created in Kr are filled through multiple (3dNNN) Auger transitions, the M-subshell ionization cross sections that are derived from Auger electron spectra are in good agreement with theoretical calculations. The measured absolute yields of Kr/sup +2/ and Kr/sup +3/ are, however, a factor of 2 smaller than those derived from the decay of inner shell vacancies. This discrepancy leads the authors to believe that multiple ionization in the intial interaction is a significant contribution to the observed yields.

  9. Multiplexed electronically programmable multimode ionization detector for chromatography

    DOEpatents

    Wise, Marcus B.; Buchanan, Michelle V.

    1989-01-01

    Method and apparatus for detecting and differentiating organic compounds based on their electron affinity. An electron capture detector cell (ECD) is operated in a plurality of multiplexed electroncially programmable operating modes to alter the detector response during a single sampling cycle to acquire multiple simultaneous chromatograms corresponding to each of the different operating modes. The cell is held at a constant subatmospheric pressure while the electron collection bias voltage applied to the cell is modulated electronically to allow acquisition of multiple chromatograms for a single sample elution from a chromatograph representing three distinctly different response modes. A system is provided which automatically controls the programmed application of bias pulses at different intervals and/or amplitudes to switch the detector from an ionization mode to the electron capture mode and various degrees therebetween to provide an improved means of tuning an ECD for multimode detection and improved specificity.

  10. Electron-impact ionization of atomic hydrogen

    SciTech Connect

    Baertschy, Mark D.

    2000-02-14

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

  11. Photo-ionization and residual electron effects in guided streamers

    SciTech Connect

    Wu, S.; Lu, X. Liu, D.; Yang, Y.; Pan, Y.; Ostrikov, K.

    2014-10-15

    Complementary experiments and numerical modeling reveal the important role of photo-ionization in the guided streamer propagation in helium-air gas mixtures. It is shown that the minimum electron concentration ∼10{sup 8 }cm{sup −3} is required for the regular, repeated propagation of the plasma bullets, while the streamers propagate in the stochastic mode below this threshold. The stochastic-to-regular mode transition is related to the higher background electron density in front of the propagating streamers. These findings help improving control of guided streamer propagation in applications from health care to nanotechnology and improve understanding of generic pre-breakdown phenomena.

  12. Impact ionization in GaAs: A screened exchange density-functional approach

    SciTech Connect

    Picozzi, S.; Asahi, R.; Geller, C. B.; Continenza, A.; Freeman, A. J.

    2001-08-13

    Results are presented of a fully ab initio calculation of impact ionization rates in GaAs within the density functional theory framework, using a screened-exchange formalism and the highly precise all-electron full-potential linearized augmented plane wave method. The calculated impact ionization rates show a marked orientation dependence in k space, indicating the strong restrictions imposed by the conservation of energy and momentum. This anisotropy diminishes as the impacting electron energy increases. A Keldysh type fit performed on the energy-dependent rate shows a rather soft edge and a threshold energy greater than the direct band gap. The consistency with available Monte Carlo and empirical pseudopotential calculations shows the reliability of our approach and paves the way to ab initio calculations of pair production rates in new and more complex materials.

  13. Neutral cloud theory of the Jovian nebula: Anomalous ionization effect of superthermal electrons

    NASA Technical Reports Server (NTRS)

    Barbosa, D. D.

    1994-01-01

    The standard model of the Jovian nebula postulates that its particle source is the extended cloud of neutral sulfur and oxygen atoms that escape from the satellite Io and become ionized through electron impact from the corotating plasma. Its energy source is the gyroenergy acquired by newly formed pickup ions as they are swept up to corotation velocity by the planetary magnetic field. Elastic collisions between plasma ions and electrons cool the ions and heat the electrons, while inelastic collisions cool the electrons and excite the ions to radiate intense line emission, which is the primary energy-loss mechanism for the plasma. This neutral cloud theory of the Io plasma torus, as it has come to be known, has been the subject of recent critcism which asserts that the theory cannot account for the observed charge state of the plasma which features O(+) and S(2+) as the dominant ions. It is shown in this work that the inclusion of a small population of super-thermal electrons is required to achieve the correct ion partitioning among various charge states. It is also argued that the anomalous ionization effect of the superthermal electrons is responsible for the overall spatial bifurcation of the nebula into a hot multiply charged plasma region outside of 5.7 Jovian radii and a cool singly ionized plasma inside this distance.

  14. Impact ionization in AlxGa1-xAsySb1-y avalanche photodiodes

    NASA Astrophysics Data System (ADS)

    Grzesik, M.; Donnelly, J.; Duerr, E.; Manfra, M.; Diagne, M.; Bailey, R.; Turner, G.; Goodhue, W.

    2014-04-01

    Avalanche photodiodes (APDs) have been fabricated in order to determine the impact ionization coefficients of electrons (α) and holes (β) in AlxGa1-xAsySb1-y lattice matched to GaSb for three alloy compositions: (x = 0.40, y = 0.035), (x = 0.55, y = 0.045), and (x = 0. 65, y = 0.054). The impact ionization coefficients were calculated from photomultiplication measurements made on specially designed APDs, which allowed for both pure electron and pure hole injection in the same device. Photo-multiplication measurements were made at temperatures ranging from 77 K to 300 K for all three alloys. A quasi-physical model with an explicit temperature dependence was used to express the impact ionization coefficients as a function of electric-field strength and temperature. For all three alloys, it was found that α < β at any given temperature. In addition, the values of the impact ionization coefficients were found to decrease as the aluminum concentration of the AlGaAsSb alloy was increased. A value between 1.2 and 4.0 was found for β/α, which is dependent on temperature, alloy composition, and electric-field strength.

  15. Avalanche multiplication and impact ionization in amorphous selenium photoconductive target

    NASA Astrophysics Data System (ADS)

    Park, Wug-Dong; Tanioka, Kenkichi

    2014-03-01

    The avalanche multiplication factor and the hole ionization coefficient in the amorphous selenium (a-Se) high-gain avalanche rushing amorphous photoconductor (HARP) target depend on the electric field. The phenomenon of avalanche multiplication and impact ionization in the 0.4-µm-thick a-Se HARP target is investigated. The hot carrier energy in the 0.4-µm-thick a-Se HARP target increases linearly as the target voltage increases. The energy relaxation length of hot carriers in the a-Se photoconductor of the 0.4-µm-thick HARP target saturates as the electric field increases. The average energy Eav of a hot carrier and the energy relaxation length λE in the a-Se photoconductor of the 0.4-µm-thick HARP target at 1 × 108 V/m were 0.25 eV and 2.5 nm, respectively. In addition, the hole ionization coefficient β and the avalanche multiplication factor M are derived as a function of the electric field, the average energy of a hot carrier, and the impact ionization energy. The experimental hole ionization coefficient β and the avalanche multiplication factor M in the 0.4-µm-thick a-Se HARP target agree with the theoretical results.

  16. A model for electron/ion recombination in ionization chambers

    SciTech Connect

    Sailor, W.C.

    1988-05-01

    The recombination of free electrons and positive ions along charged particle tracks in gases has been modeled using electron tranport equations, which assume homogeneous distribution in the vicinity of the tracks. The equations include space charge terms, which have been negelected in previous models. A formula for the electron yield as a function of detector applied potential is obtained from a perturbation solution valid when the ratio of the Debye length to the charge column radius is larger then unity. When this ratio is very large, the formula reduces to that of previous models. Pulse height measurements in a /sup 3/He ionization chamber indicate 2% to 30% losses to recombination which vary with applied field, particle type, and energy. Using reasonable values for the electron transport coefficients, the calculated loss of signal to recommendation is generally in agreement with experiment, but the variation with applied bias is stronger in the experiment.

  17. A Carbon Nanotube Electron Source Based Ionization Vacuum Gauge

    SciTech Connect

    Changkun Dong; Ganapati Myneni

    2003-10-01

    The results of fabrication and performance of an ionization vacuum gauge using a carbon nanotube (CNT) electron source are presented. The electron source was constructed with multi-wall nanotubes (MWNT), which were grown using thermal chemical vapor deposition (CVD) process. The electron emission of the source was stable in vacuum pressure up to 10-7 Torr, which is better than the metal field emitters. The measurement linearity of the gauge was better than {+-}10% from 10-6 to 10-10 Torr. The gauge sensitivity of 4 Torr-1 was achieved under 50 {micro}A electron emission in nitrogen. The gauge is expected to find applications in vacuum measurements from 10-7 Torr to below 10-11 Torr.

  18. Composite electron propagator methods for calculating ionization energies

    NASA Astrophysics Data System (ADS)

    Díaz-Tinoco, Manuel; Dolgounitcheva, O.; Zakrzewski, V. G.; Ortiz, J. V.

    2016-06-01

    Accurate ionization energies of molecules may be determined efficiently with composite electron-propagator (CEP) techniques. These methods estimate the results of a calculation with an advanced correlation method and a large basis set by performing a series of more tractable calculations in which large basis sets are used with simpler approximations and small basis sets are paired with more demanding correlation techniques. The performance of several CEP methods, in which diagonal, second-order electron propagator results with large basis sets are combined with higher-order results obtained with smaller basis sets, has been tested for the ionization energies of closed-shell molecules from the G2 set. Useful compromises of accuracy and computational efficiency employ complete-basis-set extrapolation for second-order results and small basis sets in third-order, partial third-order, renormalized partial-third order, or outer valence Green's function calculations. Analysis of results for vertical as well as adiabatic ionization energies leads to specific recommendations on the best use of regular and composite methods. Results for 22 organic molecules of interest in the design of photovoltaic devices, benzo[a]pyrene, Mg-octaethylporphyrin, and C60 illustrate the capabilities of CEP methods for calculations on large molecules.

  19. Composite electron propagator methods for calculating ionization energies.

    PubMed

    Díaz-Tinoco, Manuel; Dolgounitcheva, O; Zakrzewski, V G; Ortiz, J V

    2016-06-14

    Accurate ionization energies of molecules may be determined efficiently with composite electron-propagator (CEP) techniques. These methods estimate the results of a calculation with an advanced correlation method and a large basis set by performing a series of more tractable calculations in which large basis sets are used with simpler approximations and small basis sets are paired with more demanding correlation techniques. The performance of several CEP methods, in which diagonal, second-order electron propagator results with large basis sets are combined with higher-order results obtained with smaller basis sets, has been tested for the ionization energies of closed-shell molecules from the G2 set. Useful compromises of accuracy and computational efficiency employ complete-basis-set extrapolation for second-order results and small basis sets in third-order, partial third-order, renormalized partial-third order, or outer valence Green's function calculations. Analysis of results for vertical as well as adiabatic ionization energies leads to specific recommendations on the best use of regular and composite methods. Results for 22 organic molecules of interest in the design of photovoltaic devices, benzo[a]pyrene, Mg-octaethylporphyrin, and C60 illustrate the capabilities of CEP methods for calculations on large molecules. PMID:27305999

  20. Complete Solution of Electronic Excitation and Ionization in Electron-Hydrogen Molecule Scattering.

    PubMed

    Zammit, Mark C; Savage, Jeremy S; Fursa, Dmitry V; Bray, Igor

    2016-06-10

    The convergent close-coupling method has been used to solve the electron-hydrogen molecule scattering problem in the fixed-nuclei approximation. Excellent agreement with experiment is found for the grand total, elastic, electronic-excitation, and total ionization cross sections from the very low to the very high energies. This shows that for the electronic degrees of freedom the method provides a complete treatment of electron scattering on molecules as it does for atoms. PMID:27341229

  1. Complete solution of electronic excitation and ionization in electron-hydrogen molecule scattering

    DOE PAGESBeta

    Zammit, Mark C.; Savage, Jeremy S.; Fursa, Dmitry V.; Bray, Igor

    2016-06-01

    The convergent close-coupling method has been used to solve the electron-hydrogen molecule scattering problem in the fixed-nuclei approximation. Excellent agreement with experiment is found for the grand total, elastic, electronic-excitation, and total ionization cross sections from the very low to the very high energies. This shows that for the electronic degrees of freedom the method provides a complete treatment of electron scattering on molecules as it does for atoms.

  2. Complete Solution of Electronic Excitation and Ionization in Electron-Hydrogen Molecule Scattering

    NASA Astrophysics Data System (ADS)

    Zammit, Mark C.; Savage, Jeremy S.; Fursa, Dmitry V.; Bray, Igor

    2016-06-01

    The convergent close-coupling method has been used to solve the electron-hydrogen molecule scattering problem in the fixed-nuclei approximation. Excellent agreement with experiment is found for the grand total, elastic, electronic-excitation, and total ionization cross sections from the very low to the very high energies. This shows that for the electronic degrees of freedom the method provides a complete treatment of electron scattering on molecules as it does for atoms.

  3. Quantum-mechanical predictions of electron-induced ionization cross sections of DNA components

    SciTech Connect

    Champion, Christophe

    2013-05-14

    Ionization of biomolecules remains still today rarely investigated on both the experimental and the theoretical sides. In this context, the present work appears as one of the first quantum mechanical approaches providing a multi-differential description of the electron-induced ionization process of the main DNA components for impact energies ranging from the target ionization threshold up to about 10 keV. The cross section calculations are here performed within the 1st Born approximation framework in which the ejected electron is described by a Coulomb wave whereas the incident and the scattered electrons are both described by a plane wave. The biological targets of interest, namely, the DNA nucleobases and the sugar-phosphate backbone, are here described by means of the GAUSSIAN 09 system using the restricted Hartree-Fock method with geometry optimization. The theoretical predictions also obtained have shown a reasonable agreement with the experimental total ionization cross sections while huge discrepancies have been pointed out with existing theoretical models, mainly developed within a semi-classical framework.

  4. Electron impact cross sections for surrogates of DNA sugar phosphate backbone

    NASA Astrophysics Data System (ADS)

    Bhowmik, Pooja; Joshipura, K. N.; Pandya, Siddharth

    2012-11-01

    Ionization and elastic cross sections by electron impact on H3PO4 and OP(OCH3)3 which are substitutes for the components of DNA phosphate group. We have employed the Complex Scattering Potential-ionization contribution (CSP-ic) formalism to calculate the cross sections in the energy range from ionization threshold to 2000 eV.

  5. Effect of Electron Reflection at the Anode on Ionization Coefficient

    NASA Astrophysics Data System (ADS)

    Takeda, Akihide; Ikuta, Nobuaki

    2001-10-01

    The ionization coefficient α is determined with the gradient of log I(I:ionization current) versus gap length d assuming the energy equilibrium over full gap space. However, the equilibrium in full space is difficult as well known. The α values in H2 reported by Haydon[1] and Satoh[2] show sudden breaking of increase with increase of reduced electric field E/p0 at less than 200 Vcm-1Torr. The relaxation of electron energy distribution in H2 is much slower than that in other gases due to the low values of inelastic cross sections in particular in high-energy range, accordingly in high E/p0 condition. Hayashi pointed out[3,4] that the breaking is due to the runaway of electrons. Many electrons are lost from the anode without sufficient ionization collisions with H_2. In such a situation, it is found that the electron reflection at the anode, the ratio is considerably large in practice, gives large increase in the measured values of α d. The effect of reflection on the values of α d in H2 with the change of E/p0 and p_0d will be reported. [1]S. C. Haydon and H. M. Stock: Aust. J. Phys. 24 pp.527-42(1966). [2]K. Satoh, T. Kudoh, T. Miki, M. Kawashima, H. Itoh and H. Tagashira: T. IEEE Jpn. 119-A pp.1136-41(1999) [3]M. Hayashi, M. Ohoka and A. Miwa: 18th ICPIG pp.14-15(1987) [4]M. Hayashi: 4th ICDG Vol.1 pp.195-198(1976)

  6. Semiclassical Study of the Wave Vector Dependence of the Interband Impact Ionization Rate in Bulk Silicon

    NASA Technical Reports Server (NTRS)

    Wang, Yang; Brennan, Kevin F.

    1994-01-01

    We present calculations of the interband impact ionization rate calculated using a wave vector dependent (k-dependent) semiclassical formulation of the transition rate. The transition rate is determined using Fermi's golden rule from a two-body screened Coulomb interaction assuming energy and momentum conservation. The transition rate is calculated for the first two conduction bands of silicon by numerically integrating over the full Brillouin zone. The overlap integrals in the expression for the transition rate are determined numerically using a 15 band k-p calculation. It is found that the transition rate depends strongly on the initiating electron wave vector (k vector) and that the transition rate is greatest for electrons originating within the second conduction band than the first conduction band. An ensemble Monte Carlo simulation, which includes the numerically determined ionization transition rate as well as the full details of the first two conduction bands, is used to calculate the total impact ionization rate in bulk silicon. Good agreement with the experimentally determined electron ionization rate data is obtained.

  7. Modification of the quantum mechanical flux formula for electron-hydrogen ionization through Bohm's velocity field

    NASA Astrophysics Data System (ADS)

    Randazzo, J. M.; Ancarani, L. U.

    2015-12-01

    For the single differential cross section (SDCS) for hydrogen ionization by electron impact (e -H problem), we propose a correction to the flux formula given by R. Peterkop [Theory of Ionization of Atoms by Electron Impact (Colorado Associated University Press, Boulder, 1977)]. The modification is based on an alternative way of defining the kinetic energy fraction, using Bohm's definition of velocities instead of the usual asymptotic kinematical, or geometrical, approximation. It turns out that the solution-dependent, modified energy fraction is equally related to the components of the probability flux. Compared to what is usually observed, the correction yields a finite and well-behaved SDCS value in the asymmetrical situation where one of the continuum electrons carries all the energy while the other has zero energy. We also discuss, within the S -wave model of the e -H ionization process, the continuity of the SDCS derivative at the equal energy sharing point, a property not so clearly observed in published benchmark results obtained with integral and S -matrix formulas with unequal final states.

  8. Dissipative many-electron dynamics of ionizing systems.

    PubMed

    Tremblay, Jean Christophe; Klinkusch, Stefan; Klamroth, Tillmann; Saalfrank, Peter

    2011-01-28

    In this paper, we perform many-electron dynamics using the time-dependent configuration-interaction method in its reduced density matrix formulation (ρ-TDCI). Dissipation is treated implicitly using the Lindblad formalism. To include the effect of ionization on the state-resolved dynamics, we extend a recently introduced heuristic model for ionizing states to the ρ-TDCI method, which leads to a reduced density matrix evolution that is not norm-preserving. We apply the new method to the laser-driven excitation of H(2) in a strongly dissipative environment, for which the state-resolve lifetimes are tuned to a few femtoseconds, typical for dynamics of adsorbate at metallic surfaces. Further testing is made on the laser-induced intramolecular charge transfer in a quinone derivative as a model for a molecular switch. A modified scheme to treat ionizing states is proposed to reduce the computational burden associated with the density matrix propagation, and it is thoroughly tested and compared to the results obtained with the former model. The new approach scales favorably (∼N(2)) with the number of configurations N used to represent the reduced density matrix in the ρ-TDCI method, as compared to a N(3) scaling for the model in its original form. PMID:21280729

  9. Electron-induced ionization and dissociative ionization of iron pentacarbonyl molecules

    NASA Astrophysics Data System (ADS)

    Lacko, Michal; Papp, Peter; Wnorowski, Karol; Matejčík, Štefan

    2015-03-01

    Electron ionization (EI) and dissociative ionization (DI) of Iron pentacarbonyl molecule (Fe(CO)5) was studied using a crossed molecular and electron beam mass spectrometry technique. Positive ions FeO(CO)+, FeC(CO)2+ and CO+ of Fe(CO)5 were detected for the first time. We have determined the experimental appearance energies of positive ions, the thresholds for dissociative reactions, the experimental bond dissociation energies for (CO)nFe+-CO bond breaks (for n = 4,..., 0) and their average value for Fe-C bond energy 1.25 eV in Fe(CO)5+. We have performed extensive density functional theory (DFT) studies of the ground states of neutral molecule and fragments 1 A1' Fe(CO)5, 3B1 Fe(CO)4, 3A1Fe(CO)3, 3∑g Fe(CO)2, 3 ∑FeCO as well as positive ions 2A1 Fe(CO)5+, 4A1 Fe(CO)4+, 4A1 Fe(CO)3+, 4∑g Fe(CO)2+ and 4 ∑ FeCO+. The structures and energies of the states have beendetermined and the calculated bond dissociation energies (BDEs) were compared with present experiments as well as with previous works. Contribution to the Topical Issue "Elementary Processes with Atoms and Molecules in Isolated and Aggregated States", edited by Friedrich Aumayr, Bratislav Marinkovic, Stefan Matejick, John Tanis and Kurt H. Becker.

  10. Multifluid Modeling of the Partially Ionized Chromosphere with Effects of Impact Ionization, Radiative Recombination and Charge Exchange

    NASA Astrophysics Data System (ADS)

    Maneva, Y. G.; Poedts, D. S.; Alvarez Laguna, A.; Lani, A.

    2015-12-01

    Neutrals play an important role in the evolution of the weakly ionized solar chromosphere where the number density of neutrals can vastly exceed the number density of protons. Therefore modeling the neutral-ion interactions and studying the effect of neutrals on the ambient plasma properties is an important task for better understanding the observed emission lines and the propagation of disturbances from the photosphere to the transition region and the corona. To pursue this goal we have developed two-fluid and three-fluid simulation setups to study the interaction between electrons, ions and neutrals in a reactive gravitationally stratified collisional media. The model considers the electrons and ions within the resistive MHD approach with Coulomb collisions and anisotropic heat flux determined by Braginskii's transport coefficients. The electromagnetic fields are evolved according to the full Maxwell equations, allowing for propagation of higher frequency waves neglected by the standard MHD approximation. Separate mass, momentum and energy conservation equations are considered for the neutrals and the interaction between the different fluids is determined by the chemical reactions, such as impact ionization, radiative recombination and charge exchange, provided as additional source terms. To initialize the system we consider an ideal gas equation of state with equal initial temperatures for the electrons, ions and the neutrals and different density profiles. The initial temperature and density profiles are height-dependent and follow VAL C atmospheric model for the solar chromosphere. We have searched for a chemical and collisional equilibrium between the ions and the neutrals in the hydrostatic case to avoid unphysical outflows and artificial heating induced by initial pressure imbalances. Next we consider ion-neutral interactions in magnetized plasma with an initial magnetic profile, corresponding to emerging magnetic funnel. Finally we include an external

  11. Electron ionization of metastable nitrogen and oxygen atoms in relation to the auroral emissions

    NASA Astrophysics Data System (ADS)

    Pandya, Siddharth; Joshipura, K. N.

    Atomic and molecular excited metastable states (EMS) are exotic systems due to their special properties like long radiative life-time, large size (average radius) and large polarizability along with relatively smaller first ionization energy compared to their respective ground states (GS). The present work includes our theoretical calculations on electron impact ionization of metastable atomic states N( (2) P), N( (2) D) of nitrogen and O( (1) S), O( (1) D) of oxygen. The targets of our present interest, are found to be present in our Earth's ionosphere and they play an important role in auroral emissions observed in Earth’s auroral regions [1] as also in the emissions observed from cometary coma [2, 3] and airglow emissions. In particular, atomic oxygen in EMS can radiate, the visible O( (1) D -> (3) P) doublet 6300 - 6364 Å red doublet, the O( (1) S -> (1) D) 5577 Å green line, and the ultraviolet O( (1) S -> (3) P) 2972 Å line. For metastable atomic nitrogen one observes the similar emissions, in different wavelengths, from (2) D and (2) P states. At the Earth's auroral altitudes, from where these emissions take place in the ionosphere, energetic electrons are also present. In particular, if the metastable N as well as O atoms are ionized by the impact of electrons then these species are no longer available for emissions. This is a possible loss mechanism, and hence it is necessary to analyze the importance of electron ionization of the EMS of atomic O and N, by calculating the relevant cross sections. In the present paper we investigate electron ionization of the said metastable species by calculating relevant total cross sections. Our quantum mechanical calculations are based on projected approximate ionization contribution in the total inelastic cross sections [4]. Detailed results and discussion along with the significance of these calculations will be presented during the COSPAR-2014. References [1] A.Bhardwaj, and G. R. Gladstone, Rev. Geophys., 38

  12. Electron ionization and ion-molecule reactions of triethylborane

    NASA Astrophysics Data System (ADS)

    Jiao, Charles; Adams, Steven

    2015-09-01

    Triethylborane (TEB) is used as a radical initiator in many chemical reactions and as an excellent ignition source for jet engines and rocket engines. In this paper we will report our recent study on the ion chemistries of TEB relevant to the charged particle processes in plasmas involving TEB. The total cross section of electron ionization of TEB is found to have a maximum of 2.2×10-15 cm2 at 75 +10 eV electron energy. Product ions from the ionization include C2H2-5+, BCH4+, BC2, 4,6+, BC3H4, 6+, BC4H8, 10+ and BC6H15+, among which BC6H15+, BC4H10+ and BC2H6+ are the most abundant ions. These ions react with TEB via various mechanisms including charge-transfer, alkyde-transfer and association reaction. The common and major product ions from the ion-molecule reactions are BC4H10+ and BC2H6+, formed by simple ethide-transfer and ethide-transfer followed by dissociation (loss of C2H4) , respectively.

  13. Electron-impact-induced {ital K} plus {ital M} shell ionization in solid targets of medium-{ital Z} elements studied by means of high-resolution x-ray spectroscopy

    SciTech Connect

    Ludziejewski, T.; Rymuza, P.; Sujkowski, Z.; Dousse, J.; Rheme, C.; Polasik, M.

    1996-07-01

    The {ital K}{beta}{sub 2} x-ray spectra of zirconium, niobium, molybdenum, and palladium bombarded by 150 and 300 keV electrons were measured with a high-resolution transmission curved crystal spectrometer. Multiconfiguration Dirac-Fock calculations were used for the decomposition of the experimental spectra into the {ital K}{beta}{sub 2}{ital M}{sup 0} (diagram) and {ital K}{beta}{sub 2}{ital M}{sup 1} (satellite) components. The probabilities of energy dependent (direct Coulomb and two-step) processes were estimated from the differences in the satellite line yields for electrons and photons. The satellite yields are found to be considerably enhanced in comparison with those for the proton-induced ionization recently measured and analyzed in the same way [T. Ludziejewski {ital et} {ital al}., Phys. Rev. A {bold 52}, 2791 (1995)]. This result indicates the importance of multielectron effects in the {ital K} plus {ital M} shell ionization by energetic projectiles. {copyright} {ital 1996 The American Physical Society.}

  14. Enhanced Ionization of Embedded Clusters by Electron-Transfer-Mediated Decay in Helium Nanodroplets.

    PubMed

    LaForge, A C; Stumpf, V; Gokhberg, K; von Vangerow, J; Stienkemeier, F; Kryzhevoi, N V; O'Keeffe, P; Ciavardini, A; Krishnan, S R; Coreno, M; Prince, K C; Richter, R; Moshammer, R; Pfeifer, T; Cederbaum, L S; Mudrich, M

    2016-05-20

    We report the observation of electron-transfer-mediated decay (ETMD) involving magnesium (Mg) clusters embedded in helium (He) nanodroplets. ETMD is initiated by the ionization of He followed by removal of two electrons from the Mg clusters of which one is transferred to the He ion while the other electron is emitted into the continuum. The process is shown to be the dominant ionization mechanism for embedded clusters for photon energies above the ionization potential of He. For Mg clusters larger than five atoms we observe stable doubly ionized clusters. Thus, ETMD provides an efficient pathway to the formation of doubly ionized cold species in doped nanodroplets. PMID:27258866

  15. Enhanced Ionization of Embedded Clusters by Electron-Transfer-Mediated Decay in Helium Nanodroplets

    NASA Astrophysics Data System (ADS)

    LaForge, A. C.; Stumpf, V.; Gokhberg, K.; von Vangerow, J.; Stienkemeier, F.; Kryzhevoi, N. V.; O'Keeffe, P.; Ciavardini, A.; Krishnan, S. R.; Coreno, M.; Prince, K. C.; Richter, R.; Moshammer, R.; Pfeifer, T.; Cederbaum, L. S.; Mudrich, M.

    2016-05-01

    We report the observation of electron-transfer-mediated decay (ETMD) involving magnesium (Mg) clusters embedded in helium (He) nanodroplets. ETMD is initiated by the ionization of He followed by removal of two electrons from the Mg clusters of which one is transferred to the He ion while the other electron is emitted into the continuum. The process is shown to be the dominant ionization mechanism for embedded clusters for photon energies above the ionization potential of He. For Mg clusters larger than five atoms we observe stable doubly ionized clusters. Thus, ETMD provides an efficient pathway to the formation of doubly ionized cold species in doped nanodroplets.

  16. Separation of ionization and subsequent electronic excitation for formation of electronically excited ethanol cation in intense laser fields

    NASA Astrophysics Data System (ADS)

    Ikuta, T.; Hosaka, K.; Akagi, H.; Yokoyama, A.; Yamanouchi, K.; Kannari, F.; Itakura, R.

    2011-10-01

    Ionization and subsequent electronic excitation occurring within the same laser pulse (400 nm, 96 fs, 1.3 ~ 18 TW cm-2) are separately investigated by measuring in coincidence an electron and a product ion produced from C2H5OH. It is revealed that the nascent population in the electronically excited C2H5OH+ prepared by the ionization decreases as the laser intensity increases, while the subsequent electronic excitation is enhanced through the resonant electronic transitions. Ionization and electronic excitation mechanisms are described based on the electronic-state distributions of C2H5OH+.

  17. Compendium of Total Ionizing Dose and Displacement Damage for Candidate Spacecraft Electronics for NASA

    NASA Technical Reports Server (NTRS)

    Cochran, Donna J.; Boutte, Alvin J.; Chen, Dakai; Pellish, Jonathan A.; Ladbury, Raymond L.; Casey, Megan C.; Campola, Michael J.; Wilcox, Edward P.; Obryan, Martha V.; LaBel, Kenneth A.; Lauenstein, Jean-Marie; Batchlor, David A.; Oldham, Timothy R.

    2012-01-01

    Vulnerability of a variety of candidate spacecraft electronics to total ionizing dose and displacement damage is studied. Devices tested include optoelectronics, digital, analog, linear, and hybrid devices.

  18. Accurate Ionization Potentials and Electron Affinities of Acceptor Molecules IV: Electron-Propagator Methods.

    PubMed

    Dolgounitcheva, O; Díaz-Tinoco, Manuel; Zakrzewski, V G; Richard, Ryan M; Marom, Noa; Sherrill, C David; Ortiz, J V

    2016-02-01

    Comparison of ab initio electron-propagator predictions of vertical ionization potentials and electron affinities of organic, acceptor molecules with benchmark calculations based on the basis set-extrapolated, coupled cluster single, double, and perturbative triple substitution method has enabled identification of self-energy approximations with mean, unsigned errors between 0.1 and 0.2 eV. Among the self-energy approximations that neglect off-diagonal elements in the canonical, Hartree-Fock orbital basis, the P3 method for electron affinities, and the P3+ method for ionization potentials provide the best combination of accuracy and computational efficiency. For approximations that consider the full self-energy matrix, the NR2 methods offer the best performance. The P3+ and NR2 methods successfully identify the correct symmetry label of the lowest cationic state in two cases, naphthalenedione and benzoquinone, where some other methods fail. PMID:26730459

  19. Plasma diagnosis as a tool for the determination of the parameters of electron beam evaporation and sources of ionization

    NASA Astrophysics Data System (ADS)

    Mukherjee, Jaya; Dileep Kumar, V.; Yadav, S. P.; Barnwal, Tripti A.; Dikshit, Biswaranjan

    2016-07-01

    The atomic vapor generated by electron beam heating is partially ionized due to atom–atom collisions (Saha ionization) and electron impact ionization, which depend upon the source temperature and area of evaporation as compared to the area of electron beam bombardment on the target. When electron beam evaporation is carried out by inserting the target inside an insulating liner to reduce conductive heat loss, it is expected that the area of evaporation becomes significantly more than the area of electron beam bombardment on the target, resulting in reduced electron impact ionization. To assess this effect and to quantify the parameters of evaporation, such as temperature and area of evaporation, we have carried out experiments using zirconium, tin and aluminum as a target. By measuring the ion content using a Langmuir probe, in addition to measuring the atomic vapor flux at a specific height, and by combining the experimental data with theoretical expressions, we have established a method for simultaneously inferring the source temperature, evaporation area and ion fraction. This assumes significance because the temperature cannot be reliably measured by an optical pyrometer due to the wavelength dependent source emissivity and reflectivity of thin film mirrors. In addition, it also cannot be inferred from only the atomic flux data at a certain height as the area of evaporation is unknown (it can be much more than the area of electron bombardment, especially when the target is placed in a liner). Finally, the reason for the lower observed electron temperatures of the plasma for all the three cases is found to be the energy loss due to electron impact excitation of the atomic vapor during its expansion from the source.

  20. Electronic structure of neutral and singly ionized curium

    SciTech Connect

    Worden, E.F.; Conway, J.G.; Blaise, J.

    1985-02-01

    Extensive observations and analyses of the emission spectra of neutral and singly ionized curium, Cm I and Cm II, have resulted in the determination of 785 Cm I and 598 Cm II energy levels. These levels then combine to classify 9145 of the more than 14,250 lines of /sup 244/Cm observed between 240 and 2650 nm. Most of the levels have Lande g-values from Zeeman effect data and isotope shifts trom measurements of spectra from sources with various enrichments of /sup 244/Cm, /sup 245/Cm, /sup 246/Cm, and /sup 248/Cm. These data allowed many levels to be assigned to specific electronic configurations. The ground configurations of Cm I and Cm II are (Rn) 5f/sup 7/6d7s/sup 2/ and (Rn) 5f/sup 7/7s/sup 2/, respectively. The realtive energies of other electronic configurations of Cm are given and compared with analogous configurations in other actinides and in Gd its lanthanide analogue. 2 refs., 5 figs., 7 tabs.

  1. Development of a highly-sensitive Penning ionization electron spectrometer using the magnetic bottle effect

    NASA Astrophysics Data System (ADS)

    Ota, Masahiro; Ishiguro, Yuki; Nakajima, Yutaro; Miyauchi, Naoya; Yamakita, Yoshihiro

    2016-02-01

    This paper reports on a highly-sensitive retarding-type electron spectrometer for a continuous source of electrons, in which the electron collection efficiency is increased by utilizing the magnetic bottle effect. This study demonstrates an application to Penning ionization electron spectroscopy using collisional ionization with metastable He*(23S) atoms. Technical details and performances of the instrument are presented. This spectrometer can be used for studies of functional molecules and assemblies, and exterior electron densities are expected to be selectively observed by the Penning ionization.

  2. A search for strong-field direct two electron ionization using coincidence spectroscopy

    SciTech Connect

    Agostini, P.; Mevel, E.; Breger, P.; Walker, B.; Yang, B.; DiMauro, L.F.

    1993-05-01

    We report on our program in detecting two-electron ionization using electron-electron and electron-ion coincidence measurements. The coincidence techniques have been applied to the multiphoton ionization (MPI) of xenon atoms with 0.527 {mu}m excitation. The results show that direct two electron ionization is not occurring which is in variance with an earlier report. We also present a polarization study on the MPI of helium at 0.62 {mu}m and discuss these results in context of existing models.

  3. A search for strong-field direct two electron ionization using coincidence spectroscopy

    SciTech Connect

    Agostini, P.; Mevel, E.; Breger, P. . Service de Recherches sur les Surfaces et de l'Irradiation de la Matiere); Walker, B.; Yang, B.; DiMauro, L.F. )

    1993-01-01

    We report on our program in detecting two-electron ionization using electron-electron and electron-ion coincidence measurements. The coincidence techniques have been applied to the multiphoton ionization (MPI) of xenon atoms with 0.527 [mu]m excitation. The results show that direct two electron ionization is not occurring which is in variance with an earlier report. We also present a polarization study on the MPI of helium at 0.62 [mu]m and discuss these results in context of existing models.

  4. Elastic scattering of electrons from singly ionized argon

    SciTech Connect

    Griffin, D.C.; Pindzola, M.S.

    1996-03-01

    Recently, Greenwood {ital et} {ital al}. [Phys. Rev. Lett. {bold 75}, 1062 (1995)] reported measurements of large-angle elastic scattering of electrons from singly ionized argon at an energy of 3.3 eV. They compared their results for the differential cross section with cross sections determined using phase shifts obtained from two different scattering potentials and found large discrepancies between theory and experiment at large angles. They state that these differences may be due to the effects of polarization of the target, which are not included in their calculations, as well as inaccurate representations of electron exchange in the local scattering potentials that are employed to determine the phase shifts. In order to test these proposed explanations of the discrepancies, we have carried out calculations of elastic scattering from Ar{sup +} using the {ital R}-matrix method. We compare both a single-state calculation, which does not include polarization, and a 17-state calculation, in which the effects of dipole polarizability are included through the use of polarization pseudostates within the close-coupling expansion, to each other and with the measurements. We find some differences between the two calculations at intermediate scattering angles, but very close agreement at angles above 100{degree}. Although the calculated cross sections agree with experiment between 120{degree} and 135{degree}, large discrepancies persist at angles above 135{degree}. We conclude that the differences between the measurements and theory cannot be explained on the basis of an inaccurate representation of electron exchange or polarization of the target. {copyright} {ital 1996 The American Physical Society.}

  5. Impact ionization experiments with porous cosmic dust particle analogs

    NASA Astrophysics Data System (ADS)

    Sterken, Veerle; Moragas-Klostermeyer, Georg; Hillier, Jon; Fielding, Lee; Lovett, Joseph; Armes, Steven; Fechler, Nina; Srama, Ralf; Bugiel, Sebastian; Hornung, Klaus

    2016-04-01

    Impact ionization experiments have been performed since more than 40 years for calibration of cosmic dust instruments using a linear Van de Graaff dust accelerator. Such an accelerator can accelerate conductive dust particles of sizes between ca. a few tens of microns, and a micron in size to speeds up to 80 km/s depending on particle size. Many different materials have been used for instrument calibration, from iron in the earlier days to carbon, metal-coated minerals and most recently, minerals coated with conductive polymers. While different materials with different densities have been used for instrument calibration, no comparative analysis has been made yet of compact particles versus porous or fluffy particles of the same material. Porous or fluffy particles are increasingly found to be present in the solar system, e.g. dust from comet 67P Churyumov-Gerasimenko or aggregate grains from the plumes of Enceladus and recently also indications were found for low-density interstellar dust (ISD) from ISD data and trajectory simulations. These recalibrations are thus relevant for estimations of the size distributions of interplanetary and interstellar dust. In this talk we report about the calibrations being performed at the Heidelberg dust accelerator facility for investigating the influence of particle density on the impact ionization charge after impact. We use the Cassini Cosmic Dust Analyser as an impact target. We then explain the experiment set-up, the preparation of the materials and the materials used. We elaborate on the technical challenges, and finally about the current status of the research at this stage. We conclude the talk with the relevance of the study, being the potential influence of such calibrations on the estimates of the mass distributions of interstellar and interplanetary dust.

  6. Electron dynamics of molecular double ionization by circularly polarized laser pulses

    SciTech Connect

    Tong, Aihong; Zhou, Yueming; Huang, Cheng; Lu, Peixiang

    2013-08-21

    Using the classical ensemble method, we have investigated double ionization (DI) of diatomic molecules driven by circularly polarized laser pulses with different internuclear distances (R). The results show that the DI mechanism changes from sequential double ionization (SDI) to nonsequential double ionization (NSDI) as the internuclear distance increases. In SDI range, the structure of the electron momentum distribution changes seriously as R increases, which indicates the sensitive dependence of the release times of the two electrons on R. For NSDI, because of the circular polarization, the ionization of the second electron is not through the well-known recollision process but through a process where the first electron ionizes over the inner potential barrier of the molecule, moves directly towards the other nucleus, and kicks out the second electron.

  7. Ionizing Collisions of Electrons with Radical Species OH, H2 O2 and HO2; Theoretical Calculations

    NASA Astrophysics Data System (ADS)

    Joshipura, K. N.; Pandya, S. H.; Vaishnav, B. G.; Patel, U. R.

    2016-05-01

    In this paper we present our calculated total ionization cross sections (TICS) of electron impact on radical targets OH, H2 O2 and HO2 at energies from threshold to 2000 eV. Reactive species such as these pose difficulties in measurements of electron scattering cross sections. No measured data have been reported in this regard except an isolated TICS measurement on OH radical, and hence the present work on the title radicals hold significance. These radical species are present in an environment in which water molecules undergo dissociation (neutral or ionic) in interactions with photons or electrons. The embedding environments could be quite diverse, ranging from our atmosphere to membranes of living cells. Ionization of OH, H2 O2 or HO2 can give rise to further chemistry in the relevant bulk medium. Therefore, it is appropriate and meaningful to examine electron impact ionization of these radicals in comparison with that of water molecules, for which accurate da are available. For the OH target single-centre scattering calculations are performed by starting with a 4-term complex potential, that describes simultaneous elastic plus inelastic scattering. TICS are obtained from the total inelastic cross sections in the complex scattering potential - ionization contribution formalism , a well established method. For H2 O2 and HO2 targets, we employ the additivity rule with overlap or screening corrections. Detailed results will be presented in the Conference.

  8. Employment Impact of Electronic Business.

    ERIC Educational Resources Information Center

    Hecker, Daniel E.

    2001-01-01

    Electronic business is stimulating employment in some sectors across industries, such as computer-related and customer service occupations, and diminishing employment in others, such as administrative support and marketing/sales. Similarly, employment impacts will vary by industry. (Contains 56 notes and references.) (SK)

  9. Multiple electron processes of He and Ne by proton impact

    NASA Astrophysics Data System (ADS)

    Terekhin, Pavel Nikolaevich; Montenegro, Pablo; Quinto, Michele; Monti, Juan; Fojon, Omar; Rivarola, Roberto

    2016-05-01

    A detailed investigation of multiple electron processes (single and multiple ionization, single capture, transfer-ionization) of He and Ne is presented for proton impact at intermediate and high collision energies. Exclusive absolute cross sections for these processes have been obtained by calculation of transition probabilities in the independent electron and independent event models as a function of impact parameter in the framework of the continuum distorted wave-eikonal initial state theory. A binomial analysis is employed to calculate exclusive probabilities. The comparison with available theoretical and experimental results shows that exclusive probabilities are needed for a reliable description of the experimental data. The developed approach can be used for obtaining the input database for modeling multiple electron processes of charged particles passing through the matter.

  10. Free electron degeneracy effects on collisional excitation, ionization, de-excitation and three-body recombination

    NASA Astrophysics Data System (ADS)

    Tallents, G. J.

    2016-09-01

    Collisional-radiative models enable average ionization and ionization populations, plus the rates of absorption and emission of radiation to be calculated for plasmas not in thermal equilbrium. At high densities and low temperatures, electrons may have a high occupancy of the free electron quantum states and evaluations of rate coefficients need to take into account the free electron degeneracy. We demonstrate that electron degeneracy can reduce collisional rate coefficients by orders-of-magnitude from values calculated neglecting degeneracy. We show that assumptions regarding the collisional differential cross-section can alter collisional ionization and recombination rate coefficients by a further factor two under conditions relevant to inertial fusion.

  11. Effective impact ionization threshold and piecewise linear approximation for impact ionization coefficients in a theory of superfast ionizing fronts in semiconductors

    NASA Astrophysics Data System (ADS)

    Minarsky, Andrey; Rodin, Pavel

    2013-04-01

    We focus on theoretical description of superfast ionizing fronts in semiconductor p+-n-n+ structures and argue that in the context of this problem, Townsend's type field dependence of impact ionization coefficients α(E)=α0 exp[(-E0/E)m] can be well approximated by a threshold piecewise linear dependence α(E)=α0'(E -Eb)Θ(E -Eb), where Θ(x) is the unit step function. The possibility of such approximation explains the threshold square dependence υf˜(Em-Eb)2 of the front velocity υf on the maximum electric field Em that the theory of TRAPATT-like ionizing fronts predicts even for threshold-free Townsend's approximation. We suggest a procedure for finding the best-fit parameters of the piecewise linear dependence and determine the values Eb≈0.21 E0, α0'≈0.46α0/E0 for the power m =1 and Eb≈0.5 E0, α0'≈0.7α0/E0 for the power m =2.

  12. X-ray Thomson scattering diagnostics of impact ionization in laser-driven carbon foils

    NASA Astrophysics Data System (ADS)

    Sperling, P.; Zastrau, U.; Toleikis, S.; Glenzer, S. H.; Redmer, R.

    2015-06-01

    We have studied the light-matter interaction of ultra-short, intense optical laser fields with thin carbon foils via particle-in-cell simulations. Especially, the influence of additional impact ionization on the density and temperature of the generated plasma and on the corresponding Thomson scattering spectra was investigated. We predict a pump-probe experiment at the free electron laser FLASH in order to verify the importance of this effect in the laser-matter interaction on ultra-short time scales and to check our predictions quantitatively.

  13. Calculated ionization rates, ion densities, and airglow emission rates due to precipitating electrons in the nightside ionosphere of Mars

    NASA Technical Reports Server (NTRS)

    Haider, S. A.; Kim, J.; Nagy, A. F.; Keller, C. N.; Verigin, M. I.; Gringauz, K. I.; Shutte, N. M.; Szego, K.; Kiraly, P.

    1992-01-01

    The calculations presented in this paper clearly establish that the electron fluxes measured by the HARP instrument, carried on board Phobos 2, could cause significant electron impact ionization and excitation in the nightside atmosphere of Mars, if these electrons actually do precipitate. The calculated peak electron densities were found to be about a factor of 2 larger than the mean observed nightside densities, indicating that if a significant fraction of the measured electrons actually precipitate, they could be the dominant mechanism responsible for maintaining the nightside ionosphere. The calculated zenith column emission rates of the O I 5577-A and 6300-A and CO Cameron band emissions, due to electron impact and dissociative recombination mechanisms, were found to be significant.

  14. Electron-impact excitation of neon

    NASA Astrophysics Data System (ADS)

    Ballance, Connor; Griffin, Don

    2004-05-01

    A number of convergent close-coupling and R-matrix with pseudo-state (RMPS) calculations on H-like, He-like, Li-like, and Be-like ions have demonstrated that coupling to the target continuum can have large effects on the electron-impact excitation cross sections of neutral and low-charge species. However, no one has yet attempted such advanced calculations on a system as complex as neutral neon. We report on a series of RMPS calculations of electron-impact excitation of Ne using recently developed parallel Breit-Pauli (BP) R-matrix programs. Our largest calculation was a BP calculation with 235 spectroscopic and pseudo levels in the close-coupling expansion. Although the results of this calculation clearly reveal the importance of coupling to the target continuum in this atom, the pseudo-state expansion is not yet sufficiently complete to provide reliable cross sections for energies above the ionization limit. However, this is the largest BP calculation that can be performed with present computer resources. Thus, we have also carried out a series of RMPS calculations in LS coupling with different pseudo-state expansions. Comparisons of these results have allowed us to determine the approximate size of the pseudo-state expansion required to achieve convergence in future BP calculations for neon.

  15. Electron ionization dynamics of N2 and O2 molecules: Velocity-map imaging

    NASA Astrophysics Data System (ADS)

    Bull, James N.; Lee, Jason W. L.; Vallance, Claire

    2015-02-01

    This paper reports a crossed-beam velocity-map imaging study into the electron ionization dynamics of jet-cooled N2 and O2 molecules at electron collision energies from 35 to 100 eV. The use of velocity-map imaging detection provides insight into the detailed ionization dynamics through the dimension of the product ion kinetic energy associated with impulsive dissociation. In particular, "mesoscopic" cross sections corresponding to ionization from manifolds of energetically close states converging to the same dissociation asymptote are reported for a number of single-ionization channels. In addition, a range of double-ionization cross sections have been characterized, including those yielding X2 2 + dications. These are found to be in excellent agreement with other cross sections determined in coincidence measurements. This agreement supports a meaningful and accurate determination of the single-ionization channels.

  16. Transverse instability of a plane front of fast impact ionization waves

    SciTech Connect

    Kyuregyan, A. S.

    2012-05-15

    The transverse instability of a plane front of fast impact ionization waves in p{sup +}-n-n{sup +} semiconductor structures with a finite concentration of donors N in the n layer has been theoretically analyzed. It is assumed that the high velocity u of impact ionization waves is ensured owing to the avalanche multiplication of the uniform background of electrons and holes whose concentration {sigma}{sub b} ahead of the front is high enough for the continuum approximation to be applicable. The problem of the calculation of the growth rate s of a small harmonic perturbation with wavenumber k is reduced to the eigenvalue problem for a specific homogeneous Volterra equation of the second kind containing the sum of double and triple integrals of an unknown eigenfunction. This problem has been solved by the method of successive approximations. It has been shown that the function s(k) for small k values increases monotonically in agreement with the analytical theory reported in Thermal Engineering 58 (13), 1119 (2011), reaches a maximum s{sub M} at k = k{sub M}, then decreases, and becomes negative at k > k{sub 01}. This behavior of the function s(k) for short-wavelength perturbations is due to a decrease in the distortion of the field owing to a finite thickness of the space charge region of the front and 'smearing' of perturbation of concentrations owing to the transverse transport of charge carriers. The similarity laws for perturbations with k Greater-Than-Or-Equivalent-To k{sub M} have been established: at fixed {sigma}{sub b} values and the maximum field strength on the front E{sub 0M}, the growth rate s depends only on the ratio k/N and the boundary wavenumber k{sub 01} {proportional_to} N. The parameters s{sub M}, k{sub M}, and k{sub 01}, which determine the perturbation growth dynamics and the upper boundary of the instability region for impact ionization waves, have been presented as functions of E{sub 0M}. These dependences indicate that the model of a plane

  17. On ionization energy losses of ultra-relativistic half-bare electron

    NASA Astrophysics Data System (ADS)

    Shul'ga, N. F.; Trofymenko, S. V.

    2012-11-01

    The problem of ionization energy losses of relativistic electron after its emission from substance into vacuum and subsequent traversal of thin dielectric plate is considered. It is shown that with the increase of distance between the plate and the substance the gradual increase of electron ionization energy losses in the plate from the value defined by Fermi formula to the value defined by Bethe-Bloch formula complemented by radiation contribution to ionization occurs. It is highlighted that such change of energy losses is defined by reconstruction of the field around the electron and may occur on macroscopic distances along its trajectory.

  18. Double electron ionization in Compton scattering of high energy photons by helium atoms

    SciTech Connect

    Amusia, M.Y.; Mikhailov, A.I.

    1995-08-01

    The cross section for double-electron ionization of two-electron atoms and ions in Compton scattering of high energy photons is calculated. It is demonstrated that its dependence on the incoming photon frequency is the same as that for single-electron ionization. The ratio of {open_quotes}double-to-single{close_quotes} ionization in Compton scattering was found to be energy independent and almost identical with the corresponding value for photoionization. For the He atom it is 1.68%. This surprising result deserves experimental verification.

  19. Nuclear-Electronic Coherence in Strong-Field Dissociative Ionization

    NASA Astrophysics Data System (ADS)

    Yu, Youliang; Wang, Yujun; Zeng, Shuo; Esry, B. D.

    2015-05-01

    In strong-field dissociative ionization of molecules, the ionization step is usually modeled since direct calculation is very challenging. In most of the models used to date, ionization is assumed to occur at several well-defined times accompanied by promotion of a nuclear wave packet to the ionic Born-Oppenheimer potential. Whether these nuclear wave packets should add coherently or incoherently in general is an open question. To answer it, we solve the time-dependent Schrödinger equation for one-dimensional H2+,where ionization is included naturally, and compare the observables, such as the kinetic energy release spectrum, with those from an ionization model. We then examine the validity of such models in strong-field dissociative ionization of H2+with reduced dimensionality. We do not, however, expect this physics to depend sensitively on the dimensionality. Supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

  20. Ionization Cross Sections and Dissociation Channels of DNA Bases by Electron Collisions

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Dateo, Christopher E.; Fletcher, Graham D.

    2004-01-01

    Free secondary electrons are the most abundant secondary species in ionizing radiation. Their role in DNA damage, both direct and indirect, is an active area of research. While indirect damage by free radicals, particularly by the hydroxyl radical generated by electron collision with water. is relatively well studied, damage by direct electron collision with DNA is less well understood. Only recently Boudaiffa et al. demonstrated that electrons at energies well below ionization thresholds can induce substantial yields of single- and double-strand breaks in DNA by a resonant, dissociative attachment process. This study attracted renewed interest in electron collisions with DNA, especially in the low energy region. At higher energies ionization becomes important. While Monte Carlo track simulations of radiation damage always include ionization, the probability of dissociative ionization, i.e., simultaneous ionization and dissociation, is ignored. Just like dissociative attachment, dissociative ionization may be an important contributor to double-strand breaks since the radicals and ions produced by dissociative ionization, located in the vicinity of the DNA coil, can readily interact with other parts of the DNA. Using the improved binary-encounter dipole (iBED) formulation, we calculated the ionization cross sections of the four DNA bases, adenine, cytosine, guanine, and thymine, by electrons at energies from threshold to 1 KeV. The present calculation gives cross sections approximately 20% lower than the results by Bemhardt and Paretzke using the Deutsch-Mark and Binary-Encounter-Bethe (BEB) formalisms. The difference is most likely due to the lack of a shielding term in the dipole potential used in the Deutsch-Mark and BEB formalisms. The dissociation channels of ionization for the bases are currently being studied.

  1. Effects of atomic disorder on impact ionization rate in silicon nanodots

    SciTech Connect

    Mori, N.; Minari, H.; Tomita, M.; Watanabe, T.; Koshida, N.

    2013-12-04

    We theoretically investigate effects of atomic disorder existing near the Si/SiO{sub 2} interfaces on the impact ionization rate of a Si nanodot (SiND). We find that the impact ionization rate of a disordered SiND becomes higher near the threshold energy and approaches that of an ideal SiND for higher energy region.

  2. Modeling the electron-impact dissociation of methane

    NASA Astrophysics Data System (ADS)

    Ziółkowski, Marcin; Vikár, Anna; Mayes, Maricris Lodriguito; Bencsura, Ákos; Lendvay, György; Schatz, George C.

    2012-12-01

    The product yield of the electron-impact dissociation of methane has been studied with a combination of three theoretical methods: R-matrix theory to determine the electronically inelastic collisional excitation cross sections, high-level electronic structure methods to determine excited states energies and derivative couplings, and trajectory surface hopping (TSH) calculations to determine branching in the dissociation of the methane excited states to give CH3, CH2, and CH. The calculations involve the lowest 24 excited-state potential surfaces of methane, up to the ionization energy. According to the R-matrix calculations, electron impact preferentially produces triplet excited states, especially for electron kinetic energies close to the dissociation threshold. The potential surfaces of excited states are characterized by numerous avoided and real crossings such that the TSH calculations show rapid cascading down to the lowest excited singlet or triplet states, and then slower the dissociation of these lowest states. Product branching for electron-impact dissociation was therefore estimated by combining the electron-impact excitation cross sections with TSH product branching ratios that were obtained from the lowest singlet and triplet states, with the singlet dissociation giving a comparable formation of CH2 and CH3 while triplet dissociation gives CH3 exclusively. The overall branching in electron-impact dissociation is dominated by CH3 over CH2. A small branching yield for CH is also predicted.

  3. Total Ionizing Dose and Displacement Damage Compendium of Candidate Spacecraft Electronics for NASA

    NASA Technical Reports Server (NTRS)

    Cochran, Donna J.; Chen, Dakai; Oldham, Timothy R.; Sanders, Anthony B.; Kim, Hak S.; Campola, Michael J.; Buchner, Stephen P.; LaBel, Kenneth A.; Marshall, Cheryl J.; Pellish, Jonathan A.; Carts, Martin A.; O'Bryan, Martha V.

    2010-01-01

    Vulnerability of a variety of candidate spacecraft electronics to total ionizing dose and displacement damage is studied. Devices tested include optoelectronics, digital, analog, linear bipolar devices, and hybrid devices.

  4. Imaging Electronic Excitation of NO by Ultrafast Laser Tunneling Ionization.

    PubMed

    Endo, Tomoyuki; Matsuda, Akitaka; Fushitani, Mizuho; Yasuike, Tomokazu; Tolstikhin, Oleg I; Morishita, Toru; Hishikawa, Akiyoshi

    2016-04-22

    Tunneling-ionization imaging of photoexcitation of NO has been demonstrated by using few-cycle near-infrared intense laser pulses (8 fs, 800 nm, 1.1×10^{14}  W/cm^{2}). The ion image of N^{+} fragment ions produced by dissociative ionization of NO in the ground state, NO (X^{2}Π,2π)→NO^{+}+e^{-}→N^{+}+O+e^{-}, exhibits a characteristic momentum distribution peaked at 45° with respect to the laser polarization direction. On the other hand, a broad distribution centered at ∼0° appears when the A^{2}Σ^{+} (3sσ) excited state is prepared as the initial state by deep-UV photoexcitation. The observed angular distributions are in good agreement with the corresponding theoretical tunneling ionization yields, showing that the fragment anisotropy reflects changes of the highest-occupied molecular orbital by photoexcitation. PMID:27152798

  5. Imaging Electronic Excitation of NO by Ultrafast Laser Tunneling Ionization

    NASA Astrophysics Data System (ADS)

    Endo, Tomoyuki; Matsuda, Akitaka; Fushitani, Mizuho; Yasuike, Tomokazu; Tolstikhin, Oleg I.; Morishita, Toru; Hishikawa, Akiyoshi

    2016-04-01

    Tunneling-ionization imaging of photoexcitation of NO has been demonstrated by using few-cycle near-infrared intense laser pulses (8 fs, 800 nm, 1.1 ×1014 W /cm2 ). The ion image of N+ fragment ions produced by dissociative ionization of NO in the ground state, NO (X2Π ,2 π )→NO+ +e-→N+ +O +e- , exhibits a characteristic momentum distribution peaked at 45° with respect to the laser polarization direction. On the other hand, a broad distribution centered at ˜0 ° appears when the A2Σ+ (3 s σ ) excited state is prepared as the initial state by deep-UV photoexcitation. The observed angular distributions are in good agreement with the corresponding theoretical tunneling ionization yields, showing that the fragment anisotropy reflects changes of the highest-occupied molecular orbital by photoexcitation.

  6. Few-Photon Multiple Ionization of Ne and Ar by Strong Free-Electron-Laser Pulses

    SciTech Connect

    Moshammer, R.; Jiang, Y. H.; Rudenko, A.; Ergler, Th.; Schroeter, C. D.; Luedemann, S.; Zrost, K.; Dorn, A.; Ferger, T.; Kuehnel, K. U.; Ullrich, J.; Foucar, L.; Titze, J.; Jahnke, T.; Schoeffler, M.; Doerner, R.; Fischer, D.; Weber, T.; Zouros, T. J. M.; Duesterer, S.

    2007-05-18

    Few-photon multiple ionization of Ne and Ar atoms by strong vacuum ultraviolet laser pulses from the free-electron laser at Hamburg was investigated differentially with the Heidelberg reaction microscope. The light-intensity dependence of Ne{sup 2+} production reveals the dominance of nonsequential two-photon double ionization at intensities of I<6x10{sup 12} W/cm{sup 2} and significant contributions of three-photon ionization as I increases. Ne{sup 2+} recoil-ion-momentum distributions suggest that two electrons absorbing ''instantaneously'' two photons are ejected most likely into opposite hemispheres with similar energies.

  7. On the possible source of the ionization in the nighttime Martian ionosphere. I - Phobos 2 HARP electron spectrometer measurements

    NASA Technical Reports Server (NTRS)

    Verigin, M. I.; Gringauz, K. I.; Shutte, N. M.; Haider, S. A.; Szego, K.; Kiraly, P.; Nagy, A. F.; Gombosi, T. I.

    1991-01-01

    The measurements of electron spectra in the Martian magnetosphere by the HARP instrument on board the Phobos 2 orbiter are presented. The energy of the electrons (a few tens of electron volts) is sufficient for the impact ionization of the planetary neutral gas, and the characteristic flux of electrons (about 10 exp 8/sq cm per sec) could produce the nightside ionospheric layer with a peak density of a few thousands of electrons per cubic centimeter, which corresponds to densities observed earlier during radio occultations of the Mars 4 and 5 and Viking 1 and 2 spacecraft. The possibility of magnetospheric electron precipitation into the nightside atmosphere of Mars is in agreement with the mainly induced nature of the magnetic field in the planetary magnetotail (as at Venus), while the variability of the Martian nightside ionosphere may be explained by the partial screening of the atmosphere by a weak intrinsic magnetic field of the planet.

  8. Propagation modes for a dusty plasma ionization instability under electron beam injection

    SciTech Connect

    Donoso, J. M.; Conde, L.

    2008-09-07

    The low frequency electrostatic linear modes of a dusty plasma penetrated by an energized electron beam are investigated in the frame of a one-dimensional multifluid equations. This plasma contains with thermal and non-thermal electrons, ions and charged dust grains. The stable and unstable modes of the ionization instability are examined in relation to the injected electron beam current density. We pay special attention to the relation of the unstable modes and the injected electron current and ionization cross-section dependence with beam energy, which are proved to be the critical parameters for triggering the instability. This latter could be monitored in the laboratory experiments.

  9. Inner-shell electron effects in strong-field double ionization of Xe

    NASA Astrophysics Data System (ADS)

    Yuan, Zongqiang; Ye, Difa; Liu, Jie; Fu, Libin

    2016-06-01

    We investigate theoretically the inner-shell electron effects in strong-field double ionization of Xe by a comparative study with two different three-dimensional semiclassical models, i.e., the widely used helium-like model and an improved Green-Sellin-Zachor (GSZ) model. The enhanced double-ionization signals through sequential ionization and recollision-induced excitation with subsequent field ionization are identified as two origins of the nonstructured pattern in the correlated electron momentum spectrum observed in a recent experiment [Phys. Rev. Lett. 113, 103001 (2014), 10.1103/PhysRevLett.113.103001]. The relationship between these enhancements and the inner-shell electrons is revealed by back analysis of the classical trajectories.

  10. Monte Carlo model for the analysis and development of III-V Tunnel-FETs and Impact Ionization-MOSFETs

    NASA Astrophysics Data System (ADS)

    Talbo, V.; Mateos, J.; González, T.; Lechaux, Y.; Wichmann, N.; Bollaert, S.; Vasallo, B. G.

    2015-10-01

    Impact-ionization metal-oxide-semiconductor FETs (I-MOSFETs) are in competition with tunnel FETs (TFETs) in order to achieve the best behaviour for low power logic circuits. Concretely, III-V I-MOSFETs are being explored as promising devices due to the proper reliability, since the impact ionization events happen away from the gate oxide, and the high cutoff frequency, due to high electron mobility. To facilitate the design process from the physical point of view, a Monte Carlo (MC) model which includes both impact ionization and band-to-band tunnel is presented. Two ungated InGaAs and InAlAs/InGaAs 100 nm PIN diodes have been simulated. In both devices, the tunnel processes are more frequent than impact ionizations, so that they are found to be appropriate for TFET structures and not for I- MOSFETs. According to our simulations, other narrow bandgap candidates for the III-V heterostructure, such as InAs or GaSb, and/or PININ structures must be considered for a correct I-MOSFET design.

  11. Multiple-Auger electron ejection after inner-shell ionization and excitation

    SciTech Connect

    Viefhaus, Jens

    2003-01-24

    Results on the Auger decay of core-ionized and core-exited Ar atoms above the Ar 2p threshold and at the Ar 2p3/2 {yields}3d resonance leading to double and triple ionization states are presented. Using a multiple time-of-flight analyzer arrangement for electron-electron coincidences, we directly observe for the first time a double Auger continuum following core electron ionization. Our results show clear evidence for continuously distributed Auger electron intensity over a 160 eV range of kinetic energies. This double Auger decay represents roughly 10 % of the normal single Auger channels. In the case of the resonant Auger decay we also observe a two-electron continuum of the same order of magnitude as in the non-resonant case which can be explained due to the existence of excited states of the doubly charged ion in the vicinity or just above the triple ionization threshold. In the latter case these states can further decay via emission of a low kinetic energy electron, which makes it possible to study the electron emission characteristics of the triple electron process. Both double- and triple-electron emission Auger processes will make it possible to study electron correlations undisturbed by the symmetry properties of the photoabsorption process.

  12. H to Zn Ionization Equilibrium for the Non-Maxwellian Electron κ-distributions: Updated Calculations

    NASA Astrophysics Data System (ADS)

    Dzifčáková, E.; Dudík, J.

    2013-05-01

    New data for the calculation of ionization and recombination rates have been published in the past few years, most of which are included in the CHIANTI database. We used these data to calculate collisional ionization and recombination rates for the non-Maxwellian κ-distributions with an enhanced number of particles in the high-energy tail, which have been detected in the solar transition region and the solar wind. Ionization equilibria for elements H to Zn are derived. The κ-distributions significantly influence both the ionization and recombination rates and widen the ion abundance peaks. In comparison with the Maxwellian distribution, the ion abundance peaks can also be shifted to lower or higher temperatures. The updated ionization equilibrium calculations result in large changes for several ions, notably Fe VIII-Fe XIV. The results are supplied in electronic form compatible with the CHIANTI database.

  13. A new concept Tandem thermal dissociator/electron impact ion source for RIB generation

    SciTech Connect

    Alton, G.D.; Williams, C.

    1995-12-31

    An innovative thermal dissociation/electron impact ionization positive ion source is presently under design at the Oak Ridge National Laboratory for potential use for generating RIBs at the Holifield Radioactive Ion Beam Facility (HRIBF). Because of the low probability of simultaneously dissociating and efficiently ionizing the individual atomic constituents with conventional, hot-cathode, electron-impact ion sources, the ion beams extracted from these sources often appear as a mixture of several molecular sideband beams. In this way, the intensity of the species of interest is diluted. We have conceived an Ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high efficiency characteristics of an electron impact ionization source. If the concept proves to be a viable option, the source will be used as a complement to the electron beam plasma ion sources already in use at the HRIBF. The design features and principles of operation of the source are described in this article.

  14. Model CRAC:EPII for atmospheric ionization due to precipitating electrons: Yield function and applications

    NASA Astrophysics Data System (ADS)

    Artamonov, A. A.; Mishev, A. L.; Usoskin, I. G.

    2016-02-01

    A new model of the family of CRAC models, CRAC:EPII (Cosmic Ray Atmospheric Cascade: Electron Precipitation Induced Ionization), is presented. The model calculates atmospheric ionization induced by precipitating electrons and uses the formalism of ionization yield functions. The CRAC:EPII model is based on a full Monte Carlo simulation of electron propagation and interaction with the air molecules. It explicitly considers various physical processes, namely, pair production, Compton scattering, generation of bremsstrahlung high-energy photons, photoionization, annihilation of positrons, and multiple scattering. The simulations were performed using GEANT 4 simulation tool PLANETOCOSMICS with NRLMSISE 00 atmospheric model. The CRAC:EPII model is applicable to the entire atmosphere. The results from the simulations are given as look-up table representing the ionization yield function. The table allows one to compute ionization due to precipitating electrons for a given altitude and location considering a given electron spectrum. Application of the model for computation of ion production during electron precipitation events using spectra from balloon-borne measurements is presented.

  15. Impact excitation of neon atoms by heated seed electrons in filamentary plasma gratings.

    PubMed

    Shi, Liping; Li, Wenxue; Zhou, Hui; Ding, Liang'en; Zeng, Heping

    2013-02-15

    We demonstrate impact ionization and dissociative recombination of neon (Ne) atoms by means of seeded-electron heating and subsequent electron-atom collisions in an ultraviolet plasma grating, allowing for a substantial fraction of the neutral Ne atomic population to reside in high-lying excited states. A buffer gas with relatively low ionization potential (nitrogen or argon) was used to provide high-density seed electrons. A three-step excitation model is verified by the fluorescence emission from the impact excitation of Ne atoms. PMID:23455081

  16. High temperature electronic excitation and ionization rates in gases

    NASA Technical Reports Server (NTRS)

    Hansen, Frederick

    1991-01-01

    The relaxation times for electronic excitation due to electron bombardment of atoms was found to be quite short, so that electron kinetic temperature (T sub e) and the electron excitation temperature (T asterisk) should equilibrate quickly whenever electrons are present. However, once equilibrium has been achieved, further energy to the excited electronic states and to the kinetic energy of free electrons must be fed in by collisions with heavy particles that cause vibrational and electronic state transitions. The rate coefficients for excitation of electronic states produced by heavy particle collision have not been well known. However, a relatively simple semi-classical theory has been developed here which is analytic up to the final integration over a Boltzmann distribution of collision energies; this integral can then be evaluated numerically by quadrature. Once the rate coefficients have been determined, the relaxation of electronic excitation energy can be evaluated and compared with the relaxation rates of vibrational excitation. Then the relative importance of these two factors, electronic excitation and vibrational excitation by heavy particle collision, on the transfer of energy to free electron motion, can be assessed.

  17. State-resolved three-dimensional electron-momentum correlation in nonsequential double ionization of benzene

    NASA Astrophysics Data System (ADS)

    Winney, Alexander H.; Lin, Yun Fei; Lee, Suk Kyoung; Adhikari, Pradip; Li, Wen

    2016-03-01

    We report state-resolved electron-momentum correlation measurement of strong-field nonsequential double ionization in benzene. With a novel coincidence detection apparatus, highly efficient triple coincidence (electron-electron dication) and quadruple coincidence (electron-electron-cation-cation) are used to resolve the final ionic states and to characterize three-dimensional (3D) electron-momentum correlation. The primary states associated with dissociative and nondissociative dications are assigned. A 3D momentum anticorrelation is observed for the electrons in coincidence with dissociative benzene dication states whereas such a correlation is absent for nondissociative dication states.

  18. Hose instability and wake generation by an intense electron beam in a self-ionized gas.

    PubMed

    Deng, S; Barnes, C D; Clayton, C E; O'Connell, C; Decker, F J; Fonseca, R A; Huang, C; Hogan, M J; Iverson, R; Johnson, D K; Joshi, C; Katsouleas, T; Krejcik, P; Lu, W; Mori, W B; Muggli, P; Oz, E; Tsung, F; Walz, D; Zhou, M

    2006-02-01

    The propagation of an intense relativistic electron beam through a gas that is self-ionized by the beam's space charge and wakefields is examined analytically and with 3D particle-in-cell simulations. Instability arises from the coupling between a beam and the offset plasma channel it creates when it is perturbed. The traditional electron hose instability in a preformed plasma is replaced with this slower growth instability depending on the radius of the ionization channel compared to the electron blowout radius. A new regime for hose stable plasma wakefield acceleration is suggested. PMID:16486834

  19. Hose Instability and Wake Generation By An Intense Electron Beam in a Self-Ionized Gas

    SciTech Connect

    Deng, S.; Barnes, C.D.; Clayton, C.E.; O'Connell, C.; Decker, F.J.; Fonseca, R.A.; Huang, C.; Hogan, M.J.; Iverson, R.; Johnson, D.K.; Joshi, C.; Katsouleas, T.; Krejcik, P.; Lu, W.; Mori, W.B.; Muggli, P.; Oz, E.; Tsung, F.; Walz, D.; Zhou, M.; /Southern California U. /UCLA /SLAC

    2006-04-12

    The propagation of an intense relativistic electron beam through a gas that is self-ionized by the beam's space charge and wakefields is examined analytically and with 3D particle-in-cell simulations. Instability arises from the coupling between a beam and the offset plasma channel it creates when it is perturbed. The traditional electron hose instability in a preformed plasma is replaced with this slower growth instability depending on the radius of the ionization channel compared to the electron blowout radius. A new regime for hose stable plasma wakefield acceleration is suggested.

  20. Ionization-assisted relativistic electron generation with monoenergetic features from laser thin foil interaction

    SciTech Connect

    Glazyrin, I. V.; Karpeev, A. V.; Kotova, O. G.; Bychenkov, V. Yu.; Fedosejevs, R.; Rozmus, W.

    2012-07-11

    The concept of ionization-induced injection into the laser pulse to produce quasi-monoenergetic bunches of electrons from ultra-thin solid dense targets is analyzed. When the laser pulse propagates through semi-transparent foil the electrons from inner atom shells remain bound during the rise time of the laser pulse and are ionized by the laser intensity near its maximum amplitude, which satisfies the best injection condition for subsequent acceleration. It was found that a bunch of quasimonoenergetic electrons from inner atom shells moves co-directionally with laser pulse and acquire energy {approx}m{sub e}c{sup 2}a{sup 2}/2.

  1. Attosecond electron thermalization in laser-induced nonsequential multiple ionization: hard versus glancing collisions

    NASA Astrophysics Data System (ADS)

    Liu, X.; Figueira de Morisson Faria, C.; Becker, W.

    2008-02-01

    A recollision-based largely classical statistical model of laser-induced nonsequential multiple (N-fold) ionization of atoms is further explored. Upon its return to the ionic core, the first-ionized electron interacts with the other N- 1 bound electrons either through a contact or a Coulomb interaction. The returning electron may leave either immediately after this interaction or join the other electrons to form a thermalized complex which leaves the ion after the delay Δt, which is the sum of a thermalization time and a possible additional dwell time. Good agreement with the available triple and quadruple ionization data in neon and argon is obtained with the contact scenario and delays of Δt=0.17 T and 0.265 T, respectively, with T the laser period.

  2. Injection and Trapping of Tunnel-Ionized Electrons into Laser-Produced Wakes

    SciTech Connect

    Pak, A.; Marsh, K. A.; Joshi, C.; Martins, S. F.; Lu, W.; Mori, W. B.

    2010-01-15

    A method, which utilizes the large difference in ionization potentials between successive ionization states of trace atoms, for injecting electrons into a laser-driven wakefield is presented. Here a mixture of helium and trace amounts of nitrogen gas was used. Electrons from the K shell of nitrogen were tunnel ionized near the peak of the laser pulse and were injected into and trapped by the wake created by electrons from majority helium atoms and the L shell of nitrogen. The spectrum of the accelerated electrons, the threshold intensity at which trapping occurs, the forward transmitted laser spectrum, and the beam divergence are all consistent with this injection process. The experimental measurements are supported by theory and 3D OSIRIS simulations.

  3. Classical cutoffs for laser-induced nonsequential double ionization

    SciTech Connect

    Milosevic, D.B.; Becker, W.

    2003-12-01

    Classical cutoffs for the momenta of electrons ejected in laser-induced nonsequential double ionization are derived for the recollision-impact-ionization scenario. Such simple cutoff laws can aid in the interpretation of the observed electron spectra.

  4. Electron-nuclear energy sharing in above-threshold multiphoton dissociative ionization of H2.

    PubMed

    Wu, J; Kunitski, M; Pitzer, M; Trinter, F; Schmidt, L Ph H; Jahnke, T; Magrakvelidze, M; Madsen, C B; Madsen, L B; Thumm, U; Dörner, R

    2013-07-12

    We report experimental observation of the energy sharing between electron and nuclei in above-threshold multiphoton dissociative ionization of H2 by strong laser fields. The absorbed photon energy is shared between the ejected electron and nuclei in a correlated fashion, resulting in multiple diagonal lines in their joint energy spectrum governed by the energy conservation of all fragment particles. PMID:23889391

  5. Electron reversal ionizer for detection of trace species using a spherical cathode

    NASA Technical Reports Server (NTRS)

    Boumsellek, Said (Inventor); Chutjian, Ara (Inventor)

    1994-01-01

    A reversal electron, high-current ionizer capable of focusing a beam of electrons to a reversal region employs an indirectly heated cathode having a concave emitting surface of width of W less than 2r, where r is the radius of curvature and preferably a ratio of width to radius approximately equal to one for optimum high current for a given cathode width.

  6. E-beam ionized channel guiding of an intense relativistic electron beam

    DOEpatents

    Frost, Charles A.; Godfrey, Brendon B.; Kiekel, Paul D.; Shope, Steven L.

    1988-01-01

    An IREB is guided through a curved path by ionizing a channel in a gas with electrons from a filament, and confining the electrons to the center of the path with a magnetic field extending along the path. The magnetic field is preferably generated by a solenoid extending along the path.

  7. E-beam ionized channel guiding of an intense relativistic electron beam

    DOEpatents

    Frost, C.A.; Godfrey, B.B.; Kiekel, P.D.; Shope, S.L.

    1988-05-10

    An IREB is guided through a curved path by ionizing a channel in a gas with electrons from a filament, and confining the electrons to the center of the path with a magnetic field extending along the path. The magnetic field is preferably generated by a solenoid extending along the path. 2 figs.

  8. Electron diffraction self-imaging of molecular fragmentation in two-step double ionization of water.

    PubMed

    Sann, H; Jahnke, T; Havermeier, T; Kreidi, K; Stuck, C; Meckel, M; Schöffler, M S; Neumann, N; Wallauer, R; Voss, S; Czasch, A; Jagutzki, O; Weber, Th; Schmidt-Böcking, H; Miyabe, S; Haxton, D J; Orel, A E; Rescigno, T N; Dörner, R

    2011-04-01

    We doubly ionize H(2)O by single photon absorption at 43 eV leading to H(+) + OH(+). A direct double ionization and a sequential process in which single ionization is followed by rapid dissociation into a proton and an autoionizing OH(*) are identified. The angular distribution of this delayed autoionization electron shows a preferred emission in the direction of the emitted proton. From this diffraction feature we obtain internuclear distances of 700 to 1100 a.u. at which the autoionization of the OH(*) occurs. The experimental findings are in line with calculations of the excited potential energy surfaces and their lifetimes. PMID:21517378

  9. Impact of dissolved organic matter on the photolysis of the ionizable antibiotic norfloxacin.

    PubMed

    Liang, Chen; Zhao, Huimin; Deng, Minjie; Quan, Xie; Chen, Shuo; Wang, Hua

    2015-01-01

    Norfloxacin (NOR), an ionizable antibiotic frequently used in the aquaculture industry, has aroused public concern due to its persistence, bacterial resistance, and environmental ubiquity. Therefore, we investigated the photolysis of different species of NOR and the impact of a ubiquitous component of natural water - dissolved organic matter (DOM), which has a special photochemical activity and normally acts as a sensitizer or inhibiter in the photolysis of diverse organics; furthermore, scavenging experiments combined with electron paramagnetic resonance (EPR) were performed to evaluate the transformation of NOR in water. The results demonstated that NOR underwent direct photolysis and self-sensitized photolysis via hydroxyl radical (OH) and singlet oxygen ((1)O2) based on the scavenging experiments. In addition, DOM was found to influence the photolysis of different NOR species, and its impact was related to the concentration of DOM and type of NOR species. Photolysis of cationic NOR was photosensitized by DOM at low concentration, while zwitterionic and anionic NOR were photoinhibited by DOM, where quenching of OH predominated according to EPR experiments, accompanied by possible participation of excited triplet-state NOR and (1)O2. Photo-intermediate identification of different NOR species in solutions with/without DOM indicated that NOR underwent different photodegradation pathways including dechlorination, cleavage of the piperazine side chain and photooxidation, and DOM had little impact on the distribution but influenced the concentration evolution of photolysis intermediates. The results implied that for accurate ecological risk assessment of emerging ionizable pollutants, the impact of DOM on the environmental photochemical behavior of all dissociated species should not be ignored. PMID:25597669

  10. Multistart spiral electron vortices in ionization by circularly polarized UV pulses

    NASA Astrophysics Data System (ADS)

    Ngoko Djiokap, J. M.; Meremianin, A. V.; Manakov, N. L.; Hu, S. X.; Madsen, L. B.; Starace, Anthony F.

    2016-07-01

    Multistart spiral vortex patterns are predicted for the electron momentum distributions in the polarization plane following ionization of the helium atom by two time-delayed circularly polarized ultrashort laser pulses. For two ultraviolet (UV) pulses having the same frequency (such that two photons are required for ionization), single-color two-photon interferometry with corotating or counter-rotating time-delayed pulses is found to lead respectively to zero-start or four-start spiral vortex patterns in the ionized electron momentum distributions in the polarization plane. In contrast, two-color one-photon plus two-photon interferometry with time-delayed corotating or counter-rotating UV pulses is found to lead respectively to one-start or three-start spiral vortex patterns. These predicted multistart electron vortex patterns are found to be sensitive to the carrier frequencies, handedness, time delay, and relative phase of the two pulses. Our numerical predictions are obtained by solving the six-dimensional two-electron time-dependent Schrödinger equation (TDSE). They are explained analytically using perturbation theory (PT). Comparison of our TDSE and PT results for single-color two-photon processes probes the role played by the time-delay-dependent ionization cross channels in which one photon is absorbed from each pulse. Control of these cross channels by means of the parameters of the fields and the ionized electron detection geometries is discussed.

  11. Observation of increased space-charge limited thermionic electron emission current by neutral gas ionization in a weakly-ionized deuterium plasma

    SciTech Connect

    Hollmann, E. M.; Yu, J. H.; Doerner, R. P.; Nishijima, D.; Seraydarian, R. P.

    2015-09-14

    The thermionic electron emission current emitted from a laser-produced hot spot on a tungsten target in weakly-ionized deuterium plasma is measured. It is found to be one to two orders of magnitude larger than expected for bipolar space charge limited thermionic emission current assuming an unperturbed background plasma. This difference is attributed to the plasma being modified by ionization of background neutrals by the emitted electrons. This result indicates that the allowable level of emitted thermionic electron current can be significantly enhanced in weakly-ionized plasmas due to the presence of large neutral densities.

  12. Insertion of an electron beam ionizer in a quadrupole spectrometer for secondary neutral mass analysis

    NASA Astrophysics Data System (ADS)

    Ameziane, O.; Blanco, J. M.; Serrano, J. J.; Guzmán, B.; Aguilar, M.

    2003-06-01

    An insertable electron beam ionizer into a quadrupole-based secondary ion mass spectrometer instrument has been designed and installed to analyze sputtered neutrals. The optimum design conditions of the ionizer have been obtained by modeling various configurations of the system using a simulation program developed by us. The program has allowed us to compute the potentials and ion trajectories inside the system to test the performance of the ion optics design. We have investigated the advantages of using a large ionization volume with low electron current to minimize the space charge effect in the ionizer, as this is the major problem in this type of instrument. In addition, we have used the simulations to obtain all electrodes voltages which provide an efficient suppression of residual gas and secondary ions. A good useful yield was obtained, even with low electron densities, thanks to the high geometrical acceptance of the ionizer and its large active volume. This configuration implies less thermal radiation in the ionizer and, in addition, a longer life time of the filament. Although the signal of residual gas not suppressed (i.e. in residual gas mode) is two orders of magnitude higher than the signal of sputtered neutrals, we have achieved a good background suppression.

  13. Relativistic contributions to single and double core electron ionization energies of noble gases

    SciTech Connect

    Niskanen, J.; Norman, P.; Aksela, H.; Aagren, H.

    2011-08-07

    We have performed relativistic calculations of single and double core 1s hole states of the noble gas atoms in order to explore the relativistic corrections and their additivity to the ionization potentials. Our study unravels the interplay of progression of relaxation, dominating in the single and double ionization potentials of the light elements, versus relativistic one-electron effects and quantum electrodynamic effects, which dominate toward the heavy end. The degree of direct relative additivity of the relativistic corrections for the single electron ionization potentials to the double electron ionization potentials is found to gradually improve toward the heavy elements. The Dirac-Coulomb Hamiltonian is found to predict a scaling ratio of {approx}4 for the relaxation induced relativistic energies between double and single ionization. Z-scaling of the computed quantities were obtained by fitting to power law. The effects of nuclear size and form were also investigated and found to be small. The results indicate that accurate predictions of double core hole ionization potentials can now be made for elements across the full periodic table.

  14. Dynamics of ionization-induced electron injection in the high density regime of laser wakefield acceleration

    SciTech Connect

    Desforges, F. G.; Paradkar, B. S. Ju, J.; Audet, T. L.; Maynard, G.; Cros, B.; Hansson, M.; Senje, L.; Persson, A.; Lundh, O.; Wahlström, C.-G.; Dobosz-Dufrénoy, S.; Monot, P.; Vay, J.-L.

    2014-12-15

    The dynamics of ionization-induced electron injection in high density (∼1.2 × 10{sup 19} cm{sup −3}) regime of laser wakefield acceleration is investigated by analyzing the betatron X-ray emission. In such high density operation, the laser normalized vector potential exceeds the injection-thresholds of both ionization-injection and self-injection due to self-focusing. In this regime, direct experimental evidence of early on-set of ionization-induced injection into the plasma wave is given by mapping the X-ray emission zone inside the plasma. Particle-In-Cell simulations show that this early on-set of ionization-induced injection, due to its lower trapping threshold, suppresses the trapping of self-injected electrons. A comparative study of the electron and X-ray properties is performed for both self-injection and ionization-induced injection. An increase of X-ray fluence by at least a factor of two is observed in the case of ionization-induced injection due to increased trapped charge compared to self-injection mechanism.

  15. The Use of Ionization Electron Columns for Space-Charge Compensation in High Intensity Proton Accelerators

    SciTech Connect

    Shiltsev, V.; Alexahin, Y.; Kamerdzhiev, V.; Kapin, V.; Kuznetsov, G.

    2009-01-22

    We discuss a recent proposal to use strongly magnetized electron columns created by beam ionization of the residual gas for compensation of space charge forces of high intensity proton beams in synchrotrons and linacs. The electron columns formed by trapped ionization electrons in a longitudinal magnetic field that assures transverse distribution of electron space charge in the column is the same as in the proton beam. Electrostatic electrodes are used to control the accumulation and release of the electrons. Ions are not magnetized and drift away without affecting the compensation. Possible technical solution for the electron columns is presented. We also discuss the first numerical simulation results for space-charge compensation in the FNAL Booster and results of relevant beam studies in the Tevatron.

  16. The use of ionization electron columns for space-charge compensation in high intensity proton accelerators

    SciTech Connect

    Shiltsev, V.; Alexahin, Y.; Kamerdzhiev, V.; Kapin, V.; Kuznetsov, G.; /Fermilab

    2009-01-01

    We discuss a recent proposal to use strongly magnetized electron columns created by beam ionization of the residual gas for compensation of space charge forces of high intensity proton beams in synchrotrons and linacs. The electron columns formed by trapped ionization electrons in a longitudinal magnetic field that assures transverse distribution of electron space charge in the column is the same as in the proton beam. Electrostatic electrodes are used to control the accumulation and release of the electrons. Ions are not magnetized and drift away without affecting the compensation. Possible technical solution for the electron columns is presented. We also discuss the first numerical simulation results for space-charge compensation in the FNAL Booster and results of relevant beam studies in the Tevatron.

  17. Medium Vacuum Electron Emitter as Soft Atmospheric Pressure Chemical Ionization Source for Organic Molecules.

    PubMed

    Liedtke, Sascha; Ahlmann, Norman; Marggraf, Ulrich; Schütz, Alexander; Vautz, Wolfgang; Franzke, Joachim

    2016-05-01

    An electron emitter as a soft atmospheric pressure chemical ionization source is presented, which operates at inner pressures of the device in the medium vacuum range (>10(-3) hPa). Conventional nonradioactive electron emitters require high vacuum (<10(-6) hPa) to prevent electrical sparkovers. The emitter presented here contains structural modifications of an existing setup, which inhibits electrical breakdowns up to 10(-2) hPa at 8 kV acceleration voltage. The increased inner pressure reduces the ionization efficiency until 10(-3) hPa-achievable without a turbomolecular pump-by 2% compared to high-vacuum conditions. This can be compensated with an increase of the electron source output. The functionality of this ion source is demonstrated with mass spectrometric and ion mobility measurements of acetone, eucalyptol, and diisopropyl methanephosphonate. Additional mass spectrometric measurements of 20 different organic compounds demonstrate the soft characteristics of this ionization source. PMID:27046293

  18. Exact Potential Driving the Electron Dynamics in Enhanced Ionization of H2+

    NASA Astrophysics Data System (ADS)

    Khosravi, Elham; Abedi, Ali; Maitra, Neepa T.

    2015-12-01

    It was recently shown that the exact factorization of the electron-nuclear wave function allows the construction of a Schrödinger equation for the electronic system, in which the potential contains exactly the effect of coupling to the nuclear degrees of freedom and any external fields. Here we study the exact potential acting on the electron in charge-resonance enhanced ionization in a model one-dimensional H2+ molecule. We show there can be significant differences between the exact potential and that used in the traditional quasistatic analyses, arising from nonadiabatic coupling to the nuclear system, and that these are crucial to include for accurate simulations of time-resolved ionization dynamics and predictions of the ionization yield.

  19. Orientation and alignment effects in electron-induced ionization of a single oriented water molecule

    SciTech Connect

    Champion, C.; Rivarola, R. D.

    2010-10-15

    We here report a theoretical study about the orientation effect on the total ionization cross sections for a single oriented water molecule. The theoretical description of the ionization process is performed within the first Born framework with a collisional system including an initial state composed of a projectile and a water target molecule described by a plane wave and an accurate one-center molecular wave function, respectively, and a final state constituted by a slow ejected electron represented by a Coulomb wave and a scattered (fast) electron projectile described by a plane wave. Secondary electron energetic distributions as well as total cross sections are then compared for particular target configurations pointing out strong alignment and orientation effects on the description of the ionization process.

  20. Scaling Cross Sections for Ion-atom Impact Ionization

    SciTech Connect

    Igor D. Kaganovich; Edward Startsev; Ronald C. Davidson

    2003-06-06

    The values of ion-atom ionization cross sections are frequently needed for many applications that utilize the propagation of fast ions through matter. When experimental data and theoretical calculations are not available, approximate formulas are frequently used. This paper briefly summarizes the most important theoretical results and approaches to cross section calculations in order to place the discussion in historical perspective and offer a concise introduction to the topic. Based on experimental data and theoretical predictions, a new fit for ionization cross sections is proposed. The range of validity and accuracy of several frequently used approximations (classical trajectory, the Born approximation, and so forth) are discussed using, as examples, the ionization cross sections of hydrogen and helium atoms by various fully stripped ions.

  1. Ionization Cross Sections and Dissociation Channels of the DNA Sugar-Phosphate Backbone by Electron Collisions

    NASA Technical Reports Server (NTRS)

    Dateo, Christopher; Huo, Winifred M.; Fletcher, Graham D.

    2004-01-01

    It has been suggested that the genotoxic effects of ionizing radiation in living cells are not caused by the highly energetic incident radiation, but rather are induced by less energetic secondary species generated, the most abundant of which are free electrons.' The secondary electrons will further react to cause DNA damage via indirect and direct mechanisms. Detailed knowledge of these mechanisms is ultimately important for the development of global models of cellular radiation damage. We are studying one possible mechanism for the formation cf DNA strand breaks involving dissociative ionization of the DNA sugar-phosphate backbone induced by secondary electron co!lisions. We will present ionization cross sections at electron collision energies between threshold and 10 KeV using the improved binary encounter dipole (iBED) formulation' Preliminary results of the possible dissociative ionization pathways will be presented. It is speculated that radical fragments produced from the dissociative ionization can further react, providing a possible mechanism for double strand breaks and base damage.

  2. Relaxation Processes in Aqueous Systems upon X-ray Ionization: Entanglement of Electronic and Nuclear Dynamics.

    PubMed

    Slavíček, Petr; Kryzhevoi, Nikolai V; Aziz, Emad F; Winter, Bernd

    2016-01-21

    The knowledge of primary processes following the interaction of high-energy radiation with molecules in liquid phase is rather limited. In the present Perspective, we report on a newly discovered type of relaxation process involving simultaneous autoionization and proton transfer between adjacent molecules, so-called proton transfer mediated charge separation (PTM-CS) process. Within PTM-CS, transients with a half-transferred proton are formed within a few femtoseconds after the core-level ionization event. Subsequent nonradiative decay of the highly nonequilibrium transients leads to a series of reactive species, which have not been considered in any high-energy radiation process in water. Nonlocal electronic decay processes are surprisingly accelerated upon proton dynamics. Such strong coupling of electronic and nuclear dynamics is a general phenomenon for hydrogen-bonded systems, however, its probability correlates strongly with hydration geometry. We suggest that the newly observed processes will impact future high-energy radiation-chemistry-relevant modeling, and we envision application of autoionization spectroscopy for identification of solution structure details. PMID:26712083

  3. Femtosecond two-photon ionization and solvated electron geminate recombination in liquid-to-supercritical ammonia.

    PubMed

    Urbanek, Janus; Dahmen, Annika; Torres-Alacan, Joel; Königshoven, Peter; Lindner, Jörg; Vöhringer, Peter

    2012-02-23

    The first-ever femtosecond pump-probe study is reported on solvated electrons that were generated by multiphoton ionization of neat fluid ammonia. The initial ultrafast ionization was carried out with 266 nm laser pulses and was found to require two photons. The solvated electron was detected with a femtosecond probe pulse that was resonant with its characteristic near-infrared absorption band around 1.7 μm. Furthermore, the geminate recombination dynamics of the solvated electron were studied over wide ranges of temperature (227 K ≤ T ≤ 489 K) and density (0.17 g cm(-3) ≤ ρ ≤ 0.71 g cm(-3)), thereby covering the liquid and the supercritical phase of the solvent. The electron recombines in a first step with ammonium cations originating from the initial two-photon ionization thereby forming transient ion-pairs (e(am)(-)·NH(4)(+)), which subsequently react in a second step with amidogen radicals to reform neutral ammonia. The escape probability, i.e., the fraction of solvated electrons that can avoid the geminate annihilation, was found to be in quantitative agreement with the classical Onsager theory for the initial recombination of ions. When taking the sequential nature of the ion-pair-mediated recombination mechanism explicitly into account, the Onsager model provides a mean thermalization distance of 6.6 nm for the solvated electron, which strongly suggests that the ionization mechanism involves the conduction band of the fluid. PMID:22272761

  4. Demonstration of self-truncated ionization injection for GeV electron beams

    PubMed Central

    Mirzaie, M.; Li, S.; Zeng, M.; Hafz, N. A. M.; Chen, M.; Li, G. Y.; Zhu, Q. J.; Liao, H.; Sokollik, T.; Liu, F.; Ma, Y. Y.; Chen, L.M.; Sheng, Z. M.; Zhang, J.

    2015-01-01

    Ionization-induced injection mechanism was introduced in 2010 to reduce the laser intensity threshold for controllable electron trapping in laser wakefield accelerators (LWFA). However, usually it generates electron beams with continuous energy spectra. Subsequently, a dual-stage target separating the injection and acceleration processes was regarded as essential to achieve narrow energy-spread electron beams by ionization injection. Recently, we numerically proposed a self-truncation scenario of the ionization injection process based upon overshooting of the laser-focusing in plasma which can reduce the electron injection length down to a few hundred micrometers, leading to accelerated beams with extremely low energy-spread in a single-stage. Here, using 100 TW-class laser pulses we report experimental observations of this injection scenario in centimeter-long plasma leading to the generation of narrow energy-spread GeV electron beams, demonstrating its robustness and scalability. Compared with the self-injection and dual-stage schemes, the self-truncated ionization injection generates higher-quality electron beams at lower intensities and densities, and is therefore promising for practical applications. PMID:26423136

  5. Demonstration of self-truncated ionization injection for GeV electron beams.

    PubMed

    Mirzaie, M; Li, S; Zeng, M; Hafz, N A M; Chen, M; Li, G Y; Zhu, Q J; Liao, H; Sokollik, T; Liu, F; Ma, Y Y; Chen, L M; Sheng, Z M; Zhang, J

    2015-01-01

    Ionization-induced injection mechanism was introduced in 2010 to reduce the laser intensity threshold for controllable electron trapping in laser wakefield accelerators (LWFA). However, usually it generates electron beams with continuous energy spectra. Subsequently, a dual-stage target separating the injection and acceleration processes was regarded as essential to achieve narrow energy-spread electron beams by ionization injection. Recently, we numerically proposed a self-truncation scenario of the ionization injection process based upon overshooting of the laser-focusing in plasma which can reduce the electron injection length down to a few hundred micrometers, leading to accelerated beams with extremely low energy-spread in a single-stage. Here, using 100 TW-class laser pulses we report experimental observations of this injection scenario in centimeter-long plasma leading to the generation of narrow energy-spread GeV electron beams, demonstrating its robustness and scalability. Compared with the self-injection and dual-stage schemes, the self-truncated ionization injection generates higher-quality electron beams at lower intensities and densities, and is therefore promising for practical applications. PMID:26423136

  6. Hartree simulations of multi-electron atoms ionization in strong laser fields

    NASA Astrophysics Data System (ADS)

    Kalinski, Matt

    2007-05-01

    The recent success of classical simulations of the ionization process of few electron atom is an argument that normal electron exchange and correlations effects are negligible for certain conditions of strong field ionization and only the Coulomb effects are essential [1]. The numerical convenience of solving the Schr"odinger equation with nonlinearity instead of classical equations of the motion has been recently proved by us in case of so-called Trojan electrons in strong CP fields with Shay logarithmic quantum mechanics [2]. We present Hartree simulations of the ultra-strong field time-dependent ionization of model one dimensional atoms with up to 10 active electrons involved (10 dimensional configuration space). N coupled Schr"odinger equations is solved simultaneously on the Cartesian grid with our new nonlinear split-operator method. The continuum states are taken into account with delta grid representation of the multi electron wavefunction and the Coulomb interaction integral is calculated as the direct solution of the Poisson equation with the ultra-fast Fast Fourier convolution method developed by us to treat the supersolid formation in Bose-Einstein condensate. We calculate n-electron ionization rates for ultra-strong ultra-short few cycle pulses. [1] P. J. Ho and J. H. Eberly, Phys. Rev. Lett. 95, 193002 (2005). [2] M. Kalinski, contributed paper, APS DAMOP meeting, Lincoln, Nebraska, May, 2005 To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2007.NWS07.E3.2

  7. Cross section of the impact single ionization of B2+ by H+

    NASA Astrophysics Data System (ADS)

    Ye, Dan-Dan; Qi, Yue-Ying; Hu, Ya-Hua; Ning, Li-Na

    2013-05-01

    The ionization process of B2+ by H+ impact is studied using the continuum-distorted-wave eikonal-initial-state (CDW-EIS) method and the modified free electron peak approximation (M-FEPA), respectively. Total, single-, and double-differential cross sections from 1s and 2s orbitals are presented for the energy range from 10 keV/u to 10 MeV/u. Comparison between the results from the two methods demonstrates that the total and single-differential cross sections for the high-energy incident projectile case can be well evaluated using the simple M-FEPA model. Moreover, the M-FEPA model reproduces the essential features of the binary-encounter (BE) bump in the double-differential cross sections. Thus, the BE ionization mechanism is discussed in detail by adopting the M-FEPA model. In particular, the double- and singledifferential cross sections from the 2s orbital show a high-energy hip, which is different from those from the 1s orbital. Based on Ref. [1], the Compton profiles of B2+ for 1s and 2s orbitals are given, and the hips in DDCS and SDCS from the 2s orbital are explained.

  8. Absolute cross sections for electron loss, electron capture, and multiple ionization in collisions of Li2+ with argon

    NASA Astrophysics Data System (ADS)

    Losqui, A. L. C.; Zappa, F.; Sigaud, G. M.; Wolff, W.; Sant'Anna, M. M.; Santos, A. C. F.; Luna, H.; Melo, W. S.

    2014-02-01

    Exclusive absolute cross sections for the electron loss and capture processes, accompanied by target multiple ionization and pure target multiple ionization, as well as total electron loss and capture cross sections, in collisions of Li2+ with Ar have been measured in the 0.5-3.5 MeV energy range. The experimental data of the total electron loss cross section are compared with theoretical results based on the plane-wave Born approximation and the free-collision model, and with the available experimental data. Some discrepancies are observed when comparing the experimental data with the theoretical models, which can be attributed to the competitive mechanisms that lead to electron loss. The dependences of the single-capture and transfer-ionization processes on the projectile charge state are similar to those observed for collisions between other low-charged light ions and noble-gas targets. The same behaviour is observed when one compares the present data for the single- and double-ionization cross sections with those for He2+ projectiles on Ar. These facts indicate that the dynamics of the collision does not seem to depend on the projectile species, so that few-electron projectiles may act as structureless point charges in the intermediate- to high-velocity regime.

  9. Efficient electronic structure calculation for molecular ionization dynamics at high x-ray intensity.

    PubMed

    Hao, Yajiang; Inhester, Ludger; Hanasaki, Kota; Son, Sang-Kil; Santra, Robin

    2015-07-01

    We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL) pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed during XFEL pulses. The present method is suitable to investigate x-ray multiphoton multiple ionization dynamics and accompanying nuclear dynamics, providing essential information on the chemical dynamics relevant for high-intensity x-ray imaging. PMID:26798806

  10. Efficient electronic structure calculation for molecular ionization dynamics at high x-ray intensity

    PubMed Central

    Hao, Yajiang; Inhester, Ludger; Hanasaki, Kota; Son, Sang-Kil; Santra, Robin

    2015-01-01

    We present the implementation of an electronic-structure approach dedicated to ionization dynamics of molecules interacting with x-ray free-electron laser (XFEL) pulses. In our scheme, molecular orbitals for molecular core-hole states are represented by linear combination of numerical atomic orbitals that are solutions of corresponding atomic core-hole states. We demonstrate that our scheme efficiently calculates all possible multiple-hole configurations of molecules formed during XFEL pulses. The present method is suitable to investigate x-ray multiphoton multiple ionization dynamics and accompanying nuclear dynamics, providing essential information on the chemical dynamics relevant for high-intensity x-ray imaging. PMID:26798806

  11. Probe of the electron correlation in sequential double ionization of helium by two-color attosecond pulses

    NASA Astrophysics Data System (ADS)

    Peng, Liang-You; Zhang, Zheng; Jiang, Wei-Chao; Zhang, Gong-Qiu; Gong, Qihuang

    2012-12-01

    We theoretically study the sequential double ionization of He by two-color attosecond pulses. We show that, for short time delays between the two pulses, the ionization spectra cannot be explained by an independent model based on the time-dependent perturbation theory. By varying the time delay, one can probe the role of the electron correlation played in the double ionization, which is mostly obvious by examining the differential double-ionization yield. In the present scheme, we also identify a kind of “catch-up” interaction between the two ionized electrons.

  12. ENERGY DISTRIBUTION OF TWO-ELECTRON IONIZATION OF HELIUM IN AN INTENSE LASER FIELD.

    SciTech Connect

    LAFON,R.; CHALOUPKA,J.L.; SHEEHY,B.; DIMAURO,L.F.; PAUL,P.M.; AGOSTINI,P.; KULANDER,K.C.

    2000-09-24

    It is well known that a neutral atom interacting with a strong laser field will ionize at sufficiently high intensity even for photon energies well below the ionization threshold. When the required number of photons becomes very large, this process is best described by the suppression of the Coulomb barrier by the laser's oscillating electric field, allowing the electron to tunnel into the continuum. As the laser intensity is increased, more tightly bound electrons may be successively liberated by this mechanism. Such a sequential multiple ionization, long accepted as a reasonable approach to the formidable problem of a multielectron atom interacting nonperturbatively with an intense electromagnetic field, provides fair estimates of the various charge state appearance intensities while the tunneling rates are in excellent agreement with single ionization yields. However, more accurate measurements revealed systematic and very large deviations from the tunneling rates: near appearance intensity under standard experimental conditions, the observed double ion yield is several orders of magnitude larger than predicted by the sequential rate. It soon became clear that electrons could not be considered as independent and that electron-electron correlation had to be taken into account. Dynamic correlations have been considered in several theories. First qualitatively in the shakeoff model; then empirically through the e-2e cross-section in the quantum/classical three-step model (tunnel ionization, acceleration by the oscillating electric field and e-2e recollision with the ion); recently through the so-called intense field many-body-S-matrix theory and a purely empirical model of collective tunnel ionization. The validity of these ideas has been examined using numerical models. The measurement of total ion yields over a dynamic range exceeding ten orders of magnitude, a major breakthrough made possible by the availability of high-repetition rate lasers at the beginning of

  13. Doubly resonant three-photon double ionization of Ar atoms induced by an EUV free-electron laser

    SciTech Connect

    Gryzlova, E. V.; Ma, Ri; Fukuzawa, H.; Motomura, K.; Yamada, A.; Ueda, K.; Grum-Grzhimailo, A. N.; Strakhova, S. I.; Kabachnik, N. M.; Rouzee, A.; Hundermark, A.; Vrakking, M. J. J.; Johnsson, P.; Nagaya, K.; Yase, S.; Mizoguchi, Y.; Yao, M.; Nagasono, M.; Tono, K.; Yabashi, M.; and others

    2011-12-15

    A mechanism for three-photon double ionization of atoms by extreme-ultraviolet free-electron laser pulses is revealed, where in a sequential process the second ionization step, proceeding via resonant two-photon ionization of ions, is strongly enhanced by the excitation of ionic autoionizing states. In contrast to the conventional model, the mechanism explains the observed relative intensities of photoelectron peaks and their angular dependence in three-photon double ionization of argon.

  14. Acceleration of electrons generated during ionization of a gas by a nearly flat profile laser pulse

    SciTech Connect

    Singh, Kunwar Pal

    2009-09-15

    A scheme of acceleration of electrons generated during ionization of krypton by nearly flat radial and nearly flat temporal laser pulse profiles has been suggested. The energy spectrum of the electrons suggests that energy of the electrons is higher for a nearly flat temporal profile than that for a nearly flat radial profile. The suppression of scattering of the electrons is better for a nearly flat radial profile than that for a nearly flat temporal profile. The energy of the electrons increases, scattering decreases, and beam quality improves with an increase in flatness of radial and temporal profiles.

  15. Electrophysical and optophysical properties of air ionized by a short pulse of fast electrons

    NASA Astrophysics Data System (ADS)

    Vagin, Iu. P.; Stal', N. L.; Khokhlov, V. D.; Chernoiarskii, A. A.

    A method for solving the nonstationary kinetic equation of electron deceleration is developed which is based on the multigroup approximation. The electron distribution function in air ionized by nonstationary sources of primary electrons is determined, and the avalanche formation of secondary electrons is considered. Theoretical and experimental results are presented on the time dependence of the air luminescence intensity in two spectral intervals, one including the 391.4 nm N2(+) band and the other including the 337.1 nm N2 band, for different values of gas pressure under the effect of a short beam of electrons with energies of 100 keV.

  16. Ultrafast Electron and Ion Dynamics in Strong-Field-Ionized Liquid Water

    NASA Astrophysics Data System (ADS)

    Loh, Zhi-Heng; Li, Jialin; Nie, Zhaogang; Zheng, Yi Ying; Dong, Shuo; Low, Pei Jiang

    2016-05-01

    The ionization of liquid water functions as the principal trigger for a myriad of phenomena that are relevant to radiation chemistry and biology. The earliest events that follow the ionization of water, however, remain relatively unknown. Here, femtosecond coherence spectroscopy is combined with polarization anisotropy measurements to elucidate the ultrafast electron and ion dynamics in ionized water. The results show that strong-field ionization of liquid water produces an aligned p electron distribution. Furthermore oscillations observed in the polarization anisotropy are suggestive of valence electron motion in the highly reactive H2 O+ radical cation, whose lifetime with respect to proton transfer is found to be 196 +/- 5 fs. Coherent intermolecular motions that signal initial solvent reorganization and subsequent long-lived ballistic proton transport that involves the H3 O+ end-product are also detected in the time domain. These results offer new insight into the elementary dynamics of ionized liquid water. This work is supported by the Ministry of Education (MOE2014-T2-2-052), A*Star (122-PSF-0011), and the Nanyang Assistant Professorship.

  17. Pulsed-field ionization zero electron kinetic energy spectrum of the ground electronic state of BeOBe+.

    PubMed

    Antonov, Ivan O; Barker, Beau J; Heaven, Michael C

    2011-01-28

    The ground electronic state of BeOBe(+) was probed using the pulsed-field ionization zero electron kinetic energy photoelectron technique. Spectra were rotationally resolved and transitions to the zero-point level, the symmetric stretch fundamental and first two bending vibrational levels were observed. The rotational state symmetry selection rules confirm that the ground electronic state of the cation is (2)Σ(g)(+). Detachment of an electron from the HOMO of neutral BeOBe results in little change in the vibrational or rotational constants, indicating that this orbital is nonbonding in nature. The ionization energy of BeOBe [65480(4) cm(-1)] was refined over previous measurements. Results from recent theoretical calculations for BeOBe(+) (multireference configuration interaction) were found to be in good agreement with the experimental data. PMID:21280724

  18. Pulsed-field ionization zero electron kinetic energy spectrum of the ground electronic state of BeOBe+

    NASA Astrophysics Data System (ADS)

    Antonov, Ivan O.; Barker, Beau J.; Heaven, Michael C.

    2011-01-01

    The ground electronic state of BeOBe+ was probed using the pulsed-field ionization zero electron kinetic energy photoelectron technique. Spectra were rotationally resolved and transitions to the zero-point level, the symmetric stretch fundamental and first two bending vibrational levels were observed. The rotational state symmetry selection rules confirm that the ground electronic state of the cation is 2Σg+. Detachment of an electron from the HOMO of neutral BeOBe results in little change in the vibrational or rotational constants, indicating that this orbital is nonbonding in nature. The ionization energy of BeOBe [65480(4) cm-1] was refined over previous measurements. Results from recent theoretical calculations for BeOBe+ (multireference configuration interaction) were found to be in good agreement with the experimental data.

  19. Ratio of double to single ionization of He by photon and charged particle impact

    SciTech Connect

    Manson, S.T.

    1994-12-31

    The well-known relationship between ionization of atoms by fast charged particles and by photons, the Bethe-Born theory, is applied to the ratio of double ionization to single ionization of He, a process that has been under intense recent scrutiny. It is found that for sufficiently fast charged particles, this ratio for the single differential cross sections, differential in the energy transferred to the atom, {Delta}E, is equal to the photoionization ratio at a photon energy hv = {Delta}E, and this result is unmodified even for ionization by relativistic charged particles. In addition, a relation for the ratio of total charged particle impact ionization cross sections to the photoionization ratio is derived. The results are compared with recent experimental data and various discrepancies are uncovered. Possible sources of these discrepancies are discussed.

  20. Convergent close-coupling calculations of helium single ionization by antiproton impact

    SciTech Connect

    Abdurakhmanov, I. B.; Kadyrov, A. S.; Fursa, D. V.; Bray, I.; Stelbovics, A. T.

    2011-12-15

    We apply the fully quantum-mechanical convergent close-coupling method to the calculation of antiproton scattering on the ground state of helium. The helium target is treated as a three-body Coulomb system using frozen-core and multiconfiguration approximations. The electron-electron correlation of the target is fully treated in both cases. Though both calculations yield generally good agreement with experiment for the total ionization cross sections, the multiconfiguration results are substantially higher at the lower energies than the frozen-core ones. Calculated longitudinal ejected electron and recoil-ion momentum distributions for the single ionization of helium are in good agreement with the experiment.

  1. Role of ionization and electron drift velocity profile to Rayleigh instability in a Hall thruster plasma

    SciTech Connect

    Singh, Sukhmander; Malik, Hitendra K.

    2012-07-01

    Role of ionization to Rayleigh instability is clarified in a Hall thruster plasma under the variety of profiles of electron drift velocity, namely, step-like profile (SLP) and two different super-Gaussian profiles (SGP1 and SGP2). For this, a relevant Rayleigh equation is derived and solved numerically using fourth-order Runge-Kutta method. Interestingly, an upper cutoff frequency of oscillations {omega}{sub max} is realized for the occurrence of the instability that shows dependence on the ionization rate {alpha}, electron drift velocity u{sub 0}, electron cyclotron frequency {Omega}, azimuthal wave number k{sub y}, plasma density n{sub 0}, density gradient {partial_derivative}n{sub 0}/{partial_derivative}x, ion (electron) thermal speed V{sub thI}(V{sub thE}), and ion (electron) plasma frequency {omega}{sub pi}({omega}{sub pe}). The frequency {omega}{sub max} follows the trend {omega}{sub max} (for SGP2) >{omega}{sub max} (for SLP) >{omega}{sub max} (for SGP1) and shows a similar behaviour with ionization for all types of the velocity profiles. The instability is found to grow faster for the higher {alpha} and the ion temperature but it acquires lower rate under the effect of the higher electron temperature; the perturbed potential also varies in accordance with the growth rate. The electron temperature influences the growth rate and cutoff frequency less significantly in comparison with the ion temperature.

  2. LETTER TO THE EDITOR: Distortion of molecular electron density distributions by an intense laser field: dissociative ionization of ?

    NASA Astrophysics Data System (ADS)

    Vijayalakshmi, K.; Bhardwaj, V. R.; Safvan, C. P.; Mathur, D.

    1997-05-01

    The interaction of a tetrahedral molecule (carbon tetrachloride) with intense, 532 nm, 35 ps, 0953-4075/30/10/003/img2 linearly polarized, laser fields is explored theoretically and experimentally. Distortions caused by the laser field in the molecular electron density distributions are computed in an approximate fashion using quantum-chemical techniques. A comparative experimental study is performed of the dissociative ionization of 0953-4075/30/10/003/img3 in such an intense laser field and also by electron impact. Significant differences are observed and attempts are made to explore the possibility that these can be explained using field-distorted electron density distributions. Angular distributions of the 0953-4075/30/10/003/img4 fragment ion have also been measured and show a pronounced anisotropy with the ion signal being detected mainly along the direction of the laser's polarization axis.

  3. Ion-induced ionization and capture cross sections for DNA nucleobases impacted by light ions

    NASA Astrophysics Data System (ADS)

    Champion, Christophe; Galassi, Mariel E.; Weck, Philippe F.; Fojón, Omar; Hanssen, Jocelyn; Rivarola, Roberto D.

    2012-11-01

    Two quantum mechanical models (CB1 and CDW-EIS) are here presented for describing electron ionization and electron capture induced by heavy charged particles in DNA bases. Multiple differential and total cross sections are determined and compared with the scarce existing experimental data.

  4. Complete ligand loss in electron ionization of the weakly bound organometallic tungsten hexacarbonyl dimer.

    PubMed

    Neustetter, Michael; Mauracher, Andreas; Limão-Vieira, Paulo; Denifl, Stephan

    2016-04-21

    We observed the bare W2(+) metal cation upon electron ionization of the weakly bound W(CO)6 dimer. This metal cation can be only observed due to the fast conversion of the weak cluster bond into a strong covalent bond between the metal moieties. PMID:27006205

  5. Recent Total Ionizing Dose Results and Displacement Damage Results for Candidate Spacecraft Electronics for NASA

    NASA Technical Reports Server (NTRS)

    Cochran, Donna J.; Buchner, Stephen P.; Irwin, Tim L.; LaBel, Kenneth A.; Marshall, Cheryl J.; Reed, Robert A.; Sanders, Anthony B.; Hawkins, Donald K.; Flanigan, Ryan J.; Cox, Stephen R.

    2005-01-01

    We present data on the vulnerability of a variety of candidate spacecraft electronics to total ionizing dose and displacement damage. Devices tested include optoelectronics, digital, analog, linear bipolar devices, hybrid devices, Analog-to- Digital Converters (ADCs), and Digital-to-Analog Converters (DACs), among others. T

  6. Total Ionizing Dose Results and Displacement Damage Results for Candidate Spacecraft Electronics for NASA

    NASA Technical Reports Server (NTRS)

    Cochran, Donna J.; Kniffin, Scott D.; LaBel, Kenneth A.; OBryan, Martha V.; Reed, Robert A.; Ladbury, Ray L.; Howard, James W., Jr.; Poivey, Christian; Buchner, Stephen P.; Marshall, Cheryl J.

    2003-01-01

    We present data on the vulnerability of a variety of candidate spacecraft electronics to total ionizing dose and displacement damage. Devices tested include optoelectronics, digital, analog, linear bipolar devices, hybrid devices, Analog-to-Digital Converters (ADCs), and Digital-to-Analog Converters (DACs), among others.

  7. Atomic Ionization at the Positron-Electron Annihilation in Process of β+-DECAY

    NASA Astrophysics Data System (ADS)

    Fedotkin, S. N.; Zheltonozhskii, V. A.

    2013-03-01

    The process of atomic shell ionization during the annihilation of a positron, emitted at β+- decay with K-electron of daughter's atom, is considered. The ratio of probabilities of these processes to the probability of ordinary β+-decay is found. It excitation of atomic shell at the positron annihilation at β+-decay of was studied the 4522Ti.

  8. Current Total Ionizing Dose Results and Displacement Damage Results for Candidate Spacecraft Electronics for NASA

    NASA Technical Reports Server (NTRS)

    Cochran, Donna J.; Kniffin, Scott D.; LaBel, Kenneth A.; OBryan, Martha V.; Reed, Robert A.; Ladbury, Ray L.; Howard, James W., Jr.; Poivey, Christian; Buchner, Stephen P.; Marshall, Cheryl J.

    2004-01-01

    We present data on the vulnerability of a variety of candidate spacecraft electronics to total ionizing dose and displacement damage. Devices tested include optoelectronics, digital, analog, linear bipolar devices, hybrid devices, Analog-to-Digital Converters (ADCs), and Digital-to-Analog Converters (DACS), among others.

  9. Projectile charge state effects on electron emission in transfer ionization processes

    NASA Astrophysics Data System (ADS)

    Zhang, R. T.; Zhu, X. L.; Feng, W. T.; Guo, D. L.; Gao, Y.; Qian, D. B.; Li, B.; Yan, S. C.; Xu, S.; Zhang, P.; Ma, X.

    2015-07-01

    Electron emissions in transfer ionization processes were studied for 75 keV u-1 He2+, and 80 keV u-1 Ne8+on He collisions, using the well-developed reaction microscope techniques. Momentum distributions in the scattering plane, doubly differential distributions as a function of longitudinal momentum and emission angles of the ejected electrons were obtained. An apparent enhancement of electrons distributed around the projectile in the scattering plane was found for the Ne8+ incident case. Furthermore, we report the ratio of doubly differential distributions at the emission angle of 0° between these two transfer ionization processes, in which an abrupt rise is found at and above the electron capture to the continuum peak. This rise qualitatively agrees with the prediction within the framework of Dettmann’s theory. We conclude that this kind of enhancement was caused by the charge state effect of the projectile.

  10. Chiral asymmetry in the multiphoton ionization of methyloxirane using femtosecond electron-ion coincidence imaging.

    PubMed

    Rafiee Fanood, Mohammad M; Powis, Ivan; Janssen, Maurice H M

    2014-12-11

    Multiphoton photoelectron circular dichroism (MP-PECD) has been observed as an asymmetry in the angular distribution of photoelectrons emitted in the ionization of pure enantiomers of the small chiral molecule methyloxirane using a femtosecond laser operated at 420 nm. Energetically, this requires the uptake of four photons. By switching the laser between left- and right-circular polarization, and observing the differences in the full three-dimensional electron momentum distribution recorded in an electron-ion coincidence technique, the chiral (odd) terms in the angular distribution expression can be isolated. Electron events can additionally be filtered by coincident ion mass, providing mass-tagged electron distributions and quantitative measures of the MP-PECD asymmetry that help characterize the different ionization channels. For the production of ground state parent cation, the magnitude of the mean chiral asymmetry is measured to be 4.7%, with a peak magnitude exceeding 10% PMID:25402546

  11. Electron impact collision strengths for excitation of highly charged ions

    SciTech Connect

    Sampson, D.H. . Dept. of Astronomy and Astrophysics)

    1990-08-20

    The principle task given us by the Lawrence Livermore National Laboratory (LLNL) to perform under Subcontract 6181405 was to develop a method and corresponding computer programs to make very rapid, yet accurate, fully relativistic and quasirelativistic calculations of cross sections or collision strengths for electron impact excitation of highly charged ions with any value for the nuclear charge number Z. Also while this major code development was being done we were asked to calculate cross sections of interest using our previous rapid, more approximate codes, which used hydrogenic basis functions and screening constants with both the electron-electron Coulomb interaction and relativistic interactions included by perturbation theory. We were also asked to determine the branching ratio for ionization to various final states in complex cases, where two or more states corresponding to the final configuration of the ion were possible.

  12. Electron-ion collisions. [Basic physics of inelastic processes of excitation, ionization, and recombination

    SciTech Connect

    Crandall, D.H.

    1982-01-01

    This discussion concentrates on basic physics aspects of inelastic processes of excitation, ionization, and recombination that occur during electron-ion collisions. Except for cases of illustration along isoelectronic sequences, only multicharged (at least +2) ions will be specifically discussed with some emphasis of unique physics aspects associated with ionic charge. The material presented will be discussed from a primarily experimental viewpoint with most attention to electron-ion interacting beams experiments.

  13. Two-electron time-delay interference in atomic double ionization by attosecond pulses

    SciTech Connect

    Rescigno, Thomas N

    2009-10-04

    A two-color two-photon atomic double ionization experiment using subfemtosecond UV pulses can be designed such that the sequential two-color process dominates and one electron is ejected by each pulse. Nonetheless, ab initio calculations show that, for sufficiently short pulses, a prominent interference pattern in the joint energy distribution of the sequentially ejected electrons can be observed that is due to their indistinguishability and the exchange symmetry of the wave function.

  14. Two-Electron Time-Delay Interference in Atomic Double Ionization by Attosecond Pulses

    SciTech Connect

    Palacios, A.; Rescigno, T. N.; McCurdy, C. W.

    2009-12-18

    A two-color two-photon atomic double ionization experiment using subfemtosecond uv pulses can be designed such that the sequential two-color process dominates and one electron is ejected by each pulse. Nonetheless, ab initio calculations show that, for sufficiently short pulses, a prominent interference pattern in the joint energy distribution of the sequentially ejected electrons can be observed that is due to their indistinguishability and the exchange symmetry of the wave function.

  15. Suppression of correlated electron escape in double ionization in strong laser fields

    NASA Astrophysics Data System (ADS)

    Eckhardt, Bruno; Prauzner-Bechcicki, Jakub S.; Sacha, Krzysztof; Zakrzewski, Jakub

    2008-01-01

    The effect of the Pauli exclusion principle on double ionization of He atoms by strong, linearly polarized laser pulses is analyzed. We show that correlated electron escape, with electron momenta symmetric with respect to the field polarization axis, is suppressed if atoms are initially prepared in the metastable state S3 . The effect is a consequence of selection rules for the transition to the appropriate outgoing two-electron states. We illustrate the suppression in numerical calculations of electron and ion momentum distributions within a reduced dimensionality model.

  16. Electron Injection in Laser Plasma Accelerators by High-Order Field Ionization

    SciTech Connect

    Chen, M.; Esarey, E.; Geddes, C. G. R.; Schroeder, C. B.; Leemans, W. P.

    2010-11-04

    Electron injection and trapping in a laser wakefield accelerator by high-order field ionization is studied theoretically and by particle-in-cell simulations. To obtain low energy spread beams we use a short region of gas mixture (H+N) near the start of the stage to trap electrons, while the remainder of the stage uses pure H and is injection-free. Effects of gas mix parameters, such as concentration and length, on the final electron injection number and beam quality are studied. Laser polarization and shape effects on injection number and final electron emittance are also shown.

  17. Mass-spectrometric study of the electron-impact-induced fragmentation of the tryptophan molecule

    NASA Astrophysics Data System (ADS)

    Vukstich, V. S.; Romanova, L. G.; Megela, I. G.; Snegursky, A. V.

    2014-03-01

    The formation of ion products upon single and dissociative electron-impact ionization of the tryptophan (C11H12N2O2) molecule has been studied using mass-spectrometric techniques. The mass-spectrum of tryptophan has been obtained and interpreted, and the near-threshold ion yields from the initial molecule and the main products of its electron-impact ionization have been measured. The absolute values of ionization energy of the initial tryptophan molecule and the appearance potentials of its main fragment ions have been determined. The influence of exposure to a high-energy beam of accelerated electrons on the resulting mass spectra of initial molecule has been studied.

  18. Transverse electron momentum distribution in tunneling and over the barrier ionization by laser pulses with varying ellipticity.

    PubMed

    Ivanov, I A; Kheifets, A S; Calvert, J E; Goodall, S; Wang, X; Xu, Han; Palmer, A J; Kielpinski, D; Litvinyuk, I V; Sang, R T

    2016-01-01

    We study transverse electron momentum distribution in strong field atomic ionization driven by laser pulses with varying ellipticity. We show, both experimentally and theoretically, that the transverse electron momentum distribution in the tunneling and over the barrier ionization regimes evolves in a qualitatively different way when the ellipticity parameter describing polarization state of the driving laser pulse increases. PMID:26740072

  19. Transverse electron momentum distribution in tunneling and over the barrier ionization by laser pulses with varying ellipticity

    PubMed Central

    Ivanov, I. A.; Kheifets, A. S.; Calvert, J. E.; Goodall, S.; Wang, X.; Xu, Han; Palmer, A. J.; Kielpinski, D.; Litvinyuk, I. V.; Sang, R. T.

    2016-01-01

    We study transverse electron momentum distribution in strong field atomic ionization driven by laser pulses with varying ellipticity. We show, both experimentally and theoretically, that the transverse electron momentum distribution in the tunneling and over the barrier ionization regimes evolves in a qualitatively different way when the ellipticity parameter describing polarization state of the driving laser pulse increases. PMID:26740072

  20. Double ionization of helium by fast electrons with the Generalized Sturmian Functions method

    NASA Astrophysics Data System (ADS)

    Ambrosio, M. J.; Colavecchia, F. D.; Gasaneo, G.; Mitnik, D. M.; Ancarani, L. U.

    2015-03-01

    The double ionization of helium by high energy electron impact is studied. The corresponding four-body Schrödinger equation is transformed into a set of driven equations containing successive orders in the projectile-target interaction. The first order driven equation is solved with a generalized Sturmian functions approach. The transition amplitude, extracted from the asymptotic limit of the first order solution, is equivalent to the familiar first Born approximation. Fivefold differential cross sections are calculated for (e, 3e) processes within the high incident energy and small momentum transfer regimes. The results are compared with other numerical methods, and with the only absolute experimental data available. Our cross sections agree in shape and magnitude with those of the convergent close coupling method for the (10+10) eV and (4+4) eV emission energies. To date this had not been achieved by any two different numerical schemes when solving the three-body continuum problem for the fast projectile (e, 3e) process. Though agreement with the experimental data, in particular with respect to the magnitude, is not achieved, our findings partly clarify a long standing puzzle.

  1. Improved electron ionization ion source for the detection of supersonic molecular beams

    NASA Astrophysics Data System (ADS)

    Amirav, Aviv; Fialkov, Alexander; Gordin, Alexander

    2002-08-01

    An improved electron ionization (EI) ion source is described, based on the modification of a Brink-type EI ion source through the addition of a second cage with a fine mesh outside the ion chamber. The added outer cage shields the inner ion cage (ionization zone) against the penetration of the filament and electron repeller potentials, and thus results in the provision of ions with narrower ion energy distribution, hence improved ion-beam quality. The closer to zero electrical field inside the ion cage enables improved filtration (rejection) of ions that are produced from vacuum background compounds, based on difference in ion energies of beam and background species. The improved background ion filtration and ion-beam quality resulted in 2.6 times higher mass spectrometric ion signal, combined with 6.4 times better signal to noise ratio, in comparison with the same ion source having a single cage. The dual cage ion source further provides a smaller or no reduction of the electron emission current upon lowering the electron energy for achieving softer EI and/or electron attachment ionization. It also improves the long-term mass spectral and signal reproducibility and enables fast, automated change of the electron energy. Consequently, the dual cage EI ion source is especially effective for use with gas chromatography mass spectrometry with supersonic molecular beams (SMB), liquid chromatography mass spectrometry with SMB, ion guns with SMB, and any other experimental systems with SMB or nonthermal molecular beams.

  2. Electron residual energy due to stochastic heating in field-ionized plasma

    NASA Astrophysics Data System (ADS)

    Khalilzadeh, Elnaz; Yazdanpanah, Jam; Jahanpanah, Jafar; Chakhmachi, Amir; Yazdani, Elnaz

    2015-11-01

    The electron residual energy originated from the stochastic heating in under-dense field-ionized plasma is investigated here. Initially, the optical response of plasma is modeled by using two counter-propagating electromagnetic waves. In this case, the solution of motion equation of a single electron indicates that by including the ionization, the electron with higher residual energy compared with that without ionization could be obtained. In agreement with chaotic nature of the motion, it is found that the electron residual energy will be significantly changed by applying a minor change in the initial conditions. Extensive kinetic 1D-3V particle-in-cell simulations have been performed in order to resolve full plasma reactions. In this way, two different regimes of plasma behavior are observed by varying the pulse length. The results indicate that the amplitude of scattered fields in a proper long pulse length is high enough to act as a second counter-propagating wave and trigger the stochastic electron motion. On the contrary, the analyses of intensity spectrum reveal the fact that the dominant scattering mechanism tends to Thomson rather than Raman scattering by increasing the pulse length. A covariant formalism is used to describe the plasma heating so that it enables us to measure electron temperature inside and outside of the pulse region.

  3. Electron residual energy due to stochastic heating in field-ionized plasma

    SciTech Connect

    Khalilzadeh, Elnaz; Yazdanpanah, Jam Chakhmachi, Amir; Jahanpanah, Jafar; Yazdani, Elnaz

    2015-11-15

    The electron residual energy originated from the stochastic heating in under-dense field-ionized plasma is investigated here. Initially, the optical response of plasma is modeled by using two counter-propagating electromagnetic waves. In this case, the solution of motion equation of a single electron indicates that by including the ionization, the electron with higher residual energy compared with that without ionization could be obtained. In agreement with chaotic nature of the motion, it is found that the electron residual energy will be significantly changed by applying a minor change in the initial conditions. Extensive kinetic 1D-3V particle-in-cell simulations have been performed in order to resolve full plasma reactions. In this way, two different regimes of plasma behavior are observed by varying the pulse length. The results indicate that the amplitude of scattered fields in a proper long pulse length is high enough to act as a second counter-propagating wave and trigger the stochastic electron motion. On the contrary, the analyses of intensity spectrum reveal the fact that the dominant scattering mechanism tends to Thomson rather than Raman scattering by increasing the pulse length. A covariant formalism is used to describe the plasma heating so that it enables us to measure electron temperature inside and outside of the pulse region.

  4. Benchmark Calculations of Electron-Impact Differential Cross Sections

    SciTech Connect

    Bray, I.; Bostock, C. J.; Fursa, D. V.; Hines, C. W.; Kadyrov, A. S.; Stelbovics, A. T.

    2011-05-11

    The calculation of electron-atom excitation and ionization cross section is considered in both the non-relativistic and relativistic scattering theory. We consider electron collisions with H, He, Cs, and Hg. Differential cross sections for elastic scattering and ionization are presented.

  5. Complex-Kohn Approach to Molecular Ionization by High-Energy Electrons: Application to H2, H2O and CH4

    NASA Astrophysics Data System (ADS)

    Lin, Chih-Yuan; McCurdy, C. W.; Rescigno, T. N.

    2014-05-01

    The complex Kohn variational method, which has been extensively applied to low-energy molecule scattering, is extended to treat molecular ionization by fast electrons under the assumption that the incident and scattered electrons can be described by plane-waves. In contrast to other perturbative approches, the interaction between the slow ejected electron and the residual molecular ion is treated by a close-coupling method and for that we employ the complex Kohn variational method. The formulation reduces to the computation of the continuum generalized oscillation strength, which amounts to a generalization of the molecular photoionization problem to which the Kohn method has been successfully applied. The essential point is that the use of a correct electron-ion scattering wave function as the final state for the ejected electron enables us to treat high-energy electron impact ionization of molecules at the same level of sophistication achieved for atomic targets. We will present fully differential cross sections for ionization of water and methane, as well as for excitation/ionization of H2, along with comparisons to available experimental data. Work performed under the auspices of the US DOE by the LBNL and supported by the U.S. DOE Office of Basic Energy Sciences, Division of Chemical Sciences.

  6. Laser action in runaway electron pre-ionized diffuse discharges

    NASA Astrophysics Data System (ADS)

    Panchenko, Alexei N.; Lomaev, Mikhail I.; Panchenko, Nikolai A.; Tarasenko, Viktor F.; Suslov, Alexei I.

    2015-12-01

    Formation features of run-away electron preionized diffuse discharge (REP DD) and REP DD properties in different experimental conditions are studied. It was shown that sufficient uniformity of REP DD allows its application as an excitation source of lasers on different gas mixtures at elevated pressure. Promising results of REP DD application for development of gas lasers are shown. Stimulated radiation in the IR, visible and UV spectral ranges was obtained in the diffuse discharge. Ultimate efficiency of non-chain HF(DF) chemical and nitrogen lasers on mixtures of SF6 with H2(D2) and N2 was achieved. New operation mode of nitrogen laser is demonstrated under REP DD excitation. Kinetic model of the REP DD in mixtures of nitrogen with SF6 is developed allowing to predict the radiation parameters of nitrogen laser at λ = 337,1 nm. Long-pulse operation of rare gas halide lasers was achieved.

  7. Two-electron ionization in strong laser fields below intensity threshold: Signatures of attosecond timing in correlated spectra

    NASA Astrophysics Data System (ADS)

    Bondar, Denys I.; Liu, Wing-Ki; Ivanov, Misha Yu.

    2009-02-01

    We develop an analytical model of correlated two-electron ionization in strong infrared laser fields. The model includes all relevant interactions between the electrons, the laser field, and the ionic core nonperturbatively. We focus on the deeply quantum regime, where the energy of the active electron driven by the laser field is insufficient to collisionally ionize the parent ion, and the assistance of the laser field is required to create a doubly charged ion. In this regime, the electron-electron and the electron-ion interactions leave distinct footprints in the correlated two-electron spectra, recording the mutual dynamics of the escaping electrons.

  8. Electron Acceleration and Ionization Production in High-Power Heating Experiments at HAARP

    NASA Astrophysics Data System (ADS)

    Mishin, E. V.; Pedersen, T.

    2012-12-01

    Recent ionospheric modification experiments with the 3.6 MW transmitter at the High Frequency Active Auroral Research Program (HAARP) facility in Alaska led to discovery of artificial ionization descending from the nominal interaction altitude in the background F-region ionosphere by ~60-80 km. Artificial ionization production is indicated by significant 427.8 nm emissions from the 1st negative band of N2+ and the appearance of transmitter-induced bottomside traces in ionosonde data during the periods of most intense optical emissions. However, the exact mechanisms producing the artificial plasmas remain to be determined. Yet the only existing theoretical models explain the development of artificial plasma as an ionizing wavefront moving downward due to ionization by electrons accelerated by HF-excited strong Langmuir turbulence (SLT) generated near the plasma resonance, where the pump frequency matches the plasma frequency. However, the observations suggest also the significance of interactions with upper hybrid and electron Bernstein waves near multiples of the electron gyrofrequency. We describe recent observations and discuss suitable acceleration mechanisms.

  9. Electron energy balance and ionization in the channel of a stationary plasma thruster

    NASA Astrophysics Data System (ADS)

    Veselovzorov, A. N.; Pogorelov, A. A.; Svirskiy, E. B.; Smirnov, V. A.

    2016-03-01

    The paper presents results of numerical simulations of the electron dynamics in the field of the azimuthal and longitudinal waves excited in the channel of a stationary plasma thruster (SPT). The simulations are based on the experimentally determined wave characteristics. The simulation results show that the azimuthal wave displayed as ionization instability enhances electron transport along the thruster channel. It is established that the electron transport rate in the azimuthal wave increases as compared to the rate of diffusion caused by electron scattering from neutral atoms in proportion to the ratio between the times of electron- neutral collisions responsible for ionization and elastic electron scattering, respectively. An expression governing the plasma conductivity is derived with allowance for electron interaction with the azimuthal wave. The Hall parameter, the electron component of the discharge current, and the electron heating power in the thruster channel are calculated for two model SPTs operating with krypton and xenon. The simulation results agree well with the results of experimental studies of these two SPTs.

  10. Nanoscale Electron Bunching in Laser-Triggered Ionization Injection in Plasma Accelerators.

    PubMed

    Xu, X L; Pai, C-H; Zhang, C J; Li, F; Wan, Y; Wu, Y P; Hua, J F; Lu, W; An, W; Yu, P; Joshi, C; Mori, W B

    2016-07-15

    Ionization injection is attractive as a controllable injection scheme for generating high quality electron beams using plasma-based wakefield acceleration. Because of the phase-dependent tunneling ionization rate and the trapping dynamics within a nonlinear wake, the discrete injection of electrons within the wake is nonlinearly mapped to a discrete final phase space structure of the beam at the location where the electrons are trapped. This phenomenon is theoretically analyzed and examined by three-dimensional particle-in-cell simulations which show that three-dimensional effects limit the wave number of the modulation to between >2k_{0} and about 5k_{0}, where k_{0} is the wave number of the injection laser. Such a nanoscale bunched beam can be diagnosed by and used to generate coherent transition radiation and may find use in generating high-power ultraviolet radiation upon passage through a resonant undulator. PMID:27472116

  11. Nanoscale Electron Bunching in Laser-Triggered Ionization Injection in Plasma Accelerators

    NASA Astrophysics Data System (ADS)

    Xu, X. L.; Pai, C.-H.; Zhang, C. J.; Li, F.; Wan, Y.; Wu, Y. P.; Hua, J. F.; Lu, W.; An, W.; Yu, P.; Joshi, C.; Mori, W. B.

    2016-07-01

    Ionization injection is attractive as a controllable injection scheme for generating high quality electron beams using plasma-based wakefield acceleration. Because of the phase-dependent tunneling ionization rate and the trapping dynamics within a nonlinear wake, the discrete injection of electrons within the wake is nonlinearly mapped to a discrete final phase space structure of the beam at the location where the electrons are trapped. This phenomenon is theoretically analyzed and examined by three-dimensional particle-in-cell simulations which show that three-dimensional effects limit the wave number of the modulation to between >2 k0 and about 5 k0, where k0 is the wave number of the injection laser. Such a nanoscale bunched beam can be diagnosed by and used to generate coherent transition radiation and may find use in generating high-power ultraviolet radiation upon passage through a resonant undulator.

  12. Photon-electron-ion momentum transfer in high intensityIR laser pulse ionization

    NASA Astrophysics Data System (ADS)

    Bandrauk, Andre D.; Chelkowski, Szczefan; Corkum, Paul

    2016-05-01

    Photon momentum sharing between electrons and parent ions in high intensityIR multiphoton ionization requires going beyond the traditional perturbative dipole approximation. Using numerical solutions of the 2-D TDSE(Time dependent Schroedinger equation) for one electron atom models, we show that the radiation pressure on photoelectrons is sensitive to the ionization mechanism, either direct or by recollision. A complex electron-ion response is obtained due to the interplay between the Lorentz force and Coulomb attraction of the ion.The influence of the photon momentum sharing is shown to be discernible in IR high intensity atomic and/or molecular holographic patterns thus suggesting a new research subject in IR strong field physics.

  13. The electron-ion dynamics in ionization of lithium carbide molecule under femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Zhang, Xiaoqin; Wang, Feng; Hong, Xuhai; Su, Wenyong; Gou, Bingcong; Chen, Huimin

    2016-08-01

    The electron-ion dynamics of the linear lithium carbide molecule under femtosecond laser pulses have been investigated in the framework of Ehrenfest molecular dynamics, in which valence electrons are treated quantum mechanically by time-dependent density functional theory (TDDFT) and ions are described classically. The on- and off-resonant multiphoton ionization processes have been induced by regulating laser frequency and laser intensity. The laser pulse with on-resonant frequency induces pronounced enhancement in electron ionization, bond length vibration, and energy absorption. Moreover, the coulomb explosion is preferred to occur in the on-resonant case, which is in qualitative agreement with previous theoretical investigations. The subtle relations between escaped electron number and absorbed photon number are well discussed with the increasing of laser intensity. Finally, the effect of self-interaction error is analyzed by comparing escaped electron number calculated with LDA and LDA-ADSIC. And the revTPSS-meta-GGA, a currently more accurate nonempirical exchange-correlation energy functional from a point of static density functional theory, is introduced to display its capability for the description of ionization process within nonlinear and the nonperturbative regime of isolated systems.

  14. Ghost peaks observed after AP-MALDI experiment may disclose new ionization mechanism of matrix assisted hypersonic velocity impact ionization

    PubMed Central

    Moskovets, Eugene

    2015-01-01

    the supersonic jet from the inlet capillary accelerating detached particles to kinetic energies suitable for matrix-assisted hypersonic-velocity impact ionization. PMID:26212165

  15. A combined electron-ion spectrometer for studying complete kinematics of molecular dissociation upon shell selective ionization

    SciTech Connect

    Saha, K.; Banerjee, S. B.; Bapat, B.

    2013-07-15

    A combined electron-ion spectrometer has been built to study dissociation kinematics of molecular ions upon various electronic decay processes ensuing from ionization of neutral molecules. The apparatus can be used with various ionization agents. Ion time-of-flight (ToF) spectra arising from various electronic decay processes are acquired by triggering the ToF measurement in coincidence with energy analyzed electrons. The design and the performance of the spectrometer in a photoionization experiment is presented in detail. Electron spectra and ion time of flight spectra resulting from valence and 2p{sub 1/2} ionization of Argon and those from valence ionization of CO are presented to demonstrate the capability of the instrument. The fragment ion spectra show remarkable differences (both kinematic and cross sectional) dependent on the energy of the ejected electron, corresponding to various electron loss and decay mechanisms in dissociative photoionization of molecules.

  16. The Impact of Ionizing Radiation on the Microbial Reduction of Fe(III)

    NASA Astrophysics Data System (ADS)

    Brown, A.; Correa, E. S.; Xu, Y.; Vaughan, D. J.; Pimblott, S. M.; Goodacre, R.; Lloyd, J. R.

    2014-12-01

    Biogeochemical processes mediated by Fe(III)-reducing bacteria have the potential to impact on the post-closure evolution of a geological disposal facility (GDF) for radioactive waste. However, the organisms promoting these processes will likely be subject to significant radiation fluxes. Therefore, the impact of acute doses of ionizing radiation on the physiological status of the model Fe(III)-reducing bacterium Shewanella oneidensis was assessed. FT-IR spectroscopy and MALDI-TOF-MS suggested that the metabolic response to radiation is underpinned by alterations to lipids and proteins. Furthermore, the irradiated phenotype exhibits enhanced Fe(III)-reduction. The impact of radiation on the extracellular environment was also assessed. Exposure to gamma radiation caused activation of ferrihydrite and hematite for enzymatic reduction by S. oneidensis. TEM, SAED and Mössbauer spectroscopy revealed that this effect was a result of radiation induced changes to crystallinity leading to an increase in bioavailability of Fe(III) for respiration. To assess the impact of radiation on sediment microbial communities, a series of microcosm experiments were constructed and gamma irradiated over a two month period. Sediments irradiated at a dose rate of 0.5 Gy h-1 exhibited enhanced Fe(III) reduction despite receiving doses potentially lethal to indigenous microorganisms, whilst biogeochemical processes in sediments irradiated with 30 Gy h-1 were only partially restricted. Despite this, 16S rRNA gene pyrosequencing revealed significant dose-dependent shifts in the microbial communities in tandem with changes in microcosm biogeochemical profiles. Collectively, these results indicate that, despite significant total absorbed doses, biogeochemical processes will likely not be restricted by dose rates expected in a deep geological repository. Indeed, electron accepting processes in such environments may even be stimulated by radiation.

  17. Angular Correlation of Electrons Emitted by Double Auger Decay of K-Shell Ionized Neon

    NASA Astrophysics Data System (ADS)

    Jones, Matthew Philip

    2011-12-01

    We have investigated in detail the 4-body continuum state produced when core-ionized neon undergoes Double-Auger (DA) decay, using COLd Target Recoil Ion Momentum Spectroscopy (COLTRIMS ). We conducted the experiment at the Lawrence Berkeley National Laboratory's Advanced Light Source (LBNL-ALS) beamline 11.0.2. The synchrotron operated in 2-bunch mode and outputted an elliptically polarized, pulsed photon beam (hn=872.9eV), sufficient to K-shell ionize neon just above threshold. Our analysis supports research showing that Auger electrons tend to share energy asymmetrically. We qualitatively compared this result to Photo-Double Ionization (PDI) of helium. Further, we confirm research that shows how Auger electrons that share energy symmetrically can be modeled by the elastic-like knock-out process plus Post-Collision Interaction ( PCI) effects. New observations include the angular correlation between the photo-electron and each respective Auger electron, for specific ranges of energy sharing. We identify a broad feature in the asymmetric case that shows a level of interaction between electrons that until recently, has disagreed with theory. Additionally, we consider the angular correlation between the photo-electron and the momentum sum of the Auger electrons. We observe that the angular correlation between this sum and the photo-electron in the highly asymmetric case is nearly identical to the correlation between just the fast-Auger and the photo-electron - as expected. In the case of symmetric energy sharing, the sum momentum vector appears to be isotropic, particularly for small angles of interaction. Finally, we acknowledge two novel methods of calibration. The first, uses well known line-energies to calibrate the spectrometer. These lines correspond to the decay channels of core-excited neon, Ne(1 s-13p). The second, describes a method to statistically weight list-mode data in order to calibrate it to well known physical features (e.g., isotropic distributions).

  18. Transport of energetic electrons in a fully ionized hydrogen plasma. [in solar flares

    NASA Technical Reports Server (NTRS)

    Bai, T.

    1982-01-01

    A Monte Carlo method for calculating energetic electron transport in a plasma is presented. The energy loss and angular deflection due to Coulomb collisions as a function of travel distance and energy are derived for energetic electrons in a fully ionized plasma with a uniform magnetic field. Formulas which include the effect of nonuniform B fields on the angular deflection are derived. The Monte Carlo method is applied to the thick-target beam model in which the energetic electrons are injected vertically downward.

  19. Probing Electron Correlation via Attosecond xuv Pulses in the Two-Photon Double Ionization of Helium

    SciTech Connect

    Feist, J.; Nagele, S.; Pazourek, R.; Persson, E.; Burgdoerfer, J.; Schneider, B. I.; Collins, L. A.

    2009-08-07

    Recent experimental developments of high-intensity, short-pulse extreme ultraviolet light sources are enhancing our ability to study electron-electron correlations. We perform time-dependent calculations to investigate the so-called 'sequential' regime ((Planck constant/2pi)omega>54.4 eV) in the two-photon double ionization of helium. We show that attosecond pulses allow us not only to probe but also to induce angular and energy correlations of the emitted electrons. The final momentum distribution reveals regions dominated by the Wannier ridge breakup scenario and by postcollision interaction.

  20. Convoy electron emission following ionization of highly-charged ions excited by resonant coherent excitation

    NASA Astrophysics Data System (ADS)

    Suda, S.; Nakano, Y.; Metoki, K.; Shindo, T.; Ohtsuki, S.; Azuma, T.; Hatakeyama, A.; Komaki, K.; Nakai, Y.; Takada, E.; Murakami, T.

    2012-11-01

    Projectile ionization of highly-charged Ar and Fe ions in the excited states passing relativistically fast through a thin crystalline foil was experimentally studied. We selectively controlled the population of the excited states of the projectiles, and their alignment by choosing a specific m-state through three-dimensional resonant coherent excitation technique by periodical electric fields in a crystalline. We measured energy-differential spectra of electron emission released from projectiles at zero degree. Under the resonance condition, we found an evident enhancement of the convoy electron yield, which reflects the electron momentum distribution of the initial bound state of the excited ions.

  1. The ionized electron return phenomenon of Rydberg atom in crossed-fields

    NASA Astrophysics Data System (ADS)

    Dong, Chengwei; Wang, Peijie; Du, Mengli; Uzer, Turgay; Lan, Yueheng

    2016-05-01

    Rydberg atom is highly excited with one valence electron being in a high quantum state, which is very far away from the nucleus. The energy level is similar to that of the hydrogen atom. Introducing externally perpendicular electric and magnetic fields breaks the rotation symmetry and the traditional view is that the ionized electron crosses from the bound into the unbound region and will never return. However, we find that when the field is strong enough, the electron does not move off to infinity and there is a certain possibility of return. Three new periodic orbits are found by the variational method and the physical significance of the phenomenon is also discussed.

  2. Electron emission from single-electron capture with simultaneous single-ionization reactions in 30-keV/u He{sup 2+}-on-argon collisions

    SciTech Connect

    Ma, X.; Zhang, S. F.; Zhu, X. L.; Feng, W. T.; Li, B.; Liu, H. P.; Zhang, R. T.; Guo, D. L.; Yan, S. C.; Zhang, P. J.; Wang, Q.; Li, C. Y.; Wang, J. G.

    2011-05-15

    Electron emission from the single-electron capture with simultaneous single ionization in 30 keV/u He{sup 2+} on argon was investigated using a reaction microscope, providing the electron energy spectra and momentum distributions. Intensive peaks for electrons with near-zero kinetic energies have been observed. It is demonstrated that mechanisms contributing to the electron emission include direct transfer ionization (DTI), double-electron capture with autoionization (DECA), and single-electron capture with autoionization (SECA) of target. Comparison of resonance energies shows that Ar{sup +} ions in SECA decay mainly through the 3s3p{sup 5}3d states by emitting Auger electrons, and He** in DECA decay through the 2l2l' states. The dependence of electron emission on the transverse momentum exchange has been studied. In the transfer ionization channel studied here, the DTI process dominates the electron emission, and no saddle point electron mechanism has been found.

  3. Electron spin polarization in strong-field ionization of xenon atoms

    NASA Astrophysics Data System (ADS)

    Hartung, Alexander; Morales, Felipe; Kunitski, Maksim; Henrichs, Kevin; Laucke, Alina; Richter, Martin; Jahnke, Till; Kalinin, Anton; Schöffler, Markus; Schmidt, Lothar Ph. H.; Ivanov, Misha; Smirnova, Olga; Dörner, Reinhard

    2016-08-01

    As a fundamental property of the electron, the spin plays a decisive role in the electronic structure of matter, from solids to molecules and atoms, for example, by causing magnetism. Yet, despite its importance, the spin dynamics of the electrons released during the interaction of atoms with strong ultrashort laser pulses has remained experimentally unexplored. Here, we report the experimental detection of electron spin polarization by the strong-field ionization of xenon atoms and support our results with theoretical analysis. We found up to 30% spin polarization changing its sign with electron energy. This work opens the new dimension of spin to strong-field physics. It paves the way to the production of sub-femtosecond spin-polarized electron pulses with applications ranging from probing the magnetic properties of matter at ultrafast timescales to testing chiral molecular systems with sub-femtosecond temporal and sub-ångström spatial resolutions.

  4. LC-MS with electron ionization of cold molecules in supersonic molecular beams

    NASA Astrophysics Data System (ADS)

    Granot, Ori; Amirav, Aviv

    2005-06-01

    A new approach is described for the combination of electron ionization and LC-MS based on sample ionization as vibrationally cold molecules in a supersonic molecular beam (Cold EI). Cold EI of sample compounds in liquid solutions (methanol, acetonitrile, water, etc.) is achieved through spray formation, followed by soft thermal vaporization of the sample particles prior to their supersonic expansion and direct electron ionization of the sample compounds while they are contained in a supersonic molecular beam (SMB). Cold EI mass spectra were demonstrated to combine an enhanced molecular ion and improved mass spectral information (in comparison with standard EI), plus all the library searchable fragments. Cold EI enables the ionization of a broad range of compounds, including the full range of non-polar samples. Four orders of magnitude linear dynamic range is demonstrated and a detection limit of 2 pg was achieved for a 774 amu compound in single ion monitoring mode at m/z = 774. The method and apparatus are under continuous development and we feel that it can excel particularly in the analysis of unknown samples, while enabling fast LC-MS analysis through automated mass spectral deconvolution of coeluting LC peaks. In addition, the same MS system can also serve as an advanced GC-MS with supersonic molecular beams.

  5. Penning ionization electron spectroscopy of hydrogen sulfide by metastable helium and neon atoms.

    PubMed

    Falcinelli, Stefano; Candori, Pietro; Bettoni, Marta; Pirani, Fernando; Vecchiocattivi, Franco

    2014-08-21

    The dynamics of the Penning ionization of hydrogen sulfide molecules by collision with helium and metastable neon atoms, occurring in the thermal energy range, has been studied by analyzing the energy spectra of the emitted electrons obtained in our laboratory in a crossed beam experiment. These spectra are compared with the photoelectron spectra measured by using He(I) and Ne(I) photons under the same experimental conditions. In this way we obtained the negative energy shifts for the formation of H2S(+) ions in the first three accessible electronic states by He*(2(3,1)S1,0) and Ne*((3)P2,0) Penning ionization collisions: the 2b1 (X̃(2)B1) fundamental one, the first 5a1 (Ã(2)A1), and the second 2b2 (B̃(2)B2) excited states, respectively. The recorded energy shifts indicate that in the case of He* and Ne*-H2S the autoionization dynamics depends on the features of the collision complex and is mainly driven by an effective global attraction that comes from a balance among several non covalent intermolecular interaction components. This suggests that the Penning ionization should take place, in a specific range of intermolecular distances, as we have already observed in the case of Penning ionization of water molecules [Brunetti, B. G.; Candori, P.; Falcinelli, S.; Pirani, F.; Vecchiocattivi, F. J. Chem. Phys. 2013, 139, 164305-1-164305-8]. PMID:24796487

  6. Electron impact excitation of SF6

    NASA Technical Reports Server (NTRS)

    Trajmar, S.; Chutjian, A.

    1977-01-01

    A study of the electron impact energy-loss spectrum of SF6 under both optical (low scattering angle, high impact energy) and non-optical conditions (high scattering angle, low impact energy) has revealed a number of electronic excitation processes. With the help of theoretical calculations, several of these transitions have been assigned and approximate cross sections associated with four features have been determined. In addition, a strong resonance at 12 eV has been observed in both elastic and vibrationally inelastic (delta E = 0.092 eV) channels.

  7. Equation of motion coupled cluster methods for electron attachment and ionization potential in polyacenes

    SciTech Connect

    Bhaskaran-Nair, Kiran; Kowalski, Karol; Jarrell, Mark; Moreno, Juana; Shelton, William A.

    2015-11-05

    Polyacenes have attracted considerable attention due to their use in organic based optoelectronic materials. Polyacenes are polycyclic aromatic hydrocarbons composed of fused benzene rings. Key to understanding and design of new functional materials is an understanding of their excited state properties starting with their electron affinity (EA) and ionization potential (IP). We have developed a highly accurate and com- putationally e*fficient EA/IP equation of motion coupled cluster singles and doubles (EA/IP-EOMCCSD) method that is capable of treating large systems and large basis set. In this study we employ the EA/IP-EOMCCSD method to calculate the electron affinity and ionization potential of naphthalene, anthracene, tetracene, pentacene, hex- acene and heptacene. We have compared our results with other previous theoretical studies and experimental data. Our EA/IP results are in very good agreement with experiment and when compared with the other theoretical investigations our results represent the most accurate calculations as compared to experiment.

  8. Ionization Avalanching in Clusters Ignited by Extreme-Ultraviolet Driven Seed Electrons.

    PubMed

    Schütte, Bernd; Arbeiter, Mathias; Mermillod-Blondin, Alexandre; Vrakking, Marc J J; Rouzée, Arnaud; Fennel, Thomas

    2016-01-22

    We study the ionization dynamics of Ar clusters exposed to ultrashort near-infrared (NIR) laser pulses for intensities well below the threshold at which tunnel ionization ignites nanoplasma formation. We find that the emission of highly charged ions up to Ar^{8+} can be switched on with unit contrast by generating only a few seed electrons with an ultrashort extreme-ultraviolet (XUV) pulse prior to the NIR field. Molecular dynamics simulations can explain the experimental observations and predict a generic scenario where efficient heating via inverse bremsstrahlung and NIR avalanching is followed by resonant collective nanoplasma heating. The temporally and spatially well-controlled injection of the XUV seed electrons opens new routes for controlling avalanching and heating phenomena in nanostructures and solids, with implications for both fundamental and applied laser-matter science. PMID:26849590

  9. Enhanced single-stage laser-driven electron acceleration by self-controlled ionization injection.

    PubMed

    Li, Song; Hafz, Nasr A M; Mirzaie, Mohammad; Sokollik, Thomas; Zeng, Ming; Chen, Min; Sheng, Zhengming; Zhang, Jie

    2014-12-01

    We report on overall enhancement of a single-stage laser wakefield acceleration (LWFA) using the ionization injection in a mixture of 0.3% nitrogen gas in 99.7% helium gas. Upon the interaction of 30-TW, 30-fs laser pulses with a gas jet of the above gas mixture, >300 MeV electron beams were generated at a helium plasma densities of 3.3-8.5 × 10(18) cm(-3). Compared with the uncontrolled electron self-injection in pure helium gas jet, the ionization injection process due to the presence of ultra-low nitrogen concentrations appears to be self-controlled; it has led to the generation of electron beams with higher energies, higher charge, lower density threshold for trapping, and a narrower energy spread without dark current (low energy electrons) or multiple bunches. It is foreseen that further optimization of such a scheme is expected to bring the electron beam energy-spread down to 1%, making them suitable for driving ultra-compact free-electron lasers. PMID:25606890

  10. Hybrid modelling of open glow discharge with account of nonlocal ionization by fast electrons

    NASA Astrophysics Data System (ADS)

    Eliseev, Stepan; Eremin, Denis; Kudryavtsev, Anatoly

    2015-11-01

    Cage and open discharges as well as hollow cathode devices are used for creating negative glow plasma. In order to perform numerical simulations of such kind of plasma object properly it is necessary to account for nonlocal excitation and ionization induced by fast electrons emitted from cathode and accelerated up to energies 102-103eV in cathode voltage drop. In this work a numerical study of open discharge in argon is presented. Simulations were performed using simple hybrid model that incorporates nonlocal ionization by fast electrons into ``extended'' fluid framework. Electron energy balance is written with account of electron heating due to coulomb interaction between ``bulks'' (with energies less than 1eV) and ``intermediate'' electrons (with energies up to inelastic collisions energy threshold). Distributions of main discharge parameters, such charged particle densities, electron temperature, electric potential, current-voltage characteristics of the discharge were obtained. Comparison with experimental results showed good agreement and suggests good applicability of the model. This work was supported by Russian Science Foundation (project #14-19-00311).

  11. Electronic, structural and vibrational induced effects upon ionization of 2-quinolinone.

    PubMed

    Bellili, A; Pan, Y; Al Mogren, M M; Lau, K C; Hochlaf, M

    2016-07-01

    Using first principle methodologies, we characterize the lowest electronic states of 2-quinolinone(+) cation. The ground state of this ion is of X˜(2)A(″) nature. We deduce the adiabatic ionization energy of 2-quinolinone to be equal 8.249eV using the explicitly correlated coupled cluster level and where zero point vibrational energy, core-valence and scalar relativistic effects are taken into account. We examine also the ionization induced structural changes and vibrational shifts and analyze the electron density differences between the neutral and ionic species. These data show that the formation of 2-quinolinone(+)X˜(2)A(″) from 2-quinolinone affects strongly the HNCO group, whereas the carbon skeletal is perturbed when the upper electronic cationic states are populated. The comparison to 2-pyridone allows the elucidation of the effect of benzene ring fused with this heterocyclic ring. Since quinolones and pyridones are both model systems of DNA bases, these findings might help in understanding the charge redistribution in these biological entities upon ionization. PMID:27060413

  12. Electronic, structural and vibrational induced effects upon ionization of 2-quinolinone

    NASA Astrophysics Data System (ADS)

    Bellili, A.; Pan, Y.; Al Mogren, M. M.; Lau, K. C.; Hochlaf, M.

    2016-07-01

    Using first principle methodologies, we characterize the lowest electronic states of 2-quinolinone+ cation. The ground state of this ion is of X˜2A″ nature. We deduce the adiabatic ionization energy of 2-quinolinone to be equal 8.249 eV using the explicitly correlated coupled cluster level and where zero point vibrational energy, core-valence and scalar relativistic effects are taken into account. We examine also the ionization induced structural changes and vibrational shifts and analyze the electron density differences between the neutral and ionic species. These data show that the formation of 2-quinolinone+X˜2A″ from 2-quinolinone affects strongly the HNCO group, whereas the carbon skeletal is perturbed when the upper electronic cationic states are populated. The comparison to 2-pyridone allows the elucidation of the effect of benzene ring fused with this heterocyclic ring. Since quinolones and pyridones are both model systems of DNA bases, these findings might help in understanding the charge redistribution in these biological entities upon ionization.

  13. Ionization Injection of Electrons into a Plasma Wakefield Accelerator at FACET

    NASA Astrophysics Data System (ADS)

    Clayton, Chris; E-200 At Facet Collaboration

    2013-10-01

    In the PWFA experiments at FACET, a low ionization-potential (IP) metal vapor gas (Li) is confined within a heat-pipe oven by a higher IP buffer gas (typically He). The Li is easily field-ionized by the FACET beam. A non-linear wake is formed in the blowout regime when the 20.3 GeV bunch containing 2e10 electrons in a σz ~ 30 μm is focused to a (vacuum) σr < 25 near the ~ 10cm-long boundary region. There the Li density rises from zero up to the oven's 30cm-long flat-topped density of 2.5e17 cm-3. To obtain a mono-energetic beam from accelerated ionization-injected electrons at the far end of the oven--the goal of this experiment--it is necessary for the FACET beam to have a betatron pinch just where the flat-topped region begins; i.e., where the wake wavelength is no longer changing. If the buffer gas contains a mixture of He and a moderate IP gas, the ``impurity'' gases will also be field ionized and potentially contribute more charge to the injected bunch than with He alone. Moderate IP gases were added to the He buffer gas: 10%, 20%, and 50% Ar (balance He) and 30% Ne (balance He) have been used. Evidence for ionization injection and acceleration appears through the observation of distinct features, characterized by their very narrow size and thus angular spread, at the image plane of a magnetic imaging spectrometer. Analysis aimed at characterizing these features with respect to energy, charge, and angular spread is underway and will be presented. This work was supported by the DOE and the NSF.

  14. Calibration of impact ionization dust detectors with porous or fluffy dust particles

    NASA Astrophysics Data System (ADS)

    Sterken, V. J.; Moragas-Klostermeyer, G.; Hillier, J. K.; Bugiel, S.; Srama, R.; Armes, S. P.; Fielding; L. A.; Lovett, J. R.; Grün, E.

    2013-07-01

    Impact ionization instruments like the ones flying on Cassini, Galileo, Helios and Ulysses have been calibrated using compact particles made of conductive materials like iron, or of minerals (like Olivine, Orthopyroxene, Magnetite, Pyrite) coated with a thin layer of conductive material. These calibrations were performed by shooting cosmic dust analogues with hypervelocity speeds from 1 to 80 km/s onto the flight spares of these instruments, using the Van de Graaff dust accelerator facility in Heidelberg. Here, we perform first measurements with Cassini CDA of the influence of the density of these dust particles on the resulting signal by, for a given impact speed, comparing signals from micron-sized particles made of compact PPy-coated silica to those from (PPy-coated) hollow silica spheres. The degree of impact ionization depends on the ratio of the densities of the target material and the impactor material and hence, different signals may result from impacts with diffe! rent density or porosity.

  15. Impact ionization in Al{sub x}Ga{sub 1−x}As{sub y}Sb{sub 1−y} avalanche photodiodes

    SciTech Connect

    Grzesik, M.; Donnelly, J.; Duerr, E.; Manfra, M.; Diagne, M.; Bailey, R.; Turner, G.; Goodhue, W.

    2014-04-21

    Avalanche photodiodes (APDs) have been fabricated in order to determine the impact ionization coefficients of electrons (α) and holes (β) in Al{sub x}Ga{sub 1−x}As{sub y}Sb{sub 1−y} lattice matched to GaSb for three alloy compositions: (x = 0.40, y = 0.035), (x = 0.55, y = 0.045), and (x = 0. 65, y = 0.054). The impact ionization coefficients were calculated from photomultiplication measurements made on specially designed APDs, which allowed for both pure electron and pure hole injection in the same device. Photo-multiplication measurements were made at temperatures ranging from 77 K to 300 K for all three alloys. A quasi-physical model with an explicit temperature dependence was used to express the impact ionization coefficients as a function of electric-field strength and temperature. For all three alloys, it was found that α < β at any given temperature. In addition, the values of the impact ionization coefficients were found to decrease as the aluminum concentration of the AlGaAsSb alloy was increased. A value between 1.2 and 4.0 was found for β/α, which is dependent on temperature, alloy composition, and electric-field strength.

  16. The impact of ionizing radiation on placental trophoblasts

    PubMed Central

    Kanter, D.J.; O'Brien, M.B.; Shi, X.-H.; Chu, T.; Mishima, T.; Beriwal, S.; Epperly, M.W.; Wipf, P.; Greenberger, J.S.; Sadovsky, Y.

    2014-01-01

    Introduction Exposure to low-dose radiation is widespread and attributable to natural sources. However, occupational, medical, accidental, and terrorist-related exposures remain a significant threat. Information on radiation injury to the feto-placental unit is scant and largely observational. We hypothesized that radiation causes trophoblast injury, and alters the expression of injury-related transcripts in vitro or in vivo, thus affecting fetal growth. Methods Primary human trophoblasts (PHTs), BeWo or NCCIT cells were irradiated in vitro, and cell number and viability were determined. Pregnant C57Bl/6HNsd mice were externally irradiated on E13.5, and placentas examined on E17.5. RNA expression was analyzed using microarrays and RT-qPCR. The experiments were repeated in the presence of the gramicidin S (GS)-derived nitroxide JP4-039, used to mitigate radiation-induced cell injury. Results We found that survival of in vitro–irradiated PHT cell was better than that of irradiated BeWo trophoblast cell line or the radiosensitive NCCIT mixed germ cell tumor line. Radiation altered the expression of several trophoblast genes, with a most dramatic effect on CDKN1A (p21, CIP1). Mice exposed to radiation at E13.5 exhibited a 25% reduction in mean weight by E17.5, and a 9% reduction in placental weight, which was associated with relatively small changes in placental gene expression. JP4-039 had a minimal effect on feto-placental growth or on gene expression in irradiated PHT cells or mouse placenta. Discussion and conclusion While radiation affects placental trophoblasts, the established placenta is fairly resistant to radiation, and changes in this tissue may not fully account for fetal growth restriction induced by ionizing radiation. PMID:24418702

  17. Simultaneous ionization and excitation of helium by electron impact

    NASA Astrophysics Data System (ADS)

    Dal Cappello, C.; Roy, A. C.; Ren, X. G.; Dey, R.

    2008-02-01

    We present numerical results for He (1s2) (e, 2e) He+ reaction process for transitions to the n = 1, 2 and 3 states of He+ for noncoplanar symmetric geometry at incident energies of 1000 and 1600 eV. The calculations are performed using the plane wave impulse approximation (PWIA) and the 3C method (also called the Brauner, Briggs and Klar (BBK) model) that includes post collision interaction and multiple scattering effects. In both the methods we have used the highly correlated configuration interaction wave function for the ground state of helium. A comparison of the present theoretical cross sections with the recent measured data of Ren et al. [X.G. Ren, C.G. Ning, J.K. Deng, G.L. Su, S.F. Zhang, Y.R. Huang, G.Q. Li, Phys. Rev. A 72 (2005) 042718] shows reasonably good agreement.

  18. Evidence for electron-based ion generation in radio-frequency ionization.

    PubMed

    Olaitan, Abayomi D; Zekavat, Behrooz; Solouki, Touradj

    2016-01-01

    Radio-frequency ionization (RFI) is a novel ionization method coupled to mass spectrometry (MS) for analysis of semi-volatile and volatile organic compounds (VOCs). Despite the demonstrated capabilities of RFI MS for VOC analysis in both positive- and negative-ion modes, mechanism of RFI is not completely understood. Improved understanding of the ion generation process in RFI should expand its utility in MS. Here, we studied the possibility of electron emission in RFI using both direct charged particle current measurements and indirect electron detection in a 9.4-T Fourier transform-ion cyclotron resonance (FT-ICR) mass spectrometer. We show that RF-generated electrons can be trapped in the ICR cell and, subsequently, reacted with neutral hexafluorobenzene (C6 F6 ) molecules to generate C6 F6 (●-) . Intensity of observed C6 F6 (●-) species correlated with the number of trapped electrons and decreased as a function of electron quenching period. We also measured the electron attachment rate constant of hexafluorobenzene using a post-RF electron trapping experiment. Measured electron attachment rate constant of hexafluorobenzene (1.19 (±0.53) × 10(-9)  cm(3)  molecule(-1)  s(-1) ) for post-RF FT-ICR MS agreed with the previously reported value (1.60 (±0.30) × 10(-9)  cm(3)  molecule(-1)  s(-1) ) from low-pressure ICR MS measurements. Experimental results from direct and indirect electron measurements suggest that RFI process involves RF-generated electrons under ultrahigh vacuum conditions. PMID:26757067

  19. Hyperspherical partial-wave theory applied to electron-hydrogen-atom ionization calculation for equal-energy-sharing kinematics

    SciTech Connect

    Das, J.N.; Paul, S.; Chakrabarti, K.

    2003-04-01

    Hyperspherical partial-wave theory has been applied here in a new way in the calculation of the triple differential cross sections for the ionization of hydrogen atoms by electron impact at low energies for various equal-energy-sharing kinematic conditions. The agreement of the cross section results with the recent absolute measurements of [J. Roeder, M. Baertschy, and I. Bray, Phys. Rev. A 45, 2951 (2002)] and with the latest theoretical results of the ECS and CCC calculations [J. Roeder, M. Baertschy, and I. Bray, Phys. Rev. A (to be published)] for different kinematic conditions at 17.6 eV is very encouraging. The other calculated results, for relatively higher energies, are also generally satisfactory, particularly for large {theta}{sub ab} geometries. In view of the present results, together with the fact that it is capable of describing unequal-energy-sharing kinematics [J. N. Das, J. Phys. B 35, 1165 (2002)], it may be said that the hyperspherical partial-wave theory is quite appropriate for the description of ionization events of electron-hydrogen-type systems. It is also clear that the present approach in the implementation of the hyperspherical partial-wave theory is very appropriate.

  20. Nitrogen optical emission during nanosecond laser ablation of metals: prompt electrons or photo-ionization?

    NASA Astrophysics Data System (ADS)

    Ratynskaia, S.; Dilecce, G.; Tolias, P.

    2014-10-01

    Experiments on the interaction of metal targets with a Nd:YAG laser beam ( = 1,064 nm, intensity -) are carried out in a finite Nitrogen pressure environment. The observed spectra are unambiguous evidence of the existence of an ionization and excitation source, arriving at the observation volume prior to the plume. Such a source can be either prompt electrons or VUV radiation. The analysis reveals that the prompt electron interpretation requires energies in excess of 1 keV, incompatible with any acceleration mechanisms relevant for such laser intensities. On the other hand, VUV radiation is sufficiently strong to explain the observed spectra.

  1. SEM analysis of ionizing radiation effects in linear integrated circuits. [Scanning Electron Microscope

    NASA Technical Reports Server (NTRS)

    Stanley, A. G.; Gauthier, M. K.

    1977-01-01

    A successful diagnostic technique was developed using a scanning electron microscope (SEM) as a precision tool to determine ionization effects in integrated circuits. Previous SEM methods radiated the entire semiconductor chip or major areas. The large area exposure methods do not reveal the exact components which are sensitive to radiation. To locate these sensitive components a new method was developed, which consisted in successively irradiating selected components on the device chip with equal doses of electrons /10 to the 6th rad (Si)/, while the whole device was subjected to representative bias conditions. A suitable device parameter was measured in situ after each successive irradiation with the beam off.

  2. GeV Electrons Acceleration in Focused Laser Fields after Above-threshold Ionization

    SciTech Connect

    I.Y. Dodin; N.J. Fisch

    2003-04-09

    Electrons produced as a result of above-threshold ionization of high-Z atoms can be accelerated by currently producible laser pulses up to GeV energies, as shown recently in Hu and Starace, Phys. Rev. Lett. 88 (2002) Article No. 245003. To describe electron acceleration by general focused laser fields, we employ an analytical model based on a Hamiltonian, fully relativistic, ponderomotive approach. Analytical expressions are derived and the applicability conditions of the ponderomotive formulation are studied both analytically and numerically. The theoretical predictions are supported by the numerical simulations.

  3. Intense Laser Ionization and Acceleration of Electrons in Highly-Charged Ions Using Vortex Laser Beams

    NASA Astrophysics Data System (ADS)

    Pi, Liang-Wen; Vikartofsky, Andrew; Starace, Anthony F.

    2016-05-01

    Recent advances in laser technology have led to the development of high-power petawatt lasers, making possible laser intensities of the order of 1022 W /cm2 . An electron in a highly-charged ion can be ionized in a laser field at its peak intensity and swiftly accelerated to GeV energies. Our prior investigation of laser acceleration of electrons using linearly-polarized Gaussian beams (with zero orbital angular momentum) has revealed that the final-state energies and ejection angles of the electrons depend on the initial target ion positions relative to the laser focus. We report here recent simulations of laser ionization and acceleration of electrons using linearly-polarized vortex laser beams (i.e., Laguerre-Gaussian beams), which carry orbital angular momentum and can spin microscopic objects. These simulations show that the inherent spiral phase structure of the vortex beams leads to improved final-state energy and ejection angle distributions of the electrons. This work is supported in part by DOE, Office of Science, Division of Chemical Sciences, Geosciences, and Biosciences, under Grant No. DE-FG02-96ER14646.

  4. Multi-arm spiral electron vortices in multiphoton ionization by circularly polarized pulses

    NASA Astrophysics Data System (ADS)

    Ngoko Djiokap, Jean Marcel; Meremianin, Alexei V.; Manakov, Nikolai L.; Hu, Suxing; Madsen, Lars B.; Starace, Anthony F.

    2016-05-01

    Single ionization of helium by single-color two-photon absorption or two-color one-photon/two-photon absorption from two time-delayed circularly-polarized ultraviolet pulses are shown to produce ionized-electron momentum distributions in the polarization plane having respectively even-arm (zero- and four-start) or odd-arm (one- and three-start) spiral vortex structures. Results are obtained by both ab initio numerical solution of the six-dimensional two-electron time-dependent Schrödinger equation and by perturbation theory. The multi-arm patterns are sensitive to the carrier frequencies, handedness, time-delay, and relative phase of the two pulses, allowing control of electron angular distributions. Even-arm spiral vortices have been observed in optics. Thus, our even-arm spiral electron vortices are a dramatic example of wave-particle duality. Moreover, our odd-arm electron matter-wave vortices are consistent with recent findings in strong-field physics. Research supported in part by DOE, BES, Chem. Sciences, Geosciences, and Bio-sciences Div., Grant No. DE-FG02-96ER14646.

  5. Electron correlation in two-photon double ionization of helium from attosecond to FEL pulses

    SciTech Connect

    Collins, Lee

    2009-01-01

    We investigate the role of electron correlation in the two-photon double ionization of helium for ultrashort pulses in the extreme ultraviolet (XUV) regime with durations ranging from a hundred attoseconds to a few femtoseconds. We perform time-dependent ab initio calculations for pulses with mean frequencies in the so-called 'sequential' regime ({Dirac_h}{omega} > 54.4 eV). Electron correlation induced by the time correlation between emission events manifests itself in the angular distribution of the ejected electrons, which strongly depends on the energy sharing between them. We show that for ultrashort pulses two-photon double ionization probabilities scale non-uniformly with pulse duration depending on the energy sharing between the electrons. Most interestingly we find evidence for an interference between direct ('nonsequential') and indirect ('sequential') double photoionization with intermediate shake-up states, the strength of which is controlled by the pulse duration. This observation may provide a route towards measuring the pulse duration of x-ray free-electron laser (XFEL) pulses.

  6. Application of the many-electron weak-field asymptotic theory of tunneling ionization to atoms

    NASA Astrophysics Data System (ADS)

    Tolstikhina, Inga Yu.; Morishita, Toru; Tolstikhin, Oleg I.

    2014-11-01

    The many-electron weak-field asymptotic theory (ME-WFAT) of tunneling ionization [Tolstikhin et al., Phys. Rev. A 89, 013421 (2014), 10.1103/PhysRevA.89.013421] is applied to atoms. The procedure to extract the asymptotic coefficient of a Dyson orbital needed to implement the ME-WFAT from many-electron wave functions given by a linear combination of Slater determinants composed of one-electron orbitals, as is typically the case in practical atomic structure calculations, is discussed. It is shown that in the one-configuration approximation such wave functions enable one to consistently implement the theory and calculate the ionization rate. The effect of relaxation of the ionic orbitals and the dependence of the rate on the total orbital momentum and spin states of the atom and ion are considered. However, wave functions constructed by mixing several electronic configurations, maybe more accurate in some sense, do not have the correct asymptotic behavior required for implementing the ME-WFAT. The theory is illustrated by calculations for atoms of the first three periods with the use of one-electron orbitals obtained by the Hartree-Fock method.

  7. Impact of bias conditions on electrical stress and ionizing radiation effects in Si-based TFETs

    NASA Astrophysics Data System (ADS)

    Ding, Lili; Gnani, Elena; Gerardin, Simone; Bagatin, Marta; Driussi, Francesco; Selmi, Luca; Royer, Cyrille Le; Paccagnella, Alessandro

    2016-01-01

    The interplay between electrical stress and ionizing radiation effects is experimentally investigated in Si-based Tunnel Field Effect Transistors (TFETs). In particular, the impact of bias conditions on the performance degradation is discussed. We found that the electrical stress effects in TFETs could not be ignored in radiation tests, since they can possibly overwhelm the radiation-induced degradation. Under this circumstance, the worst-case bias condition for studying radiation effects is not straightforward to be determined when there is an interplay between electrical stress and ionizing radiation effects.

  8. Self-injection and acceleration of electrons during ionization of gas atoms by a short laser pulse

    SciTech Connect

    Singh, K.P.

    2006-04-15

    Using a relativistic three-dimensional single-particle code, acceleration of electrons created during the ionization of nitrogen and oxygen gas atoms by a laser pulse has been studied. Barrier suppression ionization model has been used to calculate ionization time of the bound electrons. The energy gained by the electrons peaks for an optimum value of laser spot size. The electrons created near the tail do not gain sufficient energy for a long duration laser pulse. The electrons created at the tail of pulse escape before fully interacting with the trailing part of the pulse for a short duration laser pulse, which causes electrons to retain sufficient energy. If a suitable frequency chirp is introduced then energy of the electrons created at the tail of the pulse further increases.

  9. Role of Coulomb repulsion in correlated-electron emission from a doubly excited state in nonsequential double ionization of molecules

    NASA Astrophysics Data System (ADS)

    Huang, Cheng; Guo, Wenliang; Zhou, Yueming; Wu, Zhengmao

    2016-01-01

    With the classical ensemble model, we investigate nonsequential double ionization of aligned molecules by few-cycle laser pulses at low intensity, where the two electrons finally are ionized through a transition doubly excited state induced by recollision. The correlated electron momentum distribution of parallel molecules exhibits the line-shaped structure parallel to the diagonal. Our analysis indicates that besides the ionization time difference of two electrons from the doubly excited state, the final-state e-e Coulomb repulsion plays a vital role in the formation of the line-shaped structural momentum distribution. For perpendicular molecules, due to the prominent near half-cycle ionization time difference between the two electrons from the doubly excited state, the momentum distribution shows clear anticorrelation behavior.

  10. Compendium of Current Total Ionizing Dose Results and Displacement Damage Results for Candidate Spacecraft Electronics for NASA

    NASA Technical Reports Server (NTRS)

    Cochran, Donna J.; O'Bryan, Martha V.; Buchner, Stephen P.; Poivey, Christian; Ladbury, Ray L.; LaBel, Kenneth A.

    2007-01-01

    Sensitivity of a variety of candidate spacecraft electronics to total ionizing dose and displacement damage is studied. Devices tested include optoelectronics, digital, analog, linear bipolar devices, and hybrid devices.

  11. Multiple Ionization Of Metal Ions By ECR Heating Of Electrons In Vacuum Arc Plasmas

    NASA Astrophysics Data System (ADS)

    Vodopyanov, A. V.; Golubev, S. V.; Mansfeld, D. A.; Nikolaev, A. G.; Oks, E. M.; Razin, S. V.; Savkin, K. P.

    2005-03-01

    A joint research and development effort has been initiated, whose ultimate goal is the enhancement the mean ion charge states in vacuum arc metal plasmas by a combination of a vacuum arc discharge and an electron cyclotron resonance (ECR) heating. Metal plasma was generated by a special vacuum arc mini-gun and injected into mirror magnetic trap. Plasma was pumped by high frequency gyrotron-generated microwave radiation (frequency 37.5 GHz, max power 100 kW, pulse duration 1.5 ms). Using of powerful microwaves makes it possible to sustain sufficient temperature of electrons needed for multiple ionizations at high plasma density (more then 1013 cm-3). Parameter of multiple ionization efficiency Neτi, where Ne is plasma density, τi, is ion lifetime, in such a case could reach rather high value ˜109 cm-3-s. In our situation τi = Ltrap/Vi, where Ltrap is trap length, Vi is plasma gun flow velocity. The results have demonstrated substantial multiple ionization of metal ions (including metals with high melting temperature). For a metal (lead, platinum) plasma, ECR heating shifted the average ion charge up to 5+. Further increase of the ion charge states will be attained by increasing the vacuum arc plasma density and optimizing the ECR heating conditions.

  12. Recollections on Sixty Years of NBS Ionizing Radiation Programs for Energetic X Rays and Electrons1

    PubMed Central

    Koch, H. William

    2006-01-01

    These recollections are on ionizing radiation programs at the National Bureau of Standards (NBS) that started in 1928 and ended in 1988 when NBS became the National Institute of Standards and Technology (NIST). The independent Council on Ionizing Radiation Measurements and Standards (CIRMS) was formed in 1992. This article focuses on how measurements and standards for x rays, gamma rays, and electrons with energies above 1 MeV began at NBS and how they progressed. It also suggests how the radiation processors of materials and foods, the medical radiographic and radiological industries, and the radiological protection interests of the government (including homeland security) represented in CIRMS can benefit from NIST programs. PMID:27274947

  13. Electron-impact excitation of holmium atoms

    SciTech Connect

    Smirnov, Yu M

    2000-06-30

    The electron-impact excitation of holmium atoms was studied by the method of extended crossing beams. The cross sections and the optical excitation functions were obtained for odd levels of Ho I, including the 22014 cm{sup -1} laser level. Over 99% of the atoms were shown to reside in the ground level prior to collisions with electrons. Also measured were the excitation cross sections for six even levels, which presumably participate in the formation of inversion population in a gas-discharge holmium vapour laser. (laser applications and other topics in quantum electronics)

  14. Resonantly Enhanced Betatron Hard X-rays from Ionization Injected Electrons in a Laser Plasma Accelerator

    PubMed Central

    Huang, K.; Li, Y. F.; Li, D. Z.; Chen, L. M.; Tao, M. Z.; Ma, Y.; Zhao, J. R.; Li, M. H.; Chen, M.; Mirzaie, M.; Hafz, N.; Sokollik, T.; Sheng, Z. M.; Zhang, J.

    2016-01-01

    Ultrafast betatron x-ray emission from electron oscillations in laser wakefield acceleration (LWFA) has been widely investigated as a promising source. Betatron x-rays are usually produced via self-injected electron beams, which are not controllable and are not optimized for x-ray yields. Here, we present a new method for bright hard x-ray emission via ionization injection from the K-shell electrons of nitrogen into the accelerating bucket. A total photon yield of 8 × 108/shot and 108 photons with energy greater than 110 keV is obtained. The yield is 10 times higher than that achieved with self-injection mode in helium under similar laser parameters. The simulation suggests that ionization-injected electrons are quickly accelerated to the driving laser region and are subsequently driven into betatron resonance. The present scheme enables the single-stage betatron radiation from LWFA to be extended to bright γ-ray radiation, which is beyond the capability of 3rd generation synchrotrons. PMID:27273170

  15. Resonantly Enhanced Betatron Hard X-rays from Ionization Injected Electrons in a Laser Plasma Accelerator.

    PubMed

    Huang, K; Li, Y F; Li, D Z; Chen, L M; Tao, M Z; Ma, Y; Zhao, J R; Li, M H; Chen, M; Mirzaie, M; Hafz, N; Sokollik, T; Sheng, Z M; Zhang, J

    2016-01-01

    Ultrafast betatron x-ray emission from electron oscillations in laser wakefield acceleration (LWFA) has been widely investigated as a promising source. Betatron x-rays are usually produced via self-injected electron beams, which are not controllable and are not optimized for x-ray yields. Here, we present a new method for bright hard x-ray emission via ionization injection from the K-shell electrons of nitrogen into the accelerating bucket. A total photon yield of 8 × 10(8)/shot and 10(8 )photons with energy greater than 110 keV is obtained. The yield is 10 times higher than that achieved with self-injection mode in helium under similar laser parameters. The simulation suggests that ionization-injected electrons are quickly accelerated to the driving laser region and are subsequently driven into betatron resonance. The present scheme enables the single-stage betatron radiation from LWFA to be extended to bright γ-ray radiation, which is beyond the capability of 3(rd) generation synchrotrons. PMID:27273170

  16. Resonantly Enhanced Betatron Hard X-rays from Ionization Injected Electrons in a Laser Plasma Accelerator

    NASA Astrophysics Data System (ADS)

    Huang, K.; Li, Y. F.; Li, D. Z.; Chen, L. M.; Tao, M. Z.; Ma, Y.; Zhao, J. R.; Li, M. H.; Chen, M.; Mirzaie, M.; Hafz, N.; Sokollik, T.; Sheng, Z. M.; Zhang, J.

    2016-06-01

    Ultrafast betatron x-ray emission from electron oscillations in laser wakefield acceleration (LWFA) has been widely investigated as a promising source. Betatron x-rays are usually produced via self-injected electron beams, which are not controllable and are not optimized for x-ray yields. Here, we present a new method for bright hard x-ray emission via ionization injection from the K-shell electrons of nitrogen into the accelerating bucket. A total photon yield of 8 × 108/shot and 108 photons with energy greater than 110 keV is obtained. The yield is 10 times higher than that achieved with self-injection mode in helium under similar laser parameters. The simulation suggests that ionization-injected electrons are quickly accelerated to the driving laser region and are subsequently driven into betatron resonance. The present scheme enables the single-stage betatron radiation from LWFA to be extended to bright γ-ray radiation, which is beyond the capability of 3rd generation synchrotrons.

  17. Band gaps, ionization potentials, and electron affinities of periodic electron systems via the adiabatic-connection fluctuation-dissipation theorem

    NASA Astrophysics Data System (ADS)

    Trushin, Egor; Betzinger, Markus; Blügel, Stefan; Görling, Andreas

    2016-08-01

    An approach to calculate fundamental band gaps, ionization energies, and electron affinities of periodic electron systems is explored. Starting from total energies obtained with the help of the adiabatic-connection fluctuation-dissipation (ACFD) theorem, these physical observables are calculated according to their basic definition by differences of the total energies of the N -, (N -1 ) -, and (N +1 ) -electron system. The response functions entering the ACFD theorem are approximated here by the direct random phase approximation (dRPA). For a set of prototypical semiconductors and insulators it is shown that even with this quite drastic approximation the resulting band gaps are very close to experiment and of a similar quality to those from the computationally more involved G W approximation. By going beyond the dRPA in the future the accuracy of the calculated band gaps may be significantly improved further.

  18. Double ionization of helium by 2-keV electrons in equal- and unequal-energy configurations

    NASA Astrophysics Data System (ADS)

    Ambrosio, M. J.; Mitnik, D. M.; Dorn, A.; Ancarani, L. U.; Gasaneo, G.

    2016-03-01

    We present theoretical and experimental fully differential cross sections, in coplanar scattering geometry, for the double ionization of helium by electron impacting at 2 keV. The observed structures for both equal and unequal sharing of the excess energy are analyzed. Although the incident energy could, in principle, be regarded as high enough for the applicability of the first Born approximation in the projectile-target interaction, the experimental cross sections, measured with a COLTRIMS apparatus, show that further orders' effects can be appreciated. The theoretical cross sections are calculated with the generalized Sturmian functions method, which exactly solves the three-body problem that stems from a first-order projectile-target perturbative treatment.

  19. High-order determinantal equation-of-motion coupled-cluster calculations for ionized and electron-attached states

    NASA Astrophysics Data System (ADS)

    Hirata, So; Nooijen, Marcel; Bartlett, Rodney J.

    2000-10-01

    General-order equation-of-motion coupled-cluster methods for ionization potentials and electron affinities (IP-EOM-CC and EA-EOM-CC) are developed by employing a determinantal algorithm. With these, principal ionization potentials or electron affinities of diatomic molecules and the excitation energies of their ionized or electron-attached counterparts are computed across different approximations of the cluster operator and the ionization (electron-attachment) operator. IP-EOM-CC(2,2h-1p)=IP-EOM-CCSD and EA-EOM-CC(2,1h-2p)=EA-EOM-CCSD or EA-EOM-CC(2,2h-3p) prove to be well-balanced models for principal ionization potentials and electron affinities, whereas for the quantitative descriptions of non-Koopmans ionization or electron-attachment processes IP-EOM-CC(3,3h-2p)=IP-EOM-CCSDT and EA-EOM-CC(2,2h-3p) appear to be the minimal levels.

  20. Electron transfer, ionization, and excitation in atomic collisions. Progress report, June 15, 1992--June 14, 1995

    SciTech Connect

    Winter, T.G.; Alston, S.G.

    1995-08-01

    The research program of Winter and Alston addresses the fundamental processes of electron transfer, ionization, and excitation in ion-atom, ion-ion, and ion-molecule collisions. Attention is focussed on one- and two-electron systems and, more recently, quasi-one-electron systems whose electron-target-core interaction can be accurately modeled by one-electron potentials. The basic computational approaches can then be taken with few, if any, approximations, and the underlying collisional mechanisms can be more clearly revealed. Winter has focussed on intermediate collision energies (e.g., proton energies for p-He{sup +} collisions on the order of 100 kilo-electron volts), in which many electron states are strongly coupled during the collision and a coupled-state approach, such as a coupled-Sturmian-pseudostate approach, is appropriate. Alston has concentrated on higher collision energies (million electron-volt energies), or asymmetric collision systems, for which the coupling of the projectile is weaker with, however, many more target states being coupled together so that high-order perturbation theory is essential. Several calculations by Winter and Alston are described, as set forth in the original proposal.