Science.gov

Sample records for electron impact ionization

  1. 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.

  2. Electron-impact ionization and dissociative ionization of biomolecules

    NASA Astrophysics Data System (ADS)

    Huo, Winifred

    2006-05-01

    Oxidative damages by ionizing radiation are the source of radiation-induced damages to human health. It is recognized that secondary electrons play a role in the damage process, particularly important is the damage of DNA by electrons, potentially leading to mutagenesis. The damage can be direct, by creating a DNA lesion, or indirect, by producing radicals that attack the DNA. Molecular-level study of electron interaction with DNA provides information on the damage pathways and dominant mechanisms. This investigation focuses on ionization and dissociative ionization (DI) of DNA fragments by electron-impact. For ionization we use the improved binary-encounter dipole (iBED) model [W.M. Huo, Phys. Rev. A64, 042719-1 (2001)]. For DI it is assumed that electron motion is much faster than nuclear motion, allowing DI to be treated as a two-step process and the DI cross section given by the product of the ionization cross section and dissociation probability. The ionization study 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'- and C5'-deoxyribose-phospate cross sections, differing by less than 5%. The result implies that certain properties of the DNA, like the total ionization cross section, are localized properties and an additivity principle may apply. This allows us to obtain properties of a larger molecular system built up from the results of smaller subsystem fragments. The DI of guanine and cytosine has been studied. For guanine, a proton is produced from the channel where the ionized electron originates from a molecular orbital with significant charge density along the N(1)-H bond. The interaction of the proton with cytosine was also studied.

  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. 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.

  6. 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.

  7. 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.

  8. Electron-impact ionization of W25+

    NASA Astrophysics Data System (ADS)

    Kynienė, A.; Pakalka, S.; Masys, Š.; Jonauskas, V.

    2016-09-01

    Electron-impact ionization cross sections for the ground level of the W25+ ion have been investigated by performing level-to-level calculations and using the Dirac-Fock-Slater method in the single-configuration approach. The main attention has been focused on the influence of the increasing principal and orbital quantum numbers on the excitation-autoionization (EA) process and its contribution to the total ionization cross sections. The obtained results demonstrate that excitations to the high-nl shells (n≥slant 9) increase cross sections of the indirect ionization process by about 60% compared to the excitations to the lower shells (n≤slant 8). It was established that excitations to the shells with the orbital quantum number l = 4 give the greatest contribution to EA. Maxwellian rate coefficients derived from the cross sections for the ground state are compared with the previously obtained values from the configuration-average distorted-wave (CADW) approximation. The rate coefficients for direct ionization (DI) are smaller than the corresponding CADW values, while the EA rate coefficients are larger than the ones from the CADW calculations. The total DI+EA rate coefficients are about 20% larger than the CADW rate coefficients.

  9. Electron Impact Ionization of the Rare Gases

    NASA Astrophysics Data System (ADS)

    Lohmann, Birgit

    2008-10-01

    Detailed information about the electron impact ionization process can be obtained from fully differential cross section measurements, in which the ionized electron is detected in coincidence with the outgoing scattered projectile electron. Incident and outgoing electron momenta are completely determined in these measurements. A considerable body of experimental and theoretical data exists for H and He targets, and the level of agreement between theory and experiment for these simple atoms is exceptional. However, there are still significant discrepancies between theory and experiment in the case of ionization of more complex atomic targets such as the heavier rare gas atoms. In this talk I will present recent measurements and theoretical predictions of fully differential cross sections for ionization of a range of rare gas targets: He, Ne, Ar and Xe. The talk will concentrate primarily on experiments which have been performed by two experimental groups, our group in Australia [1-3] and that of Lahmam-Bennani [3-5] in France. The experimental conditions span two different kinematic regimes, one with intermediate incident electron energy and low ejected electron energy, and the other with higher incident electron energy, and ejected electron energies which correspond to large energy transfer in the collision process. All experiments have been performed in a coplanar asymmetric configuration in which the scattered electron is detected at a small forward scattering angle. The experimental apparatus used in Australia is of quite different design to that in France, and I will present the results of an experiment in which the two groups have collaborated to produce data under identical kinematic conditions and for the same targets, using these two very different experimental approaches. This comprehensive set of experimental data has provided an interesting challenge to theory, and I will discuss the state of play with regard to the alignment between curent state

  10. Electron-impact ionization of ozone

    NASA Astrophysics Data System (ADS)

    Newson, Karl A.; Luc, Stephanie M.; Price, Stephen D.; Mason, Nigel J.

    1995-10-01

    Partial electron ionization cross-sections of ozone for incident electron energies from 40 to 500 eV have been determined using time-of-flight mass spectrometry. The cross-sections are derived by identifying the contribution of ozone to the ion signals recorded following ionization of a mixture of O2 and O3. Only one previous determination of these cross-sections, for energies up to 100 eV, is available in the literature. The cross-sections derived in the present study at these lower electron energies are in good agreement with the previous determination.

  11. 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.

  12. Electron impact ionization-excitation of Helium

    NASA Astrophysics Data System (ADS)

    Ancarani, Lorenzo Ugo; Gomez, A. I.; Gasaneo, G.; Mitnik, D. M.; Ambrosio, M. J.

    2016-09-01

    We calculate triple differential cross sections (TDCS) for the process of ionization-excitation of Helium by fast electron impact in which the residual ion is left in the n =2 excited state. We chose the strongly asymmetric kinematics used in the experiment performed by Dupré et al.. In a perturbative scheme, for high projectile energies the four-body problem reduces to a three-body one and, within that framework, we solve the time- independent Schrödinger equation with a Sturmian approach. The method, based on Generalized Sturmian Functions (GSF), is employed to obtain the initial ground state of Helium, the single-continuum state and the scattering wave function; for each of them, the GSF basis is constructed with the corresponding adequate asymptotic conditions. Besides, the method presents the following advantage: the scattering amplitudes can be extracted directly in the asymptotic region of the scattering solution, and thus the TDCS can be obtained without requiring a matrix element evaluation.

  13. Threshold electron attachment and electron impact ionization involving oxygen dimers

    NASA Astrophysics Data System (ADS)

    Kreil, J.; Ruf, M.-W.; Hotop, H.; Ettischer, I.; Buck, U.

    1998-12-01

    Using two different crossed-beams machines we have carried out the first quantitative study of threshold electron attachment and electron impact-induced ionization and fragmentation involving oxygen dimers (O 2) 2. In the electron attachment experiment we study electron transfer from state-selected Ar **(20d) Rydberg atoms to O 2 molecules and dimers in a skimmed supersonic beam at variable nozzle temperatures ( T0) and stagnation pressures ( p0). The relative dimer density is determined through measurements of Penning ionization by metastable Ne *(3s 3P2,0) atoms and used to estimate the absolute cross-section for O 2- formation in collisions of Ar **(20d) Rydberg atoms with O 2 dimers to be nearly 10 -17 m 2, almost four orders of magnitude larger than that for O 2- formation in collisions of Ar **(20d) Rydberg atoms with O 2 monomers. The fragmentation of the oxygen cluster beam is quantitatively characterized by the transverse helium beam scattering method which allows us to spatially separate different clusters. It is shown that in 70 eV electron impact of (O 2) 2 only 3.6(4)% of the dimers are detected as dimer ions (O 2) 2+. In additional experiments involving SF 6 clusters we show that SF 6 dimers fragment nearly completely upon 70 eV electron impact, yielding SF 5+ ions (probability for (SF 6)·SF 5+ production at most 0.3%).

  14. 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.

  15. Electron-Impact Dissociative Ionization Of Ethylene (Postprint)

    DTIC Science & Technology

    2006-02-01

    require reliable data on total and on dissociative ionization processes . Total electron-impact ion- ization rates are known rather accurately for...ciative ionization process in low electron energy regimes of electric discharge plasmas. Dissociative ionization DI processes are very important in...plasmas and DI processes involving hydrocarbons will be very important for new applications of plasma to enhance combustion. Rates for the generation

  16. Electron impact ionization of tungsten ions in a statistical model

    NASA Astrophysics Data System (ADS)

    Demura, A. V.; Kadomtsev, M. B.; Lisitsa, V. S.; Shurygin, V. A.

    2015-01-01

    The statistical model for calculations of the electron impact ionization cross sections of multielectron ions is developed for the first time. The model is based on the idea of collective excitations of atomic electrons with the local plasma frequency, while the Thomas-Fermi model is used for atomic electrons density distribution. The electron impact ionization cross sections and related ionization rates of tungsten ions from W+ up to W63+ are calculated and then compared with the vast collection of modern experimental and modeling results. The reasonable correspondence between experimental and theoretical data demonstrates the universal nature of statistical approach to the description of atomic processes in multielectron systems.

  17. Electron impact ionization of the gas-phase sorbitol

    NASA Astrophysics Data System (ADS)

    Chernyshova, Irina; Markush, Pavlo; Zavilopulo, Anatoly; Shpenik, Otto

    2015-03-01

    Ionization and dissociative ionization of the sorbitol molecule by electron impact have been studied using two different experimental methods. In the mass range of m/ z = 10-190, the mass spectra of sorbitol were recorded at the ionizing electron energies of 70 and 30 eV. The ion yield curves for the fragment ions have been analyzed and the appearance energies of these ions have been determined. The relative total ionization cross section of the sorbitol molecule was measured using monoenergetic electron beam. Possible fragmentation pathways for the sorbitol molecule were proposed.

  18. Experiments on electron-impact excitation and ionization of ions

    SciTech Connect

    Phaneuf, R.A.

    1985-01-01

    The present review covers some of the fundamental aspects of electron-impact ionization. Highlights are described of some of the important experimental results which have been produced since 1981. (MOW)

  19. Calculation of electron-impact ionization of potassium

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

    We calculate electron-impact ionization of potassium at a broad range of energies for the case where it is the valence electron that is ejected. The convergent close-coupling method is used to calculate the total and fully differential cross sections. The unusual shape of the total ionization spin asymmetries measured by Baum et al. [1] is explained. However, agreement with the fully differential cross section measurements of Murray [2] is somewhat mixed.

  20. Electron impact ionization at relativistic energies

    NASA Astrophysics Data System (ADS)

    Belkacem, Ali; Cole, Kyra; Hertlein, Marcus; Feinberg, Benedict; Schriel, Ralf; Adaniya, Hidehito; Neumann, Nadine

    2004-05-01

    We used an ion time-of-flight set up based on a pulsed high-voltage extraction technique to study the charge state distribution of He, Ne, Ar, Kr and Xe atoms after impact of 0.2 to 1.5 GeV electrons. The relativistic electron beam is produced at the booster beamline at the Advanced Light Source at the Lawrence Berkeley National Laboratory. The yield of ions drops drastically with the charge state number. Our measurements show that the ratio of doubly-charge to singly-charged ions reaches an asymptotic limit of 0.0028 for He already at electron energies below 40 MeV. However we observe a very pronounced energy dependence of the ratio of the doubly-charged to singly-charged ions for the heavier atoms such as Kr and Xe in the 0.2 - 1.5 GeV energy range. This energy dependence takes place way above the energy at which theories based on the equivalent photon method or the born- approximation predict the asymptotic limit to be reached. This may be an indication of new physics coming into play in the photoionization process due to relativistic effects.

  1. 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.

  2. Electron impact double ionization cross sections of light elements

    NASA Astrophysics Data System (ADS)

    Talukder, M. R.; Haque, A. K. F.; Uddin, M. A.

    2009-06-01

    A simple user-friendly semiempirical model is proposed to calculate electron impact double ionization cross sections of He, Li, Li+, B+, C+, C3+, O, O2+, O3+, Ne, Ne+, Ne2+, Na, Mg, Al3+, S, and Arq+ (q=0-7) targets for the incident electron energies from threshold to 106 eV. The contributions in the total double ionization cross sections from the direct double ionization and inner-shell ionization processes are taken into account on the basis of experimental data considered. The results of the present analysis are compared with the available experimental data and theoretical calculations. The model is found successful for the description of experimental cross sections. Since, this model may be a prudent selection to meet the demand level in plasma modeling due to its simple inherent structure.

  3. 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.

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

    PubMed Central

    2016-01-01

    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. PMID:26931697

  5. 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.

  6. Storage Ring Measurements of Electron Impact Ionization for Solar Physics

    NASA Astrophysics Data System (ADS)

    Hahn, Michael; 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.

    2013-07-01

    The interpretation of astrophysical spectra requires knowledge of the charge state distribution (CSD) of the plasma. The CSD is determined by the rates of ionization and recombination. Thus, accurate electron impact ionization (EII) data are needed to calculate the CSD of the solar atmosphere as well as for other electron-ionized astrophysical objects, such as stars, supernovae, galaxies, and clusters of galaxies. We are studying EII for astrophysically important ions using the TSR storage ring located at the Max Plank Institute for Nuclear Physics in Heidelberg, Germany. Storage ring measurements are largely free of the metastable contamination found in other experimental geometries, resulting in unambiguous EII data. We have found discrepancies of about 10% - 30% between our measured cross sections and those commonly used in CSD models. Because it is impractical to perform experimental measurements for every astrophysically relevant ion, theory must provide the bulk of the necessary EII data. These experimental results provide an essential benchmark for such EII calculations.

  7. Temperature dependence of electron impact ionization coefficient in bulk silicon

    NASA Astrophysics Data System (ADS)

    Ahmed, Mowfaq Jalil

    2017-09-01

    This work exhibits a modified procedure to compute the electron impact ionization coefficient of silicon for temperatures between 77 and 800K and electric fields ranging from 70 to 400 kV/cm. The ionization coefficients are computed from the electron momentum distribution function through solving the Boltzmann transport equation (BTE). The arrangement is acquired by joining Legendre polynomial extension with BTE. The resulting BTE is solved by differences-differential method using MATLAB®. Six (X) equivalent ellipsoidal and non-parabolic valleys of the conduction band of silicon are taken into account. Concerning the scattering mechanisms, the interval acoustic scattering, non-polar optical scattering and II scattering are taken into consideration. This investigation showed that the ionization coefficients decrease with increasing temperature. The overall results are in good agreement with previous experimental and theoretical reported data predominantly at high electric fields.

  8. 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. PMID:27446718

  9. Electron-impact dissociation and ionization of CN+ ions

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

    Absolute cross sections are reported for electron-impact ionization and dissociation of CN+ ions. Simple ionization to CN2 + ions and formation of singly charged C+ and N+ and doubly charged C2 + and N2 + fragments have been investigated. The animated electron-ion crossed-beam method has been applied in the energy range from the respective reaction thresholds up to 2.5 keV. The maximum of the simple ionization cross section is found to be (5.37 ±0.14 ) ×10-18 cm2 at 115 eV. The maximum total cross sections for N+ and C+ fragment production are found to be (22.2 ±2.7 ) ×10-17 and (18.9 ±1.2 ) ×10-17 cm2 at 85 eV, respectively. By performing careful magnetic field scans of the collected ions, contributions of dissociative excitation and dissociative ionization to the C+ and N+ fragment production are determined separately. The cross sections for asymmetric dissociative ionization to C2 + and N2 + are found to be more than one order of magnitude smaller. The kinetic energy release distributions are determined for all dissociation processes at selected electron energies. These distributions, together with the energy thresholds, provide additional information about the ground and excited states of the molecular ion.

  10. Coulomb crystal as a detector in electron impact ionization experiment

    NASA Astrophysics Data System (ADS)

    Klosowski, Lukasz; Piwinski, Mariusz; Wojtewicz, Szymon; Lisak, Daniel; Dziczek, Darek; Chwirot, Stanislaw

    2016-09-01

    Ensembles of ions in trap at sufficiently low temperature can form a structure called Coulomb crystal. Some species of such ions can be optically cooled and observed using CCD camera. Number of ions composing the crystal can be determined with high accuracy. Other, invisible species of ions can be sympathetically cooled and detected indirectly by observation of their influence on visible ones. Thus, the efficiency of ionization processes leading to Coulomb crystal formation can be determined. We present preliminary results for electron-impact-ionized molecules forming a multi-species Coulomb crystal in a linear segmented Paul trap together with atomic calcium ions.

  11. 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.

  12. 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.

  13. Double differential cross sections for electron impact ionization of helium

    NASA Astrophysics Data System (ADS)

    Yun-fei, Yao; Zhang-jin, Chen

    1999-03-01

    The double differential cross sections for electron impact ionization of helium at incident energies of 200 eV, 100 eV and 64.6 eV have been calculated in the BBK model. The present results are found to be in generally good agreement with the latest measurements of Röder et al. and the theoretical results of the convergent close-coupling method although some quantitative discrepancy remains.

  14. 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.

  15. 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.

  16. Electron impact ionization dynamics of para-benzoquinone

    NASA Astrophysics Data System (ADS)

    Jones, D. B.; Ali, E.; Ning, C. G.; Colgan, J.; Ingólfsson, O.; Madison, D. H.; Brunger, M. J.

    2016-10-01

    Triple differential cross sections (TDCSs) for the electron impact ionization of the unresolved combination of the 4 highest occupied molecular orbitals (4b3g, 5b2u, 1b1g, and 2b3u) of para-benzoquinone are reported. These were obtained in an asymmetric coplanar geometry with the scattered electron being observed at the angles -7.5°, -10.0°, -12.5° and -15.0°. The experimental cross sections are compared to theoretical calculations performed at the molecular 3-body distorted wave level, with a marginal level of agreement between them being found. The character of the ionized orbitals, through calculated momentum profiles, provides some qualitative interpretation for the measured angular distributions of the TDCS.

  17. Electron Impact Ionization of He atom using screening potential

    NASA Astrophysics Data System (ADS)

    Saha, Hari P.

    2012-06-01

    We will report the results of our investigation on electron impact ionization of helium atom using our extended MCHF method [1] for electron impact ionization of atoms. The initial state wave function will be calculated with both HF and MCHF approximations and the electron correlation between the two final state continuum electrons will be obtained using the screening potential [2-4]. Calculations will be made for triple differential cross sections for 4 eV excess energy sharing equally by the two final state continuum electrons. The results will be presented for all scattering angles and all kinematics. Comparison will be made with available experimental and theoretical data. [4pt] [1] Hari P. Saha, Phys. Rev. A82, 042703 (2010); J.Phys. B44, 065202 (2011).[0pt] [2] M.R.H. Rudge and M.J. Seaton, Proc. Roy. Soc. A293. 262 (1965).[0pt] [3] M.R.H. Rudge, Rev. Mod. Phys. 40, 564 (1968).[0pt] [4] C.Pan and A.F Starace, Phys. Rev. Lett. 67, 185 (1991); Phys. Rev. A45, 4588 (1992).

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-06-01

    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.

  20. 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.

  1. 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.

  2. 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.

  3. 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.

  4. Doubly Differential Multiple Ionization of Neon by Electron Impact*

    NASA Astrophysics Data System (ADS)

    Santos, A. C. F.; Dubois, R. D.; Hasan, A.

    2003-05-01

    Absolute doubly differential cross sections for single, double and triple ionization of Ne atoms have been measured for 750 eV electron impact as a function of projectile energy loss and scattering angle. Angular distributions between 0 and +/- 12 degrees were obtained for energy losses between 0 and 600 eV. In this energy-loss range only L shell electrons are available for target ionization. The data were normalized to total ionization cross sections available in the literature. A comparison is made with photoionization data as well as with argon data taken using similar methods in order to study the role played by the static target potential. 1- R. D. DuBois, C. Doudna, C. Lloyd, M. Kahveci, Kh Khayyat, Y. Zhou, and D. H. Madison, J. Phys. B 34 (2001) L783-L789. 2- R. D. DuBois, Kh Khayyat, C. Doudna, C. Lloyd, NIM B 192 (2002) 63-66. 3- A. C. F. Santos, A. Hasan, T. Yates, R. D. DuBois, submitted to Phys. Rev. A (2003).

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

    PubMed

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

    2004-12-15

    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> or =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. (c) 2004 American Institute of Physics

  6. 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.

  7. Theoretical study of electron impact-ionization of molecules

    NASA Astrophysics Data System (ADS)

    Al-Hagan, Ola

    There has been impressive progress in the area of theoretical treatments of electron impact ionization (e,2e) of atoms and molecules in the last decade. Most recently, low to intermediate incident electron energies have been reported for molecular systems. In this dissertation, different theoretical models will be used to calculate the fully differential cross section (FDCS) for (e,2e) processes for low to intermediate incident electron energies for a variety of final state electron angles and energies for the diatomic molecules H2 and N2, the triatomic molecule H2O, and the boimolecule HCOOH. In addition, there has been a large amount of interest in diatomic molecules inspired by the possibility of observing an interference effect due to the two molecular centers playing the role of a double slit. In this dissertation, the interference effect for the diatomic molecules H2 and N2 will be examined. Finally, there is presently considerable experimental effort directed towards measuring the FDCS for a specific molecular orientation. Most recently, the FDCS for single ionization of aligned hydrogen molecules was measured by Alexander Dorn's experimental group in Heidelberg, Germany. These measurements were successful for the first time to observe features of the FDCS for different alignment of H2. Theoretical calculations for aligned H2 will be presented. These calculations were able to obtain good agreement with the experimental data especially in the binary peak region.

  8. Electron Impact K-shell Ionization of Atomic Targets

    NASA Astrophysics Data System (ADS)

    Saha, Bidhan; Basak, Arun K.; Alfaz Uddin, M.; Patoary, A. A. R.

    2008-05-01

    In spite of considerable progress -both theoretically and experimentally- recently in evaluating accurate K-shell ionization cross sections that play a decisive role for quantitative analyses using (i) electron probe microanalysis, (ii) Auger electron spectroscopy and (iii) electron energy loss spectra, attempts are still continuing to search for a model that can easily generate reliable cross sections for a wide range of energies and for various targets needed for plasma modeling code We report few modifications of the widely used binary encounter approximation (BEA) [1,2] and have tested by evaluating the electron impact K-shell ionization of few neutral targets at various projectile energies. Details will be presented at the meeting. [1] M. Gryziniski, Phys. Rev. A 138, 336 (1965); [2] L. Vriens, Proc. Phys. Soc. (London) 89, 13, (1966). [3M. A. Uddin , A. K. F. Haque, M. M. Billah, A. K. Basak, K, R, Karim and B. C. Saha, ,Phys. Rev. A 71,032715 (2005); [4] M. A. Uddin, A. K. Basak, and B. C. Saha, Int. J. Quan. Chem 100, 184 (2004).

  9. 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.

  10. 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

  11. 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.

  12. Electron impact ionization and attachment cross sections for H2S. [in comet and planetary atmospheres

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

    Experiments were performed to measure, by electron impact, appearance potentials and the cross sections for ionization, dissociative ionization, and electron attachment for H2S. Results are presented, and discussed individually, for both positive and negative ions. A schematic diagram of the experimental setup is included.

  13. Electron Impact Ionization Cross Sections of n-decane

    NASA Astrophysics Data System (ADS)

    Jiao, Charles; Dejoseph, Charles; Garscadden, Alan

    2001-10-01

    The ionization and dissociation of hydrocarbon fuels with various plasma excitation schemes including pulsed high E/n discharges have been proposed to alleviate the problem of ignition in supersonic flow combustors and operations at high altitudes. The fuel which is also used for cooling, must not pyrolyse at operational temperatures. We have examined the electron ionization collision processes in n-decane using high resolution Fourier transform mass spectrometry that permits measurements of the 24 ions with cross sections larger than 10-19cm2. These generally fall into two broad categories: those with five or more carbon atoms whose ionization cross sections rise rapidly and essentially saturate within twice the appearance potential and those with four carbon atoms and less whose cross sections rise more gradually and are only saturating at energies above 70 eV. The total ionization cross section is large, rising to 7x10-16cm2. Studies were made with deuterated samples to distinguish the potential mechanisms in fragment ion induced dissociation of the parent gas. The results are compared with similar data for octane.

  14. 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.

  15. Inner-shell ionization of atomic targets by Electron Impact

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

    The knowledge of inner-shell ionization cross sections has not only fundamental importance for understanding collision dynamics of electron-atom interactions, etc, but also is used extensively in many applied fields such as radiation science, astrophysics, plasma physics, etc. The enormous demands of ionization cross sections can only be met by suitable analytical formula that are easy to use and can produce reliable result. We report here an extension of the CVTS [1] model incorporating both the relativistic and ionic factors and tested on 23 atomic targets ranging from He to U [2] with excellent account of the experimental cross sections. [4pt] [1] C. S. Campos, M. A. Z. Vasconcellos, J. C. Trincavelli, and S. Segui, J. Phys. B. 40, 3835 (2007).[0pt] [2] A K F Haque, M R Talukder, M. Shahjahan, M A Uddin, A K Basak and B C Saha, J. Phys. B.; At. Mol. Opt. Phys (under consideration), (2010).

  16. Electron impact, electron capture negative ionization and positive chemical ionization mass spectra of organophosphorus flame retardants and plasticizers.

    PubMed

    Ma, Yuning; Hites, Ronald A

    2013-08-01

    Phosphate esters are important commercial products that have been used both as flame retardants and as plasticizers. To analyze these compounds by gas chromatographic mass spectrometry, it is important to understand the mass spectra of these compounds using various ionization modes. This paper is a systematic overview of the electron impact (EI), electron capture negative ionization (ECNI) and positive chemical ionization (PCI) mass spectra of 13 organophosphate esters. These data are useful for developing and optimizing analytical measurements. The EI spectra of these 13 compounds are dominated by ions such as H4 PO4 (+) , (M - Cl)(+) , (M - CH2 Cl)(+) or (M)(+) depending on specific chemical structures. The ECNI spectra are generally dominated by (M - R)(-) . The PCI spectra are mainly dominated by the protonated molecular ion (M + H)(+) . The branching of the alkyl substituents, the halogenation of the substituents and, for aromatic phosphate esters, ortho alkylation of the ring are all significant factors controlling the details of the fragmentation processes. EI provides the best sensitivity for the quantitative measurement of these compounds, but PCI and ECNI both have considerable qualitative selectivity. Copyright © 2013 John Wiley & Sons, Ltd.

  17. Electron impact ionization cross-sections for few-electron uranium ions

    NASA Astrophysics Data System (ADS)

    Guerra, M.; Stöhlker, Th; Amaro, P.; Machado, J.; Santos, J. P.

    2015-07-01

    Electron impact ionization cross sections for the U88+, U89+, U90+ and U91+ ions were calculated with the relativistic binary encounter Bethe model (RBEB), the modified RBEB (MRBEB) and the new MRBEB corrected by the ionic factor (MRBR-IF). Our results were compared with the available three sets of experimental data and the most used theoretical results. The MRBEB-IF results are the ones that better agree with the experimental data of the four analysed ions.

  18. Photoelectron emission as an alternative electron impact ionization source for ion trap mass spectrometry.

    PubMed

    Gamez, Gerardo; Zhu, Liang; Schmitz, Thomas A; Zenobi, Renato

    2008-09-01

    Electron impact ionization has several known advantages; however, heated filament electron sources have pressure limitations and their power consumption can be significant for certain applications, such as in field-portable instruments. Herein, we evaluate a VUV krypton lamp as an alternative source for ionization inside the ion trap of a mass spectrometer. The observed fragmentation patterns are more characteristic of electron impact ionization than photoionization. In addition, mass spectra of analytes with ionization potentials higher than the lamp's photon energy (10.6 eV) can be easily obtained. A photoelectron impact ionization mechanism is suggested by the observed data allowed by the work function of the ion trap electrodes (4.5 eV), which is well within the lamp's photon energy. In this case, the photoelectrons emitted at the surface of the ion trap end-cap electrode are accelerated by the applied rf field to the ring electrode. This allows the photoelectrons to gain sufficient energy to ionize compounds with high ionization potentials to yield mass spectra characteristic of electron impact. In this manner, electron impact ionization can be used in ion trap mass spectrometers at low powers and without the limitations imposed by elevated pressures on heated filaments.

  19. 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.}

  20. Calculations for electron-impact excitation and ionization of beryllium

    NASA Astrophysics Data System (ADS)

    Zatsarinny, Oleg; Bartschat, Klaus; Fursa, Dmitry V.; Bray, Igor

    2016-12-01

    The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium over an energy range from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with other available results based on nonperturbative convergent pseudostate and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a prominent shape resonance. The ionization from the {(2s2p)}3P and {(2s2p)}1P states strongly depends on the respective term. The current predictions represent an extensive set of electron scattering data for neutral beryllium, which should be sufficient for most modeling applications.

  1. 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.

  2. 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.

  3. Role of ionization-excitation processes in the cross section for direct ionization of heavy atomic ions by electron impact

    NASA Astrophysics Data System (ADS)

    Zeng, J. L.; Liu, L. P.; Liu, P. F.; Yuan, J. M.

    2014-10-01

    The contribution to the ionization cross section of ionization-excitation processes by electron impact is usually negligibly small for low- and medium-Z elements. We demonstrate here, however, that for heavy atomic ions with the outermost shell being n d (n =4 ,5 ) the ionization-excitation processes play an evident role in the ionization cross section. For the 4 s24 p64 d10 ground level of Gd18 +, the ionization-excitation cross section due to the excitation of levels in the 4 s24 p64 d84 f configuration is comparable to the direct 4 p and 4 s ionization cross sections of (4s24 p54 d10) 1 /2 and (4s 4 p64 d10) 1 /2. The total ionization cross section will be underestimated by 15% without including the contribution from ionization-excitation processes. This is a general conclusion for heavy atomic ions, which is verified by taking Pd-like ions of Sn4 +,Ba10 +,Nd14 +,Tb19 +,Yb24 +, and W28 + as examples. The role of ionization-excitation processes can be understood from the overlapping of the wave functions between the 4 d and 4 f orbitals.

  4. 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.

  5. 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.

  6. Three-dimensional cross sections for electron impact ionization of atoms and molecules

    NASA Astrophysics Data System (ADS)

    Ren, X.; Senftleben, A.; Pflüger, T.; Holzwarth, M.; Dorn, A.; Bartschat, K.; Bray, I.; Fursa, D. V.; Colgan, J.; Pindzola, M. S.; Al-Hagan, O.; Madison, D. H.; Ullrich, J.

    2010-02-01

    Using a multi-particle momentum spectrometer (reaction microscope), three-dimensional and fully differential cross sections (FDCS) for electron impact ionization are obtained, providing benchmark data for comprehensive tests of theoretical calculations. Since all final-state particles, including the scattered projectile were detected, a good momentum transfer resolution was obtained also for heavy targets like Ar. Results for ionization of the Ar 3p- and He 1s-orbitals by 200 eV electron impact are presented. The cross section patterns display rich structure, which is partially reproduced by theory, although differences persist out-of-the scattering plane. Kinematically complete experiments for electron impact ionization of simple diatomic molecules have attracted increased attention concerning molecular structure effects. (e, 2e) on He and H2 is studied at equivalent collision kinematics to explore the differences of atomic and molecular ionization. Here FDCS were obtained covering the whole solid angle.

  7. Electron-impact excitation and ionization of boron

    NASA Astrophysics Data System (ADS)

    Wang, Kedong; Zatsarinny, Oleg; Bartschat, Klaus

    2016-09-01

    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, momentum-transfer, 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 multi-configuration Hartree-Fock method with non-orthogonal term-dependent orbitals was used to generate accurate wavefunctions 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.

  8. Single and double ionization of magnesium by electron impact: A classical study

    NASA Astrophysics Data System (ADS)

    Dubois, J.; Berman, S. A.; Chandre, C.; Uzer, T.

    2017-02-01

    We consider electron impact-driven single and double ionization of magnesium in the energy range of 10 to 100 eV. Our classical Hamiltonian model of these (e ,2 e ) and (e ,3 e ) processes sheds light on their total cross sections and reveals the underlying ionization mechanisms. Two pathways are at play in single ionization: delayed and direct. In contrast, only the direct process is observed in double ionization, ruling out the excitation-autoionization channel. We also provide evidence that the so-called Two-Step 2 mechanism predominates over the Two-Step 1 mechanism, in agreement with experiments.

  9. 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.

  10. 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.

  11. Electronic relativistic effects in K-shell ionization by proton impact

    SciTech Connect

    Mukoyama, T.; Sarkadi, L.

    1983-09-01

    The relativistic plane-wave Born-approximation calculations have been performed for K-shell ionization by proton impact. The K-shell ionization cross sections have been obtained by the use of relativistic hydrogenic (Dirac) wave functions for target electrons. The ratio of the relativistic cross section to the nonrelativistic one is evaluated and compared with various approximate correction methods for the electronic relativistic effects. Similar comparison is made for the K-shell ionization cross sections corrected for binding-energy and Coulomb-deflection effects. These results are also compared with the experimental data.

  12. 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.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Electron Impact Ionization cross sections and rate coefficients for α-tetra hydro furfuryl alcohol

    NASA Astrophysics Data System (ADS)

    Kumar, Neeraj; Pal, Satyendra

    2013-09-01

    α - tetrahydrofurfuryl alcohol (THFA; C5H10O2) is an aromatic compound having the molecular structure similar to that of 2-deoxy-D-ribose (deoxyribose). This molecule has attracted enormous interest in the field of research because its electron charge cloud possesses a quite significant spatial extent (dipole polarizability, α = 70.18 au) and has a relatively strong permanent dipole moment (μ ~ 2D). In the present work, we have extended and generalized the modified Jain-Khare 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 α-tetrahydrofurfuryl alcohol (THFA; C5H10O2) , in the energy range varying from ionization threshold to 1000 eV. The evaluated cross sections revealed a reasonably good agreement with the experimental and theoretical data, wherever available. We have also calculated the ionization rate coefficients as a function of electron energy, using the evaluated total ionization cross sections and the Maxwell-Boltzmann distribution.

  18. Electron-Impact Excitation and Ionization in Air

    DTIC Science & Technology

    2009-09-01

    also exist in other disciplines dealing with plasma, including astrophysics , fusion science, plasma processing in microelectronics, etc. While the...cross sections, and ionization fractions for astrophysically abundant elements. I. Carbon and nitrogen,” The Astrophysical Journal Supplement Series Vol

  19. Electron impact double ionization of krypton ions (q = 14-17)

    NASA Astrophysics Data System (ADS)

    Khouilid, M.; Cherkani-Hassani, S.; Adimi, N.; Rachafi, S.; Defrance, P.

    2001-08-01

    Absolute cross sections for electron impact double ionization of krypton ions Krq + (q = 14-17) have been measured from threshold to 5 keV. The animated crossed beam method has been employed. Direct double ionization is seen to reduce strongly along the isonuclear sequence. Ionization-autoionization from the inner L-shell is seen to be the dominant process. It is roughly approximated by the semi-empirical Lotz formula assuming total autoionization of the ionic intermediate states. Resonant capture and excitation processes implying the L-shell are also obtained for charge states 14-16.

  20. Electron-Impact Total Ionization Cross Sections of CH and C2H2

    PubMed Central

    Kim, Yong-Ki; Ali, M. Asgar; Rudd, M. Eugene

    1997-01-01

    Electron-impact total ionization cross sections for the CH radical and C2H2 (acetylene) have been calculated using the Binary-Encounter-Bethe (BEB) model. The BEB model combines the Mott cross section and the asymptotic form of the Bethe theory, and has been shown to generate reliable ionization cross sections for a large variety of molecules. The BEB cross sections for CH and C2H2 are in good agreement with the available experimental data from ionization thresholds to hundreds of eV in incident energies. PMID:27805116

  1. Evidence for unnatural-parity contributions to electron-impact ionization of laser-aligned atoms

    SciTech Connect

    Armstrong, Gregory S. J.; Colgan, James Patrick; Pindzola, M. S.; Amami, S.; Madison, D. H.; Pursehouse, J.; Nixon, K. L.; Murray, A. J.

    2015-09-11

    Recent measurements have examined the electron-impact ionization of excited-state laser-aligned Mg atoms. In this paper we show that the ionization cross section arising from the geometry where the aligned atom is perpendicular to the scattering plane directly probes the unnatural parity contributions to the ionization amplitude. The contributions from natural parity partial waves cancel exactly in this geometry. Our calculations resolve the discrepancy between the nonzero measured cross sections in this plane and the zero cross section predicted by distorted-wave approaches. Finally, we demonstrate that this is a general feature of ionization from p-state targets by additional studies of ionization from excited Ca and Na atoms.

  2. 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.

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

    SciTech Connect

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

    2016-05-14

    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, L{sub 3}-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.

  4. 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.

  5. 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.

  6. Electron-impact-ionization dynamics of five C2 to C4 perfluorocarbons

    NASA Astrophysics Data System (ADS)

    Bull, James N.; Bart, Mark; Vallance, Claire; Harland, Peter W.

    2013-12-01

    Perfluorocarbons (PFCs) are man-made compounds whose ion physics exhibit complex interplays between statistical and nonstatistical fragmentation and intramolecular rearrangement processes. One probe of such processes is the energy-dependent electron-impact-ionization cross section. Partial electron-impact-ionization cross sections are reported for the fragments arising from five C2 to C4 PFCs, namely, C2F6, C3F8, C3F6, CF2=CF-CF=CF2, and CF3-C≡C-CF3, over the energy range from threshold to ˜210 eV. Care was taken to maximize ion collection efficiency and to minimize discrimination against ions produced with high kinetic-energy release, and the measured cross sections have been calibrated using independent absolute total (gross) ionization efficiency curves measured previously in the same laboratory with an instrument that was designed to essentially have unit detection efficiency. Total ionization cross sections have also been modeled using the binary-encounter Bethe model, and the shortcomings of the model when applied to perfluorinated compounds are discussed. Analysis of the mass spectral fragmentation patterns in combination with ab initio energetics suggests that nonstatistical dissociative ionization processes play a significant role in the fragmentation dynamics of saturated PFCs. In contrast, unsaturated PFCs exhibit long-lived parent ions, which tend to undergo a higher degree of statistical dissociation following ionization, involving considerable intramolecular rearrangement.

  7. 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.

  8. 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.

  9. Evidence for unnatural-parity contributions to electron-impact ionization of laser-aligned atoms

    DOE PAGES

    Armstrong, Gregory S. J.; Colgan, James Patrick; Pindzola, M. S.; ...

    2015-09-11

    Recent measurements have examined the electron-impact ionization of excited-state laser-aligned Mg atoms. In this paper we show that the ionization cross section arising from the geometry where the aligned atom is perpendicular to the scattering plane directly probes the unnatural parity contributions to the ionization amplitude. The contributions from natural parity partial waves cancel exactly in this geometry. Our calculations resolve the discrepancy between the nonzero measured cross sections in this plane and the zero cross section predicted by distorted-wave approaches. Finally, we demonstrate that this is a general feature of ionization from p-state targets by additional studies of ionizationmore » from excited Ca and Na atoms.« less

  10. Angular distributions in the double ionization of DNA bases by electron impact

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

    Ab initio calculations of the five-fold differential cross sections for electron-impact double ionization of thymine, cytosine, adenine and guanine are performed in the first Born approximation for an incident energy close to 5500 eV. The wavefunctions of the DNA bases are constructed using the multi-center wave functions from the Gaussian 03 program. These multi-center wave functions are converted into single-center expansions of Slater-type functions. For the final state, the two ejected electrons are described by two Coulomb wave functions. The electron-electron repulsion between the two ejected electrons is also taken into account. Mechanisms of the double ionization are discussed for each case and the best choices of the kinematical parameters are determined for next experiments.

  11. 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.

  12. Electron impact-induced ionization and dissociation of the freon-12 molecule

    NASA Astrophysics Data System (ADS)

    Zavilopulo, A. N.; Agafonova, A. S.; Snegurskii, A. V.

    2010-12-01

    An experimental technique is described, and the relative cross sections of the single and dissociative electron-impact ionizations of the freon-12 molecule (CCl2F2) in the near-threshold energy range are obtained. The experiment is performed on a device that provides the mass separation and recording of ions with a monopole mass spectrometer. The mass spectrum of the freon-12 molecule is measured at various ionizing-electron energies, and the relative cross sections of dissociative ionization are measured for the most intense ion fragments, including isotope-containing fragments. The threshold dependences of these cross sections are used to determine the appearance potentials of the ion fragments. The isotope shift in the thresh-old appearance energies of ion fragments [C35ClF2]+ and [C37ClF2]+ is measured for the first time.

  13. 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.

  14. 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.

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

    SciTech Connect

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

    2016-05-06

    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 Q{sub ion} and the summed-electronic excitation cross section ΣQ{sub exc} 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.

  16. 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.

  17. Theoretical calculations of the total and ionization cross sections for electron impact on some simple biomolecules

    NASA Astrophysics Data System (ADS)

    Vinodkumar, Minaxi; Joshipura, K. N.; Limbachiya, Chetan; Mason, Nigel

    2006-08-01

    In this paper we report total cross sections (TCS), QT , total elastic cross sections, Qel , and total ionization cross section, Qion for electron impact on water, formaldehyde, formic acid, and the formyl radical from circa 15eVto2KeV . The results are compared where possible, with previous theoretical and experimental results and, in general, are found to be in good agreement. The total and elastic cross sections for HCHO, HCOOH, and CHO radical are reported.

  18. Auger contributions to electron impact ionization of Li-like ions

    NASA Astrophysics Data System (ADS)

    Hahn, Yukap

    1980-07-01

    Electron impact ionization by a two-step process of inner-shell excitation followed by an Auger emission is estimated for the Li-like Oxygen and Fe ions. Result for the O 5+ is in good agreement with a recent experiment by Crandall et al. for incident energies above the twice of threshold energy. The Auger cross section is very much reduced in the case of Fe 23+ because of a large fluorescence yield.

  19. 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.

  20. Experimental determination of multiple ionization cross sections in Si by electron impact

    NASA Astrophysics Data System (ADS)

    Pérez, Pablo Daniel; Sepúlveda, Andrés; Castellano, Gustavo; Trincavelli, Jorge

    2015-12-01

    The thin sample method is often used to experimentally determine ionization cross sections, especially when focusing on the low overvoltage region. The simplicity of the formalism involved in this method is very appealing, but some experimental complications arise in the preparation of thin films. In this work, a thick sample method was used to measure the Si-K x-ray production cross section by electron impact. The good agreement between the results obtained and the values reported in the literature validates the method and the parameters used. The advantages and disadvantages of the method are discussed and its application is extended to the determination of Si multiple-ionization cross sections, where the very low emission rates (around two orders of magnitude lower than the single-ionization case) make the use of the thin sample method impracticable.

  1. Electron Impact Ionization and Fragmentation Dynamics of Small Atomic and Molecular Clusters

    NASA Astrophysics Data System (ADS)

    Dorn, Alexander

    2016-09-01

    New ionization and fragmentation reactions emerge if target atoms or molecules are embedded in an environment as it is the case in small clusters or in the condensed phase. These can be intermolecular energy and charge transfer processes or a completely modified fragmentation behavior of the molecular ions. Here we study low energy electron impact induced ionization with a multi-electron and ion imaging spectrometer (reaction microscope) and a supersonic gas jet target which can produce small clusters of various target species. Interatomic reactions are studied for the model system of weakly bound Ar2 dimers. Here, the coincident detection of three electrons and two ions gives detailed insight in interatomic Coulombic decay and radiative charge transfer processes. Such processes were also found in bio-relevant systems like water clusters. We studied pure and water-mixed clusters of tetrahydrofuran (C4H8O, THF) which is the simplest analog of deoxyribose in the DNA backbone. One observation is that ionization of the outermost valence orbital for the monomer leads to stable THF ions. In contrast if THF is bound to another THF or a water molecule the molecular ring breaks. In addition we identify intermolecular Coulombic decay induced by energy transfer from a water molecule ionized in the inner valence shell to the neighboring THF molecule.

  2. 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.

  3. 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.

  4. 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.

  5. 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.

  6. Positron-impact ionization, positronium formation, and electronic excitation cross sections for diatomic molecules

    SciTech Connect

    Marler, J. P.; Surko, C. M.

    2005-12-15

    Absolute measurements are presented for the positron-impact cross sections for positronium formation, direct ionization, and total ionization of the diatomic molecules N{sub 2}, CO, and O{sub 2}, in the range of energies from threshold to 90 eV. Cross sections for the electronic excitation of the a {sup 1}{pi} and a{sup '} {sup 1}{sigma} state in N{sub 2} and the A {sup 1}{pi} state in CO near threshold are also presented. The experiment uses a cold, trap-based positron beam and the technique of studying positron scattering in a strong magnetic field. In O{sub 2}, a feature previously seen in the total ionization cross section is observed in both the positronium formation and total ionization cross sections. The possible origin of this feature and its relationship to positron-induced dissociation is discussed. In N{sub 2}, the near-threshold electronic excitation cross section is larger than that for positronium formation. This likely explains the relatively high efficiency of this molecule when used for buffer-gas positron trapping.

  7. 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.

  8. STORAGE RING CROSS SECTION MEASUREMENTS FOR ELECTRON IMPACT IONIZATION OF Fe{sup 7+}

    SciTech Connect

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

    2015-11-01

    We have measured electron impact ionization for Fe{sup 7+} 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 and 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. 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.

  11. Electronic relativistic effects on L-shell ionization of atoms by light-ion impact

    SciTech Connect

    Mukoyama, T.; Sarkadi, L.

    1982-03-01

    The L-shell ionization cross sections by charged-particle impact have been calculated in the plane-wave Born approximation, using relativistic hydrogen wave functions for the target electrons. The effects of the binding-energy increase due to penetration of the projectile and the Coulomb deflection of the projectile are taken into account. The calculated values are compared with the corresponding values obtained by other theoretical models as well as the experimental data. It is found that the present theoretical predictions are in satisfactory agreement with the experimental results for low-energy protons.

  12. Low-energy triple differential cross sections for electron-impact ionization of helium

    NASA Astrophysics Data System (ADS)

    Chen, Zhangjin; Zhang, Suimeng; Shi, Qicun; Chen, Ji; Xu, Kezun

    1997-11-01

    The BBK model is modified by the introduction of effective Sommerfeld parameters for both symmetric and asymmetric geometries on an empirical basis, while still maintaining the philosophy that all three Coulomb interactions are included on an equal footing. The triple differential cross sections for electron-impact ionization of atomic helium at an incident energy of 40 eV in an asymmetric geometry are calculated. Results of this approach are compared with the absolute measurements and the only existing theoretical results of the convergent close-coupling method.

  13. Metastable McLafferty rearrangement reaction in the electron impact ionization of stearic acid methyl ester

    NASA Astrophysics Data System (ADS)

    Takayama, Mitsuo

    1995-06-01

    The metastable peaks for the McLafferty rearrangement and double hydrogen rearrangement reactions have been observed in the stearic acid methyl ester system under electron impact ionization. The metastable ion spectrum of the M+. ion gave peaks corresponding to the ions at m/z 74, 75, 87 and 88, whereas the collision-induced dissociation spectrum showed low intensity ions at m/z 75 and 88 which come from double hydrogen rearrangement reactions of M+. ions. The kinetics for the change of the molecular ions to different structures before fragmentation have been discussed.

  14. Doubly differential single and multiple ionization of krypton by electron impact

    SciTech Connect

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

    2007-05-15

    Differential measurements for single and multiple ionization of Kr by 240 and 500 eV electron impact are presented. Using a pulsed extraction field, Kr{sup +}, Kr{sup 2+}, and Kr{sup 3+} ions were measured in coincidence with scattered electrons for energy losses up to 120 eV and scattering angles between 16 degree sign and 90 degree sign . Scaling properties of the doubly differential cross sections (DDCS) are investigated as a function of energy loss, scattering angle, and momentum transfer. It is shown that scaling the DDCS as outlined by Kim and Inokuti and plotting them versus a parameter consisting of the momentum transfer divided by the square root of the impact energy times 1-cos({theta}), where {theta} is the scattering angle, yielded similar curves, but with different magnitudes, for single and multiple ionization. Normalizing these curves together produced two universal curves, one appropriate for single and multiple electron emission at larger scattering angles ({theta}{>=}30 degree sign ) and one appropriate for small scattering angles ({theta}<30 degree sign )

  15. Energy partitioning in {sup 1}S-wave electron-impact ionization of atomic hydrogen

    SciTech Connect

    Shakeshaft, Robin

    2010-03-15

    Results of calculations of the integrated cross section and the energy distribution for ionization of ground-state hydrogen by {sup 1}S-wave electron impact are presented. The breakup amplitude is expressed as a volume integral that contains an approximate final-state wave function which accounts for postcollision dynamic screening. The error in this wave function is accounted for by the response function, which is represented on a real discrete (Sturmian) basis, with its physical branch specified by the arrow of time. It is found that the energy distribution is primarily convex for impact energies from about 2 to 10 eV above threshold, and primarily flat from about 10 to 20 eV above threshold. The shape of the energy distribution appears to reflect both the competition between escape and recapture, and the substantial postcollision exchange of energy between the electrons. A rough, nonclassical criterion for predicting the curvature of the energy distribution is derived.

  16. 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.

  17. Effect of electron impact ionization in laser-metal-cluster interactions

    NASA Astrophysics Data System (ADS)

    Liang, Zhenfeng; Zhang, Bo; Liu, Hongjie; Li, Xibo; Luo, Jiangshan; Zhou, Weimin; Cao, Leifeng; Yi, Yougen; Gu, Yuqiu

    2017-05-01

    The effects of electron impact ionization (EII) in laser-metal-cluster interactions are investigated with two-dimensional particle-in-cell simulations. For large Cu clusters (R = 10 nm) heated by moderate laser pulses (peak intensities I M = 8.8 × 1015 W cm-2), the effects of EII depend on the atom/ion density of neutral cluster or cluster plasma. In high density neutral cluster (HDNC), EII is the dominant ionization mechanism and EII efficiency reaches 55%. However, in the case of low density cluster plasma (LDCP), EII plays a minor role that only increases the mean ion charges by 5%. Moreover, when EII is considered, the energy of ions with the same charges is reduced by 60% in the HDNC case but not in the LDCP case. This is due to the fact that ions in HDNC mainly gain energy through hydrodynamic expansion while ions in LDCP obtain energy through Coulomb explosion. More importantly, it is found that EII efficiency increases when the density of cluster plasma increases and is most pronounced in the neutral cluster. The density dependence of the EII efficiency provides a control mechanism for cluster ionization products with pump-probe technology.

  18. Absolute Cross Sections for Electron-Impact Ionization of Li-like Ions

    NASA Astrophysics Data System (ADS)

    Bannister, M. E.; Smith, A. C. H.; Djurić, N.; Wallbank, B.; Woitke, O.; Dunn, G. H.

    1998-05-01

    Absolute cross sections for the ionization of lithium-like B^2+ and C^3+ ions by electron-impact have been measured using a crossed-beams technique.(M. E. Bannister, Phys. Rev. A 54), 1435 (1996). Recently, several new sophisticated calculations(P. J. Marchalant et al), J. Phys. B 30, L435 (1997).^,( M. S. Pindzola and N. R. Badnell (private communication).) have been performed for B^2+ in an attempt to understand the disagreement between theory and previous experimental results,(D. H. Crandall et al.), Phys. Rev. A 34, 1757 (1986). a discrepancy of about 20% near the cross section peak. The present measurements for B^2+ are in very good agreement with these recent calculations and with the measurements of Hofmann et al.(G. Hofmann, A. Müller, K. Tinschert, and E. Salzborn, Z. Phys. D 16), 113 (1990). over the range that they report direct ionization cross sections. Experimental cross sections for ionization of C^3+ are also compared to recent theoretical predictions.

  19. Electron impact, hyperthermal surface ionization and fast GC-MS in supersonic molecular beams

    SciTech Connect

    Amirav, A.; Dagan, S.

    1995-03-01

    Supersonic Molecular Beams (SMB) are characterized by undirectional motion with controlled hyperthermal kinetic energy (0.1-30 eV), intramolecular vibrational super-cooling, mass focusing as in an ideal high load jet separator, very high flow rate (on the gas chromatography flow rate scale) up to 240 ml/min and sample inlet at atmospheric pressure. These features make SMB an ideal sample introduction method, enable a unique fast GC inlet and result in important implications to molecular ionization processes including electron impact (EI) and hyperthermal. surface ionization (HSI). The authors` research is aimed at exploring and exposing the benefits of SMB for analytical organic mass spectrometry. The experimental apparatus is shown and is described. A 50 cm long megabore capillary column connects the atmospheric pressure open inlet to a supersonic nozzle, and serves as an ultra fast GC short column. The authors demonstrate ultrafast GC-MS achieved with this 50 cm transfer line capillary. One of the main features of this unique GC is the carrier gas relatively high flow rate of up to 240 ml/min which is possible due to the flow rates involved with the supersonic beam interface. This ultrafast GC is extensively described. Alternatively, a conventional GC with a short (4 meter) column serves as a fast GC inlet with intermediate GC resolution and unlimited choice of column length, ID and flow rate. Electron impact ionization in supersonic molecular beams is achieved using a Brink type open ion source operated with {approximately} 10-20 mA emission current. A background ion filtration method is applied, based on differences in the ion energy emerging from the hyperthermal molecular kinetic energy in the seeded SMB. Background ion filtration is achieved in the authors` VG-SXP-600 quadrupole through biasing of its exit lens and the cancellation of its internal ion energy ramping with mass.

  20. 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.

  1. Strong molecular alignment dependence of H2 electron impact ionization dynamics.

    PubMed

    Ren, X; Pflüger, T; Xu, S; Colgan, J; Pindzola, M S; Senftleben, A; Ullrich, J; Dorn, A

    2012-09-21

    Low-energy (E(0) = 54 eV) electron impact single ionization of molecular hydrogen (H(2)) has been investigated as a function of molecular alignment in order to benchmark recent theoretical predictions [Colgan et al., Phys. Rev. Lett. 101, 233201 (2008) and Al-Hagan et al., Nature Phys. 5, 59 (2009)]. In contrast to any previous work, we observe distinct alignment dependence of the (e,2e) cross sections in the perpendicular plane in good overall agreement with results from time-dependent close-coupling calculations. The cross section behavior can be consistently explained by a rescattering of the ejected electron in the molecular potential resulting in an effective focusing along the molecular axis.

  2. Strong Molecular Alignment Dependence of H2 Electron Impact Ionization Dynamics

    NASA Astrophysics Data System (ADS)

    Ren, X.; Pflüger, T.; Xu, S.; Colgan, J.; Pindzola, M. S.; Senftleben, A.; Ullrich, J.; Dorn, A.

    2012-09-01

    Low-energy (E0=54eV) electron impact single ionization of molecular hydrogen (H2) has been investigated as a function of molecular alignment in order to benchmark recent theoretical predictions [Colgan , Phys. Rev. Lett.PRLTAO0031-9007 101, 233201 (2008)10.1103/PhysRevLett.101.233201 and Al-Hagan , Nature Phys.NPAHAX1745-2473 5, 59 (2009)10.1038/nphys1135]. In contrast to any previous work, we observe distinct alignment dependence of the (e,2e) cross sections in the perpendicular plane in good overall agreement with results from time-dependent close-coupling calculations. The cross section behavior can be consistently explained by a rescattering of the ejected electron in the molecular potential resulting in an effective focusing along the molecular axis.

  3. Electron Impact Ionization/Dissociation of Molecules: Production of Energetic Radical Ions and Anions

    NASA Astrophysics Data System (ADS)

    Feil, S.; Sulzer, P.; Mauracher, A.; Beikircher, M.; Wendt, N.; Aleem, A.; Denifl, S.; Zappa, F.; Matt-Leubner, S.; Bacher, A.; Matejcik, S.; Probst, M.; Scheier, P.; Märk, T. D.

    2007-10-01

    In order to provide quantitative information on electron collision processes involving various plasma constituents (in particular hydrocarbons) and to elucidate the properties of cations and anions produced we have carried out the past years a series of studies with a variety of techniques in our laboratory in Innsbruck. In the present review we will present some recent results on electron impact ionization and attachment in order to illustrate recent progress in this field in particular concerning the production of energetic fragment cations for hydrocarbons and differences in the attachment of isomers for nitro-organics. Using a Nier type electron impact ion source in combination with a double focusing two sector field mass spectrometer, partial cross sections for electron impact ionization of acetylene, propene and other hydrocarbons have been measured for electron energies up to 1000 eV. Discrimination factors for ions have been determined using the deflection field method in combination with a three-dimensional ion trajectory simulation of ions produced in the ion source. Analysis of the ion yield curves obtained by scanning the deflectors allows the assignment of ions with the same mass-to-charge ratio to specific production channels on the basis of their different kinetic energy distributions. This analysis also allows to determine, besides kinetic energy distributions of fragment ions, partial cross sections differential in kinetic energy. Moreover charge separation reactions (for instance in case of acetylene the Coulomb explosion of the doubly-charged parent ions C2H2++ into the fragment ions C2H+ and H+) are investigated by means of a number of metastable mass spectrometry methods and the associated mean kinetic energy release is deduced. Free electron attachment to the three different isomers of mono-nitrotoluene molecules in the gas phase is studied using two different crossed electron-molecule beams technique. In contrast to previous studies for a

  4. 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.

  5. 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).

  6. 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.

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

    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.

  10. 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.

  11. 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.

  12. Electron-impact dissociative excitation and ionization of N{sub 2}D{sup +}

    SciTech Connect

    Fogle, M.; Bahati, E. M.; Bannister, M. E.; Deng, S. H. M.; Vane, C. R.; Thomas, R. D.; Zhaunerchyk, V.

    2011-09-15

    Absolute cross sections for electron-impact dissociation of N{sub 2}D{sup +} producing N{sub 2}{sup +}, ND{sup +}, and N{sup +} ion fragments were measured in the 5- to 100-eV range using a crossed electron-ion beams technique. In the 5- to 20-eV region, in which dissociative excitation (DE) is the principal contributing mechanism, N{sub 2}{sup +} production dominates. The N{sub 2}{sup +} + D dissociation channel shows a large resonant-like structure in the DE cross section, as observed previously in electron impact dissociation of triatomic dihydride species [M. Fogle, E. M. Bahati, M. E. Bannister, S. H. M. Deng, C. R. Vane, R. D. Thomas, and V. Zhaunerchyk, Phys. Rev. A 82, 042720 (2010)]. In the dissociative ionization (DI) region, 20- to 100-eV, N{sub 2}{sup +}, ND{sup +}, and N{sup +} ion fragment production are comparable. The observance of the ND{sup +} and N{sup +} ion fragments indicate breaking of the N - N bond along certain dissociation channels.

  13. Electron-impact dissociative excitation and ionization of N2D+

    SciTech Connect

    FogleJr, Michael R; Bahati Musafiri, Eric; Bannister, Mark E; Deng, Shihu; Vane, C Randy; Thomas, R. D.; Zhaunerchyk, Vitali

    2011-01-01

    Absolute cross sections for electron-impact dissociation of N{sub 2}D{sub +} producing N{sub 2}{sub +}, ND{sub +}, and N{sub +} ion fragments were measured in the 5- to 100-eV range using a crossed electron-ion beams technique. In the 5- to 20-eV region, in which dissociative excitation (DE) is the principal contributing mechanism, N{sub 2}{sub +} production dominates. The N{sub 2}{sub +} + D dissociation channel shows a large resonant-like structure in the DE cross section, as observed previously in electron impact dissociation of triatomic dihydride species [ M. Fogle, E. M. Bahati, M. E. Bannister, S. H. M. Deng, C. R. Vane, R. D. Thomas and V. Zhaunerchyk Phys. Rev. A 82 042720 (2010)]. In the dissociative ionization (DI) region, 20- to 100-eV, N{sub 2}{sub +}, ND{sub +}, and N{sub +} ion fragment production are comparable. The observance of the ND{sub +} and N{sub +} ion fragments indicate breaking of the N - N bond along certain dissociation channels.

  14. Electron-impact ionization of diatomic molecules using a configuration-average distorted-wave method

    SciTech Connect

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

    2007-07-15

    Electron-impact ionization cross sections for diatomic molecules are calculated in a configuration-average distorted-wave method. Core bound orbitals for the molecular ion are calculated using a single-configuration self-consistent-field method based on a linear combination of Slater-type orbitals. The core bound orbitals are then transformed onto a two-dimensional (r,{theta}) numerical lattice from which a Hartree potential with local exchange is constructed. The single-particle Schroedinger equation is then solved for the valence bound orbital and continuum distorted-wave orbitals with S-matrix boundary conditions. Total cross section results for H{sub 2} and N{sub 2} are compared with those from semiempirical calculations and experimental measurements.

  15. 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.

  16. Computation of electron-impact K-shell ionization cross sections of atoms

    SciTech Connect

    Uddin, M.A.; Haque, A.K.F.; Billah, M. Masum; Basak, A.K.; Karim, K.R.; Saha, B.C.

    2005-03-01

    The total cross sections of electron impact single K-shell ionization of atomic targets, with a wide range of atomic numbers from Z=6-50, are evaluated in the energy range up to about 10 MeV employing the recently proposed modified version of the improved binary-encounter dipole (RQIBED) model [Uddin et al., Phys. Rev. A 70, 032706 (2004)], which incorporates the ionic and relativistic effects. The experimental cross sections for all targets are reproduced satisfactorily even in the relativistic energies using fixed generic values of the two parameters in the RQIBED model. The relativistic effect is found to be significant in all targets except for C, being profound in Ag and Sn.

  17. Electron Impact K-shell Ionization Cross Sections at high energies

    NASA Astrophysics Data System (ADS)

    Haque, A. K. F.; Sarker, M. S. I.; Patoary, M. A. R.; Shahjahan, M.; Ismail Hossain, M.; Alfaz Uddin, M.; Basak, A. K.; Saha, Bidhan

    2008-10-01

    A simple modification of the empirical model of Deutsh et. al. [1] by incorporating both the ionic [2] and relativistic corrections [3] is proposed for evaluating the electron impact K -shell ionization cross sections of neutral atomic targets. Present results for 30 atomic targets with atomic number Z=1 -- 92 for incident energies up to E=2 GeV, agree well with available experimental cross sections. Comparisons with other theoretical findings will also be presented at the conference. [1] H. Deutsh, K. Becker, T. D. Mark, Int. J. Mass Spect. 177, 47 (1998). [2] M. A. Uddin, A. K. F. Haque, M. M. Billah, A. K. Basak, K. R. Karim, B. C. Saha, Phys. Rev. A 71, 032715 (2005).; Phys. Rev. A 73, 012708 (2006). [3] M. Gryzinski, Phys. Rev 138, 336 (1965).

  18. Absolute cross section for electron-impact ionization of He (1 s 2 s 3S)

    NASA Astrophysics Data System (ADS)

    Génévriez, Matthieu; Jureta, Jozo J.; Defrance, Pierre; Urbain, Xavier

    2017-07-01

    We present an experimental determination of the electron-impact ionization cross section of the 1 s 2 s 3S state of helium, for which there is a serious long-lasting discrepancy between theory and experiment. A technique for the production of a fast, intense beam of helium in the 1 s 2 s 3S state only has been developed for this purpose, based on photodetachment of the He- anion. The cross section is measured using the animated crossed beam technique. The present results are much lower than the experimental data of Dixon et al. [J. Phys. B 9, 2617 (1976), 10.1088/0022-3700/9/15/013] and are in excellent agreement with the calculation of Fursa and Bray [J. Phys. B 36, 1663 (2003), 10.1088/0953-4075/36/8/317].

  19. Electron ionization of acetylene.

    PubMed

    King, Simon J; Price, Stephen D

    2007-11-07

    Relative partial ionization cross sections and precursor specific relative partial ionization cross sections for fragment ions formed by electron ionization of C2H2 have been measured using time-of-flight mass spectrometry coupled with a 2D ion-ion coincidence technique. We report data for the formation of H+, H+2, C2+, C+/C2+ 2, CH+/C2H+2, CH+2, C+2, and C2H+ relative to the formation of C2H+2, as a function of ionizing electron energy from 30-200 eV. While excellent agreement is found between our data and one set of previously published absolute partial ionization cross sections, some discrepancies exist between the results presented here and two other recent determinations of these absolute partial ionization cross sections. We attribute these differences to the loss of some translationally energetic fragment ions in these earlier studies. Our relative precursor-specific partial ionization cross sections enable us, for the first time, to quantify the contribution to the yield of each fragment ion from single, double, and triple ionization. Analysis shows that at 50 eV double ionization contributes 2% to the total ion yield, increasing to over 10% at an ionizing energy of 100 eV. From our ion-ion coincidence data, we have derived branching ratios for charge separating dissociations of the acetylene dication. Comparison of our data to recent ab initio/RRKM calculations suggest that close to the double ionization potential C2H2+2 dissociates predominantly on the ground triplet potential energy surface (3Sigma*g) with a much smaller contribution from dissociation via the lowest singlet potential energy surface (1Delta g). Measurements of the kinetic energy released in the fragmentation reactions of C2H2+2 have been used to obtain precursor state energies for the formation of product ion pairs, and are shown to be in good agreement with available experimental data and with theory.

  20. 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.

  1. Electron impact ionization of the outer valence orbital 1t2 of CH4

    NASA Astrophysics Data System (ADS)

    Granados-Castro, Carlos Mario; Ancarani, Lorenzo Ugo

    2017-03-01

    The electron impact single ionization of the outer valence orbital 1t2 of methane is investigated theoretically within a Sturmian approach. Using an expansion on a basis set of Generalized Sturmian Functions, all with correct asymptotic behavior, the ionization scattering amplitude is extracted directly from the expansion coefficients without the need of calculating a transition matrix element. Triple differential cross sections are obtained for several coplanar asymmetric geometries, and are compared with two sets of relative experimental data (incident energy of 500 eV and 250 eV). An absolute scale comparison with other available theoretical models is also presented, and the binary-to-recoil ratio, experimental and theoretical, is analyzed as a function of the momentum transfer. Like other theoretical results, ours reproduce only partially the experimentally observed cross sections features. Important differences in the position and height of the recoil peak, in particular, clearly indicate an agreement breakdown between the measurements and the presently available theories including ours. Finally, for an incident energy of 250 eV, ejected energy of 30 eV and a scattering angle of - 20°, we predict a double peak structure in the cross section binary region, which is a clear signature of the p-nature of the molecular orbital. Contribution to the Topical Issue "Many Particle Spectroscopy of Atoms, Molecules, Clusters and Surfaces", edited by A.N. Grum-Grzhimailo, E.V. Gryzlova, Yu V. Popov, and A.V. Solov'yov.

  2. 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.

  3. Nonperturbative Treatment of Electron-Impact Ionization of Ar(3p)

    NASA Astrophysics Data System (ADS)

    Bartschat, Klaus; Zatsarinny, Oleg

    2012-06-01

    We present triple-differential cross sections for electron-impact ionization of a 3p electron in Ar. Results from a fully non-perturbative close-coupling formalism using our B-Spline R-matrix with Pseudo-States (BSRMPS) approach [1] are compared with those from a hybrid distorted-wave plus R-matrix expansion [2] as well as recent experimental data [3]. We find overall good agreement between the two sets of entirely independent theoretical predictions, but serious discrepancies with the published experimental data. A detailed investigation of the dependence of the results on the fixed detection angle of the ``scattered projectile'', i.e., the faster of the two outgoing electrons, suggests that obtaining reliable results, both experimentally and theoretically, is highly challenging in the regime where the largest discrepancies occur. Consequently, care should be taken before much weight is put on the remaining deviations between experiment and theory. Further independent tests seem highly desirable.[4pt] [1] O. Zatsarinny and K. Bartschat, Phys. Rev. Lett. 107 (2011) 023203.[0pt] [2] K. Bartschat and O. K. Vorov, Phys. Rev. A 72 (2005) 022728.[0pt] [3] X. Ren, A. Senftleben, T. Pfl"uger, A. Dorn, K. Bartschat, and J. Ullrich, Phys. Rev. A 83 (2011) 052714.

  4. 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.

  5. 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.

  6. 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.

  7. Triply differential measurements of single ionization of argon by 1-keV positron and electron impact

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

    By establishing coincidences between target ions and scattered projectiles, and coincidences between target ions, scattered projectiles, and ejected electrons, triply differential cross-section (TDCS) information was generated in terms of projectile energy loss and scattering angles for interactions between 1-keV positrons and electrons and Ar atoms. The conversion of the raw experimental information to the TDCS is discussed. The single-ionization TDCS exhibits two distinguishable regions (lobes) where binary and recoil interactions can be described by two peaks. A comparison of the positron and electron impact data shows that the relative intensity of both binary and recoil interactions decreases exponentially as a function of the momentum transfer and is larger when ionization is induced by positron impact, when compared with electron impact.

  8. A laser desorption-electron impact ionization ion trap mass spectrometer for real-time analysis of single atmospheric particles

    NASA Astrophysics Data System (ADS)

    Simpson, E. A.; Campuzano-Jost, P.; Hanna, S. J.; Robb, D. B.; Hepburn, J. H.; Blades, M. W.; Bertram, A. K.

    2009-04-01

    A novel aerosol ion trap mass spectrometer combining pulsed IR laser desorption with electron impact (EI) ionization for single particle studies is described. The strengths of this instrument include a two-step desorption and ionization process to minimize matrix effects; electron impact ionization, a universal and well-characterized ionization technique; vaporization and ionization inside the ion trap to improve sensitivity; and an ion trap mass spectrometer for MSn experiments. The instrument has been used for mass spectral identification of laboratory generated pure aerosols in the 600 nm-1.1 [mu]m geometric diameter range of a variety of aromatic and aliphatic compounds, as well as for tandem mass spectrometry studies (up to MS3) of single caffeine particles. We investigate the effect of various operational parameters on the mass spectrum and fragmentation patterns. The single particle detection limit of the instrument was found to be a 325 nm geometric diameter particle (8.7 × 107 molecules or 22 fg) for 2,4-dihydroxybenzoic acid. Lower single particle detection limits are predicted to be attainable by modifying the EI pulse. The use of laser desorption-electron impact (LD-EI) in an ion trap is a promising technique for determining the size and chemical composition of single aerosol particles in real time.

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

    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.

  12. 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

  13. 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.

  14. 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.

  15. Ionization of 4,4'-bis(phenylethynyl) anthracene by electron impact.

    PubMed

    Kukhta, A V; Kukhta, I N; Zavilopulo, A N; Agafonova, A S; Shpenik, O B

    2009-01-01

    Ionization of a 4,4'-bis(phenylethynyl)anthracene (C(30)H(18), BPEA) molecule is studied for the first time at different energies of bombarding electrons in crossed electron and molecular beams. The relative cross-section of single ionization of a BPEA molecule in the energy range of 5-55 eV is measured. The ionization potential, E(I) = 7.62 +/- 0.2 eV, is determined using the threshold region of C(30)H(18)(+) ion yield energy dependence. A scheme of the BPEA molecule fragmentation is proposed. Experimental results are in reasonable accordance with calculations made in the framework of the density functional theory.

  16. 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.

  17. 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.

  18. 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.

  19. Electron impact total ionization cross sections for simple bio-molecules (H2CO, HCOOH and CH3COOH) using ICSP-ic method

    NASA Astrophysics Data System (ADS)

    Bhutadia, Harshad; Vinodkumar, Minaxi; Antony, Bobby

    2012-11-01

    In the present work we compute total ionization cross sections for simple bio-molecules viz. formaldehyde, formic acid and acetic acid on electron impact. The total ionization cross sections are extracted from total inelastic cross section using Improved Complex Scattering Potential-ionization contribution method.

  20. A coincidence study of electron and positron impact ionization of Ar (3p) at 1 keV

    NASA Astrophysics Data System (ADS)

    Campeanu, Radu I.; Walters, James H. R.; Whelan, Colm T.

    2015-10-01

    Distorted-wave calculations of the triple differential cross section (TDCS) are presented for electron and positron impact ionization of Ar(3p) in coplanar asymmetric geometry at an impact energy of 1 keV and are compared with a recent experiment. The experiment indicates that the positron TDCS is generally larger than the equivalent electron TDCS. It is shown that the magnitude of the TDCS is extremely sensitive to the energy of the ejected electron and that only when the cross section is averaged over energy do we get a reasonable agreement with experiment.

  1. A coincidence study of electron and positron impact ionization of Ar (3p) at 1 keV

    NASA Astrophysics Data System (ADS)

    Campeanu, Radu I.; Walters, James H. R.; Whelan, Colm T.

    2015-10-01

    Distorted-wave calculations of the triple differential cross section (TDCS) are presented for electron and positron impact ionization of Ar(3 p) in coplanar asymmetric geometry at an impact energy of 1 keV and are compared with a recent experiment. The experiment indicates that the positron TDCS is generally larger than the equivalent electron TDCS. It is shown that the magnitude of the TDCS is extremely sensitive to the energy of the ejected electron and that only when the cross section is averaged over energy do we get a reasonable agreement with experiment.

  2. Experimental investigation of the electron impact ionization cross-section behaviour near threshold

    SciTech Connect

    Winkler, C.; Maerk, T.D.

    1995-12-31

    The shape of the electron impact ionization cross-section near the threshold and the appearance energies AE of atomic or molecular ions are of fundamental interest in atomic physics as well as in many applications, e.g. in plasma physics. A large number of experiments and several theoretical approaches have already been presented, which predict either a linear dependences or a cross-section given by {rho} {proportional_to} (E{sub e}-AE){sup 1.13}, as reported for the first time by Wannier. Indeed, until today it is not yet clear what dependence actually has to be assumed; especially in the experiments two serious problems arise, namely the determination of the absolute energy scale and the influence of the energy spread on the measured curve. In this work a further attempt is made to deduce the shape of the ionisation cross-section near threshold and the appearance energy from experimental data obtained by using a novel molecular beam apparatus in combination with a time-of-flight technique.

  3. 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).

  4. Electron-impact ionization excitation of helium in the quasiphoton regime

    SciTech Connect

    Ngoko Djiokap, J. M.; Foumouo, E.; Urbain, X.; Piraux, B.; Kwato Njock, M. G.

    2010-04-15

    The triply differential cross section of ionization excitation of helium, leaving the residual ion in the n=2 excited states, is evaluated for the kinematics considered experimentally by Dupreet al. [J. Phys. B 25, 259 (1992)]. The interaction of the incident electron with the target is described at the first order, while the interaction of the ejected electron with the residual ion is treated very accurately within the formalism of the Jacobi matrix method. In the quasiphoton limit and for low ejected electron energies, the presence of series of doubly excited states, mainly below the n=3 single ionization threshold in helium, makes the triply differential cross sections extremely sensitive to both the energy and the emission angle of the ejected electron. We show that the convolution of our results with a Gaussian energy profile, in which the full width at half-maximum corresponds to the energy resolution in the experiment, has a significant effect. Our results suggest that it is also important to account for the finite resolution on the measurement of the scattering angle when the experimental data are compared to the theoretical predictions. Comparison of our theoretical results convoluted both in energy and in angle with the experimental data demonstrates the importance of an accurate description of the helium spectrum. A possible two-step mechanism involving single ionization of the target followed by excitation of the core electron is proposed to explain the remaining discrepancies.

  5. Electron-impact ionization excitation of helium in the quasiphoton regime

    NASA Astrophysics Data System (ADS)

    Ngoko Djiokap, J. M.; Foumouo, E.; Kwato Njock, M. G.; Urbain, X.; Piraux, B.

    2010-04-01

    The triply differential cross section of ionization excitation of helium, leaving the residual ion in the n=2 excited states, is evaluated for the kinematics considered experimentally by Dupré [J. Phys. B 25, 259 (1992)]. The interaction of the incident electron with the target is described at the first order, while the interaction of the ejected electron with the residual ion is treated very accurately within the formalism of the Jacobi matrix method. In the quasiphoton limit and for low ejected electron energies, the presence of series of doubly excited states, mainly below the n=3 single ionization threshold in helium, makes the triply differential cross sections extremely sensitive to both the energy and the emission angle of the ejected electron. We show that the convolution of our results with a Gaussian energy profile, in which the full width at half-maximum corresponds to the energy resolution in the experiment, has a significant effect. Our results suggest that it is also important to account for the finite resolution on the measurement of the scattering angle when the experimental data are compared to the theoretical predictions. Comparison of our theoretical results convoluted both in energy and in angle with the experimental data demonstrates the importance of an accurate description of the helium spectrum. A possible two-step mechanism involving single ionization of the target followed by excitation of the core electron is proposed to explain the remaining discrepancies.

  6. Electron-impact ionization-excitation of helium in the quasi-photon regime

    NASA Astrophysics Data System (ADS)

    Marcel Ngoko Djiokap, Jean; Foumouo, Emmanuel; Njock, Moise Godfroy Kwato; Urbain, Xavier; Piraux, Bernard

    2010-03-01

    The triply differential cross section (TDCS) for ionization and excitation of helium (leaving the residual ion in the n=2 excited states) is evaluated for the kinematics considered experimentally by Dupr'e et al. [J. Phys. B 25, 259 (1992)]. The interaction of the incident electron with the target is described in first order, while that of the ejected electron with the residual ion is treated accurately within the Jacobi matrix method formalism. In the quasi-photon limit and for small ejected electron energies, the presence of series of doubly excited states below the n=3 single ionization threshold in helium makes the TDCS extremely sensitive to both the energy and angle of the ejected electron. Comparison of our theoretical results (convoluted both in energy and angle) with the experimental data demonstrates the importance of an accurate description of the He spectrum. A possible two-step mechanism involving single ionization of the target followed by excitation of the core electron is proposed in order to explain the remaining discrepancies.

  7. Ionization of a lithium ion by electron impact in a strong laser field

    SciTech Connect

    Ghosh Deb, S.; Sinha, C.; Chattopadhyay, A.

    2011-12-15

    The modification in the dynamics of the electron-impact ionization process of a Li{sup +} ion due to an intense linearly polarized monochromatic laser field (n{gamma}e,2e) is studied theoretically using coplanar geometry. Significant laser modifications are noted due to multiphoton effects both in the shape and magnitude of the triple-differential cross sections (TDCSs) with respect to the field-free (FF) situation. The net effect of the laser field is to suppress the FF cross sections in the zeroth-order approximation [Coulomb-Volkov (CV)] of the ejected electron wave function, while in the first order [modified Coulomb-Volkov (MCV)], the TDCSs are found to be enhanced or suppressed depending on the kinematics of the process. The strong FF recoil dominance for the (e,2e) process of an ionic target at low incident energy is destroyed in the presence of the laser field. The FF binary-to-recoil ratio changes remarkably in the presence of the laser field, particularly at low incident energies. The difference between the multiphoton CV and the FF results indicates that for the ionic target, the Kroll-Watson sum rule does not hold well at the present energy range in contrast to the neutral atom (He) case. The TDCSs are found to be quite sensitive with respect to the initial phase of the laser field, particularly at higher incident energies. A significant qualitative difference is noted in the multiphoton ejected energy distribution (double-differential cross sections) between the CV and the MCV models. Variation of the TDCSs with respect to the laser phase is also studied.

  8. 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.

  9. Electron-Impact Ionization and Electron Attachment Cross Sections of Radicals Important in Transient Gaseous Discharges

    DTIC Science & Technology

    1990-01-25

    Semetuk. Can J Chem. ;8 455: Acknow ledgement F.A. Houle and J L. Beauchamp. J km Chem. Soc. ,2 (1979) 4067. 131 L. Friedman. FA. Long and Sl. WAolfsberg...attaIchment of1 lo\\%- energ > electrons to BCI, and in\\ N hIDepciideceo1ihw Ci niimsi nhcl1j~ ~rn stUir\\ i~et for a stifficienflk Iona time such that it

  10. Asymmetric electron energy sharing in electron-impact double ionization of helium

    NASA Astrophysics Data System (ADS)

    Silenou Mengoue, M.; Tetchou Nganso, H. M.

    2016-12-01

    We present the fully fivefold differential cross sections (FDCSs) for (e ,3 e ) processes in helium within the first Born approximation. The calculation is performed for a coplanar geometry in which the incident electron is fast (˜6 keV), the momentum transfer is small (0.24 a.u.), and for an asymmetric energy sharing between both slow ejected electrons at excess energy of 20 eV. Two cases have been considered: E1=15 eV, E2=5 eV and E1=8 eV, E2=12 eV. While waiting for new theoretical and experimental results for confrontations, in particular for asymmetric energy sharing, our results clearly demonstrate that, for the same incident energy, the same momentum transfer and the same excess energy, the (e ,3 e ) process in helium with asymmetric energy sharing between ejected electrons is more likely than the case with symmetric energy sharing. The two- and three-dimensional representation of the FDCSs covering all possible values of the angle of ejections are presented and discussed. The theoretical cross sections are calculated by using a compact-kernel-integral-equation approach associated with the Jacobi matrix method to calculate a three-body wave function and which leads to a full convergence in terms of the basis size.

  11. 20-150-keV proton-impact-induced ionization of uracil: Fragmentation ratios and branching ratios for electron capture and direct ionization

    SciTech Connect

    Tabet, J.; Eden, S.; Feil, S.; Abdoul-Carime, H.; Farizon, B.; Farizon, M.; Ouaskit, S.; Maerk, T. D.

    2010-01-15

    Fragmentation ratios and branching ratios are measured for ionization and dissociative ionization for 20-150 keV (0.9-2.4v{sub 0}) proton collisions with gas-phase uracil molecules. Through event-by-event determination of the postcollision projectile charge, it is possible for such a key biomolecule to distinguish between electron capture (EC) by the incident proton and direct ionization (DI) without projectile neutralization. While the same fragment ion groups are observed in the mass spectra for both processes, EC induces dissociation with greater efficiency than DI in the impact energy range of 35-150 keV (1.2-2.4v{sub 0}). In this range EC is also less abundant than DI with a branching ratio for EC/total ionization of <50%. Moreover, whereas fragmentation ratios do not change with energy in the case of EC, DI mass spectra show a tendency for increased fragmentation at lower impact energies.

  12. LETTER TO THE EDITOR: The electron-impact ionization of ? ions

    NASA Astrophysics Data System (ADS)

    Thomason, J. W. G.; Peart, B.

    1998-02-01

    The absolute cross section for the ionization of 0953-4075/31/4/013/img2 from threshold to 400 eV has been measured using an electron beam modulation technique. The results are significantly higher than those of Crandall et al, and are in good agreement with recent convergent close-coupling and pseudo-state R-matrix calculations by Badnell et al for the direct contribution to the cross section below 80 eV. In addition, a fast energy-scanning technique has been employed to make detailed measurements of the cross section between 65 and 117 eV. Considerable structure due to indirect ionization was revealed and many of the individual features can be identified with particular autoionization processes involving the excitation of a 2p electron.

  13. Electron impact ionization of helium from its ground and metastable states

    NASA Astrophysics Data System (ADS)

    Zhang-jin, Chen; Ke-zun, Xu

    1999-05-01

    The triple differential cross sections for the ionization of helium from its ground state 1 1S and metastable states 2 1S and 2 3S in coplanar asymmetric geometry by 150, 250 and 400 eV electrons have been calculated in the BBK model. The present results are compared with the experimental data and/or the other theoretical ones. It has been found that the structures for the metastable states differ markedly from those for the ground state. The collision mechanisms for the new structures appearing in the cross sections for the ionization from metastable states have been analysed. And it has been shown how the intensity of recoil peak changes due to the size of the electron orbital. In addition, the optimal kinematical situations for the cross sections are explored for future experiment.

  14. The kinetic energy spectrum of protons produced by the dissociative ionization of H2 by electron impact

    NASA Technical Reports Server (NTRS)

    Khakoo, M. A.; Srivastava, S. K.

    1985-01-01

    The kinetic energy spectra of protons resulting from the dissociative ionization of H2 by electron impact have been measured for electron impact energies from threshold (approximately 17 eV) to 160 eV at 90 deg and 30 deg detection angles, using a crossed-beam experimental arrangement. To check reliability, two separate proton energy analysis methods have been employed, i.e., a time-of-flight proton energy analysis and an electrostatic hemispherical energy analyzer. The present results are compared with previous measurements.

  15. The kinetic energy spectrum of protons produced by the dissociative ionization of H2 by electron impact

    NASA Technical Reports Server (NTRS)

    Khakoo, M. A.; Srivastava, S. K.

    1985-01-01

    The kinetic energy spectra of protons resulting from the dissociative ionization of H2 by electron impact have been measured for electron impact energies from threshold (approximately 17 eV) to 160 eV at 90 deg and 30 deg detection angles, using a crossed-beam experimental arrangement. To check reliability, two separate proton energy analysis methods have been employed, i.e., a time-of-flight proton energy analysis and an electrostatic hemispherical energy analyzer. The present results are compared with previous measurements.

  16. 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.

  17. New Data for Modeling Hypersonic Entry into Earth's Atmosphere: Electron-impact Ionization of Atomic Nitrogen

    NASA Astrophysics Data System (ADS)

    Savin, Daniel Wolf; Ciccarino, Christopher

    2017-06-01

    Meteors passing through Earth’s atmosphere and space vehicles returning to Earth from beyond orbit enter the atmosphere at hypersonic velocities (greater than Mach 5). The resulting shock front generates a high temperature reactive plasma around the meteor or vehicle (with temperatures greater than 10,000 K). This intense heat is transferred to the entering object by radiative and convective processes. Modeling the processes a meteor undergoes as it passes through the atmosphere and designing vehicles to withstand these conditions requires an accurate understanding of the underlying non-equilibrium high temperature chemistry. Nitrogen chemistry is particularly important given the abundance of nitrogen in Earth's atmosphere. Line emission by atomic nitrogen is a major source of radiative heating during atomspheric entry. Our ability to accurately calculate this heating is hindered by uncertainties in the electron-impact ionization (EII) rate coefficient for atomic nitrogen.Here we present new EII calculations for atomic nitrogen. The atom is treated as a 69 level system, incorporating Rydberg values up to n=20. Level-specific cross sections are from published B-Spline R-Matrix-with-Pseudostates results for the first three levels and binary-encounter Bethe (BEB) calculations that we have carried out for the remaining 59 levels. These cross section data have been convolved into level-specific rate coefficients and fit with the commonly-used Arrhenius-Kooij formula for ease of use in hypersonic chemical models. The rate coefficient data can be readily scaled by the relevant atomic nitrogen partition function which varies in time and space around the meteor or reentry vehicle. Providing data up to n=20 also enables modelers to account for the density-dependent lowering of the continuum.

  18. Experimental and theoretical triple differential cross sections for electron-impact ionization of Ar (3p) for equal energy final state electrons

    NASA Astrophysics Data System (ADS)

    Amami, Sadek; Ozer, Zehra N.; Dogan, Mevlut; Yavuz, Murat; Varol, Onur; Madison, Don

    2016-09-01

    There have been several studies of electron-impact ionization of inert gases for asymmetric final state energy sharing and normally one electron has an energy significantly higher than the other. However, there have been relatively few studies examining equal energy final state electrons. Here we report experimental and theoretical triple differential cross sections for electron impact ionization of Ar (3p) for equal energy sharing of the outgoing electrons. Previous experimental results combined with some new measurements are compared with distorted wave born approximation (DWBA) results, DWBA results using the Ward-Macek (WM) approximation for the post collision interaction (PCI), and three-body distorted wave (3DW) which includes PCI without approximation. The results show that it is crucially important to include PCI in the calculation particularly for lower energies and that the WM approximation is valid only for high energies. The 3DW, on the other hand, is in reasonably good agreement with data down to fairly low energies.

  19. Ionization of excited xenon atoms by electrons

    NASA Astrophysics Data System (ADS)

    Erwin, Daniel A.; Kunc, Joseph A.

    2004-08-01

    Measured cross sections for electron-impact ionization of excited Xe atoms are not presently available. Therefore, we combine in this work the formalisms of the binary encounter approximation and Sommerfeld’s quantization of atomic orbits and derive from first-principles cross sections for ionization of excited atoms by electrons of low and moderate energies (up to a few hundred eV ). The approach of this work can be used to calculate the cross sections for electron-impact ionization of excited atoms and atomic ions other than xenon.

  20. Theoretical and experimental (e ,2 e ) study of electron-impact ionization of laser-aligned Mg atoms

    NASA Astrophysics Data System (ADS)

    Amami, Sadek; Murray, Andrew; Stauffer, Al; Nixon, Kate; Armstrong, Gregory; Colgan, James; Madison, Don

    2014-12-01

    We have performed calculations of the fully differential cross sections for electron-impact ionization of magnesium atoms. Three theoretical approximations, the time-dependent close coupling, the three-body distorted wave, and the distorted wave Born approximation, are compared with experiment in this article. Results will be shown for ionization of the 3 s ground state of Mg for both asymmetric and symmetric coplanar geometries. Results will also be shown for ionization of the 3 p state which has been excited by a linearly polarized laser which produces a charge cloud aligned perpendicular to the laser beam direction and parallel to the linear polarization. Theoretical and experimental results will be compared for several different alignment angles, both in the scattering plane as well as in the plane perpendicular to the incident beam direction.

  1. Electron and hole impact ionization coefficients in GaAs-Al(x)Ga(1-x)As superlattices

    NASA Technical Reports Server (NTRS)

    Juang, F.-Y.; Das, U.; Nashimoto, Y.; Bhattacharya, P. K.

    1985-01-01

    Electron and hole multiplication and impact ionization coefficients have been measured with pure carrier injection in p(+)-n(-)-n(+) diodes grown by molecular beam epitaxy. Values of the electron and hole ionization coefficient ratio alpha/beta = 2-5 are measured for superlattices with well width Lz greater than or equal to 100 A and alpha/beta greater than 10 is measured in a graded band-gap superlattice with a total well and barrier width LB + LZ = 120 A. The ratio decreases and becomes less than unity for smaller well sizes. This is caused by an increase in beta (E) while alpha (E) remains fairly constant. The results have been interpreted by considering varying hole confinement and scattering in the coupled quantum wells.

  2. Distorted-wave calculation of cross sections for inner-shell ionization by electron and positron impact

    SciTech Connect

    Segui, Silvina; Dingfelder, Michael; Salvat, Francesc

    2003-06-01

    The relativistic distorted-wave Born approximation is used to calculate differential and total cross sections for inner shell ionization of neutral atoms by electron and positron impact. The target atom is described within the independent-electron approximation using the self-consistent Dirac-Fock-Slater potential. The distorting potential for the projectile is also set equal to the Dirac-Fock-Slater potential. For electrons, this guarantees orthogonality of all the orbitals involved and simplifies the calculation of exchange T-matrix elements. The interaction between the projectile and the target electrons is assumed to reduce to the instantaneous Coulomb interaction. The adopted numerical algorithm allows the calculation of differential and total cross sections for projectiles with kinetic energies ranging from the ionization threshold up to about ten times this value. Algorithm accuracy and stability are demonstrated by comparing differential cross sections calculated by our code with the distorting potential set to zero with equivalent results generated by a more robust code that uses the conventional plane-wave Born approximation. Sample calculation results are presented for ionization of K- and L-shells of various elements and compared with the available experimental data.

  3. Benchmark calculations for electron-impact excitation and ionization of beryllium

    NASA Astrophysics Data System (ADS)

    Zatsarinny, Oleg; Bartschat, Klaus; Fursa, Dmitry V.; Bray, Igor

    2016-09-01

    The B-spline R-matrix and the convergent close-coupling methods are used to study electron collisions with neutral beryllium for energies from threshold to 100 eV. Coupling to the target continuum significantly affects the results for transitions from the ground state, but to a lesser extent the strong transitions between excited states. Cross sections are presented for selected transitions between low-lying physical bound states of beryllium, as well as for elastic scattering, momentum transfer, and ionization. The present cross sections for transitions from the ground state from the two methods are in excellent agreement with each other, and also with previous results based on nonperturbative convergent pseudostate and time-dependent close-coupling models. The elastic cross section at low energies is dominated by a shape resonance. The ionization from the (2 s 2 p) 3 P and (2 s 2 p) 1 P states strongly depends on the respective term. The current predictions represent an extensive set of electron scattering data for neutral beryllium, which should be sufficient for most modeling applications. This work was supported by the United States National Science Foundation (OZ and KB) and the Australian Research Council (DVF and IB).

  4. Cross sections of electron capture and electron capture with ionization of argon atoms by fast 3He2+ ions at various impact parameters

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    The absolute differential cross sections of scattering of fast particles formed in processes with capture of one or two electrons from Ar atoms have been measured for 6-keV He2+ ions in the interval of scattering angles within 0°-2.5°. The cross sections of electron capture and electron capture with ionization have been determined as functions of the impact parameter. The probabilities of these processes are compared to the distribution of electron density in various shells of target atoms. Applicability of the models of screened Coulomb interaction potentials to description of the scattering of recharged particles is assessed.

  5. 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.

  6. 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.

  7. 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)].

  8. Reducing Collisional Breakup Of A System Of Charged Particles To Practical Computation: Electron-Impact Ionization Of Hydrogen

    SciTech Connect

    McCurdy, C.W.; Baertschy, M.; Isaacs, W.A.; Rescigno, T.N.

    2001-08-24

    It has been a goal of researchers in the area of atomic collisions for nearly half a century to reduce to practical computation the simplest problem in collisional ionization: the electron-impact ionization of atomic hydrogen. The principal barrier to solving this problem has been the difficult boundary conditions that apply to the complete breakup of a system charged particles. We describe how this goal has been accomplished in the last five years by the application of the mathematical transformation of ''exterior complex scaling'' together with an appropriate formalism for computing the breakup amplitudes from a numerical representation of the complete solution of the Schrodinger equation. Some successes of other recent approaches to this problem are also described.

  9. 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.

  10. Ion kinetic energy distributions and cross sections for the electron impact ionization of ethyl tert-butyl ether

    NASA Astrophysics Data System (ADS)

    Di Palma, T. M.; Apicella, B.; Armenante, M.; Velotta, R.; Wang, X.; Spinelli, N.

    2005-11-01

    The kinetic energy distributions and the cross sections of the ions produced in the electron impact of ethyl tert-butyl ether (ETBE) have been studied by time of flight (TOF) mass spectrometry. The kinetic energy distributions have been deduced from the TOF peak shape analysis and a Montecarlo simulation method of the ion trajectories has been used to evaluate the collection efficiency of the spectrometer as a function of the ion initial kinetic energy. The measured ion yields have been corrected for the collection efficiency and the partial and total ionization cross sections of ETBE determined in the range 20-150 eV.

  11. Low energy electron-impact ionization of hydrogen atom for coplanar equal-energy-sharing kinematics in Debye plasmas

    NASA Astrophysics Data System (ADS)

    Li, Jun; Zhang, Song Bin; Ye, Bang Jiao; Wang, Jian Guo; Janev, R. K.

    2016-12-01

    Low energy electron-impact ionization of hydrogen atom in Debye plasmas has been investigated by employing the exterior complex scaling method. The interactions between the charged particles in the plasma have been represented by Debye-Hückel potentials. Triple differential cross sections (TDCS) in the coplanar equal-energy-sharing geometry at an incident energy of 15.6 eV for different screening lengths are reported. As the screening strength increases, TDCS change significantly. The evolutions of dominant typical peak structures of the TDCS are studied in detail for different screening lengths and for different coplanar equal-energy-sharing geometries.

  12. Electron-impact-ionization cross sections of H{sub 2} for low outgoing electron energies from 1 to 10 eV

    SciTech Connect

    Al-Hagan, Ola; Madison, D. H.; Murray, A. J.; Kaiser, C.; Colgan, J.

    2010-03-15

    Theoretical and experimental fully differential cross sections are presented for electron-impact ionization of molecular hydrogen in a plane perpendicular to the incident beam direction. The experimental data exhibit a maximum for 1-eV electrons detected 180 deg. apart and a minimum for 10-eV electrons. We investigate the different physical effects which cause back-to-back scattering and demonstrate that, over the energy range from 10 to 1 eV, a direct transition is observed from a region where Wannier threshold physics is essentially unimportant to where it completely dominates.

  13. Double-K-vacancy states in electron-impact single ionization of metastable two-electron N5+(1s2s 3S1) ions

    NASA Astrophysics Data System (ADS)

    Müller, A.; Borovik, A.; Huber, K.; Schippers, S.; Fursa, D. V.; Bray, I.

    2014-07-01

    The role of hollow states intermediately produced in electron-impact ionization of metastable He-like N5+(1s2s3S1) ions has been investigated in detail. A crossed-beam setup and suitable experimental techniques were employed for the measurement of accurate absolute cross sections and precise energy-scan data. Fine structures arising from K-shell excitations and associated resonances have been observed for this two-electron ion with less than ±0.5 eV uncertainty on the energy scale. Fine details, such as interference of the reaction pathways of direct ionization and excitation with capture of the incident electron followed by double-Auger decay, could be revealed. Ab initio calculations based on the convergent close coupling (CCC) approach are in good agreement with the experiment.

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

    SciTech Connect

    Aydinol, M.; Aydeniz, D.

    2016-03-25

    L shell ionization cross section and {sub Li} subshells ionization cross sections of Os, Pt, Hg, Pb, Po atoms calculated. For each atom, ten different electron impacty energy values E{sub oi} used. Calculations carried out by using nonrelativistic Lotz equation in Matlab. Ionization cross section values obtained for Eoi values in the energy range of E{sub Li} ≤E{sub oi}≤4E{sub Li} for each atom. Starting allmost from E{sub oi} = E{sub Li} (i = 1,2,3) values of the each subshell ionization threshold energy, ionization cross section are increasing rapidly with E{sub oi}. For a fixed E{sub oi} = 3. E{sub Li} 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 σ{sub Li} subshells.

  15. 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.

  16. Highly charged ions from laser-cluster interactions: local-field-enhanced impact ionization and frustrated electron-ion recombination.

    PubMed

    Fennel, Thomas; Ramunno, Lora; Brabec, Thomas

    2007-12-07

    Our molecular dynamics analysis of Xe_{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.

  17. 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.

  18. Electron impact ionization of O2 and the interference effect from forward-backward asymmetry

    NASA Astrophysics Data System (ADS)

    Chowdhury, Madhusree Roy; Tribedi, Lokesh C.

    2017-08-01

    Absolute double differential cross sections (DDCSs) of secondary electrons emitted from O2 under the impact of 7 keV electrons were measured for different emission angles between 30° and 145° having energies from 1-600 eV. The forward-backward angular asymmetry was observed from angular distribution of the DDCS of secondary electrons. The asymmetry parameter, thus obtained from the DDCS of two complementary angles, showed a clear signature of interference oscillation. The Cohen-Fano model of Young type electron interference at a molecular double slit is found to provide a good fit to the observed oscillatory structures. The present observation is in qualitative agreement with the recent results obtained from photoionization.

  19. 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.

  20. 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.

  1. Charged-Particle Impact Ionization of Atoms

    SciTech Connect

    Bartschat, Klaus; Guan Xiaoxu

    2008-08-08

    We have developed a hybrid method to treat charged-particle impact ionization of complex atoms and ions. The essential idea is to describe the interaction between a fast projectile and the target perturbatively, up to second order, while the initial bound state and the ejected-electron--residual-ion interaction can be handled via a convergent R-matrix with pseudo-states (close-coupling) expansion. Example results for ionization of the heavy noble gases (Ne-Xe) by positron and electron impact are presented. The general scheme for a distorted-wave treatment of ionization by heavy-particle impact is described.

  2. Observation of fast and slow interatomic Coulombic decay in argon dimers induced by electron-impact ionization

    NASA Astrophysics Data System (ADS)

    Ren, Xueguang; Miteva, Tsveta; Kolorenč, Přemysl; Gokhberg, Kirill; Kuleff, Alexander I.; Cederbaum, Lorenz S.; Dorn, Alexander

    2017-09-01

    We investigate the interatomic Coulombic decay (ICD) in argon dimers induced by electron-impact ionization (E0=90 eV ) using a multiparticle coincidence experiment in which the momentum vectors and, consequently, the kinetic energies for electrons and fragment ions are determined. The signature of the ICD process is obtained from a correlation map between ejected electron energy and kinetic energy release (KER) for Ar++Ar+ fragment ions where low-energy ICD electrons can be identified. Furthermore, two types of ICD processes, termed fast and slow interatomic decay, are separated by the ICD initial-state energies and projectile energy losses. The dependence of the energies of emitted low-energy ICD electrons on the initial-state energy is studied. ICD electron energy spectra and KER spectra are obtained separately for fast and slow decay processes where the KER spectra for the slow decay channel are strongly influenced by nuclear motion. The KER and ICD electron energy spectra are well reproduced by ab initio calculations.

  3. 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.

  4. 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).

  5. Electron-impact total ionization cross sections of CF4, C2F6, and C3F8

    NASA Astrophysics Data System (ADS)

    Nishimura, H.; Huo, Winifred M.; Ali, M. A.; Kim, Yong-Ki

    1999-02-01

    Both theoretical and experimental electron-impact total ionization cross sections of CF4, C2F6, and C3F8 are presented. The experimental cross sections have been measured as a function of incident electron energy T from threshold to 3 keV. A parallel plate condenser type apparatus was used. The molecular polarizability for C3F8 was empirically estimated to be α=10.6 Å3±0.8 Å3. Theoretical cross sections calculated from the binary-encounter-Bethe (BEB) method, which combines a modified form of the Mott cross section and the Bethe cross section, are compared with the experimental cross sections. The BEB cross sections calculated from correlated molecular wave functions with theoretical estimates for multiple ionization are about 10% higher than the experimental data at the peak for CF4, while they are in excellent agreement with the experimental data for C2F6 and C3F8. Our analysis shows that the BEB theory implicitly includes part of neutral dissociation, such as CF4→CF3+F, and hence tends to be an upper limit to the total ionization cross section. We found that the difference between our best theory for CF4 and the present experimental cross section exhibits a remarkable similarity to the shape of the recently measured cross section for neutral dissociation, though there is no a priori reason for the similarity. Owing to the large number of bound electrons, the correlation included in our wave functions for C2F6 and C3F8 is more limited than for CF4. Hence, we believe that for these two molecules the calculated cross sections are lower than the true BEB values, in spite of the apparent excellent agreement between the theory and the experiment.

  6. New Results in Electron-Atom Ionization

    NASA Astrophysics Data System (ADS)

    Madison, Don

    1997-10-01

    A deeper insight into atomic ionization by electron impact is gained by studying electron-electron correlation in a model-independent approach for calculating (e,2e) triply-differential cross sections using correlated (three-body) wave functions of arbitrary complexity. Results will be presented from the continuum distorted wave (CDW) model, three Coulomb-wave (3C) model, three-body distorted-wave Born approximation (3DWBA), Alt and Mukhamedzhanov (AM) model, dynamic-screening three Coulomb-wave (DS3C) model, and the eikonal approximation (EA). The sucesses and failures of the above models can be used to gain a better understanding of ionization processes.

  7. 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.

  8. Benchmark experiment for electron-impact ionization of argon: Absolute triple-differential cross sections via three-dimensional electron emission images

    SciTech Connect

    Ren Xueguang; Senftleben, Arne; Pflueger, Thomas; Dorn, Alexander; Ullrich, Joachim; Bartschat, Klaus

    2011-05-15

    Single ionization of argon by 195-eV electron impact is studied in an experiment, where the absolute triple-differential cross sections are presented as three-dimensional electron emission images for a series of kinematic conditions. Thereby a comprehensive set of experimental data for electron-impact ionization of a many-electron system is produced to provide a benchmark for comparison with theoretical predictions. Theoretical models using a hybrid first-order and second-order distorted-wave Born plus R-matrix approach are employed to compare their predictions with the experimental data. While the relative shape of the calculated cross section is generally in reasonable agreement with experiment, the magnitude appears to be the most significant problem with the theoretical treatment for the conditions studied in the present work. This suggests that the most significant challenge in the further development of theory for this process may lie in the reproduction of the absolute scale rather than the angular dependence of the cross section.

  9. Absolute partial and total electron-impact-ionization cross sections for CF4 from threshold up to 500 eV

    NASA Astrophysics Data System (ADS)

    Ma, Ce; Bruce, M. R.; Bonham, R. A.

    1991-09-01

    Electron-impact dissociative ionization of tetrafluoromethane (CF4) was studied with the use of a pulsed electron beam time-of-flight apparatus. The absolute partial ionization cross sections of CF+3, CF+2, CF2+3, CF+, CF2+2, F+, and C+ were measured from threshold up to 500 eV. The total ionization cross section was obtained by charge weighted summing of all the observed partial ionization cross sections. A total cross section for dissociation into neutral fragments was inferred from our total ionization cross section and the total dissociation cross section of Winters and Inokuti [Phys. Rev. A 25, 1420 (1982)]. The present results for the partial ionization cross sections are as much as 9% (CF+3) to 81% (F+) higher than the previously published absolute measurements of Stephan, Deutsch, and Märk [J. Chem. Phys. 83, 5712 (1985)] at 80 eV, but are in agreement with their recently revised estimates for the singly charged ions. We also found that dissociative ionization was a dominant process for electron-impact energies above 30 eV, accounting for 85% of the total dissociation cross section at 80 eV.

  10. Double ionization of helium by particle impact

    NASA Technical Reports Server (NTRS)

    Jacobsen, Finn M.

    1990-01-01

    Experimental results are reviewed of the ratio, R sq., of double to single ionization of He by proton, antiproton, electron and positron impact in the energy range from 0.15 to about 10 MeV/amu. At high velocities (greater than 1 to 2 MeV/amu) values of R sq. caused by electron impact merge with those for the proton with the antiproton, electron values being up to a factor of 2 greater than that for the p, positron. At these velocities the single ionization cross sections caused by impact of any of these four particles are indistinguishable.

  11. Cyclic acyloxonium ions as diagnostic aids in the characterization of chloropropanol esters under electron impact (EI), electrospray ionization (ESI), and atmospheric pressure chemical ionization (APCI) conditions.

    PubMed

    Rahn, Anja K K; Yaylayan, Varoujan A

    2013-06-26

    During mass spectrometric analysis of various lipids and lipid derivatives such as the chlorinated counterparts of triacylglycerols, the detailed structure of the characteristic and common ions formed under electron impact (EI), electrospray ionization (ESI), and atmospheric pressure chemical ionization (APCI) conditions by the loss of a single fatty acid remains ambiguous. These ions are designated in the literature as "diacylglyceride ions" and are frequently depicted with a molecular formula without showing any structural features and sometimes represented as cyclic acyloxonium ions. Characterization of these ions is of considerable importance due to their utility in structural identification of lipid derivatives. This study provides complementary evidence on the cyclic nature of "diacylglyceride ions" through the use of the simplest 3-monochloropropanediol diester as a model and the use of isotope labeling technique. Tandem MS/MS studies have indicated that the ion at m/z 135.6 generated from 1,2-bis(acetoyl)-3-chloropropane through the loss of an acetyl group was identical to the ion at m/z 135.6 generated from 4-chloromethyl-2,2-dimethyl-1,3-dioxolane, the latter being generated from a cyclic precursor through the loss of a methyl radical, keeping the dioxolane ring structure intact, thus confirming the cyclic nature of these ions. The corresponding cyclic oxonium ions generated from longer chain chloropropanol diesters, such as the ion at m/z 331.2 originating from 3-monochloropropanediol (3-MCPD) diesters containing palmitic acid(s), could serve as chemical markers for the presence chloropropanol esters.

  12. Ultrafast electron dynamics following outer-valence ionization: The impact of low-lying relaxation satellite states

    NASA Astrophysics Data System (ADS)

    Lünnemann, Siegfried; Kuleff, Alexander I.; Cederbaum, Lorenz S.

    2009-04-01

    Low-lying relaxation satellites give rise to ultrafast electron dynamics following outer-valence ionization of a molecular system. To demonstrate the impact of such satellites, the evolution of the electronic cloud after sudden removal of an electron from the highest occupied molecular orbital (HOMO) of the organic unsaturated nitroso compound 2-nitroso[1,3]oxazolo[5,4-d][1,3]oxazole is traced in real time and space using ab initio methods only. Our results show that the initially created hole charge remains stationary but on top of it the system reacts by an ultrafast π-π ∗ excitation followed by a cyclic excitation-de-excitation process which leads to a redistribution of the charge. The π-π ∗ excitation following the removal of the HOMO electron takes place on a subfemtosecond time scale and the period of the excitation-de-excitation alternations is about 1.4 fs. In real space the processes of excitation and de-excitation represent ultrafast delocalization and localization of the charge. The results are analyzed by simple two- and three-state models.

  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. Destabilization of a cylindrically confined electron cloud by impact ionization of background neutrals: 2D3v PIC simulation with Monte-Carlo-collisions

    NASA Astrophysics Data System (ADS)

    Sengupta, M.; Ganesh, R.

    2017-03-01

    In this paper, we have investigated, through simulation, the process of destabilization of a cylindrically confined electron cloud due to the presence of a single species of neutral atoms, Ar in the background of the trap at a pressure relevant to experiments. The destabilization occurs because of a gradual accumulation of Ar+ in the cloud by the electron-impact ionization of the background neutrals. The trapped ions gradually collectively form a sizeable ion cloud which engages in a rotational two-stream instability (the ion resonance instability) with the electron cloud. The instability excites a growing fundamental diocotron mode on both components of the mixed non-neutral cloud. With the help of a set of numerical diagnostics, we have investigated the nonlinear evolution of the excited fundamental mode under the combined influence of two ongoing processes viz, (i) the changing electron and ion populations caused by electron impact ionization of the background Ar, and also by the radial loss of both charged species to the grounded trap wall at later stages and (ii) the elastic scattering of electrons and ions that make non-ionizing collisions with the background neutrals. The 2D collisionless dynamics of the instability has been simulated using a 2D Particle-in-Cell code operating on a Cartesian grid laid out on the cylindrical trap's cross-section, and the 3D ionizing and non-ionizing collisions between charged particles and background neutrals have been simulated using the technique of Monte-Carlo-Collisions.

  15. Time-independent and time-dependent close-coupling methods for the electron-impact ionization of ?, ? and ?

    NASA Astrophysics Data System (ADS)

    Badnell, N. R.; Pindzola, M. S.; Bray, I.; Griffin, D. C.

    1998-02-01

    The electron-impact ionization cross sections of 0953-4075/31/4/032/img10, 0953-4075/31/4/032/img11 and 0953-4075/31/4/032/img12 are calculated using both time-independent and time-dependent close-coupling methods. The time-independent methods are R-matrix and convergent close-coupling solutions based on a total wavefunction constructed using antisymmetrized products of Laguerre pseudo-orbitals and physical bound orbitals. The time-dependent method is based on the propagation of wavepackets constructed using excited-state orbitals calculated in a core pseudo-potential. The results of all three methods are in good agreement for 0953-4075/31/4/032/img10; there is also good agreement between the R-matrix and time-dependent methods for 0953-4075/31/4/032/img11 and 0953-4075/31/4/032/img12, and all three methods yield ionization cross sections that lie substantially above the experimental crossed-beams measurements of Crandall et al. There is better accord with the crossed-beams measurements of Peart et al for 0953-4075/31/4/032/img10, but the theoretical results still lie 10% higher at 50 eV. Some disagreement is noted, for both 0953-4075/31/4/032/img11 and 0953-4075/31/4/032/img12, between the convergent close-coupling results and the R-matrix and time-dependent results.

  16. Soft or hard ionization of molecules in helium nanodroplets? An electron impact investigation of alcohols and ethers.

    PubMed

    Yang, Shengfu; Brereton, Scott M; Wheeler, Martyn D; Ellis, Andrew M

    2005-12-21

    Electron impact (70 eV) mass spectra of a series of C1-C6 alcohols encased in large superfluid liquid helium nanodroplets (approximately 60,000 helium atoms) have been recorded. 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, most notably cleavage of the C(alpha)-H bond in the parent ion to form the corresponding oxonium ion. Parent ion intensities are also enhanced by the helium, 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. To demonstrate that these findings are not unique to alcohols, we have also investigated several ethers. The results obtained for both alcohols and ethers 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. The set of molecules explored in this work suggest that electron impact ionization of doped helium nanodroplets does not provide a sufficiently large softening effect to be useful in analytical mass spectrometry.

  17. Ionizing Emissions and Electronics,

    DTIC Science & Technology

    1984-05-22

    modes of operation (factor of construction/design, the factor of mode /conditions), etc. In the radiobiology for the evaluation of the biological...radio-electronic equipment of space objects it is necessary to consider the dynamics of motion and the concrete/specific/actual mode of orbit or...is shown. The same figure gives the lines of the equal particle flux densities, recorded with the aid of a Geiger counter, arranged/located after the

  18. Investigation of a vortex in Coulomb-Born calculations of inner-shell ionization of carbon by electron impact

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

    Previously, we reported vortices in Coulomb-Born calculations of inner-shell ionization of carbon by electron impact. A vortex was obtained for the kinematics of an incident energy Ei = 1801 . 2 eV , scattering angle θf =4° , energy of the ejected electron Ek = 5 . 524 eV and angle of the ejected electron θk =239° . We showed that for this set of kinematics, the real and imaginary parts of the T-matrix are zero at the same angle (to a good approximation). Furthermore, we showed the velocity field rotates about the position of the vortex. Recently, following the treatment of Botero and Macek, we decomposed the Coulomb-Born T-matrix into its multipole components. We show that the T-matrix and the quintuple differential cross section obtained by simply adding the l = 1 , m = +/- 1 multipole components to the l = 0 --> 4 , m = 0 components is very close to the Coulomb-Born T-matrix and the quintuple differential cross section, respectively. Our analysis shows the importance of the l = 1 , m = +/- 1 multipole components in obtaining a vortex in the Coulomb-Born calculation. S.J.W. acknowledges support from NSF under grant no. PHYS-0968638. J.H.M. acknowledges support by the D.O.E. under grant number DE-FG02-02ER15283.

  19. Electron impact ionization of liquid and gaseous water: a single-center partial-wave approach.

    PubMed

    Champion, C

    2010-01-07

    In this work, we report a unified methodology to express the molecular wavefunctions of water in both vapor and liquid phases by means of a single-center approach. These latter are then used as input data in a theoretical treatment--previously published and successfully tested--for describing the water ionization process in the first Born approximation (Champion et al 2006 Phys. Rev. A 73 012717). The multi-differential and total cross sections also obtained are reported for the two thermodynamical phases investigated and compared to the rare existing experimental and theoretical data.

  20. Double ionization of neon by electron impact: use of correlated wave functions*

    NASA Astrophysics Data System (ADS)

    Kada, Imene; Cappello, Claude Dal; Mansouri, Abdelaziz

    2017-02-01

    A model including correlation both in the initial state and in the final state is applied to the case of the double ionization of neon. The results of our model are compared to the available experimental data performed at high incident energy. Fully (fivefold) differential cross sections (FDCS) have been studied by applying the first Born approximation. Four ion states of Ne++, which are not resolved in the experiments, have been included in our calculation. Contribution to the Topical Issue "Many Particle Spectroscopy of Atoms, Molecules, Clusters and Surfaces", edited by A.N. Grum-Grzhimailo, E.V. Gryzlova, Yu V. Popov, and A.V. Solov'yov.

  1. 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.

  2. Double L{sub 3}M ionization of Pd induced by impact with medium-energy electrons

    SciTech Connect

    Cao, W.; Dousse, J.-Cl.; Hoszowska, J.; Kayser, Y.; Schenker, J.-L.; Kavcic, M.; Zitnik, M.

    2011-02-15

    The electron-induced L{sub 3}M two-step double ionization cross sections of metallic Pd were determined experimentally for incident electron beam energies ranging from the double ionization threshold up to 18 keV. The double L{sub 3}M ionization cross sections were derived from the intensity ratios (I{sub L{alpha}M}:I{sub L{alpha}}) of the resolved M satellites to the parent diagram lines. The sample was bombarded with monoenergetic electrons from an energy-tunable 20-kV electron gun. The diagram and M-satellite x-ray lines were measured by means of high-resolution x-ray spectroscopy, using a reflection-type von Hamos bent crystal spectrometer. The two-step partial cross sections were determined by subtracting from the measured total double ionization cross sections the contributions due to the shake process and L{sub 1}-L{sub 3}M{sub 4,5} Coster-Kronig transitions. Despite the thick target employed in the present study, the dependence of the two-step cross sections on the incoming electron energy could be derived using a target slice decomposition method. It is shown that the obtained energy dependence can be well reproduced by the semiempirical parametrization model of Pattard and Rost.

  3. 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.

  4. 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.

  5. Calculation of the Cross Section of Helium Ionization by an Electron Impact with the Formation of a Helium Ion in an Excited State

    SciTech Connect

    Elizarov, A.Yu.; Tupitsyn, I.I.

    2005-11-15

    The total cross sections of He and He{sup +} ionization by an electron impact are calculated in the first Born approximation. Calculations of the matrix elements are carried out by the Fock-Dirac multiconfiguration relativistic method using an intermediate type of coupling with orthogonal functions of the initial and final states. A single-electron wave function of the continuous spectrum for an Auger electron is obtained using the Fock-Dirac single-configuration method. The results of the calculations performed with orthogonal and nonorthogonal wave functions of the initial and final states are compared. The ionization cross sections are calculated for cases in which a knock-on electron of the continuous spectrum is described by both the orthogonal and nonorthogonal wave functions with respect to the wave functions of the core electrons.

  6. Ionization from soft electron precipitation in the auroral F region

    NASA Technical Reports Server (NTRS)

    Labelle, J.; Sica, R. J.; Kletzing, C.; Earle, G. D.; Kelley, M. C.

    1989-01-01

    Rocket-borne instrumentation, launched into the morning sector auroral zone from Sondre Stromfjord, Greenland, detects electron density enhancements correlated with enhancements in the flux of soft (less than 1 keV) downgoing electrons. These electron density enhancements seem most likely to have been generated by direct production of ionization at F region altitudes. Model calculations of the electron impact ionization rate, based on the measured electron spectrum, lend support to this hypothesis.

  7. Ionization from soft electron precipitation in the auroral F region

    NASA Technical Reports Server (NTRS)

    Labelle, J.; Sica, R. J.; Kletzing, C.; Earle, G. D.; Kelley, M. C.

    1989-01-01

    Rocket-borne instrumentation, launched into the morning sector auroral zone from Sondre Stromfjord, Greenland, detects electron density enhancements correlated with enhancements in the flux of soft (less than 1 keV) downgoing electrons. These electron density enhancements seem most likely to have been generated by direct production of ionization at F region altitudes. Model calculations of the electron impact ionization rate, based on the measured electron spectrum, lend support to this hypothesis.

  8. Cross Sections for Ionization of Rare Gas Excimers by Electron Impact and Atomic and Molecular Processes in Excimer Lasers.

    DTIC Science & Technology

    1980-03-01

    Theoretical cross sections for ionization of msetastable excimers - helium , neon, argon, krypton and zenon - and of metastable mercury are presented...AO-A086 698 GEORGIA INST OF TECH ATLANTA SCHOOL. OF PHYSICS FB20/5 CROSS SECTION1S FOR IONIZATION OF RARE GAS EXCIMERS By ELECTRON -- ETC(O) MAR 80 M...in Excimer Lasers. - -- 7 AUT 4OR(u) 8. CONTRACT OR GRANT NUMBER-) M. Raymond Flannery aW K. J./McCann . I F33615-78-C-20 128 9 PERFORMING

  9. 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.

  10. 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)

  11. 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)

  12. Electrospray ionization tandem mass spectrometric and electron impact mass spectrometric characterization of mycosporine-like amino acids.

    PubMed

    Whitehead, Kenia; Hedges, John I

    2003-01-01

    Positive-ion mass spectral fragmentations of seven mycosporine-like amino acids (MAAs) are reported and discussed. The MAAs studied are small compounds composed of a cycloheximine ring substituted with amino acid or amino alcohol units. Techniques used include electron impact (EI) and electrospray ionization (ESI) with tandem mass spectrometry (MS/MS). ESI-MS/MS showed unusual small radical losses, generally resulting from the loss of a methyl group with the exception of shinorine and porphyra for which the initial losses were 30 and 44 Da, respectively. As expected from structural similarities, porphyra, shinorine and palythinol displayed similar fragmentation patterns, while palythenic acid and palythene fragmented in a similar manner. Overall, the ESI-MS/MS fragmentations at m/z <200 exhibited a distinctive pattern for all seven MAAs with characteristic ions at m/z 137, 168, 186, and 197 or 199. Several ions were observed for each of the MAAs analyzed, and together provide a useful and potentially diagnostic pattern for identification of MAAs and as an aid in structure elucidation of novel MAAs. For GC/EI-MS analysis, trimethylsilyl (TMS) derivatives were made. The EI-MS fragmentation patterns of TMS-MAAs showed many features typical of TMS-derivatized alpha-amines. The precursor TMS-MAA ion was not detected, but a [M-90](+ radical) ion was the highest-mass intense peak observed for palythine, palythinol and shinorine, while palythene gave a [M-116](+ radical) ion. Besides determining the number of acidic hydrogens, EI-MS of TMS-derivatized MAAs will aid in structure elucidation of novel MAAs. Copyright 2003 John Wiley & Sons, Ltd.

  13. Direct evidence of a strong isomer effect in electron-impact double ionization of C{sub 3}H{sub 4}

    SciTech Connect

    Scully, S.W.J.; Senthil, V.; Wyer, J.A.; Shah, M.B.; Montenegro, E.C.; Kimura, M.; Tawara, H.

    2005-09-15

    The electron-impact double ionization of two isomers of C{sub 3}H{sub 4} (allene and propyne) between 25 and 1000 eV has been investigated using time-of-flight mass spectrometry. Unambiguous differences in the partial double-ionization spectra of these isomers are observed over the entire energy range. These isomer effects have been observed in C{sub 3}H{sub 4} through the recording of target product channels and, in particular, when hard collisions involving the transfer of a large amount of energy is involved. Measurements of double-ionization events which fragment through Coulomb explosion are also reported. Coincidences between the charged fragment ions and protons were measured and shown to only exhibit isomer effects in the channel involving production of H{sup +}+CH{sub 2}{sup +}.

  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. B-spline R-matrix-with-pseudostates calculations for electron-impact excitation and ionization of nitrogen

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Zatsarinny, Oleg; Bartschat, Klaus

    2014-06-01

    The B-spline R-matrix-with-pseudostates (BSR) method is employed to treat electron collisions with nitrogen atoms. Predictions for elastic scattering, excitation, and ionization are presented for all transitions between the lowest 21 states of nitrogen in the energy range from threshold to 120 eV. The structure description has been further improved compared to a previous BSR calculation by Tayal and Zatsarinny [J. Phys. B 38, 3631 (2005), 10.1088/0953-4075/38/20/001]. This change in the structure model, together with the inclusion of a large number of pseudostates in the close-coupling expansion, has a major influence on the theoretical predictions, especially at intermediate energies, where many of the excitation cross sections are reduced significantly. Ionization cross sections for the ground and metastable initial states are also provided. Finally, we carry out an accurate ab initio treatment of the prominent shape resonance just above the elastic threshold.

  16. Fragmentation dynamics of argon clusters (Arn, n =2 to 11) following electron-impact ionization: Modeling and comparison with experiment

    NASA Astrophysics Data System (ADS)

    Bonhommeau, David; Halberstadt, Nadine; Viel, Alexandra

    2006-05-01

    The fragmentation dynamics of argon clusters ionized by electron impact is investigated for initial cluster sizes up to n =11 atoms. The dynamics of the argon atoms is modeled using a mixed quantum-classical method in which the nuclei are treated classically and the transitions between electronic states quantum mechanically. The potential-energy surfaces are derived from a diatomics-in-molecules model with the addition of the induced dipole-induced dipole and spin-orbit interactions. The results show extensive and fast fragmentation. The dimer is the most abundant ionic fragment, with a proportion increasing from 66% for n =2 to a maximum of 95% for n =6 and then decreasing down to 67% for n =11. The next abundant fragment is the monomer for n <7 and the trimer otherwise. The parent ion dissociation lifetimes are all in the range of 1ps. Long-lived trajectories appear for initial cluster sizes of seven and higher, and favor the formation of the larger fragments (trimers and tetramers). Our results show quantitative agreement with available experimental results concerning the extensive character of the fragmentation: Ar+ and Ar2+ are the only ionic fragments for sizes up to five atoms; their overall proportion is in quantitative agreement for all the studied sizes; Ar2+ is the main fragment for all sizes; stable Ar3+ fragments only appear for n ⩾5, and their proportion increases smoothly with cluster size from there. However, the individual ionic monomer and dimer fragment proportions differ. The experimental ones exhibit oscillations with initial cluster size, with a slight tendency to decrease on average for the monomer. In contrast our results show a monotonic, systematic evolution, similar to what was found in our earlier studies on neon and krypton clusters. Several hypotheses are discussed in order to find the origin of this discrepancy. Finally, the metastable II(1/2)u and II(1/2)g states of Ar2+ are found to decay with a lifetime of 3.5 and 0.1ps

  17. 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.

  18. Particle-in-Cell Simulations of Electron-Impact and Tunneling Ionization Effects for Beam-Plasma and Laser-Plasma Applications

    NASA Astrophysics Data System (ADS)

    Bruhwiler, David

    2002-11-01

    Laser-driven (LWFA) and beam-driven (PWFA) plasma accelerators can sustain electron plasma waves with longitudinal electric fields on the order of the nonrelativistic wave breaking field, which is routinely of order 100 GV/m in table-top LWFA experiments. The laser pulse can create its own plasma from a gas jet via field-induced tunneling ionization of the neutral atoms, which leads to blue-shifting at the leading edge of the pulse, as well as steepening due to pump depletion and other effects. Tunneling ionization is also a critical issue for some proposed PWFA experiments, with gradients exceeding 5 GV/m. In addition, electron impact ionization can lead to important effects like particle trapping in PWFA concepts. We will present simulation results from the particle-in-cell code OOPIC [D.L. Bruhwiler et al., Phys. Rev. S.T. A, Issue 10 (2001); www.techxhome.com/products/oopic/], which demonstrate the physical effects of these ionization processes in a few interesting cases, including detailed comparison with experiments from the l'OASIS lab at LBNL [W.P. Leemans et al., Phys. Plasmas 8, 2510 (2001)] and a brief discussion of the algorithms.

  19. Electron-impact ionization of air molecules and its application to the abatement of volatile organic compounds

    SciTech Connect

    Penetrante, B.M.; Hsiao, M.C.; Bardsley, J.N.; Merritt, B.T.; Vogtlin, G.E.; Wallman, P.H.; Kuthi, A.; Burkhart, C.P.; Bayless, J.R.

    1995-05-21

    In this paper the authors present data on the non-thermal plasma processing of two representative VOCs: carbon tetrachloride and methanol. The investigation used a compact electron beam reactor, and two types of discharge reactors: a pulsed corona and a dielectric-barrier discharge. To the knowledge of the authors, this is the first comparison of the energy efficiency of electron beam, pulsed corona and dielectric-barrier discharge processing of these VOCs under identical gas conditions. For most electrical discharge reactors the analysis suggests that the attainable electron mean energy is rather limited and cannot be significantly enhanced by changing the electrode configuration or voltage waveform. The experimental data confirms that there is no significant difference in the performance of the pulsed corona and dielectric-barrier discharge reactors. The authors observe that electron beam processing is remarkably more energy efficiency than electrical discharge processing in decomposing either of these VOC molecules. During electron beam processing, the specific energy consumption is consistent with the energy required for the ionization of the background air molecules. For carbon tetrachloride, the dominant decomposition pathway is dissociative electron attachment. For methanol, the dominant decomposition pathway is dissociative charge exchange.

  20. Momentum correlation of electron-hydrogen ionization

    NASA Astrophysics Data System (ADS)

    Sui-meng, Zhang; Zhang-jin, Chen

    1999-07-01

    Following the work of Berakdar, the momentum correlation in the three-body Coulomb continuum problem is considered by the introduction of effective Sommerfeld parameters for both symmetric and asymmetric geometry. The triple differential cross sections for electron impact ionization of atomic hydrogen at incident energies of 54.4 and 150eV in asymmetric geometry are calculated. Results are compared with the related measurements and the only existing theoretical results of the convergent close-coupling method. They are in good agreement with experiment, though some small quantitative discrepancies remain.

  1. 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

    SciTech Connect

    Ayinol, M.; Aydeniz, D.

    2016-03-25

    L shell ionization cross section and L{sub i} subshells ionization cross sections of Rn, Ra, Th, U, Pu atoms calculated. For each of atoms, ten different electron impact energy values (E{sub o}) 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. σ{sub L} total and σ{sub Li}(i = 1,2,3) subshells ionisation cross section values obtained for E{sub o} values in the energy range of E{sub Li} ionization threshold energy, σ{sub L} total and σ{sub Li} (i = 1,2,3) are increasing rapidly with E{sub o}. For a fixed E{sub o} = 3.E{sub Li}), while Z increases from 86electron-atom impact studies.

  2. 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.

  3. 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.

  4. 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.

  5. Electron ionization of H2O

    NASA Astrophysics Data System (ADS)

    King, Simon J.; Price, Stephen D.

    2008-11-01

    Relative partial ionization cross-sections and precursor-specific relative partial ionization cross-sections for fragment ions formed by electron ionization of H2O have been measured using time-of-flight mass spectrometry coupled with a 2D ion coincidence technique. We report data for the formation of H+, H2+, O2+, O+ and OH+ relative to the formation of H2O+, as a function of ionizing electron energy from 30 to 200 eV. This data includes, for the first time, measurements on the formation all positive ion pairs and ion triples by dissociative multiple electron ionization of H2O. Through determinations of the kinetic energy release involved in ion pair formation we provide further evidence that indirect processes contribute significantly to the yield of H+ + OH+ ion pairs below the vertical double ionization threshold.

  6. Following electron impact excitation of single (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) atom L subshells ionization cross section calculations by using Lotz's equation

    NASA Astrophysics Data System (ADS)

    Aydinol, Mahmut

    2017-02-01

    L shell and Li subshells ionization cross sections[σL and σLi i = 1, 2, 3 following electron impact on (Sc, Ti, V, Cr, Mn, Fe, Co, Ni) atoms calculated. By using Lotz' equation for non-relativistic cases in Matlab σL and σLi cross section values obtained for ten electron impact(Eo) values in the range of ELiionization threshold energy), σL and σLi are increasing rapidly with Eo. For a fixed Eo value(≈3.ELi), while Z value increases from 21≤Z≤28 σL and σLi decrease. Results show that for smaller values of Eo(close to ELi), x-ray yields formation of Li(i =1,2,3) subshells decreases while competing other yields are increase. Results may help to understand similar findings which obtained from other electron impact excitation of L shell σL, Li subshells σLi studies for single atoms.

  7. Following electron impact excitation of single (N, O, F, Ne, Na, Mg, Al, Si) atom L subshells ionization cross section calculations by using Lotz's equation

    NASA Astrophysics Data System (ADS)

    Aydinol, Mahmut

    2017-02-01

    L shell and L subshells ionization cross sections σL and σLi (i = 1, 2, 3) following electron impact on (N,O, F, Ne, Na, Mg, Al, Si) atoms calculated. By using Lotz' equation for nonrelativistic cases in Matlab σL and σLi cross section values obtained for ten electron impact(Eo) values in the range of ELiionization threshold energy), σL and σLi are increasing rapidly with Eo. For a fixed Eo value(≈3.ELi), while Z value increases from 7≤Z≤14 σL and σLi decrease. Results show that for smaller values of Eo(close to ELi), x-ray yields formation of Li(i=1,2,3) subshells decreases while competing other yields are increase. Results may help to understand similar findings which obtained from other electron impact excitation of L shell σL and subshells σLi studies for single atoms.

  8. Electron impact ionization of individual sub-shells and total of L and M shells of atomic targets with Z = 38–92

    NASA Astrophysics Data System (ADS)

    Haque, A. K. F.; Maaza, M.; Uddin, M. A.; Patoary, M. Atiqur R.; Ismail Hossain, M.; Basak, A. K.; Saha, B. C.; Mahbub, M. Selim

    2017-03-01

    We report an extension and modification of the MCN model of Haque et al (2013 Rad. Phys. Chem. 91 50–9) (XMCN) to study the electron impact ionization of inner L and M shells of neutral atoms by introducing new parameters of the MCN model. The extended XMCN model, including the relativistic effect, has been applied with success to evaluate ionization cross-sections of various atomic targets with Z = 38–92 for both individual subshells and total L-shell and the corresponding cross-sections for the M shell for Z = 79–92 at incident energies E Threshold ≤slant T ≤slant 1 GeV. A comparison with other available theoretical and experimental cross-sections reveals that our results reproduce the experimental measurements with a reasonable accuracy.

  9. Cross section database for carbon atoms and ions: Electron-impact ionization, excitation, and charge exchange in collisions with hydrogen atoms

    SciTech Connect

    Suno, Hiroya . E-mail: suno@jamstec.go.jp; Kato, Takako

    2006-07-15

    A database has been constructed consisting of the recommended cross sections for electron-impact excitation and ionization of carbon atoms and ions C, C{sup +}-C{sup 5+}, asl as for charge exchange processes between carbon ions C{sup +}-C{sup 6+} and hydrogen atoms. We have collected a large amount of theoretical and experimental cross section data from the literature, and have critically assessed their accuracy. The recommended cross sections, the best values for use, are expressed in the form of simple analytical functions. These are also presented in graphical form.

  10. Multiple-ionization of xenon atoms by positron impact

    NASA Technical Reports Server (NTRS)

    Kruse, Georg; Quermann, Andreas; Raith, Wilhelm; Sinapius, Guenther

    1990-01-01

    Previously the cross sections were measured for positronium formation and single ionization by positron impact for He and H2. With the same apparatus, slightly modified, the single and multiple ionization of xenon is now investigated. The principle of the method is the detection of ion and positron in time correlation which allows the discrimination of positronium formation (whereby the positron vanishes) and the destinction of single, double and triple impact ionization (which lead to different ion flight times from the gas target to the ion detector). By using secondary electrons from the positron moderator, similar measurements were performed on electron impact ionization. By comparing with literature values for electron multiple ionization cross sections, the detection-probability ratios were determined for the differently charged ions.

  11. Electron-impact ionization of H2O at low projectile energy: Internormalized triple-differential cross sections in three-dimensional kinematics

    NASA Astrophysics Data System (ADS)

    Ren, Xueguang; Amami, Sadek; Hossen, Khokon; Ali, Esam; Ning, ChuanGang; Colgan, James; Madison, Don; Dorn, Alexander

    2017-02-01

    We report a combined experimental and theoretical study of the electron-impact ionization of water (H2O ) at the relatively low incident energy of E0=81 eV in which either the 1 b1 or 3 a1 orbitals are ionized leading to the stable H2O+ cation. The experimental data were measured by using a reaction microscope, which can cover nearly the entire 4 π solid angle for the secondary electron emission over a range of ejection energies. We present experimental data for the scattering angles of 6∘ and 10∘ for the faster of the two outgoing electrons as a function of the detection angle of the secondary electron with energies of 5 and 10 eV. The experimental triple-differential cross sections are internormalized across the measured scattering angles and ejected energies. The experimental data are compared with predictions from two molecular three-body distorted-wave approaches: one applying the orientation-averaged molecular orbital (OAMO) approximation and one using a proper average (PA) over orientation-dependent cross sections. The PA calculations are in better agreement with the experimental data than the OAMO calculations for both the angular dependence and the relative magnitude of the observed cross-section structures.

  12. Measurements of K-shell ionization cross sections of Al and L-shell x-ray production cross sections of Se by intermediate-energy electron impact

    NASA Astrophysics Data System (ADS)

    Mei, C. S.; Wu, Y.; Yuan, Y.; Chang, C. H.; Qian, Z. C.; Zhu, J. J.; Moharram, Khalid

    2016-12-01

    The K-shell ionization cross sections of Al (Z = 13) and the total L-shell x-ray production cross sections of Se (Z = 34) from electron impacts with kinetic energies ranging from several keV to several tenths of keV have been measured by using an improved experimental setup. An Al target of monoatomic and grid carbon substrate, which consisted of ultrathin Al film (∼3 nm) deposited onto grid carbon substrate (∼200 nm) with a layer of monoatomic carbon between the film and the grid substrate, was first proposed and measured. In addition, targets of Al film (∼3 nm) and Se film (∼7.8 nm) deposited respectively onto thick carbon substrate (∼2 mm) were also measured. Our experimental results are compared with the distorted-wave Born approximation (DWBA) theory and experimental data from the literature. It has been observed that within the uncertainties, the DWBA agrees with our experimental measurements of K-shell ionization cross sections of Al and the total L-shell x-ray production cross sections of Se, and our measured data of Al K-shell ionization cross sections are consistent with the available experimental data. This is the first time that experimental data of Se-L-shell x-ray production cross sections in the intermediate-energy region have been published.

  13. Equivalent electron correlations in nonsequential double ionization of noble atoms

    NASA Astrophysics Data System (ADS)

    Dong, Shansi; Han, Qiujing; Zhang, Jingtao

    2017-02-01

    Electron correlation is encoded directly in the distribution of the energetic electrons produced in a recollision-impact double ionization process, and varies with the laser field and the target atoms. In order to get equivalent electron correlation effects, one should enlarge the laser intensity cubically and the laser frequency linearly in proportion to the second ionization potentials of the target atoms. The physical mechanism behind the transform is to keep the ponderomotive parameter unchanged when the laser frequency is enlarged. Project supported by the National Natural Science Foundation of China (Grant Nos. 61475168 and 11674231) and sponsored by Shanghai Gaofeng & Gaoyuan Project for University Academic Program Development (Zhang).

  14. 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

  15. Identification of fatty acids in fishes collected from the Ohio River using gas chromatography-mass spectrometry in chemical ionization and electron impact modes.

    PubMed

    Dayhuff, Le-Ellen; Wells, Martha J M

    2005-12-09

    Analyses of fatty acid (FA) composition in freshwater fishes promote understanding of the potential relationship between fish health or human nutrition and specific FAs. Therefore, the chemical identity of FAs in endemic fishes must be established. Paddlefish, sauger, and white bass were collected from the Ohio River. The structural identification of esterified FAs from fish-fillet lipids was conducted using gas chromatography-mass spectrometry (GC-MS). The same 13 FAs, composing more than 90% of the mass of FAs extracted by techniques used in this research, were found in all three species examined. Carbon chain length and degree and position of unsaturation were determined from the characteristic ionization and fragmentation of FA methyl esters (FAMEs) resulting from GC-MS electron impact (EI) and chemical ionization (CI) modes. Assignment of structure to the extracted FAs required complementary interpretation of both EI and CI MS. The EI spectra observed substantiate findings reported in the literature. The novelty of this research is in the thorough interpretation of CI spectra for which less data are available. The observations reported for analyses of fishes will be useful to all researchers studying FAs regardless of sample media.

  16. 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

  17. Theoretical Investigation of Wave-Vector-Dependent Analytical and Numerical Formulations of the Interband Impact-Ionization Transition Rate for Electron 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, and a more exact, numerical method of Y. Wang and K. F. Brennan. 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 formula, 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 (he 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 (he overlap integrals of the Bloch state which can only be

  18. 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

  19. Theoretical Investigation of Wave-Vector-Dependent Analytical and Numerical Formulations of the Interband Impact-Ionization Transition Rate for Electron 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, and a more exact, numerical method of Y. Wang and K. F. Brennan. 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 formula, 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 (he 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 (he overlap integrals of the Bloch state which can only be

  20. Three-body multiparameter correlations in electron-ion ionization

    SciTech Connect

    Golden, D.E.; Song, L.; Zhang, Y.; Mueller, D.W. )

    1993-06-05

    We have constructed an apparatus to measure multiparameter angular correlation between reaction products following electron impact ionization of ionic targets to obtain alignment and orientation information. With molecular targets, ground and excited state potential energy diagrams may also be obtained. For incident energies sufficiently large compared to the ionization energy, we will also study final-state interactions between the charged projectile and the outgoing electrons. We will measure the momentum of all raction products and provide a stringent experimental test of near threshold three-body theory which could lead to a general theoretical treatment for three particles interacting via a Coloumb field.

  1. Three-body multiparameter correlations in electron-ion ionization

    NASA Astrophysics Data System (ADS)

    Golden, D. E.; Song, L.; Zhang, Y.; Mueller, D. W.

    1993-06-01

    We have constructed an apparatus to measure multiparameter angular correlation between reaction products following electron impact ionization of ionic targets to obtain alignment and orientation information. With molecular targets, ground and excited state potential energy diagrams may also be obtained. For incident energies sufficiently large compared to the ionization energy, we will also study final-state interactions between the charged projectile and the outgoing electrons. We will measure the momentum of all raction products and provide a stringent experimental test of near threshold three-body theory which could lead to a general theoretical treatment for three particles interacting via a Coloumb field.

  2. Impact-Ionization Cooling in Laser-Induced Plasma Filaments

    SciTech Connect

    Filin, A.; Romanov, D. A.; Compton, R.; Levis, R. J.

    2009-04-17

    The ionization rates and subsequent electron dynamics for laser-induced plasma channels are measured for the noble gas series He, Ne, Ar, Kr, and Xe at 1.0 atm. The cw fluorescence emission increases superlinearly in the series from He to Xe in agreement with Ammosov-Delone-Krainov tunnel ionization calculations. The electron temperature after laser-induced plasma formation, measured by four-wave mixing, evolves from >20 eV to <1 eV kinetic energies with time constants ranging from 1 ns for He to 100 ps for Xe in agreement with an impact-ionization cooling model.

  3. Runaway electrons in a fully and partially ionized nonideal plasma

    SciTech Connect

    Ramazanov, T.S.; Turekhanova, K.M.

    2005-10-01

    This paper reports on a study of electron runaway for a nonideal plasma in an external electric field. Based on pseudopotential models of nonideal fully and partially ionized plasmas, the friction force was derived as a function of electron velocities. Dependences of the electron free path on plasma density and nonideality parameters were obtained. The impact of the relative number of runaway electrons on their velocity and temperature was considered for classical and semiclassical models of a nonideal plasma. It has been shown that for the defined intervals of the coupled plasma parameter, the difference between the relative numbers of runaway electron values is essential for various plasma models.

  4. 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 +}.

  5. 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

    2014-10-07

    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(+).

  6. Electron-induced double ionization of oriented methane molecules

    NASA Astrophysics Data System (ADS)

    Oubaziz, Dahbia; Aitelhadjali, Zakia; Quinto, Michele Arcangelo; Boulifa, Rachida; Champion, Christophe

    2017-06-01

    We report here a theoretical study of the target orientation effect on the total cross sections for the double ionization of methane molecules impacted by electrons. The theoretical description is performed within the first Born approximation. The initial state of the collisional system is composed of an electron projectile modeled by a plane wave and a molecular target described by a one-center wave function while the final state is constituted by a scattered electron described by a plane wave and two ejected electrons both represented by a Coulomb wave and coupled with a Gamow factor. Secondary electron energetic distributions and total cross sections are reported for particular target configurations. Strong orientation effects on the double-ionization process are pointed out in particular when scrutinized orbital by orbital.

  7. Electron Vortices in Femtosecond Multiphoton Ionization

    NASA Astrophysics Data System (ADS)

    Pengel, D.; Kerbstadt, S.; Johannmeyer, D.; Englert, L.; Bayer, T.; Wollenhaupt, M.

    2017-02-01

    Multiphoton ionization of potassium atoms with a sequence of two counter-rotating circularly polarized femtosecond laser pulses produces vortex-shaped photoelectron momentum distributions in the polarization plane describing Archimedean spirals. The pulse sequences are produced by polarization shaping and the three-dimensional photoelectron distributions are tomographically reconstructed from velocity map imaging measurements. We show that perturbative ionization leads to electron vortices with c6 rotational symmetry. A change from c6 to c4 rotational symmetry of the vortices is demonstrated for nonperturbative interaction.

  8. 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.

  9. Electronic transport in partially ionized water plasmas

    NASA Astrophysics Data System (ADS)

    French, Martin; Redmer, Ronald

    2017-09-01

    We use ab initio simulations based on density functional theory to calculate the electrical and thermal conductivities of electrons in partially ionized water plasmas at densities above 0.1 g/cm3. The resulting conductivity data are then fitted to analytic expressions for convenient application. For low densities, we develop a simple and fully analytic model for electronic transport in low-density plasmas in the chemical picture using the relaxation-time approximation. In doing so, we derive a useful analytic expression for electronic transport cross sections with neutral particles, based on a model potential. In the regime of thermal ionization, electrical conductivities from the analytic model agree with the ab initio data within a factor of 2. Larger deviations are observed for the thermal conductivity, and their origin is discussed. Our results are relevant for modeling the interior and evolution of water-rich planets as well as for technical plasma applications.

  10. Single differential electron impact ionization cross sections in the binary-encounter-Bethe approximation for the low binding energy regime

    NASA Astrophysics Data System (ADS)

    Guerra, M.; Amaro, P.; Machado, J.; Santos, J. P.

    2015-09-01

    An analytical expression based on the binary-encounter-Bethe model for energy differential cross sections in the low binding energy regime is presented. Both the binary-encounter-Bethe model and its modified counterpart are extended to shells with very low binding energy by removing the constraints in the interference term of the Mott cross section, originally introduced by Kim et al. The influence of the ionic factor is also studied for such targets. All the binary-encounter-Bethe based models presented here are checked against experimental results of low binding energy targets, such as the total ionization cross sections of alkali metals. The energy differential cross sections for H and He, at several incident energies, are also compared to available experimental and theoretical values.

  11. 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.

  12. X-ray-induced electron cascades in dielectrics modeled with XCASCADE code: effect of impact ionization cross sections

    NASA Astrophysics Data System (ADS)

    Medvedev, Nikita A.

    2015-05-01

    Characterization of a free-electron laser (FEL) pulse can be done with a pump-probe scheme, using an FEL pump and a visible light probe on an optically transparent solid-state target. With such experimental scheme, pulse duration can be monitored on a shot-to-shot basis. It relies on the changes in optical properties induced by the FEL excitation of electrons. Here we analyze effects of different cross sections used in the modeling of electron kinetics. XCASCADE, a Monte Carlo toolkit for modeling x-ray-induced electron cascades (N. Medvedev, Appl. Phys. B 118 (2015) 417), is used for this purpose. Two different cross sections are compared: atomic BEB model vs complex-dielectric function formalism that accounts for collective effects in solids. It is shown that for photon and electron energies above a few tens of eV, the both models coincide very closely. For lower energies in the VUV regime, the difference in the cross sections become more significant, nevertheless producing qualitatively similar electron kinetics and increase in the density of excited electrons.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Electron induced inelastic and ionization cross section for plasma modeling

    NASA Astrophysics Data System (ADS)

    Verma, Pankaj; Mahato, Dibyendu; Kaur, Jaspreet; Antony, Bobby

    2016-09-01

    The present paper reports electron impact total inelastic and ionization cross section for silicon, germanium, and tin tetrahalides at energies varying from ionization threshold of the target to 5000 eV. These cross section data over a wide energy domain are very essential to understand the physico-chemical processes involved in various environments such as plasma modeling, semiconductor etching, atmospheric sciences, biological sciences, and radiation physics. However, the cross section data on the above mentioned molecules are scarce. In the present article, we report the computation of total inelastic cross section using spherical complex optical potential formalism and the estimation of ionization cross section through a semi-empirical method. The present ionization cross section result obtained for SiCl4 shows excellent agreement with previous measurements, while other molecules have not yet been investigated experimentally. Present results show more consistent behaviour than previous theoretical estimates. Besides cross sections, we have also studied the correlation of maximum ionization cross section with the square root of the ratio of polarizability to ionization potential for the molecules with known polarizabilities. A linear relation is observed between these quantities. This correlation is used to obtain approximate polarizability volumes for SiBr4, SiI4, GeCl4, GeBr4, and GeI4 molecules.

  18. Detection and quantitation of amphetamine and methamphetamine: electron impact and chemical ionization with ammonia--comparative investigation on Shimadzu QP 5000 GC-MS system.

    PubMed

    Dallakian, P; Budzikiewicz, H; Brzezinka, H

    1996-01-01

    Gas chromatographic-mass spectrometric (GC-MS) analyses of amphetamine and methamphetamine with chemical ionization (CI) (NH3) and electron impact (EI) were compared after solid-phase extraction from urine. The optimal CI (NH3) conditions for amphetamines were selected; the CI mass spectra of amphetamine, methamphetamine, methylenedioxyamphetamine (MDA), methylenedioxymethamphetamine (MDMA), and methylenedioxyethylamphetamine (MDEA) were obtained. Amphetamine and methamphetamine were monitored as [M+H]+ ions in SIM mode. Under these conditions the GC-MS limits of detection and quantitation were determined for amphetamine (2.1 and 5.0 mg/L, respectively) and for methamphetamine (0.9 and 2.0 mg/L, respectively). The heptafluorobutanoyl (HFB) derivatives were used to increase the sensitivity of the GC-MS analysis of amphetamines. Under CI (NH3) conditions these compounds form mainly the cluster ions [M+NH4]+. For HFB-derivatives the limits of detection and quantitation for CI (NH3) were 95 and 170 micrograms/L, respectively, for amphetamine (m/z 349) and 90 and 160 micrograms/L, respectively, for methamphetamine (m/z 363). For EI they were 10 and 30 micrograms/L, respectively, for amphetamine (m/z 240) and 9 and 27 micrograms/L, respectively, for methamphetamine (m/z 254). The GC-MS-CI (NH3) technique was found to be suitable for confirmation of amphetamine and methamphetamine in urine samples in addition to the routine GC-MS-EI method.

  19. 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.

  20. 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

  1. 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.

  2. Electron- and proton-induced ionization of pyrimidine

    DOE PAGES

    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

  3. Total and ionization cross sections of electron scattering by fluorocarbons

    NASA Astrophysics Data System (ADS)

    Antony, B. K.; Joshipura, K. N.; Mason, N. J.

    2005-02-01

    Electron impact total cross sections (50-2000 eV) and total ionization cross sections (threshold to 2000 eV) are calculated for typical plasma etching molecules CF4, C2F4, C2F6, C3F8 and CF3I and the CFx (x = 1-3) radicals. The total elastic and inelastic cross sections are determined in the spherical complex potential formalism. The sum of the two gives the total cross section and the total inelastic cross section is used to calculate the total ionization cross sections. The present total and ionization cross sections are found to be consistent with other theories and experimental measurements, where they exist. Our total cross section results for CFx (x = 1-3) radicals presented here are first estimates on these species.

  4. Absolute cross sections for excitation of the 2s 2S-->2p 2P transition in B2+ and for electron-impact single ionization of B2+

    NASA Astrophysics Data System (ADS)

    Woitke, O.; Djurić, N.; Dunn, G. H.; Bannister, M. E.; Smith, A. C.; Wallbank, B.; Badnell, N. R.; Pindzola, M. S.

    1998-12-01

    Absolute cross sections for electron-impact excitation of the 2s 2S-->2p 2P transition of B2+ measured between 5.4 and 7.0 eV are presented. The results are in good agreement with the R-matrix-with-pseudostates (RMPS) calculation of Marchalant et al. [J. Phys. B 30, L435 (1997)]. Also presented are cross sections for electron-impact single ionization of B2+, including measurements between 25 and 200 eV and calculations using the RMPS and time-dependent close-coupling methods. The measured ionization cross sections are about 14% higher near the peak than previous measurements by Crandall et al. [Phys. Rev. A 34, 1757 (1986)], but agree well with experimental data of Hofmann et al. [Z. Phys. D 16, 113 (1990)] and with the present and other theoretical predictions.

  5. Dead space approximation for impact ionization in silicon

    NASA Astrophysics Data System (ADS)

    Spinelli, A.; Pacelli, A.; Lacaita, A. L.

    1996-12-01

    We demonstrate the validity of the dead space approximation for impact ionization in silicon. Monte Carlo simulations are used to obtain realistic ionization probabilities, and the corresponding avalanche gain in constant field structures is computed. We show that the hard-threshold dead space model is in good agreement with a more refined model taking into account soft-threshold effects, if an effective threshold energy of 3 eV is adopted for electrons. We also show that hole nonlocal effects do not significantly affect the result.

  6. 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.

  7. 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.

  8. 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.

  9. Electron ionization mass spectrum of tellurium hexafluoride.

    PubMed

    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 electron ionization mass spectrum of tellurium hexafluoride (TeF6) is reported for the first time. 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 odd fluoride bearing ions, TeF1(+) < TeF3(+) < TeF5(+), and a decreasing abundance was observed for the even fragment series, Te(F0)(+) > 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(+).

  10. 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+.

  11. Evidence for impact ionization in vanadium dioxide

    DOE PAGES

    Holleman, Joshua; Bishop, Michael M.; Garcia, Carlos; ...

    2016-10-17

    Pump-probe optical spectroscopy was used to investigate charge carrier multiplication via impact ionization in the M1 insulating phase of VO2. By comparing the transient reflectivities of the film when pumped at less than and then more than twice the band-gap energy, we observed an enhancement of the ultrafast response with the higher energy pump color while the film was still transiently in the insulating phase. We additionally identified multiple timescales within the charge dynamics and analyzed how these changed when the pump and probe wavelengths were varied. This experiment provided evidence that impact ionization acts efficiently as a carrier multiplicationmore » process in this prototypical strongly-correlated insulator.« less

  12. Evidence for impact ionization in vanadium dioxide

    SciTech Connect

    Holleman, Joshua; Bishop, Michael M.; Garcia, Carlos; Vellore Winfred, J. S. R.; Lee, Shinbuhm; Lee, Ho Nyung; Beekman, Christianne; Manousakis, Efstratios; McGill, Stephen A.

    2016-10-17

    Pump-probe optical spectroscopy was used to investigate charge carrier multiplication via impact ionization in the M1 insulating phase of VO2. By comparing the transient reflectivities of the film when pumped at less than and then more than twice the band-gap energy, we observed an enhancement of the ultrafast response with the higher energy pump color while the film was still transiently in the insulating phase. We additionally identified multiple timescales within the charge dynamics and analyzed how these changed when the pump and probe wavelengths were varied. This experiment provided evidence that impact ionization acts efficiently as a carrier multiplication process in this prototypical strongly-correlated insulator.

  13. Two-electron cusp in the double ionization of helium

    SciTech Connect

    Gulyas, L.; Sarkadi, L.; Igarashi, A.; Kirchner, T.

    2010-09-15

    We analyze the double ionization of He under the impact of 100 keV He{sup 2+} projectiles. The process is described within the framework of the impact parameter and frozen-correlation approximations where the one-electron events are treated by the continuum distorted wave method. Correlation between the emitted electrons, which plays an important role in forming the shape of the differential distribution of the electron emission, is described by the Coulomb density of states approximation (CDS). Special attention is paid to the region of the two-electron cusp that has been observed in a recent experiment for 100 keV He{sup 0}+He collisions [L. Sarkadi and A. Orban, Phys. Rev. Lett. 100, 133201 (2008)]. In the cusp region the correlated motion of the two electrons is influenced dominantly by the outgoing projectile, that is, the correlation function of the CDS treatment is expected to depend on the electron momenta measured relative to the projectile rather than to the target nucleus. A qualitative agreement with the experiment is achieved with a CDS model based on the use of such a projectile-centered correlation function that applies effective charges as given in the dynamically screened three-Coulomb wave function.

  14. Two-electron cusp in the double ionization of helium

    NASA Astrophysics Data System (ADS)

    Gulyás, L.; Sarkadi, L.; Igarashi, A.; Kirchner, T.

    2010-09-01

    We analyze the double ionization of He under the impact of 100 keV He2+ projectiles. The process is described within the framework of the impact parameter and frozen-correlation approximations where the one-electron events are treated by the continuum distorted wave method. Correlation between the emitted electrons, which plays an important role in forming the shape of the differential distribution of the electron emission, is described by the Coulomb density of states approximation (CDS). Special attention is paid to the region of the two-electron cusp that has been observed in a recent experiment for 100 keV He0+He collisions [L. Sarkadi and A. Orbán, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.100.133201 100, 133201 (2008)]. In the cusp region the correlated motion of the two electrons is influenced dominantly by the outgoing projectile, that is, the correlation function of the CDS treatment is expected to depend on the electron momenta measured relative to the projectile rather than to the target nucleus. A qualitative agreement with the experiment is achieved with a CDS model based on the use of such a projectile-centered correlation function that applies effective charges as given in the dynamically screened three-Coulomb wave function.

  15. The simultaneous separation and determination of chloropropanols in soy sauce and other flavoring with gas chromatography-mass spectrometry in negative chemical and electron impact ionization modes.

    PubMed

    Xu, Xiaomin; Ren, Yiping; Wu, Pinggu; Han, Jianlong; Shen, Xianghong

    2006-02-01

    Both gas chromatography-mass spectrometry in electron ionization (GC-MS-EI) and negative chemical ionization (GC-MS-NCI) modes are reported in this paper for the simultaneous determination of 1,3-dichloropropan-2-ol (1,3-DCP), 2,3-dichloropropan-1-ol (2,3-DCP), 3-chloropropane-1,2-diol (3-MCPD) and 2-chloropropane-1,3-diol (2-MCPD) in soy sauce and other flavoring. D(5)-3-MCPD (for 3-MCPD and 2-MCPD) and d(5)-1,3-DCP (for 1,3-DCP and 2,3-DCP) were used as the deuterium isotopic labelled internal standards. The feasibility of using heptafluorobutyric anhydride modified with triethylamine (HFBA-Et(3)N) as a new derivatization reagent to replace heptafluorobutyrylimidazole (HFBI) is proposed. Liquid/liquid extraction with hexane was introduced for high lipid content samples. A small survey was carried out of soy sauces (103 samples) and instant noodles (45 samples) and the applicability of GC-MS-NCI and GC-MS-EI was assessed in these different matrices.

  16. 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.

  17. Cosmic-ray electron injection from the ionization of nuclei.

    PubMed

    Morlino, Giovanni

    2009-09-18

    We show that the secondary electrons ejected from the ionization of heavy ions can be injected into the acceleration process that occurs at supernova remnant shocks. This electron injection mechanism works since ions are ionized during the acceleration when they move already with relativistic speed, just like ejected electrons do. Using the abundances of heavy nuclei measured in cosmic rays measured at the Earth, we estimate the electron/proton ratio at the source to be approximately 10;{-4}, big enough to account for the nonthermal synchrotron emission observed in young supernova remnants. We also show that the ionization process can limit the maximum energy that heavy ions can reach.

  18. 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.

  19. Electron Beam Diagnostics in Plasmas Based on Electron Beam Ionization

    NASA Astrophysics Data System (ADS)

    Leonhardt, Darrin; Leal-Quiros, Edbertho; Blackwell, David; Walton, Scott; Murphy, Donald; Fernsler, Richard; Meger, Robert

    2001-10-01

    Over the last few years, electron beam ionization has been shown to be a viable generator of high density plasmas with numerous applications in materials modification. To better understand these plasmas, we have fielded electron beam diagnostics to more clearly understand the propagation of the beam as it travels through the background gas and creates the plasma. These diagnostics vary greatly in sophistication, ranging from differentially pumped systems with energy selective elements to metal 'hockey pucks' covered with thin layers of insulation to electrically isolate the detector from the plasma but pass high energy beam electrons. Most importantly, absolute measurements of spatially resolved beam current densities are measured in a variety of pulsed and continuous beam sources. The energy distribution of the beam current(s) will be further discussed, through experiments incorporating various energy resolving elements such as simple grids and more sophisticated cylindrical lens geometries. The results are compared with other experiments of high energy electron beams through gases and appropriate disparities and caveats will be discussed. Finally, plasma parameters are correlated to the measured beam parameters for a more global picture of electron beam produced plasmas.

  20. 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.

  1. Laser-assisted positron-impact ionization of atomic hydrogen.

    PubMed

    Pan, Juan; Li, Shu-Min; Berakdar, Jamal

    2007-03-15

    We study the ionization of atomic hydrogen by a fast positron in the presence of an external linearly polarized laser field. We concentrate on the limit of a small momentum transfer and describe the fast positron's continuum states by Volkov wave functions. The ejected electron is described by a Coulomb-Volkov wave function. We are limited to small laser intensities such that the dressed state of the target is treatable within the time-dependent perturbation theory, even though the laser intensity is still quite high by laboratory standards. Numerical results for the triply differential cross sections and their dependencies on laser-field parameters are discussed and compared with the results of laser-assisted ionization by electron impact.

  2. Feasibility study of thin films deposited on a self-supporting carbon grid substrate target on the measurement of atomic inner-shell ionization cross-sections impacted by 3-30 keV electrons

    NASA Astrophysics Data System (ADS)

    Qian, Z. C.; Wu, Y.; Chang, C. H.; Yuan, Y.; Mei, C. S.; Zhu, J. J.; Moharram, K.

    2017-04-01

    In this paper, we have measured the Lα , Lβ and Mα β X-ray production cross-sections of the W element and the K-shell ionization cross-sections of the Al element impacted by 3-30 keV electrons. A new kind of target consisting of a thin film deposited on a self-supporting carbon grid substrate has been used in this work. The self-supporting carbon grid substrate is made of several layers of super-aligned carbon nanotube arrays (the mass thickness of each layer of super-aligned carbon nanotube arrays is 20 μg/cm2). As a comparison, three kinds of targets consisting of a) the studied element deposited onto four layers of super-aligned carbon nanotube arrays and separated from each other by one layer of single carbon atoms, b) the studied element deposited directly onto four layers of super-aligned carbon nanotube arrays, and c) the studied element deposited directly onto two layers of super-aligned carbon nanotube arrays, were respectively prepared to figure out which type is fit for the measurement of inner-shell ionization cross-sections induced by 3-30 keV electrons. The experimental data are compared with the distorted-wave Born approximation (DWBA) theoretical predictions and with the available experimental data from other references. The results show that the first and the second targets are both suitable for the inner-shell ionization cross-section measurements by 3-30 keV electrons, but the third target is not. Besides, we present the M-shell X-ray production cross-sections of the W element by 5-30 keV electrons in this paper for the first time.

  3. 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.

  4. Probing electron delays in above-threshold ionization

    SciTech Connect

    Zipp, Lucas J.; Natan, Adi; Bucksbaum, Philip H.

    2014-11-21

    Recent experiments have revealed attosecond delays in the emission of electrons from atoms ionized by extreme UV light, offering a glimpse into the ultrafast nature of light-induced electron dynamics. In this work, we extend these measurements to the strong-field above-threshold ionization (ATI) regime, by measuring delays in the photoemission of electrons from argon in the presence of an intense laser field. We probe the ATI process with a weak coherent reference, at half the laser frequency. The interfering ionization signal reveals the relative spectral phase of adjacent ATI channels, with an equivalent resolution of a few attoseconds. These relative delays depend on the strong field, and approach zero at higher intensity. Our phase measurements of ATI electrons show how strong fields alter ionization dynamics in atoms.

  5. Probing electron delays in above-threshold ionization

    DOE PAGES

    Zipp, Lucas J.; Natan, Adi; Bucksbaum, Philip H.

    2014-11-21

    Recent experiments have revealed attosecond delays in the emission of electrons from atoms ionized by extreme UV light, offering a glimpse into the ultrafast nature of light-induced electron dynamics. In this work, we extend these measurements to the strong-field above-threshold ionization (ATI) regime, by measuring delays in the photoemission of electrons from argon in the presence of an intense laser field. We probe the ATI process with a weak coherent reference, at half the laser frequency. The interfering ionization signal reveals the relative spectral phase of adjacent ATI channels, with an equivalent resolution of a few attoseconds. These relative delaysmore » depend on the strong field, and approach zero at higher intensity. Our phase measurements of ATI electrons show how strong fields alter ionization dynamics in atoms.« less

  6. Optimization of quadrupole ion storage mass spectrometric conditions for the analysis of selected polybrominated diphenyl ethers. Comparative approach with negative chemical ionization and electron impact mass spectrometry.

    PubMed

    Larrazábal, David; Angeles Martínez, Ma; Eljarrat, Ethel; Barceló, Damiá; Fabrellas, Begoña

    2004-10-01

    Gas chromatography coupled to quadrupole ion storage mass spectrometry (QISTMS) operating in the non-resonant mode is presented as an innovative approach for the analysis of selected polybrominated diphenyl ethers (PBDEs). Although reductions in complexity and time needed for optimization are achieved in comparison with the resonant option, precise adjustment of the mass spectrometric conditions is required. Differences in isolation and fragmentation patterns of target species with degree of bromination were observed. The reliability of the method was confirmed by using standard solutions through the evaluation of certain quality parameters such as accuracy (92-108%), injection repeatability and reproducibility (coefficient of variation below 10% and 15%, respectively). Detection limits ranged from 62 to 621 fg, providing sensitivity similar to that of negative chemical ionisation (NCIMS) and greater than that of electron ionization mass spectrometry. The applicability of QISTMS method to real samples and matrix effects were evaluated through the analysis of some PBDE congeners in a sewage sludge sample from a Spanish waste-water treatment plant. Comparable results were obtained using QISTMS and NCIMS. According to these observations, QISTMS performed in the non-resonant mode may constitute a low-cost, rapid and reliable alternative to high-resolution devices for the analysis of selected PBDEs in environmental samples.

  7. Terahertz-Induced Impact Ionization Effect in Semiconductor Heterojunctions

    NASA Astrophysics Data System (ADS)

    Cao, J. C.

    2005-10-01

    We have extended the balance equations to account for conduction-valence interband impact ionization (II) induced by an intense terahertz (THz) electromagnetic irradiation in two-dimensional semiconductors. We have studied the effect of II on electron transport and electron-hole pair generation-recombination rate in THz-driven InAs/AlSb heterojunctions (HJs). As many as needed multiphoton channels are self-consistently taken into account. Usually II acts as a cooling mechanism in semiconductors. In the present THz-radiation-driven case with a multiphoton process, the electron temperature with II, however, is higher than that without this process. We propose to explain the counterintuitive behavior of electron temperature in THz-radiation-driven HJs.

  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. Kinetic theory of transport processes in partially ionized reactive plasma, II: Electron transport properties

    NASA Astrophysics Data System (ADS)

    Zhdanov, V. M.; Stepanenko, A. A.

    2016-11-01

    The previously obtained in (Zhdanov and Stepanenko, 2016) general transport equations for partially ionized reactive plasma are employed for analysis of electron transport properties in molecular and atomic plasmas. We account for both elastic and inelastic interaction channels of electrons with atoms and molecules of plasma and also the processes of electron impact ionization of neutral particles and three-body ion-electron recombination. The system of scalar transport equations for electrons is discussed and the expressions for non-equilibrium corrections to electron ionization and recombination rates and the diagonal part of the electron pressure tensor are derived. Special attention is paid to analysis of electron energy relaxation during collisions with plasma particles having internal degrees of freedom and the expression for the electron coefficient of inelastic energy losses is deduced. We also derive the expressions for electron vector and tensorial transport fluxes and the corresponding transport coefficients for partially ionized reactive plasma, which represent a generalization of the well-known results obtained by Devoto (1967). The results of numerical evaluation of contribution from electron inelastic collisions with neutral particles to electron transport properties are presented for a series of molecular and atomic gases.

  10. 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.

  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.

  12. Excitation and ionization of 4He clusters by electrons

    NASA Astrophysics Data System (ADS)

    Buchenau, H.; Toennies, J. P.; Northby, J. A.

    1991-12-01

    Clusters are produced by expanding high pressure (P0≤20 bar), low temperature (T0≥5 K) helium gas through a 5 μm nozzle into a vacuum. The neutral beam time-of-flight distribution has three peaks which we associate with distinct groups of large and small clusters, and atoms. The beam is ionized by electron impact and the resulting time resolved charged fragment mass distribution reveals in addition to previously observed anomalies (``magic numbers'') a new strong He+4 signal at high source pressures and low temperatures. The dependence of the various charged and neutral metastable fragment currents on the bombarding electron energy reveals that each has a unique appearance potential. A comparison with the calculated energy required for an electron to create various electronic excitations in the interior of a large cluster indicates that the production and dynamical evolution of metastable 3S1 atomic and a 3Σ+u molecular excitations plays a significant role in the formation of charged fragments from large clusters, but that the production of detectable metastable cluster fragments apparently proceeds via decay of high lying excitonic states. The strong He+4 signal does not appear until the incident electron has about enough energy to create two metastable 3S1 excitations in a cluster. Thus we propose that this ion signal results from the recombination of a pair of a 3Σ+u molecular excitons in or on a large cluster, or possibly from the dynamical evolution of a metastable spin quartet bound hole-exciton pair.

  13. Application of laser induced electron impact ionization to the deposition chemistry in the hot-wire chemical vapor deposition process with SiH4-NH3 gas mixtures.

    PubMed

    Eustergerling, Brett; Hèden, Martin; Shi, Yujun

    2007-11-01

    The application of a laser-induced electron impact (LIEI) ionization source in studying the gas-phase chemistry of the SiH(4)/NH(3) hot-wire chemical vapor deposition (HWCVD) system has been investigated. The LIEI source is achieved by directing an unfocused laser beam containing both 118 nm (10.5 eV) vacuum ultraviolet (VUV) and 355 nm UV radiations to the repeller plate in a time-of-flight mass spectrometer. Comparison of the LIEI source with the conventional 118 nm VUV single-photon ionization (SPI) method has demonstrated that the intensities of the chemical species with ionization potentials (IP) above 10.5 eV, e.g., H(2), N(2) and He, have been significantly enhanced with the incorporation of the LIEI source. It is found that the SPI source due to the 118 nm VUV light coexists in the LIEI source. This allows simultaneous observations of parent ions with enhanced intensity from VUV SPI and their "fingerprint" fragmentation ions from LIEI. It is, therefore, an effective tool to diagnose the gas-phase chemical species involved with both NH(3) and SiH(4) in the HWCVD reactor. In using the LIEI source to SiH(4), NH(3) and their mixtures, it has been shown that the NH(3) decomposition is suppressed with the addition of SiH(4) molecules. Examination of the NH(3) decomposition percentage and the time to reach the N(2) and H(2) steady-state intensities for various NH(3)/SiH(4) mixtures suggests that the extent of the suppression is enhanced with more SiH(4) content in the mixture. With increasing filament temperatures, the negative effect of SiH(4) becomes less important.

  14. Electronic oscillations in ionized sodium nanoclusters

    NASA Astrophysics Data System (ADS)

    Bystryi, Roman G.; Morozov, Igor V.

    2015-01-01

    Irradiation of nanosized metallic clusters by femtosecond laser pulses of moderate intensities ({{10}12}-{{10}14} W c{{m}-2}) leads to creation of the so-called electron-ion nanoplasma with size-dependent properties. Electron oscillations in such plasma are of interest in view of resonance absorption or probing of cluster dynamics in experiments. We study the electronic oscillations via molecular dynamics simulations for interacting classical electrons and ions. In particular, surface and volume plasmons are analyzed depending on the cluster size, plasma density, the ion ordering parameter and the short range part of the interaction potential. The volume plasmons are observed only for clusters greater than a threshold cluster size. By means of GPU computing, the long-range Coulomb interactions between particles are treated without typical approximations such as PPPM or TreeMD.

  15. Electron impact ionization cross section studies of C2Fx (x = 1 - 6) and C3Fx (x = 1 - 8) fluorocarbon species

    NASA Astrophysics Data System (ADS)

    Gupta, Dhanoj; Choi, Heechol; Song, Mi-Young; Karwasz, Grzegorz P.; Yoon, Jung-Sik

    2017-05-01

    The total ionization cross section for C2Fx (x = 1 - 6) and C3Fx (x = 1 - 8) fluorocarbon species are studied with the Binary-Encounter Bethe (BEB) model using various orbital parameters calculated from restricted/unrestricted Hartree-Fock (RHF/UHF) and Density Functional Theory (DFT). All the targets were optimized for their minimal structures and energies with several ab-initio methods with the aug-cc-pVTZ basis set. Among them, the present results with RHF/UHF orbital energies showed good agreement with the experimental results for stable targets C2F6, C2F4, C3F6 and C3F8. The results with the DFT (ωB97X/ωB97X-D) showed a reasonable agreement with the recent calculation of Bull et al. [J.N. Bull, M. Bart, C. Vallance, P.W. Harland, Phys. Rev. A 88, 062710 (2013)] for C2F6, C3F6 and C3F8 targets. The ionization cross section for C2F, C2F2, C2F3, C3F, C3F2, C3F3, C3F4, C3F5 and C3F7 were computed for the first time in the present study. We have also computed the vertical ionization potentials and polarizability for all the targets and compared them with other experimental and theoretical values. A good agreement is found between the present and the previous results. The calculated polarizability in turn is used to study the correlation with maximum ionization cross section and in general a good correlation is found among them, confirming the consistency and reliability of the present data. The cross section data reported in this article are very important for plasma modeling especially related to fluorocarbon plasmas. Contribution to the Topical Issue "Atomic and Molecular Data and their Applications", edited by Gordon W.F. Drake, Jung-Sik Yoon, Daiji Kato, Grzegorz Karwasz.

  16. 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.

  17. Ionization rate in the presence of runaway electrons

    SciTech Connect

    Bulanov, S.V.; Lontano, M.; Sasorov, P.V.

    1997-04-01

    The role of a fast electron population, produced by the strong electric field driving the axial current in a capillary discharge, can be essential in order to justify the appreciable concentration of highly charged C ions (C{sup 5+}, C{sup 6+}) as observed in many experiments with low electron temperature. Under the assumption that a quasistationary state is established during the discharge, the runaway electron distribution function is determined analytically for Z{sub eff}{gt}1, following the approximated method developed by Lebedev [A. N. Lebedev, Sov. Phys. JETP {bold 21}, 931 (1965)]. The strong enhancement of the ionization rate, due to the presence of an electron tail in the energy range of the ionization potential, is then demonstrated. {copyright} {ital 1997 American Institute of Physics.}

  18. A Miniaturized Linear Wire Ion Trap with Electron Ionization and Single Photon Ionization Sources

    NASA Astrophysics Data System (ADS)

    Wu, Qinghao; Tian, Yuan; Li, Ailin; Andrews, Derek; Hawkins, Aaron R.; Austin, Daniel E.

    2017-05-01

    A linear wire ion trap (LWIT) with both electron ionization (EI) and single photon ionization (SPI) sources was built. The SPI was provided by a vacuum ultraviolet (VUV) lamp with the ability to softly ionize organic compounds. The VUV lamp was driven by a pulse amplifier, which was controlled by a pulse generator, to avoid the detection of photons during ion detection. Sample gas was introduced through a leak valve, and the pressure in the system is shown to affect the signal-to-noise ratio and resolving power. Under optimized conditions, the limit of detection (LOD) for benzene was 80 ppbv using SPI, better than the LOD using EI (137 ppbv). System performance was demonstrated by distinguishing compounds in different classes from gasoline.

  19. A Miniaturized Linear Wire Ion Trap with Electron Ionization and Single Photon Ionization Sources

    NASA Astrophysics Data System (ADS)

    Wu, Qinghao; Tian, Yuan; Li, Ailin; Andrews, Derek; Hawkins, Aaron R.; Austin, Daniel E.

    2017-01-01

    A linear wire ion trap (LWIT) with both electron ionization (EI) and single photon ionization (SPI) sources was built. The SPI was provided by a vacuum ultraviolet (VUV) lamp with the ability to softly ionize organic compounds. The VUV lamp was driven by a pulse amplifier, which was controlled by a pulse generator, to avoid the detection of photons during ion detection. Sample gas was introduced through a leak valve, and the pressure in the system is shown to affect the signal-to-noise ratio and resolving power. Under optimized conditions, the limit of detection (LOD) for benzene was 80 ppbv using SPI, better than the LOD using EI (137 ppbv). System performance was demonstrated by distinguishing compounds in different classes from gasoline.

  20. Detection of sputtered and evaporated carbon aggregates: relative and absolute electron ionization fragmentation yields

    NASA Astrophysics Data System (ADS)

    Mair, C.; Deutsch, H.; Becker, K.; Märk, T. D.; Vietzke, E.

    2001-03-01

    The present study is a first attempt to determine electron impact ionization efficiencies for C 2 and C 3. A novel method has been applied to obtain the partial cross-section values for the reactions C 2+e→C +,C 2+e→C 2+ and C 3+e→C +,C 3+e→C 2+ and C 3+e→C 3+. The neutral target consisting of C, C 2 and C 3 is produced by thermal evaporation from a heated graphite sample and the neutral precursors in the subsequent ionization process can be distinguished by their different flight-time distributions acquired in the evaporation process. The partial ionization cross-section ratios obtained in this experiment have been calibrated with calculated absolute total ionization cross section curves of C 2 and C 3 using the Deutsch-Märk (DM) formalism.

  1. 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.

  2. Attosecond Electron Correlation Dynamics in Double Ionization of Benzene Probed with Two-Electron Angular Streaking

    NASA Astrophysics Data System (ADS)

    Winney, Alexander H.; Lee, Suk Kyoung; Lin, Yun Fei; Liao, Qing; Adhikari, Pradip; Basnayake, Gihan; Schlegel, H. Bernhard; Li, Wen

    2017-09-01

    With a novel three-dimensional electron-electron coincidence imaging technique and two-electron angular streaking method, we show that the emission time delay between two electrons can be measured from tens of attoseconds to more than 1 fs. Surprisingly, in benzene, the double ionization rate decays as the time delay between the first and second electron emission increases during the first 500 as. This is further supported by the decay of the Coulomb repulsion in the direction perpendicular to the laser polarization. This result reveals that laser-induced electron correlation plays a major role in strong field double ionization of benzene driven by a nearly circularly polarized field.

  3. Frustrated double ionization in two-electron triatomic molecules

    NASA Astrophysics Data System (ADS)

    Chen, A.; Price, H.; Staudte, A.; Emmanouilidou, A.

    2016-10-01

    Using a semiclassical model, we investigate frustrated double ionization (FDI) in D3+ , a two-electron triatomic molecule, when driven by an intense, linearly polarized, near-infrared (800 nm) laser field. We compute the kinetic energy release of the nuclei and find a good agreement between experiment and our model. We explore the two pathways of FDI and show that, with increasing field strength, over-the-barrier ionization overtakes tunnel ionization as the underlying mechanism of FDI. Moreover, we compute the angular distribution of the ion fragments for FDI and identify a feature that can potentially be observed experimentally and is a signature of only one of the two pathways of FDI.

  4. Bethe binary-encounter peaks in the double-differential cross sections for high-energy electron-impact ionization of H2 and He

    NASA Astrophysics Data System (ADS)

    Chatterjee, S.; Agnihotri, A. N.; Stia, C. R.; Fojón, O. A.; Rivarola, R. D.; Tribedi, L. C.

    2010-11-01

    We study the Bethe binary-encounter (BE) region in the ejected-electron double-differential emission spectrum of H2 and He targets in collisions with 8-keV electrons. We compare the absolute cross sections for these isoelectronic systems at high emission energies. The experimental data are analyzed in terms of a state-of-the-art theoretical model based on a two-effective-center approximation. In the case of the H2 molecule the binary peak in the double-differential cross sections (DDCS) is enhanced due to the two-center Young-type interference. The observed undulation in the DDCS ratio is explained in terms of the combined contributions of the Compton profile mismatch and the interference effect. The influence of the interference effect is thus observed for higher-energy electrons compared to most of the earlier studies which focused on low-energy electrons produced in soft collisions.

  5. Bethe binary-encounter peaks in the double-differential cross sections for high-energy electron-impact ionization of H{sub 2} and He

    SciTech Connect

    Chatterjee, S.; Agnihotri, A. N.; Tribedi, L. C.; Stia, C. R.; Fojon, O. A.; Rivarola, R. D.

    2010-11-15

    We study the Bethe binary-encounter (BE) region in the ejected-electron double-differential emission spectrum of H{sub 2} and He targets in collisions with 8-keV electrons. We compare the absolute cross sections for these isoelectronic systems at high emission energies. The experimental data are analyzed in terms of a state-of-the-art theoretical model based on a two-effective-center approximation. In the case of the H{sub 2} molecule the binary peak in the double-differential cross sections (DDCS) is enhanced due to the two-center Young-type interference. The observed undulation in the DDCS ratio is explained in terms of the combined contributions of the Compton profile mismatch and the interference effect. The influence of the interference effect is thus observed for higher-energy electrons compared to most of the earlier studies which focused on low-energy electrons produced in soft collisions.

  6. 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.

  7. 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.

  8. Reversal electron attachment ionizer for detection of trace species

    NASA Technical Reports Server (NTRS)

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

    1989-01-01

    An in-line reversal electron, high-current ionizer capable of focusing a beam of electrons to a reversal region and executing a reversal of the 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.

  9. 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.

  10. 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.

  11. 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.

  12. Electron gyroharmonic effects in ionization and electron acceleration during high-frequency pumping in the ionosphere.

    PubMed

    Gustavsson, B; Leyser, T B; Kosch, M; Rietveld, M T; Steen, A; Brändström, B U E; Aso, T

    2006-11-10

    Optical emissions and incoherent scatter radar data obtained during high-frequency electromagnetic pumping of the ionospheric plasma from the ground give data on electron energization in an energy range from 2 to 100 eV. Optical emissions at 4278 A from N2+ that require electrons with energies above the 18 eV ionization energy give the first images ever of pump-induced ionization of the thermosphere. The intensity at 4278 A is asymmetric around the ionospheric electron gyroharmonic, being stronger above the gyroresonance. This contrasts with emissions at 6300 A from O(1D) and of electron temperature enhancements, which have minima at the gyroharmonic but have no apparent asymmetry. This direct evidence of pump-induced ionization contradicts previous indirect evidence, which indicated that ionization is most efficiently produced when the pump frequency was below the gyroharmonic.

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

    NASA Technical Reports Server (NTRS)

    Zwickl, R. D.; Baker, D. N.; Bame, S. J.; Feldman, W. C.; Fuselier, S. A.

    1986-01-01

    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.

  14. Symmetry breaking and hole localization in multiple core electron ionization.

    PubMed

    Carravetta, V; Ågren, H

    2013-08-08

    Motivated by recent opportunitites to study hollow molecules with multiple core holes offered by X-ray free electron lasers, we revisit the core-hole localization and symmetry breaking problem, now studying ionization of more than one core electron. It is shown, using a N2 molecule with one, two, three, and four core holes, for example, that in a multiconfigurational determination of the core ionization potentials employing a molecular point group with broken inversion symmetry, one particular configuration is sufficient to account for the symmetry breaking relaxation energy in an independent particle approximation in the case of one or three holes, whereas the choice of point group symmetry is unessential for two and four holes. The relaxation energy follows a quadratic dependence on the number of holes in both representations.

  15. 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.

  16. 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.

  17. Electron cascades in sensors for optical detection of ionizing radiation

    SciTech Connect

    London, Richard A.; Lowry, Mark E.; Vernon, Stephen P.; Stewart, Richard E.

    2013-10-21

    A new class of high-speed detectors, called RadOptic detectors, measures ionizing radiation incident on a transparent semiconductor by sensing changes in the refractive index with an optical probe beam. We describe the role of radiation-initiated electron cascades in setting the sensitivity and the spatial and temporal resolution of RadOptic detectors. We model electron cascades with both analytical and Monte Carlo computational methods. We find that the timescale for the development of an electron cascade is less than of order 100 fs and is not expected to affect the time response of a detector. The characteristic size of the electron cloud is typically less than 2 μm, enabling high spatial resolution in imaging systems. The electron-hole pair density created by single x-rays is much smaller than the saturation density and, therefore, single events should not saturate the detector.

  18. Laboratory astrophysics with ion-beams: Cross sections for dielectronic recombination, photoionization and electron-impact ionization from heavy-ion storage-rings and synchrotron light-sources

    NASA Astrophysics Data System (ADS)

    Schippers, Stefan

    2010-03-01

    Laboratory experiments yield vitally needed benchmarks of atomic data for plasma modeling. An effort to provide rate coefficients for dielectronic recombination (DR) and electron impact ionization (EII) of highly charged atomic ions is being carried out at the Heidelberg heavy-ion storage ring TSRfootnotetextE. W. Schmidt et al., ApJL 641 (2006) L157; A&A 492 (2008) 265; M. Lestinsky et al., ApJ 698 (2009) 648 and references therein.. Popular compilations of DR data sometimes underestimate low-temperature DR rate coefficients by orders of magnitude as has already been suspected e.g. for Fe-M shell ions on the basis of the modeling of x-ray spectra from active galactic nucleifootnotetextH. Netzer, ApJ 604 (2004) 551; S. Kraemer et al., Apj 604 (2004) 556.. Even modern theoretical calculations often deviate strongly from our experimental results. This is due to the fundamental difficulty to calculate low-energy DR resonance positions of complex ions with sufficient accuracy. For these ions, storage-ring DR experiments are the only reliable source for low-temperature DR data. Astrophysically relevant results from storage-ring EII measurements and photon-ion experiments at synchrotron light sources will also be presented.

  19. Quantum efficiencies exceeding unity due to impact ionization in silicon solar cells

    NASA Astrophysics Data System (ADS)

    Kolodinski, Sabine; Werner, Jürgen H.; Wittchen, Thomas; Queisser, Hans J.

    1993-10-01

    Absolute measurements demonstrate internal quantum efficiencies in silicon solar cells to exceed unity for photon energies above the first direct band gap and to show distinct spectral features that correspond to specific points in the Brillouin zone. Ultraviolet radiation can generate hot carriers with sufficient energy to cause impact ionization which results in two electron hole pairs per incident photon.

  20. Interference oscillations in the angular distribution of laser-ionized electrons near ionization threshold.

    PubMed

    Arbó, D G; Yoshida, S; Persson, E; Dimitriou, K I; Burgdörfer, J

    2006-04-14

    We analyze the two-dimensional momentum distribution of electrons ionized by few-cycle laser pulses in the transition regime from multiphoton absorption to tunneling by solving the time-dependent Schrödinger equation and by a classical-trajectory Monte-Carlo simulation with tunneling (CTMC-T). We find a complex two-dimensional interference pattern that resembles above threshold ionization (ATI) rings at higher energies and displays Ramsauer-Townsend-type diffraction oscillations in the angular distribution near threshold. CTMC-T calculations provide a semiclassical explanation for the dominance of selected partial waves. While the present calculation pertains to hydrogen, we find surprising qualitative agreement with recent experimental data for rare gases [A. Rudenko, J. Phys. B 37, L407 (2004)].

  1. 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.

  2. Electronic relativistic effects on K-shell ionization by low-energy protons

    SciTech Connect

    Mukoyama, T.; Sarkadi, L.

    1981-01-01

    K-shell ionization cross sections by low-energy proton impact have been calculated in the relativistic plane-wave Born approximation, taking into account the effects of binding-energy increase and Coulomb deflection. The calculated values are compared with the recent experimental cross sections of Zander and Andrews. It is found that the use of Dirac wave functions for target electrons improves agreement with the experimental results, but the theoretical predictions are still systematically higher at the lower proton energies.

  3. 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.

  4. 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.

  5. 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.

  6. 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.

  7. Examination of a molecular se beam by mass spectrometry with electron ionization

    NASA Astrophysics Data System (ADS)

    Zavilopulo, A. N.; Shpenik, O. B.; Mylymko, A. M.

    2017-03-01

    The methodology and results of mass-spectrometric studies of producing positive ions as a result of the dissociative ionization of a molecular selenium beam by electron impact are discussed. The appearance energies of fragment ions were determined from the ionization efficiency curves. The dynamics of production of molecular selenium ions in the temperature range of 420-500 K was also examined. The energy dependences of efficiency of production of singly charged Se n + ions for n = 1-4 and the doubly charged selenium ion in the interval from the threshold to 36 eV were studied for the first time. The observed specific features of effective ionization cross sections were analyzed.

  8. 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.

  9. Characterization of breakdown behavior of diamond Schottky barrier diodes using impact ionization coefficients

    NASA Astrophysics Data System (ADS)

    Driche, Khaled; Umezawa, Hitoshi; Rouger, Nicolas; Chicot, Gauthier; Gheeraert, Etienne

    2017-04-01

    Diamond has the advantage of having an exceptionally high critical electric field owing to its large band gap, which implies its high ability to withstand high voltages. At this maximum electric field, the operation of Schottky barrier diodes (SBDs), as well as FETs, may be limited by impact ionization, leading to avalanche multiplication, and hence the devices may breakdown. In this study, three of the reported impact ionization coefficients for electrons, αn, and holes, αp, in diamond at room temperature (300 K) are analyzed. Experimental data on reverse operation characteristics obtained from two different diamond SBDs are compared with those obtained from their corresponding simulated structures. Owing to the crucial role played by the impact ionization rate in determining the carrier transport, the three reported avalanche parameters implemented affect the behavior not only of the breakdown voltage but also of the leakage current for the same structure.

  10. Low-energy electron rescattering in laser-induced ionization

    NASA Astrophysics Data System (ADS)

    Becker, W.; Goreslavski, S. P.; Milošević, D. B.; Paulus, G. G.

    2014-10-01

    The low-energy structure (LES) in the energy spectrum of above-threshold ionization of rare-gas atoms is reinvestigated from three different points of view. First, the role of forward rescattering in the completely classical simple-man model (SMM) is considered. Then, the corresponding classical electronic trajectories are retrieved in the quantum-mechanical ionization amplitude derived in the strong-field approximation augmented to allow for rescattering. Third, classical trajectories in the presence of both the laser field and the Coulomb field are scrutinized in order to see how they are related to the LES. It is concluded that the LES is already rooted in the SMM. The Coulomb field enhances the structure so that it can successfully compete with other contributions and become visible in the total spectrum.

  11. Complete solution of electronic excitation and ionization in electron-hydrogen molecule scattering

    SciTech Connect

    Zammit, Mark C.; Savage, Jeremy S.; Fursa, Dmitry V.; Bray, Igor

    2016-06-08

    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.

  12. Complete solution of electronic excitation and ionization in electron-hydrogen molecule scattering

    DOE PAGES

    Zammit, Mark C.; Savage, Jeremy S.; Fursa, Dmitry V.; ...

    2016-06-08

    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.

  13. 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.

  14. 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.

  15. Dissipative many-electron dynamics of ionizing systems

    NASA Astrophysics Data System (ADS)

    Tremblay, Jean Christophe; Klinkusch, Stefan; Klamroth, Tillmann; Saalfrank, Peter

    2011-01-01

    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.

  16. Unambiguous ionization amplitudes for electron-hydrogen scattering

    SciTech Connect

    Bartlett, P. L.; Bray, I.; Jones, S.; Stelbovics, A. T.; Kadyrov, A. S.; Bartschat, K.; Ver Steeg, G. L.; Scott, M. P.; Burke, P. G.

    2003-08-01

    According to quantum collision theory, scattering amplitudes are complex numbers, which are completely defined by their magnitude and phase. Although the phase information is generally not determined entirely in collision experiments, the phases are well defined and can be used to check computational models. We use four state-of-the-art approaches to calculate the magnitude and phase of the electron-hydrogen ionization amplitude in the Temkin-Poet S-wave model. We demonstrate that the correct phase can be extracted for each method by using the appropriate final-state continuum functions.

  17. Ionization of pyridine: Interplay of orbital relaxation and electron correlation

    NASA Astrophysics Data System (ADS)

    Trofimov, A. B.; Holland, D. M. P.; Powis, I.; Menzies, R. C.; Potts, A. W.; Karlsson, L.; Gromov, E. V.; Badsyuk, I. L.; Schirmer, J.

    2017-06-01

    The valence shell ionization spectrum of pyridine was studied using the third-order algebraic-diagrammatic construction approximation scheme for the one-particle Green's function and the outer-valence Green's function method. The results were used to interpret angle resolved photoelectron spectra recorded with synchrotron radiation in the photon energy range of 17-120 eV. The lowest four states of the pyridine radical cation, namely, 2A2(1 a2 -1), 2A1(7 a1 -1), 2B1(2 b1 -1), and 2B2(5 b2 -1), were studied in detail using various high-level electronic structure calculation methods. The vertical ionization energies were established using the equation-of-motion coupled-cluster approach with single, double, and triple excitations (EOM-IP-CCSDT) and the complete basis set extrapolation technique. Further interpretation of the electronic structure results was accomplished using Dyson orbitals, electron density difference plots, and a second-order perturbation theory treatment for the relaxation energy. Strong orbital relaxation and electron correlation effects were shown to accompany ionization of the 7a1 orbital, which formally represents the nonbonding σ-type nitrogen lone-pair (nσ) orbital. The theoretical work establishes the important roles of the π-system (π-π* excitations) in the screening of the nσ-hole and of the relaxation of the molecular orbitals in the formation of the 7a1(nσ)-1 state. Equilibrium geometric parameters were computed using the MP2 (second-order Møller-Plesset perturbation theory) and CCSD methods, and the harmonic vibrational frequencies were obtained at the MP2 level of theory for the lowest three cation states. The results were used to estimate the adiabatic 0-0 ionization energies, which were then compared to the available experimental and theoretical data. Photoelectron anisotropy parameters and photoionization partial cross sections, derived from the experimental spectra, were compared to predictions obtained with the continuum

  18. Ionization Induced Instability in an Electron Collecting Sheath,

    DTIC Science & Technology

    1985-06-01

    shown to be equivalent to a mean free path for ionization by electrons "Xie < 6iiii ’ ( DS /aJ’ where DS is the sheath thickness and at is a- geometry...CLASSIFICATION UNCLASSIFOEO/UNLIMI1TEO - SAME AS RPT IDTIC USERS .UNCLASSIFIED 22a. ’JAME OF RESPONSIBLE INDIVIDUAL 22b TELEPHONE NUMBER 22c CFF CE SyABCL Michael...anode does not emit, then we have the usual planar Child -Langmuir diode ( Child , 1911; Langmuir, 1913) where the separation DCL, potential drop V, and

  19. Field ionization of Rydberg atoms for high-brightness electron and ion beams

    NASA Astrophysics Data System (ADS)

    McCulloch, A. J.; Speirs, R. W.; Grimmel, J.; Sparkes, B. M.; Comparat, D.; Scholten, R. E.

    2017-06-01

    We present an ionization mechanism for use in a cold atom electron source with the goal of producing highly monochromatic electron beams. We experimentally produce a map of the Stark states of 85Rb below the ionization threshold and identify states that undergo selective field ionization. The properties of an electron beam produced by field-assisted ionization of such states are quantified. A theoretical framework is established to predict the improvement to beam quality when ionization is conducted above the ionization threshold, where ionization conditions are typically more favorable than below the threshold. Calculations suggest that selective ionization of Rydberg states may offer a pathway to the production of high-brightness, highly monochromatic ion and electron beams.

  20. Electron-impact ionization of atomic hydrogen

    SciTech Connect

    Baertschy, Mark D.

    2000-02-01

    Since the invention of quantum mechanics, even the simplest example of collisional breakup in a system of charged particles, e- + H → H+ + e- + e+, 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.

  1. 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.

  2. Two-effective-center approximation for proton-impact single ionization of hydrogen molecules

    NASA Astrophysics Data System (ADS)

    Ghanbari-Adivi, Ebrahim

    2015-10-01

    Some closed-form expressions are derived for the partial direct and indirect transition amplitudes for proton-impact single ionization of the hydrogen molecules using a first-order two-effective center continuum-wave approximation. The method satisfies the correct boundary conditions in the entrance channel. The basic assumption in this model is that when the active electron is ionized from one of the atomic centers in the molecule, the other scattering center is completely screened by the passive electron. Consequently, the transition amplitude can be expressed as a superposition of the partial ionization amplitudes from two independent scattering centers located at a constant distance from each other. The superposition of the partial amplitudes leads to different interference patterns for various orientations of the molecular target. The calculated cross sections are compared with the experiments and also with other theories. The comparison shows that the present results are reliable.

  3. State-specific transport properties of partially ionized flows of electronically excited atomic gases

    NASA Astrophysics Data System (ADS)

    Istomin, V. A.; Kustova, E. V.

    2017-03-01

    State-to-state approach for theoretical study of transport properties in atomic gases with excited electronic degrees of freedom of both neutral and ionized species is developed. The dependence of atomic radius on the electronic configuration of excited atoms is taken into account in the transport algorithm. Different cutoff criteria for increasing atomic radius are discussed and the limits of applicability for these criteria are evaluated. The validity of a Slater-like model for the calculation of state-resolved transport coefficients in neutral and ionized atomic gases is shown. For ionized flows, a method of evaluation for effective cross-sections of resonant charge-transfer collisions is suggested. Accurate kinetic theory algorithms for modelling the state-specific transport properties are applied for the prediction of transport coefficients in shock heated flows. Based on the numerical observations, different distributions over electronic states behind the shock front are considered. For the Boltzmann-like distributions at temperatures greater than 14,000 K, an important effect of electronic excitation on the partial thermal conductivity and viscosity coefficients is found for both neutral and ionized atomic gases: increasing radius of excited atoms causes a strong decrease in these transport coefficients. Similarly, the presence of electronically excited states with increased atomic radii leads to reduced diffusion coefficients. Nevertheless the overall impact of increasing effective cross-sections on the transport properties just behind the shock front under hypersonic reentry conditions is found to be minor since the populations of high-lying electronic energy levels behind the shock waves are low.

  4. Impact ionization in quantum well infrared photodetectors with different number of periods

    NASA Astrophysics Data System (ADS)

    Dong, Shan; Li, Ning; Chen, Sihai; Liu, Xihui; Lu, Wei

    2012-02-01

    This paper presents the detailed investigation of the photocurrent accompanied with impact ionization effect in In0.15Ga0.85As/GaAs multiple quantum well infrared photodetectors (QWIPs) with 10 and 50 periods. The sample with 50 periods exhibits remarkable enhancement at high electric field while a negative differential conductivity (NDC) phenomenon is observed in the sample with 10 periods. The enhancement at high electric field is attributed to impact ionization across the conduction-band-edge discontinuity between incident hot electrons and the electrons confined in the wells. The different behavior of these two samples indicates that the length of the multiplication region strongly affects the multiplication factor M. We also measured the photocurrent of GaAs/Al0.15Ga0.85As QWIPs, which do not show an obvious multiplication phenomenon. This is attributed to a different impact ionization coefficient α. A theoretical model of the multiplication factor M varying with impact ionization coefficient α, capture probability pc, and well number N is provided to clarify these phenomena and compared with experimental result.

  5. L-shell ionization of gold by nitrogen ion impact

    SciTech Connect

    Palinkas, J.; Bauer, C.; Brankoff, K.; Grambole, D.; Kalman, Gy.; Sarkadi, L.; Schlenk, B.; Torok, I.

    1983-04-01

    Measuring the angular distributions and the absolute intensities of the L x-ray lines of gold at 2.4-18.2 MeV nitrogen ion impact, the absolute subshell ionization cross-sections and the alignment parameter of the L/sub 3/-subshell have been determined and compared to the theoretical results.

  6. 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.

  7. Structure and Electronic Properties of Ionized PAH Clusters

    NASA Astrophysics Data System (ADS)

    Joblin, Christine; Kokkin, Damian L.; Sabbah, Hassan; Bonnamy, Anthony; Dontot, Leo; Rapacioli, Mathias; Simon, Aude; Spiegelman, Fernand; Parneix, Pascal; Pino, Thomas; Pirali, Olivier; Falvo, Cyril; Gamboa, Antonio; Brechignac, Philippe; Garcia, Gustavo A.; Nahon, Laurent

    2014-06-01

    Polycyclic aromatic hydrocarbon (PAH) clusters have been proposed as candidates for evaporating very small grains that are revealed by their mid-IR emission at the surface of UV-irradiated clouds in interstellar space. This suggestion is a motivation for further characterization of the properties of these clusters in particular when they are ionized. We have used a molecular beam coupled to the photoelectron-photoion coincidence spectrometer DELICIOUS II/ III at the VUV beamline DESIRS of the synchrotron SOLEIL to characterize the electronic properties of cationic coronene (C24H12) and pyrene (C16H10) clusters up to the pentamer and heptamer, respectively. These experimental results are analysed in the light of electronic structure calculations. Simulations of the properties of ionized PAH clusters are faced with the difficulty of describing charge delocalization in these large systems. We will show that recent developments combining a Density Functional Tight Binding method with Configuration Interaction scheme is successful in simulating the ionization potential, which gives strong confidence into the predicted structures for these PAH clusters. We will also present current effort to study charge transfer states by performing complementary measurements with the PIRENEA ion trap set-up. Joint ANR project GASPARIM, ANR-10-BLAN-501 M. Rapacioli, C. Joblin and P. Boissel Astron. & Astrophys., 429 (2005), 193-204. G. Garcia, H. Soldi-Lose and L. Nahon Rev. Sci. Instrum., 80 (2009), 023102; G. Garcia, B. Cunha de Miranda, M. Tia, S. Daly, L. Nahon, Rev. Sci. Instrum., 84 (2013), 053112 M. Rapacioli, A. Simon, L. Dontot and F. Spiegelman Phys. Status Solidi B, 249 (2) (2012), 245-258; L. Dontot, M. Rapacioli and F. Spiegelman (2014) submitted

  8. Orientation effect on the secondary-electron distributions for the HCl double ionization

    NASA Astrophysics Data System (ADS)

    Mokrani, S.; Aouchiche, H.; Champion, C.

    2017-07-01

    Multiple differential cross sections of the double ionization of hydrogen chloride molecule impacted by electrons are here provided within the first Born approximation. The incident and scattered electrons are represented by plane wave functions, whereas the target is described by means of a single-center molecular wave function. The two ejected electrons are modeled by Coulomb wave functions and a Gamow factor is introduced to take into account the Coulomb repulsion between the two outgoing particles. In this work, we study the relative contributions of the four outermost orbitals of the HCl molecule to the double ionization process in the particular case of two electrons ejected from different subshells. The multiple differential cross sections are analyzed for specific target orientations and compared in terms of magnitude and shape. We report a strong dependence of the cross sections versus the target orientation by pointing out the signature of the well-known double ionizing processes, namely, the shake-off and the two-step 1 mechanisms.

  9. 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.

  10. Ionization damage in NPN transistors caused by lower energy electrons

    NASA Astrophysics Data System (ADS)

    Li, Xingji; Xiao, Jingdong; Liu, Chaoming; Zhao, Zhiming; Geng, Hongbin; Lan, Mujie; Yang, Dezhuang; He, Shiyu

    2010-09-01

    Electrical degradation of two type NPN bipolar junction transistors (BJTs) with different emitter sizes was examined under exposures of 70 and 110 keV electrons. Base and collector currents as a function of base-emitter voltage were in-situ measured during exposure. Experimental results show that both the 70 and 110 keV electrons produce an evident ionization damage to the NPN BJTs. With increasing fluence, collector currents of the NPN BJTs hardly change in the whole range of base-emitter voltage from 0 to 1.2 V, while base currents increase in a gradually mitigative trend. Base currents vary more at lower base-emitter voltages than at higher ones for a given fluence. The change in the reciprocal of current gain at a fixed base-emitter voltage of 0.65 V increases non-linearly at lower fluences and tends to be gradually saturated at higher fluences. Sensitivity to ionization damage increases for BJTs with an emitter having a larger perimeter-to-area ratio.

  11. Young electron interference effects in atomic ionization collisions

    NASA Astrophysics Data System (ADS)

    Barrachina, R. O.

    2007-03-01

    Even though the concept of interference was already implicit in Newton's 1688 explanation of the anomaly of the tides in the Gulf of Tongkin, it was Thomas Young in his Bakerian Lectures who generalized this idea and applied it to a variety of situations. His celebrated interference experiment has been regarded as a prime demonstration of the wave-nature of light and, when applied to electrons, was recently voted as the most beautiful experiment in Physics. Since the foundational times of Modern Physics, the appearance of electron interference effects in different atomic processes has never failed to attract considerable attention. In this communication we review some interference mechanisms that occur in ionization collisions. Furthermore, we show how some of these mechanisms resemble at an atomic-size level three different versions of Young's famous demonstration.

  12. 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

  13. Measurements of absolute total and partial cross sections for the electron ionization of tungsten hexafluoride (WF6)

    NASA Astrophysics Data System (ADS)

    Basner, R.; Schmidt, M.; Becker, K.

    2004-04-01

    We measured absolute partial cross sections for the formation of positive ions followed by electron impact on tungsten hexafluoride (WF6) from threshold to 900 eV using a time-of-flight mass spectrometer (TOF-MS). Dissociative ionization processes resulting in seven different singly charged ions (F+, W+, WFx+, x=1-5) and five doubly charged ions (W2+, WFx2+, x=1-4) were found to be the dominant ionization channels. The ion spectrum at all impact energies is dominated by WF5+ fragment ions. At 120 eV impact energy, the partial WF5+ ionization cross section has a maximum value of 3.92×10-16 cm2 that corresponds to 43% of the total ion yield. The cross section values of all the other singly charged fragment ions at 120 eV range between 0.39×10-16 and 0.73×10-16 cm2. The ionization cross sections of the doubly charged ions are more than one order of magnitude lower than the cross section of WF5+. Double ionization processes account for 21% of the total ion yield at 120 eV. The absolute total ionization cross section of WF6 was obtained as the sum of all measured partial ionization cross sections and is compared with available calculated cross sections.

  14. Quantum control via a genetic algorithm of the field ionization pathway of a Rydberg electron

    NASA Astrophysics Data System (ADS)

    Gregoric, Vincent C.; Kang, Xinyue; Liu, Zhimin Cheryl; Rowley, Zoe A.; Carroll, Thomas J.; Noel, Michael W.

    2017-08-01

    Quantum control of the pathway along which a Rydberg electron field ionizes is experimentally and computationally demonstrated. Selective field ionization is typically done with a slowly rising electric field pulse. The (1/n*)4 scaling of the classical ionization threshold leads to a rough mapping between arrival time of the electron signal and principal quantum number of the Rydberg electron. This is complicated by the many avoided level crossings that the electron must traverse on the way to ionization, which in general leads to broadening of the time-resolved field ionization signal. In order to control the ionization pathway, thus directing the signal to the desired arrival time, a perturbing electric field produced by an arbitrary wave-form generator is added to a slowly rising electric field. A genetic algorithm evolves the perturbing field in an effort to achieve the target time-resolved field ionization signal.

  15. 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.

  16. Capillary atmospheric pressure electron capture ionization (cAPECI): a highly efficient ionization method for nitroaromatic compounds.

    PubMed

    Derpmann, Valerie; Mueller, David; Bejan, Iustinian; Sonderfeld, Hannah; Wilberscheid, Sonja; Koppmann, Ralf; Brockmann, Klaus J; Benter, Thorsten

    2014-03-01

    We report on a novel method for atmospheric pressure ionization of compounds with elevated electron affinity (e.g., nitroaromatic compounds) or gas phase acidity (e.g., phenols), respectively. The method is based on the generation of thermal electrons by the photo-electric effect, followed by electron capture of oxygen when air is the gas matrix yielding O2(-) or of the analyte directly with nitrogen as matrix. Charge transfer or proton abstraction by O2(-) leads to the ionization of the analytes. The interaction of UV-light with metals is a clean method for the generation of thermal electrons at atmospheric pressure. Furthermore, only negative ions are generated and neutral radical formation is minimized, in contrast to discharge- or dopant assisted methods. Ionization takes place inside the transfer capillary of the mass spectrometer leading to comparably short transfer times of ions to the high vacuum region of the mass spectrometer. This strongly reduces ion transformation processes, resulting in mass spectra that more closely relate to the neutral analyte distribution. cAPECI is thus a soft and selective ionization method with detection limits in the pptV range. In comparison to standard ionization methods (e.g., PTR), cAPECI is superior with respect to both selectivity and achievable detection limits. cAPECI demonstrates to be a promising ionization method for applications in relevant fields as, for example, explosives detection and atmospheric chemistry.

  17. Effect of B-B impact ionization on GRPVC output: a semiconductor-nuclear physics interface

    NASA Astrophysics Data System (ADS)

    Liakos, John K.

    2009-07-01

    We present calculations of efficiency, η, and open circuit voltage, Voc, of gamma ray photovoltaic cell (GRPVCs), in which impact ionization processes initiated by electrons in the conduction band (C-B) are taken into account. The contributions made to η and Voc by multiple e-h-pair production, caused by high energy γ-photons, are incorporated by summing up all possible higher order processes for given γ-photon energy. The discussion is divided into two types of impact ionization: (i) in type-I, pair creation by γ-photons and by subsequent photons due to electron impact are treated on an equal footing; (ii) in type-II the probability for impact ionization by electrons is a function of the γ-photon energy, and the latter is subject to constraints set by the energy threshold parameter Θe. We find that for a GRPVC energy gap Eg = 3.5 eV, and single e-h pair creation probability Pe-h =0.8, driven by Th-229m1(Eγ = variable, T1/2 = 45 h)-like nuclear isomers, Voc reaches the maximum Vocmax = 2.7 V at ηmax ≈ 95% when Eγ = 25 eV. In type-II processes the higher orders of e-h production do not make as high a contribution to η and Voc because of higher energy losses. Output power is also calculated for both types of processes and comparisons are made.

  18. 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

  19. Coulomb-tail effect of electron-electron interaction on nonsequential double ionization

    NASA Astrophysics Data System (ADS)

    Zhou, Yueming; Huang, Cheng; Lu, Peixiang

    2011-08-01

    With the classical ensemble model, we investigate the manifestations of the Coulomb tail of electron-electron interaction in nonsequential double ionization by comparing the results from the short-range electron-electron interaction with those from the Coulombic electron-electron interaction. At the intensity below the recollision threshold, the two-electron momentum distributions in the direction parallel to the laser polarization show an anticorrelated behavior for the Coulombic electron-electron interaction while a correlated behavior for the short-range interaction, which indicates the responsibility of the Coulomb tail of the electron-electron interaction for the experimentally observed anticorrelated emission [Y. Liu, S. Tschuch, A. Rudenko, M. Durr, M. Siegel, U. Morgner, R. Moshammer, and J. Ullrich, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.101.053001 101, 053001 (2008)]. In the transverse direction, for the Coulombic electron-electron interaction, the two electrons exhibit no effect of repulsion at an intensity below the recollision threshold while a strong repulsion effect at an intensity above the threshold, which becomes weaker as the laser intensity further increases. Back analysis shows that the role of the Coulomb tail of electron-electron interaction leads asymmetric energy sharing (AES) to be prevalent at recollision. This AES results in the two electrons leaving the ion at different times or with different initial momenta, which is responsible for the anticorrelated behavior in the parallel direction and the intensity-dependent repulsion effect in the transverse direction.

  20. Coulomb-tail effect of electron-electron interaction on nonsequential double ionization

    SciTech Connect

    Zhou Yueming; Huang Cheng; Lu Peixiang

    2011-08-15

    With the classical ensemble model, we investigate the manifestations of the Coulomb tail of electron-electron interaction in nonsequential double ionization by comparing the results from the short-range electron-electron interaction with those from the Coulombic electron-electron interaction. At the intensity below the recollision threshold, the two-electron momentum distributions in the direction parallel to the laser polarization show an anticorrelated behavior for the Coulombic electron-electron interaction while a correlated behavior for the short-range interaction, which indicates the responsibility of the Coulomb tail of the electron-electron interaction for the experimentally observed anticorrelated emission [Y. Liu, S. Tschuch, A. Rudenko, M. Durr, M. Siegel, U. Morgner, R. Moshammer, and J. Ullrich, Phys. Rev. Lett. 101, 053001 (2008)]. In the transverse direction, for the Coulombic electron-electron interaction, the two electrons exhibit no effect of repulsion at an intensity below the recollision threshold while a strong repulsion effect at an intensity above the threshold, which becomes weaker as the laser intensity further increases. Back analysis shows that the role of the Coulomb tail of electron-electron interaction leads asymmetric energy sharing (AES) to be prevalent at recollision. This AES results in the two electrons leaving the ion at different times or with different initial momenta, which is responsible for the anticorrelated behavior in the parallel direction and the intensity-dependent repulsion effect in the transverse direction.

  1. 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.; hide

    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.

  2. Electron shell ionization of atoms with classical, relativistic scattering.

    PubMed

    Ekanayake, N; Luo, S; Grugan, P D; Crosby, W B; Camilo, A D; McCowan, C V; Scalzi, R; Tramontozzi, A; Howard, L E; Wells, S J; Mancuso, C; Stanev, T; Decamp, M F; Walker, B C

    2013-05-17

    We investigate forward scattering of ionization from neon, argon, and xenon in ultrahigh intensities of 2 × 10(19) W/cm(2). Comparisons between the gases reveal the energy of the outgoing photoelectron determines its momentum, which can be scattered as far forward as 45° from the laser wave vector k(laser) for energies greater than 1 MeV. The shell structure in the atom manifests itself as modulations in the photoelectron yield and the width of the angular distributions. We arrive at an agreement with theory by using an independent electron model for the atom, a dipole approximation for the bound state interaction, and a relativistic, three-dimensional, classical radiation field including the laser magnetic field. The studies provide the atomic physics within plasmas, radiation, and particle acceleration in ultrastrong fields.

  3. Tunneling site of electrons in strong-field-enhanced ionization of molecules

    NASA Astrophysics Data System (ADS)

    Huang, Cheng; Lan, Pengfei; Zhou, Yueming; Zhang, Qingbin; Liu, Kunlong; Lu, Peixiang

    2014-10-01

    We investigated electron emissions in strong-field-enhanced ionization of asymmetric diatomic molecules by quantum calculations. It is demonstrated that the widely used intuitive physical picture, i.e., electron wave-packet direct ionization from the up-field site (DIU), is incomplete. Besides DIU, we find another two ionization channels: the field-induced excitation with subsequent ionization from the down-field site and that from the up-field site. The contributions from these channels depend on the molecular asymmetry and internuclear distance. Our work provides a more comprehensive physical picture for the long-standing issue about enhanced ionization of diatomic molecules.

  4. Ionization of biomolecular targets by ion impact: input data for radiobiological applications

    NASA Astrophysics Data System (ADS)

    de Vera, Pablo; Abril, Isabel; Garcia-Molina, Rafael; Solov'yov, Andrey V.

    2013-06-01

    In this work we review and further develop a semiempirical model recently proposed for the ion impact ionization of complex biological media. The model is based on the dielectric formalism, and makes use of a semiempirical parametrization of the optical energy-loss function of bioorganic compounds, allowing the calculation of single and total ionization cross sections and related quantities for condensed biological targets, such as liquid water, DNA and its components, proteins, lipids, carbohydrates or cell constituents. The model shows a very good agreement with experimental data for water, adenine and uracil, and allows the comparison of the ionization efficiency of different biological targets, and also the average kinetic energy of the ejected secondary electrons.

  5. Double gate impact ionization MOS transistor: Proposal and investigation

    NASA Astrophysics Data System (ADS)

    Yang, Zhaonian; Zhang, Yue; Yang, Yuan; Yu, Ningmei

    2017-02-01

    In this paper, a double gate impact ionization MOS (DG-IMOS) transistor with improved performance is proposed and investigated by TCAD simulation. In the proposed design, a second gate is introduced in a conventional impact ionization MOS (IMOS) transistor that lengthens the equivalent channel length and suppresses the band-to-band tunneling. The OFF-state leakage current is reduced by over four orders of magnitude. At the ON-state, the second gate is negatively biased in order to enhance the electric field in the intrinsic region. As a result, the operating voltage does not increase with the increase in the channel length. The simulation result verifies that the proposed DG-IMOS achieves a better switching characteristic than the conventional is achieved. Lastly, the application of the DG-IMOS is discussed theoretically.

  6. Soft x-ray spectra and collisional ionization equilibrium of iron ions with data upgrade of electron-ion collisions

    NASA Astrophysics Data System (ADS)

    Liang, G. Y.; Wei, H. G.; Zhao, G.; Zhong, J. Y.

    2016-06-01

    Line emissivities and ionic fraction in (non-)equilibrium are crucial for understanding the x-ray and extreme ultraviolet (EUV) spectra. These emission originate from electron-impact excitations for a level population of highly charged ions in coronal-like plasma. Recently, a large amount of excitation data was generated within the R-matrix framework by the computational atomic physics community, especially the UK APAP network. These data take resonances in electron-ion collisions into account appropriately, which enhances the effective excitation rates and also the line emissivities in x-ray and EUV regions. For ionization equilibrium data, the earlier compilation by Mazzotta et al (1998 Astron. Astrophys. Supp. Ser. 133 403) was used extensively by the astronomical community until the update by Bryans et al (2006 Astrophys. J. Supp. Ser. 167 343), as well as the compilation of Dere (2007 Astron. Astrophys. 466 771) for electron-impact ionization rates. In past years, many experimental measurements have been performed of highly charged iron ions in heavy-ion storage ring facilities. In this work, we will investigate the line emissivities and ionization equilibrium of highly charged iron ions by using recent theoretical or experimental data of electron-impact excitations and ionizations.

  7. Development of a highly-sensitive Penning ionization electron spectrometer using the magnetic bottle effect

    SciTech Connect

    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*(2{sup 3}S) 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.

  8. Motion of ionized electrons under the intense electromagnetic field of the beam

    SciTech Connect

    Kamiya, Y.

    1983-09-01

    The motion of an electron ionized from residual gas by the beam becomes relativistic in the case of a high-density beam as in SLC, while the ions produced by the beam remain nonrelativistic. The ionized relativistic electron will be dragged by the beam, and will go away from the beam (electron beam) before the beam passes, even for the very short bunch of SLC. In this note, we discuss the motions of electrons ionized by the electron beam or by the positron beam. We assume that the density of the beam is uniform and the shape cylindrical (transversely round and longitudinally rectangular).

  9. Few-cycle attosecond pulse chirp effects on asymmetries in ionized electron momentum distributions

    SciTech Connect

    Peng Liangyou; Tan Fang; Gong Qihuang; Pronin, Evgeny A.; Starace, Anthony F.

    2009-07-15

    The momentum distributions of electrons ionized from H atoms by chirped few-cycle attosecond pulses are investigated by numerically solving the time-dependent Schroedinger equation. The central carrier frequency of the pulse is chosen to be 25 eV, which is well above the ionization threshold. The asymmetry (or difference) in the yield of electrons ionized along and opposite to the direction of linear laser polarization is found to be very sensitive to the pulse chirp (for pulses with fixed carrier-envelope phase), both for a fixed electron energy and for the energy-integrated yield. In particular, the larger the pulse chirp, the larger the number of times the asymmetry changes sign as a function of ionized electron energy. For a fixed chirp, the ionized electron asymmetry is found to be sensitive also to the carrier-envelope phase of the few-cycle pulse.

  10. 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.

  11. Momentum spectra for single and double electron ionization of He in relativistic collisions

    NASA Astrophysics Data System (ADS)

    Wood, C. J.; Olson, R. E.; Schmitt, W.; Moshammer, R.; Ullrich, J.

    1997-11-01

    The complete momentum spectra for single and double ionization of He by 1-GeV/u (β=0.88) U92+ have been investigated using a classical trajectory Monte Carlo method corrected for the relativistic projectile. The 1/r12 electron-electron interaction has been included in the post-collision region for double ionization to incorporate the effects of both the nuclear-electron and electron-electron ionizing interactions, and to access the effects of electron correlation in the electron spectra. Experimental measurements were able to determine the longitudinal momentum spectra for single ionization; these observations are in accordance with the theoretical predictions for the three-body momentum balance between projectile, recoil ion, and ionized electron. In particular, the Lorentz contraction of the Coulomb interaction of the projectile manifests itself in the decrease of the post-collision interaction of the projectile with the electron and recoil ion, causing them to recoil back-to-back as in the case for a short electromagnetic pulse. This feature is clearly displayed in both the theoretical and experimental longitudinal momentum spectra, and by comparing to calculations that are performed at the same collision speed but do not include the relativistic potentials. Moreover, collision plane spectra of the three particles demonstrate that the momenta of the recoil ion and ionized electron are preferentially equal, and opposite, to each other. The electron spectra for double ionization show that the inclusion of the electron-electron interaction in the post-collision regime partitions the combined ionization momentum of the electrons so that the electrons are preferentially emitted in opposite azimuthal angles to one another. This is in contrast to calculations made assuming independent electrons.

  12. Enhanced production of low energy electrons by alpha particle impact

    PubMed Central

    Kim, Hong-Keun; Titze, Jasmin; Schöffler, Markus; Trinter, Florian; Waitz, Markus; Voigtsberger, Jörg; Sann, Hendrik; Meckel, Moritz; Stuck, Christian; Lenz, Ute; Odenweller, Matthias; Neumann, Nadine; Schössler, Sven; Ullmann-Pfleger, Klaus; Ulrich, Birte; Fraga, Rui Costa; Petridis, Nikos; Metz, Daniel; Jung, Annika; Grisenti, Robert; Czasch, Achim; Jagutzki, Ottmar; Schmidt, Lothar; Jahnke, Till; Schmidt-Böcking, Horst; Dörner, Reinhard

    2011-01-01

    Radiation damage to living tissue stems not only from primary ionizing particles but to a substantial fraction from the dissociative attachment of secondary electrons with energies below the ionization threshold. We show that the emission yield of those low energy electrons increases dramatically in ion–atom collisions depending on whether or not the target atoms are isolated or embedded in an environment. Only when the atom that has been ionized and excited by the primary particle impact is in immediate proximity of another atom is a fragmentation route known as interatomic Coulombic decay (ICD) enabled. This leads to the emission of a low energy electron. Over the past decade ICD was explored in several experiments following photoionization. Most recent results show its observation even in water clusters. Here we show the quantitative role of ICD for the production of low energy electrons by ion impact, thus approaching a scenario closer to that of radiation damage by alpha particles: We choose ion energies on the maximum of the Bragg peak where energy is most efficiently deposited in tissue. We compare the electron production after colliding He+ ions on isolated Ne atoms and on Ne dimers (Ne2). In the latter case the Ne atom impacted is surrounded by a most simple environment already opening ICD as a deexcitation channel. As a consequence, we find a dramatically enhanced low energy electron yield. The results suggest that ICD may have a significant influence on cell survival after exposure to ionizing radiation. PMID:21730184

  13. Enhanced production of low energy electrons by alpha particle impact.

    PubMed

    Kim, Hong-Keun; Titze, Jasmin; Schöffler, Markus; Trinter, Florian; Waitz, Markus; Voigtsberger, Jörg; Sann, Hendrik; Meckel, Moritz; Stuck, Christian; Lenz, Ute; Odenweller, Matthias; Neumann, Nadine; Schössler, Sven; Ullmann-Pfleger, Klaus; Ulrich, Birte; Fraga, Rui Costa; Petridis, Nikos; Metz, Daniel; Jung, Annika; Grisenti, Robert; Czasch, Achim; Jagutzki, Ottmar; Schmidt, Lothar; Jahnke, Till; Schmidt-Böcking, Horst; Dörner, Reinhard

    2011-07-19

    Radiation damage to living tissue stems not only from primary ionizing particles but to a substantial fraction from the dissociative attachment of secondary electrons with energies below the ionization threshold. We show that the emission yield of those low energy electrons increases dramatically in ion-atom collisions depending on whether or not the target atoms are isolated or embedded in an environment. Only when the atom that has been ionized and excited by the primary particle impact is in immediate proximity of another atom is a fragmentation route known as interatomic Coulombic decay (ICD) enabled. This leads to the emission of a low energy electron. Over the past decade ICD was explored in several experiments following photoionization. Most recent results show its observation even in water clusters. Here we show the quantitative role of ICD for the production of low energy electrons by ion impact, thus approaching a scenario closer to that of radiation damage by alpha particles: We choose ion energies on the maximum of the Bragg peak where energy is most efficiently deposited in tissue. We compare the electron production after colliding He(+) ions on isolated Ne atoms and on Ne dimers (Ne(2)). In the latter case the Ne atom impacted is surrounded by a most simple environment already opening ICD as a deexcitation channel. As a consequence, we find a dramatically enhanced low energy electron yield. The results suggest that ICD may have a significant influence on cell survival after exposure to ionizing radiation.

  14. 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.

  15. Decomposition reaction of the veterinary antibiotic ciprofloxacin using electron ionizing energy.

    PubMed

    Cho, Jae Young; Chung, Byung Yeoup; Lee, Kyeong-Bo; Lee, Geon-Hwi; Hwang, Seon Ah

    2014-12-01

    The application of electron ionizing energy for degrading veterinary antibiotic ciprofloxacin (CFX) in aqueous solution was elucidated. The degradation efficiency of CFX after irradiation with electron ionizing energy was 38% at 1 kGy, 80% at 5kGy, and 97% at 10 kGy. Total organic carbon of CFX in aqueous solution after irradiation with electron ionizing energy decreased 2% at 1 kGy, 18% at 5 kGy, and 53% at 10 kGy. The CFX degradation products after irradiation with electron ionizing energy were CFX1 ([M+H] m/z 330), CFX2 ([M+H] m/z 314), and CFX3 ([M+H] m/z 263). CFX1 had an F atom substituted with OH and CFX2 was expected to originate from CFX via loss of F or H2O. CFX3 was expected to originate from CFX via loss of the piperazynilic ring. Among the several radicals, hydrate electron (eaq(-)) is expected to play an important role in degradation of veterinary antibiotic during irradiation with electron ionizing energy. The toxicity of the degraded products formed during irradiation with electron ionizing energy was evaluated using microbes such as Escherichia coli, Pseudomonas putida, and Bacillus subtilis, and the results revealed that the toxicity decreased with irradiation. These results demonstrate that irradiation technology using electron ionizing energy is an effective was to remove veterinary antibiotics from an aquatic ecosystem.

  16. Extreme ultraviolet ionization of pure He nanodroplets: Mass-correlated photoelectron imaging, Penning ionization, and electron energy-loss spectra

    SciTech Connect

    Buchta, D.; Stienkemeier, F.; Mudrich, M.; Krishnan, S. R.; Moshammer, R.; Brauer, N. B.; Drabbels, M.; O’Keeffe, P.; Coreno, M.; Devetta, M.; Di Fraia, M.; Callegari, C.; Richter, R.; Prince, K. C.; Ullrich, J.

    2013-08-28

    The ionization dynamics of pure He nanodroplets irradiated by Extreme ultraviolet radiation is studied using Velocity-Map Imaging PhotoElectron-PhotoIon COincidence spectroscopy. We present photoelectron energy spectra and angular distributions measured in coincidence with the most abundant ions He{sup +}, He{sub 2}{sup +}, and He{sub 3}{sup +}. Surprisingly, below the autoionization threshold of He droplets, we find indications for multiple excitation and subsequent ionization of the droplets by a Penning-like process. At high photon energies we observe inelastic collisions of photoelectrons with the surrounding He atoms in the droplets.

  17. 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.

  18. 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.

  19. 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.

  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. Valence double ionization electron spectra of CH3F, CH3Cl and CH3I

    NASA Astrophysics Data System (ADS)

    Hult Roos, A.; Eland, J. H. D.; Koulentianos, D.; Squibb, R. J.; Karlsson, L.; Feifel, R.

    2017-07-01

    Valence double ionization electron spectra of the methyl fluoride, methyl chloride, and methyl iodide molecules have been recorded using a time-of-flight photoelectron-photoelectron coincidence technique. The spectra are interpreted by comparison with existing ionization data, Auger spectra, and theoretical calculations. The lowest double ionization energies have been found to be around 35.0 eV, 30.6 eV, and 26.67 eV for CH3F, CH3Cl and CH3I, respectively. These energies are also compared with the predictions and implications of an empirical rule for the lowest double ionization energy in molecules.

  2. 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.

  3. Single ionization and capture cross sections from biological molecules by bare projectile impact*

    NASA Astrophysics Data System (ADS)

    Quinto, Michele A.; Monti, Juan M.; Montenegro, Pablo D.; Fojón, Omar A.; Champion, Christophe; Rivarola, Roberto D.

    2017-02-01

    We report calculations on single differential and total cross sections for single ionization and single electron capture from biological targets, namely, vapor water and DNA nucleobasese molecules, by bare projectile impact: H+, He2+, and C6+. They are performed within the Continuum Distorted Wave - Eikonal Initial State approximation and compared to several existing experimental data. This study is oriented to the obtention of a reliable set of theoretical data to be used as input in a Monte Carlo code destined to micro- and nano- dosimetry.

  4. Double-differential cross sections for the ionization-excitation of the helium by fast proton and antiproton impact

    NASA Astrophysics Data System (ADS)

    Osváth, Z.; Nagy, L.

    2000-07-01

    Calculated double differential cross sections are presented for the simultaneous ionization and excitation into the 2p state of the helium atom by fast proton and antiproton impact. We have used the semiclassical impact parameter method and the transition amplitude was calculated in second-order perturbation approximation. We have investigated the dependence of the cross sections on the sign of the projectile charge, and have analyzed the influence on the results of the inclusion of electron correlation in the initial state.

  5. Transition from nonsequential to sequential double ionization in many-electron systems

    NASA Astrophysics Data System (ADS)

    Pullen, Michael G.; Wolter, Benjamin; Wang, Xu; Tong, Xiao-Min; Sclafani, Michele; Baudisch, Matthias; Pires, Hugo; Schröter, Claus Dieter; Ullrich, Joachim; Pfeifer, Thomas; Moshammer, Robert; Eberly, J. H.; Biegert, Jens

    2017-09-01

    Understanding strong-field double ionization of many-electron systems is an important fundamental problem with potential implications for molecular imaging within this regime. Using mid-IR radiation, we unambiguously identify the transition from nonsequential (e , 2 e ) to sequential double ionization in Xe at an intensity below 1014W /c m2 . Ionization from excited orbitals is found to be decisive at low intensities, but we demonstrate that such mechanisms are unimportant in the sequential regime. We utilize these facts to successfully image a molecular dication using laser-induced electron diffraction. This methodology can be used to study molecular dynamics on unprecedented few-femtosecond time scales.

  6. Effect of bound electron wave packet displacement on the multiphoton ionization of a lithium atom

    NASA Astrophysics Data System (ADS)

    Jheng, Shih-Da; Jiang, T. F.

    2017-10-01

    We study numerically the strong-field single ionization of a Li atom over a wide range of wavelengths (400 nm–1600 nm) in the multiphoton regime. By observing the behavior of the ionization probabilities and the occupation of excited states, we found that the occupied 2p state in different wavelength regimes exhibit different bound electron wave packet motion. The motion is in phase in the long-wavelength regime, out of phase in the short-wavelength regime and lagged when the wavelength is close to resonance with the 2p state. We then demonstrate how these different motions of the bound electron wave packet affect the ionization probability.

  7. State-resolved ultrafast dynamics of impact ionization in InSb

    PubMed Central

    Tanimura, H.; Kanasaki, J.; Tanimura, K.

    2014-01-01

    Impact ionization (IMP) is a fundamental process in semiconductors, which results in carrier multiplication through the decay of a hot electron into a low-energy state while generating an electron-hole pair. IMP is essentially a state selective process, which is triggered by electron-electron interaction involving four electronic states specified precisely by energy and momentum conservations. However, important state-selective features remain undetermined due to methodological limitations in identifying the energy and momentum of the states involved, at sufficient temporal resolution, to reveal the fundamental dynamics. Here we report state-resolved ultrafast hot electron dynamics of IMP in InSb, a semiconductor with the lowest band-gap energy. The ultrafast decay of state-resolved hot-electron populations and the corresponding population increase at the conduction band minimum are directly captured, and the rate of IMP is unambiguously determined. Our analysis, based on the direct knowledge of state-resolved hot electrons, provides far deeper insight into the physics of ultrafast electron correlation in semiconductors. PMID:25355408

  8. State-resolved ultrafast dynamics of impact ionization in InSb

    NASA Astrophysics Data System (ADS)

    Tanimura, H.; Kanasaki, J.; Tanimura, K.

    2014-10-01

    Impact ionization (IMP) is a fundamental process in semiconductors, which results in carrier multiplication through the decay of a hot electron into a low-energy state while generating an electron-hole pair. IMP is essentially a state selective process, which is triggered by electron-electron interaction involving four electronic states specified precisely by energy and momentum conservations. However, important state-selective features remain undetermined due to methodological limitations in identifying the energy and momentum of the states involved, at sufficient temporal resolution, to reveal the fundamental dynamics. Here we report state-resolved ultrafast hot electron dynamics of IMP in InSb, a semiconductor with the lowest band-gap energy. The ultrafast decay of state-resolved hot-electron populations and the corresponding population increase at the conduction band minimum are directly captured, and the rate of IMP is unambiguously determined. Our analysis, based on the direct knowledge of state-resolved hot electrons, provides far deeper insight into the physics of ultrafast electron correlation in semiconductors.

  9. Impact ionization can explain carrier multiplication in PbSe quantum dots.

    PubMed

    Franceschetti, A; An, J M; Zunger, A

    2006-10-01

    The efficiency of conventional solar cells is limited because the excess energy of absorbed photons converts to heat instead of producing electron-hole pairs. Recently, efficient carrier multiplication has been observed in semiconductor quantum dots. In this process, a single, high-energy photon generates multiple electron-hole pairs. Rather exotic mechanisms have been proposed to explain the efficiency of carrier multiplication in PbSe quantum dots. Using atomistic pseudopotential calculations, we show here that the more conventional impact ionization mechanism, whereby a photogenerated electron-hole pair decays into a biexciton in a process driven by Coulomb interactions between the carriers, can explain both the rate (<1 ps) and the energy threshold ( approximately 2.2 times the band gap) of carrier multiplication, without the need to invoke alternative mechanisms.

  10. Electron Impact Fragmentation of CH4 Molecules

    NASA Astrophysics Data System (ADS)

    Suzuki, Ryoji; Oguri, Kazuhiro; Makochekanwa, Casten; Kitajima, Masashi; Tanaka, Hiroshi

    2004-09-01

    Absolute electron-molecule impact dissociation cross sections are of interest in many fields of physics and chemistry, plasma etching of microelectronic devices and other industrial applications. However, experimental data on these cross sections is scarce mainly because of the difficulties involved in measuring neutral fragments [1]. Electron impact dissociation of CH4 molecules into the CH3 radicals have been investigated over the energy range 15.0 to 37.0 eV. The experimental procedure involves a dual-electron-beam in a two-stage collision system in conjunction with a quadrupole mass spectrometer (QMS). This is similar to the threshold-ionization mass spectrometry method [2]. Significant differences, in magnitude up to four times at 100 eV, exist between the only available absolute measurements by Sugai et al. [2] and Moore et al. [3]. Our data shows very close agreement with the Moore et al. data, which which show reasonable consistency with the available CH4 total dissociation data by Winters [3]. [1] L. S. Polak and D. I. Slovetsky, Int. J. Rad. Phys. Chem. 8, 257 (1976). [2] H. Sugai, H. Toyoda and T. Nakano, Jpn. J. Appl. Phys. 30, 2912 (1991). [3] H. F. Winters, J. Chem. Phys. 63, 3462 (1975).

  11. Footprints of electron correlation in strong-field double ionization of Kr close to the sequential-ionization regime

    NASA Astrophysics Data System (ADS)

    Li, Xiaokai; Wang, Chuncheng; Yuan, Zongqiang; Ye, Difa; Ma, Pan; Hu, Wenhui; Luo, Sizuo; Fu, Libin; Ding, Dajun

    2017-09-01

    By combining kinematically complete measurements and a semiclassical Monte Carlo simulation we study the correlated-electron dynamics in the strong-field double ionization of Kr. Interestingly, we find that, as we step into the sequential-ionization regime, there are still signatures of correlation in the two-electron joint momentum spectrum and, more intriguingly, the scaling law of the high-energy tail is completely different from early predictions on the low-Z atom (He). These experimental observations are well reproduced by our generalized semiclassical model adapting a Green-Sellin-Zachor potential. It is revealed that the competition between the screening effect of inner-shell electrons and the Coulomb focusing of nuclei leads to a non-inverse-square central force, which twists the returned electron trajectory at the vicinity of the parent core and thus significantly increases the probability of hard recollisions between two electrons. Our results might have promising applications ranging from accurately retrieving atomic structures to simulating celestial phenomena in the laboratory.

  12. 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.

  13. 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.

  14. Electron impact excitation of Hg/+/

    NASA Technical Reports Server (NTRS)

    Crandall, D. H.; Phaneuf, R. A.; Dunn, G. H.

    1974-01-01

    A crossed charged beam technique was employed in the investigation reported. The ion beam was crossed at right angles by a magnetically confined electron beam. Cross sections were determined as a function of electron impact energy. Considerable structure in the excitation cross section appears immediately above the threshold. It is pointed out that a primary application of cross sections is related to the calculation of plasma rate coefficients.

  15. Effects of inner electrons on atomic strong-field-ionization dynamics

    NASA Astrophysics Data System (ADS)

    Rapp, J.; Bauer, D.

    2014-03-01

    The influence of inner electrons on the ionization dynamics in strong laser fields is investigated in a wavelength regime where the inner electron dynamics is usually assumed to be negligible. The role of inner electrons is of particular interest for the application of frozen-core approximations and pseudopotentials in time-dependent density functional theory (TDDFT) and the single-active-electron (SAE) approximation in strong-field laser physics. Results of TDDFT and SAE calculations are compared with exact ones obtained by the numerical ab initio solution of the three-electron time-dependent Schrödinger equation for a lithium model atom. It is found that dynamical antiscreening, i.e., a particular form of dynamical core polarization, may substantially alter the ionization rate in the single-photon regime. Requirements for the validity of the approximations in the single and multiphoton ionization domain are identified.

  16. Electron attachment and electron ionization of acetic acid clusters embedded in helium nanodroplets.

    PubMed

    Ferreira da Silva, F; Jaksch, S; Martins, G; Dang, H M; Dampc, M; Denifl, S; Märk, T D; Limão-Vieira, P; Liu, J; Yang, S; Ellis, A M; Scheier, P

    2009-12-28

    The effect of incident electrons on acetic acid clusters is explored for the first time. The acetic acid clusters are formed inside liquid helium nanodroplets and both cationic and anionic products ejected into the gas phase are detected by mass spectrometry. The cation chemistry (induced by electron ionization at 100 eV) is dominated by production of protonated acetic acid (Ac) clusters, Ac(n)H(+), although some fragmentation is also observed. In the case of anion production (at 2.8 eV electron energy) there is a clear distinction between the monomer and the clusters. For the monomer the dominant product is the dehydrogenated species, [Ac-H](-), whereas for the clusters both the parent anion, Ac(n)(-), and the dehydrogenated species, [Ac(n)-H](-), have similar abundances. A particularly intriguing contrast between the monomer and cluster anions is that helium atoms are seen attached to the latter whereas no evidence of helium atom attachment is found for the monomer. This surprising observation is attributed to the formation of acyclic (head-to-tail) acetic acid clusters in helium nanodroplets, which have more favourable electronic properties for binding helium atoms. The acyclic clusters represent a local minimum on the potential energy surface and in the case of the dimer this is distinct from the cyclic isomer (the global minimum) identified in gas phase experiments.

  17. Quantitation of monosaccharide isotopic enrichment in physiologic fluids by electron ionization or negative chemical ionization GC/MS using di-O-isopropylidene derivatives.

    PubMed

    Hachey, D L; Parsons, W R; McKay, S; Haymond, M W

    1999-10-15

    The aldonitrile pentaacetate and other derivatives lack ions in the electron ionization (EI) spectra possessing an intact hexose structure and thus must be analyzed by chemical ionization GC/MS in order to study multiple isotopomers. We report methods for quantitation of hexose di-O-isopropylidene acetate (IPAc) or pentafluorobenzoyl (PFBz) esters. These were prepared in a two-step procedure using inexpensive reagents that do not adversely impact the isotopomer structure of the sugar. The acetate derivative possesses an abundant [M - CH3] ion in the EI spectrum which is suitable for quantitative analysis of isotopomers. The negative chemical ionization (NCI) spectrum of the corresponding pentafluorobenzoyl derivative has a dominant molecular anion. Moreover, the PFBz derivative is about 100-fold more sensitive than the acetate, which offers some advantages for analysis of minor hexoses found in plasma. Isotopic calibration curves of [U-13C]glucose are linear over the 0.1-60% tracer/tracee range tested. The useful range for isotopic tracer studies is 25-2500 pmol for EI analysis of the acetate derivative and 0.1-55 pmol for NCI analysis of PFBz derivative (sample amount injected). For most studies where sample size is not limited, EI-GC/MS analysis of the IPAc derivative is preferred. NCI-GC/MS analysis is reserved when sample size is limiting or when studies involve hexoses other than glucose that are normally present at low concentration.

  18. Double-differential cross sections for single ionization of simple polyatomic molecules by proton impact

    NASA Astrophysics Data System (ADS)

    Mondal, A.; Halder, S.; Mukherjee, S.; Mandal, C. R.; Purkait, M.

    2017-09-01

    A theoretical study of double-differential cross sections (DDCSs) for single ionization of CH4andNH3 molecules by collision with proton is presented at 0.25, 1, and 2 MeV, respectively. For the final state, we use a continuum distorted wave that contains the product of three-Coulomb distortion due to pairwise Coulombic interactions for which it is called the three-Coulomb wave model. In the entrance channel, the Coulomb distortion between the incoming projectile and the target is taken. In this model, the ground state of the polyatomic molecule is described by means of an accurate one-center molecular wave function, which is a linear combination of atomic orbitals. The contributions of DDCSs for different molecular orbitals of the polyatomic molecules to the spectrum of angular distributions at different electron emission energies have also been analyzed. Generally the preference for ionization depends on the binding energy of the active electron in molecular orbital in the ascending order of loosely bound electrons to more tightly bound electrons. At large ejected electron and projectile energy, the lesser bound electrons in the molecules dominate the DDCS at extreme forward emission angles. The present DDCS results are compared with available experimental and the theoretical findings. In case of ammonia molecules, good agreement is observed at all projectile energies, showing that the present model is sufficient to explain all the experimental data for double-differential cross sections. However, some degree of discrepancy is observed at 2 MeV proton impact for small electron emission angles when CH4 molecular target is considered.

  19. 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.

  20. 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)

  1. Quasimonoenergic collimated electrons from the ionization of nitrogen by a chirped intense laser pulse

    SciTech Connect

    Singh, Kunwar Pal; Sajal, Vivek

    2009-04-15

    A scheme is proposed for quasimonoenergic collimated GeV electrons generated during ionization of nitrogen by a chirped intense laser pulse. The electrons accelerated by a laser pulse without a frequency chirp are known for poor-quality beams. If a suitable frequency chirp is introduced, then the energy of the electrons increases significantly. It is shown that quasimonoenergic collimated GeV electrons can be produced using a right choice of laser spot size, frequency chirp, and pulse duration.

  2. Observation of an impact-parameter window in low-velocity ionizing collisions of Ne+ on Ne proceeding through quasimolecular states

    NASA Astrophysics Data System (ADS)

    Abdallah, M. A.; Wolff, W.; Wolf, H. E.; Cocke, C. L.; Stöckli, M.

    1998-11-01

    Target ionization in collisions of singly charged Ne+ ions with Ne has been investigated at projectile velocities from 0.25 to 0.55 a.u. using electron and recoil momentum imaging techniques. The momentum distributions of the ejected electrons were found to carry a distinct signature strongly suggesting that ionization is taking place by successive promotions through molecular orbitals. The observed recoil transverse momentum distributions are donut-shaped, indicating that single ionization is confined to a well-defined impact-parameter window.

  3. Green's function and Dyson orbital studies of the electronic structure of cage compounds and flexible molecules: A confrontation of many-body quantum mechanics with electron momentum, photo-electron and penning ionization electron spectroscopies

    NASA Astrophysics Data System (ADS)

    Knippenberg, Stefan

    Electron Momentum Spectroscopy (EMS) has emerged in recent years as a powerful experimental technique for studying the valence electronic structure of molecules and solids. With such experiments, orbital Momentum Distributions (MDs) are reconstructed from an angular analysis of electron impact ionization energies in the limit of the binary encounter, the Born (sudden) and the plane wave impulse approximations. In this thesis, the possibilities and limitations of ubiquitous orbital depictions (Hartree-Fock, Kohn-Sham and Dyson orbitals) are emphasized through theoretical studies of EMS experiments on two extreme cases: rigid cage compounds and conformationally versatile molecules. These EMS studies employ benchmark Green's Function (GF) calculations of valence one-electron and shake-up ionization spectra, as well as spherically averaged MDs derived from the related Dyson orbitals. Shortcomings of empirical analyses of EMS experiments based on Kohn-Sham orbitals and the related eigen-energies are comparatively discussed. Our work demonstrates that, owing to recent advances in energy and momentum resolution, EMS is now at a stage to very finely image the influence of the molecular conformation on orbital topologies, or changes in the effective topology of orbitals at varying distances from the molecular center. GF and Dyson orbital calculations are advocated in particular in order to safely identify complications such as distorted wave effects, vibronic coupling, nuclear dynamics, or a breakdown of the standard orbital picture of ionization. As an example, ionization experiments at large enough electron binding energies seem to result into an ultrafast intramolecular Coulomb decay and fragmentation of norbornane. On the experimental side, our work also advocates accurate enough determination of the absolute temperature in ionization experiments of all kind.

  4. Subcycle electron emission in sequential double ionization by elliptical laser pulses

    NASA Astrophysics Data System (ADS)

    Tong, Ai-Hong; Li, Ying-Bin

    2016-12-01

    Using a classical ensemble method, we have investigated sequential double ionization (SDI) of Ar atoms driven by elliptical laser pulses. The results show that the ion momentum distribution of the Ar atoms depends strongly on the pulse duration. As the pulse duration increases, the ion momentum distribution changes from two bands to four bands and then to six bands and finally to an eight-band structure. Back analysis of double ionization trajectories shows that the variation of the band structure originates from pulse duration dependent multiple ionization bursts of the second electron. Our calculations indicate that the subcycle electron emission in the SDI could be more easily accessed by using elliptical laser pulses with a longer wavelength. Moreover, we show that there is good correspondence between the scaled radial momentum and the ionization time.

  5. 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.

  6. Controlling and Reading Interference Structures Created by Strong Field Ionizing Attosecond Electron Wave Packets

    NASA Astrophysics Data System (ADS)

    Xie, X.; Roither, S.; Kartashov, D.; Zhang, L.; Persson, E.; Gräfe, S.; Schöffler, M.; Burgdörfer, J.; Baltuška, A.; Kitzler, M.

    We use cycle-sculpted two-color waveforms to drive electronic wavepackets generated by strong-field ionization from helium gas atoms and analyse their momentum spectra measured by electron-ion coincidence momentum spectroscopy. Varying the relative phase of the two colors allows to sculpt the ionizing field and hence to control the emission times and motion of the wavepackets on an attosecond timescale. We show that the measured electron momentum spectra contain interference patterns created by pairs of electron wavepackets that are released within a single laser-field-cycle. We experimentally distinguish these sub-cycle interference structures from above-threshold ionization (ATI) peaks and argue that they can be used to extract the sub-cycle phase-evolution of the laser-driven complex bound-state wavefunction.

  7. Electron-nuclear correlation in above-threshold double ionization of molecules

    NASA Astrophysics Data System (ADS)

    Lu, Peifen; Zhang, Wenbin; Gong, Xiaochun; Song, Qiying; Lin, Kang; Ji, Qinying; Ma, Junyang; He, Feng; Zeng, Heping; Wu, Jian

    2017-03-01

    We report on the experimental observation of photon energy sharing among two electrons and two ions ejected from a doubly ionized molecule exposed to an intense ultraviolet femtosecond laser pulse. Although two electrons are successively released one after the other, bridged by the nuclear motion via their interactions, photon energy sharing among four particles is observed as multiple energy conservation lines in their joint energy spectrum. For sequential double ionization of H2, the electron-nuclear joint energy spectrum allows us to identify three pathways towards the charge-resonance enhanced ionization of the stretching H2+ in strong laser fields. By counting the photon number absorbed by the molecule, we trace the accessibility, enhancement, and suppression of various pathways. The correlated electron-nuclear motion provides profound insights of the complicated strong-field dynamics of molecules.

  8. Study of Electron Ionization and Fragmentation of Non-hydrated and Hydrated Tetrahydrofuran Clusters

    NASA Astrophysics Data System (ADS)

    Neustetter, Michael; Mahmoodi-Darian, Masoomeh; Denifl, Stephan

    2017-05-01

    Mass spectroscopic investigations on tetrahydrofuran (THF, C4H8O), a common model molecule of the DNA-backbone, have been carried out. We irradiated isolated THF and (hydrated) THF clusters with low energy electrons (electron energy 70 eV) in order to study electron ionization and ionic fragmentation. For elucidation of fragmentation pathways, deuterated TDF (C4D8O) was investigated as well. One major observation is that the cluster environment shows overall a protective behavior on THF. However, also new fragmentation channels open in the cluster. In this context, we were able to solve a discrepancy in the literature about the fragment ion peak at mass 55 u in the electron ionization mass spectrum of THF. We ascribe this ion yield to the fragmentation of ionized THF clusters.

  9. Study of Electron Ionization and Fragmentation of Non-hydrated and Hydrated Tetrahydrofuran Clusters

    NASA Astrophysics Data System (ADS)

    Neustetter, Michael; Mahmoodi-Darian, Masoomeh; Denifl, Stephan

    2017-03-01

    Mass spectroscopic investigations on tetrahydrofuran (THF, C4H8O), a common model molecule of the DNA-backbone, have been carried out. We irradiated isolated THF and (hydrated) THF clusters with low energy electrons (electron energy 70 eV) in order to study electron ionization and ionic fragmentation. For elucidation of fragmentation pathways, deuterated TDF (C4D8O) was investigated as well. One major observation is that the cluster environment shows overall a protective behavior on THF. However, also new fragmentation channels open in the cluster. In this context, we were able to solve a discrepancy in the literature about the fragment ion peak at mass 55 u in the electron ionization mass spectrum of THF. We ascribe this ion yield to the fragmentation of ionized THF clusters.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. 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.

  15. CO2 impact ionization-driven plasma instability observed by Pioneer Venus Orbiter at Periapsis

    NASA Technical Reports Server (NTRS)

    Curtis, S. A.; Brace, L. H.; Niemann, H. B.; Scarf, F. L.

    1985-01-01

    Observations of enhanced ac electric field noise about Pioneer Venus periapsis are shown to be related to spacecraft-generated impact ionization of the ambient CO2. The frequency of the electric field noise is found to peak in the vicinity of the CO2(+) ion plasma frequency and to closely follow the form of the neutral CO2 density profile. When the electric field noise in all channels is normalized by the square root of the CO2 number density, the ratio is constant. Since the impact electron density measured by the Pioneer Venus Langmuir probe, is observed to scale directly with the neutral CO2, the growth of the electric field amplitude is found to be linear in time with a growth rate proportional to the CO2(+) ion plasma frequency. On the basis of these results the impact ionization-driven instability is shown to be the ion acoustic instability. Implications for the lack of observations by Pioneer Venus of reflected-O(+)-driven instabilities, as have been proposed for the space shuttle, are discussed.

  16. Nonequilibrium evolution of strong-field anisotropic ionized electrons towards a delayed plasma-state.

    PubMed

    Pasenow, B; Moloney, J V; Koch, S W; Chen, S H; Becker, A; Jaroń-Becker, A

    2012-01-30

    Rigorous quantum calculations of the femtosecond ionization of hydrogen atoms in air lead to highly anisotropic electron and ion angular (momentum) distributions. A quantum Monte-Carlo analysis of the subsequent many-body dynamics reveals two distinct relaxation steps, first to a nearly isotropic hot nonequilibrium and then to a quasi-equilibrium configuration. The collective isotropic plasma state is reached on a picosecond timescale well after the ultrashort ionizing pulse has passed.

  17. 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.

  18. Atmospheric ionization induced by precipitating electrons: Comparison of CRAC:EPII model with a parametrization model

    NASA Astrophysics Data System (ADS)

    Artamonov, A. A.; Mishev, A. L.; Usoskin, I. G.

    2016-11-01

    Results of a comparison of a new model CRAC:EPII (Cosmic Ray Atmospheric Cascade: Electron Precipitation Induced Ionization) with a commonly used parametric model of atmospheric ionization is presented. The CRAC:EPII is based on a Monte Carlo simulation of precipitating electrons propagation and interaction with matter in the Earth's atmosphere. It explicitly considers energy deposit: ionization, pair production, Compton scattering, generation of Bremsstrahlung high energy photons, photo-ionization and annihilation of positrons, multiple scattering as physical processes accordingly. Propagation of precipitating electrons and their interactions with air is simulated with the GEANT4 simulation tool PLANETOCOSMICS code using NRLMSISE-00 atmospheric model. Ionization yields are computed and compared with a parametrization model for different energies of incident precipitating energetic electrons, using simulated fluxes of mono-energetic particles. A good agreement between the two models is achieved in the mesosphere but the contribution of Bremsstrahlung in the stratosphere, which is not accounted for in the parametric models, is found significant. As an example, we calculated profiles of the ion production rates in the middle and upper atmosphere (below 100 km) on the basis of balloon-born measured spectra of precipitating electrons for 30-October-2002 and 07-January-2004.

  19. Relativistic contributions to single and double core electron ionization energies of noble gases.

    PubMed

    Niskanen, J; Norman, P; Aksela, H; Agren, 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 ∼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.

  20. 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.

  1. Ionizing Radiation Changes the Electronic Properties of Melanin and Enhances the Growth of Melanized Fungi

    PubMed Central

    Dadachova, Ekaterina; Bryan, Ruth A.; Huang, Xianchun; Moadel, Tiffany; Schweitzer, Andrew D.; Aisen, Philip; Nosanchuk, Joshua D.; Casadevall, Arturo

    2007-01-01

    Background Melanin pigments are ubiquitous in nature. Melanized microorganisms are often the dominating species in certain extreme environments, such as soils contaminated with radionuclides, suggesting that the presence of melanin is beneficial in their life cycle. We hypothesized that ionizing radiation could change the electronic properties of melanin and might enhance the growth of melanized microorganisms. Methodology/Principal Findings Ionizing irradiation changed the electron spin resonance (ESR) signal of melanin, consistent with changes in electronic structure. Irradiated melanin manifested a 4-fold increase in its capacity to reduce NADH relative to non-irradiated melanin. HPLC analysis of melanin from fungi grown on different substrates revealed chemical complexity, dependence of melanin composition on the growth substrate and possible influence of melanin composition on its interaction with ionizing radiation. XTT/MTT assays showed increased metabolic activity of melanized C. neoformans cells relative to non-melanized cells, and exposure to ionizing radiation enhanced the electron-transfer properties of melanin in melanized cells. Melanized Wangiella dermatitidis and Cryptococcus neoformans cells exposed to ionizing radiation approximately 500 times higher than background grew significantly faster as indicated by higher CFUs, more dry weight biomass and 3-fold greater incorporation of 14C-acetate than non-irradiated melanized cells or irradiated albino mutants. In addition, radiation enhanced the growth of melanized Cladosporium sphaerospermum cells under limited nutrients conditions. Conclusions/Significance Exposure of melanin to ionizing radiation, and possibly other forms of electromagnetic radiation, changes its electronic properties. Melanized fungal cells manifested increased growth relative to non-melanized cells after exposure to ionizing radiation, raising intriguing questions about a potential role for melanin in energy capture and

  2. Positron Impact Ionization in Noble Gas Atoms and Diatomic Molecules

    NASA Astrophysics Data System (ADS)

    Marler, J. P.

    2005-05-01

    Results are presented for absolute positronium formation and direct ionization by positron impact on Ne, Ar, Kr, Xe, N2, CO and O2 at energies from threshold up to 90 eV. The experiments use a high-resolution, trap-based positron beam and exploit the properties of positron orbits in a magnetic field [1]. Results for the noble gases are compared with theoretical predictions and with measurements obtained using a significantly different method [2]. Results for diatomic molecules are compared to other available measurements and theoretical calculations where available. There is generally good agreement between the experimental measurements, providing an important benchmark for theoretical calculations. Intriguing features in Ar and O2 will be discussed. [1] J.P. Sullivan, S.J. Gilbert, J.P. Marler, R.G. Greaves, S.J. Buckman and C.M. Surko., Phys. Rev. A. 66, 042708 (2002) [2] J.P. Marler, J.P. Sullivan and C.M. Surko, Phys. Rev. A (2005), in press.

  3. 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.

  4. 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.

  5. Exact Potential Driving the Electron Dynamics in Enhanced Ionization of H(2)(+).

    PubMed

    Khosravi, Elham; Abedi, Ali; Maitra, Neepa T

    2015-12-31

    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 H(2)(+) 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.

  6. Multislice theory of fast electron scattering incorporating atomic inner-shell ionization.

    PubMed

    Dwyer, C

    2005-09-01

    It is demonstrated how atomic inner-shell ionization can be incorporated into a multislice theory of fast electron scattering. The resulting theory therefore accounts for both inelastic scattering due to inner-shell ionization and dynamical elastic scattering. The theory uses a description of the ionization process based on the angular momentum representation for both the initial and final states of the atomic electron. For energy losses near threshold, only a small number of independent states of the ejected atomic electron need to be considered, reducing demands on computing time, and eliminating the need for tabulated inelastic scattering factors. The theory is used to investigate the influence of the collection aperture size on the spatial origin of the silicon K-shell EELS signal generated by a STEM probe. The validity of a so-called local approximation is also considered.

  7. 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.

  8. 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.

  9. 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

  10. 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

  11. Electron collisional detachment processes for a 250 2keV D(-) ion beam in a partially ionized hydrogen target

    NASA Astrophysics Data System (ADS)

    Savas, S. E.

    1980-09-01

    The efficiency with which neutral atoms can be produced by electron detachment in partially ionized hydrogen plasma neutralizers was investigated. Applications to magnetic fusion devices are discussed.

  12. 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.

  13. Theoretical study on interfacial impact ionization in AlN/GaN periodically stacked structure

    NASA Astrophysics Data System (ADS)

    Zheng, Jiyuan; Wang, Lai; Wu, Xingzhao; Hao, Zhibiao; Sun, Changzheng; Xiong, Bing; Luo, Yi; Han, Yanjun; Wang, Jian; Li, Hongtao; Li, Mo; Kang, Jianbin; Li, Qian

    2017-07-01

    A theoretical study on interfacial ionization in the AlN/GaN periodically stacked structure (PSS) avalanche photodiode (APD) has been carried out to explain why the experimental electron ionization coefficient is higher than that in the simulation result. Full band structures for GaN and AlN are combined at the heterojunction interface of the PSS APD for the calculation of the suitable initial ionization state in AlN. Many suitable initial states exist in the Γ valley of AlN, where scattering rates are restricted and ultimately result in a higher ionization coefficient.

  14. Frustrated double and single ionization in a two-electron triatomic molecule H+ 3

    NASA Astrophysics Data System (ADS)

    Chen, A.; Lazarou, C.; Price, H.; Emmanouilidou, A.

    2016-12-01

    Using a semi-classical model, we study the formation of highly excited neutral fragments during the fragmentation of {{{H}}}3+, a two-electron triatomic molecule, driven by an intense near-IR laser field. To do so, we first formulate a microcanonical distribution for arbitrary one-electron triatomic molecules. We then study frustrated double and single ionization in strongly driven {{{H}}}3+ and compute the kinetic energy release of the nuclei for these two processes. Moreover, we investigate the dependence of frustrated ionization on the strength of the laser field as well as on the geometry of the initial molecular state.

  15. 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

  16. Single and double ionization of helium by the impact of fast charged particles

    NASA Astrophysics Data System (ADS)

    Jones, S.; Madison, D. H.; Macek, Joseph H.

    2005-12-01

    A survey of the recent literature shows that paradoxes abound in electron- and ion-impact ionization of helium. For example, Schulz et al. [M. Schulz, R. Moshammer, D. Fischer, H. Kollmus, D.H. Madison, S. Jones, J. Ullrich, Nature 422 (2003) 48] found that first-Born and three-body distorted-wave (3DW) theories reproduced their data for single ionization of helium by very fast fully stripped carbon ions in the scattering plane, but not outside the scattering plane. For much slower impacting carbon ions, however, Madison et al. [D.H. Madison, D. Fischer, M. Foster, M. Schulz, R. Moshammer, S. Jones, J. Ullrich, Phys. Rev. Lett. 91 (2003) 253201] found good agreement between 3DW theory and experiment, even outside the scattering plane. This creates a dilemma, since distorted-wave perturbation theories are generally thought to improve with increasing, not decreasing, projectile speed! In this contribution, we will address these and other issues, and suggest possible ways of proceeding.

  17. 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.

  18. Ionization-assisted Relativistic Electron Generation with Monoenergetic Features from Laser Thin Foil Interaction

    NASA Astrophysics Data System (ADS)

    Karpeev, Artem; Glazyrin, Igor; Kotova, Olga; Bychenkov, Valery; Fedosejevs, Robert; Rozmus, Wojciech

    2013-10-01

    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. The 2D3V PIC code PICNIC was used for simulation of a linearly polarized laser pulse with a wavelength λ = 1 . 053 μ m normally incident onto nano-sized DLC target. We performed simulations for 3 cases: (1) 5 nm carbon foil ionized due to field ionization (FI); (2) the same, but already ionized foil, i.e. the foil in the form of a plasma slab with average charge < Z > = 3.4; (3) 42 nm carbon foil with FI. Comparison of the results obtained with different target models shows that a correct description of the interaction of a high contrast laser pulse with an ultra-thin solid dense target should include the FI effect. It was found that for the case (1) a bunch of quasimonoenergetic electrons from inner atom shells moves co-directionally with laser pulse and acquire energy ~mec2a2 / 2 .

  19. 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.

  20. 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.

  1. Probing spin-orbit-interaction-induced electron dynamics in the carbon atom by multiphoton ionization

    NASA Astrophysics Data System (ADS)

    Rey, H. F.; van der Hart, H. W.

    2014-09-01

    We use R-matrix theory with time dependence (RMT) to investigate multiphoton ionization of ground-state atomic carbon with initial orbital magnetic quantum number ML=0 and ML=1 at a laser wavelength of 390 nm and peak intensity of 1014W/cm2. Significant differences in ionization yield and ejected-electron momentum distribution are observed between the two values for ML. We use our theoretical results to model how the spin-orbit interaction affects electron emission along the laser polarization axis. Under the assumption that an initial C atom is prepared at zero time delay with ML=0, the dynamics with respect to time delay of an ionizing probe pulse modeled by using RMT theory is found to be in good agreement with available experimental data.

  2. 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.

  3. The cosmic dust analyzer: Experimental evaluation of an impact ionization model. [considering thermal equilibrium plasma

    NASA Technical Reports Server (NTRS)

    Friichtenicht, J. F.; Roy, N. L.; Becker, D. G.

    1973-01-01

    A thermal equilibrium plasma model is used to process data from an impact ionization time-of-flight mass spectrometer in order to convert the raw ion data to relative abundances of the elemental constituents of cosmic dust particles.

  4. 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. Copyright © 2014. Published by Elsevier B.V.

  5. 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.

  6. Two-electron processes in multiple ionization under strong soft-x-ray radiation

    NASA Astrophysics Data System (ADS)

    Ilchen, M.; Mazza, T.; Karamatskos, E. T.; Markellos, D.; Bakhtiarzadeh, S.; Rafipoor, A. J.; Kelly, T. J.; Walsh, N.; Costello, J. T.; O'Keeffe, P.; Gerken, N.; Martins, M.; Lambropoulos, P.; Meyer, M.

    2016-07-01

    In a combined experimental and theoretical study we have investigated the ionization of atomic argon upon irradiation with intense soft-x-ray pulses of 105 eV photon energy from the free-electron laser FLASH. The measured ion yields show charge states up to Ar7 +. The comparison with the theoretical study of the underlying photoionization dynamics highlights the importance of excited states in general and of processes governed by electron correlation in particular, namely, ionization with excitation and shake-off, processes usually inaccessible by measurements of ionic yields only. The Ar7 + yield shows a clear deviation from the predictions of the commonly used model of sequential ionization via single-electron processes and the observed signal can only be explained by taking into account the full multiplet structure of the involved configurations and by inclusion of two-electron processes. The competing process of two-photon ionization from the ground state of Ar6 + is calculated to be orders of magnitude smaller.

  7. Comment on Double K -shell ionization in the electron capture decay of sup 55 Fe''

    SciTech Connect

    Hindi, M.M.; Kozub, R.L. ); Nagy, H.J. ); Schupp, G. )

    1991-11-01

    The corrections made in a recent paper to the published values for double {ital K}-shell ionization in the electron capture decays of {sup 54}Mn and {sup 65}Zn are not applicable to the data from which these values were derived. Attention is called to a recent article that is relevant to the topic of the paper.

  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. 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.

  10. 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

  11. The role of molecular electron distribution in strong-field ionization and dissociation of heteronuclear molecules

    NASA Astrophysics Data System (ADS)

    Lai, Wei; Guo, Chunlei

    2016-11-01

    A comparison study of double-ionization induced dissociation in strong laser fields between a homonuclear diatomic molecule, O2, and a heteronuclear diatomic molecule, NO, shows that two electrons can easily be removed from one O atom of O2 to form a O2++O, however, two electrons can hardly be removed from the O atom of NO to form a N+O2+. Instead, for NO, two electrons are preferentially removed from the N atom to form a N2++O, even though the N atom requires higher ionization energy than the O atom. This indicates that atomic ionization energy does not play a significant role here. Our further study on the formation dynamics of the N2++O channel shows that the initial electron distribution of the NO molecule plays an important role in influencing the strong-field ionization and dissociation of NO and this effect seems to commonly exist in heteronuclear molecules when interacting with strong laser fields.

  12. Impact ionization in InSb probed by terahertz pump—terahertz probe spectroscopy

    NASA Astrophysics Data System (ADS)

    Hoffmann, Matthias C.; Hebling, János; Hwang, Harold Y.; Yeh, Ka-Lo; Nelson, Keith A.

    2009-04-01

    Picosecond carrier dynamics in indium antimonide (InSb) following excitation by below band gap broadband far-infrared radiation was investigated at 200 and 80 K. Using a THz-pump/THz-probe scheme with pump THz fields of 100 kV/cm and an intensity of 100MW/cm2 , we observed carrier heating and impact ionization dynamics. The number of carriers produced exceeds 1016cm-3 , corresponding to a change in carrier density ΔN/N of 700% at 80 K. The onset of a well-defined absorption peak at 1.2 THz is an indication of changes in longitudinal optical (LO) and longitudinal acoustic (LA) phonon populations due to cooling of the hot electrons.

  13. Impact ionization of molecular oxygen by 3.5-MeV/u bare carbon ions

    NASA Astrophysics Data System (ADS)

    Nandi, Saikat; Agnihotri, Aditya N.; Kasthurirangan, S.; Kumar, Ajay; Tachino, Carmen A.; Rivarola, Roberto D.; Martín, F.; Tribedi, Lokesh C.

    2012-06-01

    We have measured the absolute double-differential cross sections (DDCSs) for electron emission in ionization of O2 molecules under the impact of 3.5-MeV/u C6+ ions. The data were collected between 10 and 600 eV, in an angular range of 30∘ to 150∘. The single-differential cross sections (SDCSs) in emission angle and electron energy are deduced from the electron DDCS spectra. Also, the total cross section has been obtained from the SDCS spectra. The DDCS spectra as well as the SDCS spectra are compared with continuum distorted-wave eikonal initial-state calculations which employ molecular wave functions built as linear combinations of atomic orbitals. The DDCS ratio i.e. σO2/2σO, derived by dividing the experimental DDCS for molecular oxygen with the theoretical DDCS for atomic oxygen, does not show any primary or secondary oscillations arising from Young-type interference, which is apparently in contrast to what has been observed earlier for H2 and in agreement with the model calculation. Similarly, the forward-backward angular asymmetry increases monotonically with the velocity of the emitted electrons. However, the results on the DDCSs, SDCSs, the asymmetry parameter, and the nonexistence of oscillations are in qualitative agreement with the predictions of the model used.

  14. The electronic states of 2-furanmethanol (furfuryl alcohol) studied by photon absorption and electron impact spectroscopies

    NASA Astrophysics Data System (ADS)

    Giuliani, A.; Walker, I. C.; Delwiche, J.; Hoffmann, S. V.; Limão-Vieira, P.; Mason, N. J.; Heyne, B.; Hoebeke, M.; Hubin-Franskin, M.-J.

    2003-10-01

    The photoelectron spectrum of 2-furanmethanol (furfuryl alcohol) has been measured for ionization energies between 8 and 11.2 eV and the first three ionization bands assigned to π3, π2, and no ionizations in order of increasing binding energy. The photoabsorption spectrum has been recorded in the gas phase using both a synchrotron radiation source (5-9.91 eV, 248-125 nm) and electron energy-loss spectroscopy under electric-dipole conditions (5-10.9 eV, 248-90 nm). The (UV) absorption spectrum has also been recorded in solution (4.2-6.36 eV, 292-195 nm). The electronic excitation spectrum appears to be dominated by transitions between π and π* orbitals in the aromatic ring, leading to the conclusion that the frontier molecular orbitals of furan are affected only slightly on replacement of a H atom by the -CH2OH group. Additional experiments investigating electron impact at near-threshold energies have revealed two low-lying triplet states and at least one electron/molecule shape resonance. Dissociative electron attachment also shows to be widespread in furfuryl alcohol.

  15. Electronic spectroscopy of large van der waals molecules by resonant two-photon ionization

    NASA Astrophysics Data System (ADS)

    Leutwyler, Samuel; Even, Uzi; Jortner, Joshua

    1982-03-01

    Tunable laser two-photon ionization of large van der Waals molecules, combined with time-of-flight mass spectroscopy. was applied to the identification of the electronic origin and of some low vibrational excitations of the S 0 — S 1 electronic transition of fluorene·Ar 1, fluorene·Ar 2 and fluorene·Kr 1 produced in supersonic expansions.

  16. Interference in tunneling ionization involving an electron bound by two short-range potentials

    NASA Astrophysics Data System (ADS)

    Golovinski, P. A.; Drobyshev, A. A.

    2017-02-01

    The phenomenon of tunneling ionization involving electron bound by two delta-potentials under the action of a constant electric field has been studied. Distributions of the electron-current density for two different initial states are found. Dependence of the emission current on the orientation of potentials relative to the field direction and the distance between their centers is established. Conditions of manifestation of the interference effects are determined.

  17. Residual energy in optical-field-ionized plasmas with the longitudinal motion of electrons included.

    PubMed

    He, Bin; Chang, Tie-Qiang

    2005-06-01

    The space-charge effect on the residual energy of electrons in optical-field-ionized plasmas is studied in detail by an extended simplified model and the cloud-in-cell simulation, with the longitudinal motion of electrons included. It is found that in moderate conditions the space-charge field can influence the residual energy of electrons effectively by matching the space-charge field with laser pulse. The effect of stimulated Raman scattering on electron temperature is also investigated in detail. Finally, a comparison is made between the results and experimental data.

  18. A reexamination of electron density diagnostics for ionized gaseous nebulae

    NASA Astrophysics Data System (ADS)

    Wang, W.; Liu, X.-W.; Zhang, Y.; Barlow, M. J.

    2004-12-01

    We present a comparison of electron densities derived from optical forbidden line diagnostic ratios for a sample of over a hundred nebulae. We consider four density indicators, the [O II] λ3729/λ3726, [S II] λ6716/λ6731, [Cl III] λ5517/λ5537 and [Ar IV] λ4711/λ4740 doublet ratios. Except for a few H II regions for which data from the literature were used, diagnostic line ratios were derived from our own high quality spectra. For the [O II] λ3729/λ3726 doublet ratio, we find that our default atomic data set, consisting of transition probabilities from Zeippen (\\cite{zeippen1982}) and collision strengths from Pradhan (\\cite{pradhan}), fit the observations well, although at high electron densities, the [O II] doublet ratio yields densities systematically lower than those given by the [S II] λ6716/λ6731 doublet ratio, suggesting that the ratio of transition probabilities of the [O II] doublet, A(λ3729)/A(λ3726), given by Zeippen (\\cite{zeippen1982}) may need to be revised upwards by approximately 6 per cent. Our analysis also shows that the more recent calculations of [O II] transition probabilities by Zeippen (\\cite{zeippen1987a}) and collision strengths by McLaughlin & Bell (\\cite{mclaughlin}) are inconsistent with the observations at the high and low density limits, respectively, and can therefore be ruled out. We confirm the earlier result of Copetti & Writzl (\\cite{copetti2002}) that the [O II] transition probabilities calculated by Wiese et al. (\\cite{wiese}) yield electron densities systematically lower than those deduced from the [S II] λ6716/λ6731 doublet ratio and that the discrepancy is most likely caused by errors in the transition probabilities calculated by Wiese et al. (\\cite{wiese}). Using our default atomic data set for [O II], we find that Ne([O II]) ⪉ Ne([S II]) ≈ Ne([Cl III])< Ne([Ar IV]).

  19. 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.

  20. 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.

  1. 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.

  2. Complete momentum balance in ionization of H2 by 75-keV-proton impact for varying projectile coherence

    NASA Astrophysics Data System (ADS)

    Sharma, S.; Arthanayaka, T. P.; Hasan, A.; Lamichhane, B. R.; Remolina, J.; Smith, A.; Schulz, M.

    2014-05-01

    We report on a kinematically complete experiment on ionization of H2 by proton impact. While a significant impact of the projectile coherence properties on the scattering-angle dependence of double-differential cross sections (DDCSs), reported earlier, is confirmed by the present data, only weak coherence effects are found in the electron and recoil-ion momentum dependence of the DDCSs. This suggests that the phase angle in the interference term is determined primarily by the projectile momentum transfer rather than by the recoil-ion momentum. We therefore cannot rule out the possibility that the interference observed in our data is not primarily due to a two-center effect.

  3. Multiple Ionization of Free Ubiquitin Molecular Ions in Extreme Ultraviolet Free-Electron Laser Pulses.

    PubMed

    Schlathölter, Thomas; Reitsma, Geert; Egorov, Dmitrii; Gonzalez-Magaña, Olmo; Bari, Sadia; Boschman, Leon; Bodewits, Erwin; Schnorr, Kirsten; Schmid, Georg; Schröter, Claus Dieter; Moshammer, Robert; Hoekstra, Ronnie

    2016-08-26

    The fragmentation of free tenfold protonated ubiquitin in intense 70 femtosecond pulses of 90 eV photons from the FLASH facility was investigated. Mass spectrometric investigation of the fragment cations produced after removal of many electrons revealed fragmentation predominantly into immonium ions and related ions, with yields increasing linearly with intensity. Ionization clearly triggers a localized molecular response that occurs before the excitation energy equilibrates. Consistent with this interpretation, the effect is almost unaffected by the charge state, as fragmentation of sixfold deprotonated ubiquitin leads to a very similar fragmentation pattern. Ubiquitin responds to EUV multiphoton ionization as an ensemble of small peptides.

  4. An analytical equation of electron beams percentage depth ionization curve along the central axis.

    PubMed

    Chen, F S

    1988-01-01

    An analytical equation is proposed in this article. This equation contains four parameters. One of them is the depth of maximum ionization (dm) which can be determined from experiments. The other three parameters can be calculated from the measured percentage depth ionization curve. The values calculated with this equation fit very well with measured data in the buildup region with a difference of 2% or less, and in the falloff region with an error of 2 mm or less in terms of depth. The electron beam energy ranged from 6 to 20 MeV from a Therac 20 Saturne Linear Accelerator. This equation can not be applied beyond the practical range Rp.

  5. 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.

  6. 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.

  7. A model of impact ionization due to the primary hole in silicon for a full band Monte Carlo simulation

    NASA Astrophysics Data System (ADS)

    Kunikiyo, Tatsuya; Takenaka, Masahiro; Morifuji, Masato; Taniguchi, Kenji; Hamaguchi, Chihiro

    1996-05-01

    The rate of impact ionization due to the primary hole in silicon is numerically derived from pseudo-wave-functions and realistic energy band structure based on a nonlocal empirical pseudopotential method including the spin-orbit interaction. The calculated impact-ionization rate SII [s-1] is well fitted to an analytical formula with a power exponent of 3.4, indicating a soft threshold of the impact ionization rate: SII [s-1]=1.14×1012 [s-1 eV-3.4]×(ɛ [eV]-1. 49 [eV])3.4, where ɛ [eV] is the energy of the primary hole relative to the valence band edge. The soft threshold originates from the complexity of the silicon band structure. The calculated impact-ionization rate shows strong anisotropy at low hole energies (ɛ<3 eV), while it becomes isotropic at high hole energies, indicating the isotropy of the joint density of states at high energies. Numerical calculation also makes it clear that average energies of secondary generated carriers ɛ¯ depend linearly on primary hole energies at the moment of their generation. The calculated average energies of secondary generated holes ɛ¯(hole) [eV] and electrons ɛ¯(electron) [eV] are well fitted to linear functions of primary hole energy ɛ [eV]: ɛ¯(hole) [eV]=3.75×10-1 ɛ [eV]-4.76×10-1 [eV],ɛ¯(electr on) [eV]=-3.14×10-1 ɛ [eV]-8.60×10-1 [eV]. The standard deviations of secondary generated carriers are also presented.

  8. Electron-impact detachment from B-

    NASA Astrophysics Data System (ADS)

    Andersen, L. H.; Jensen, M. J.; Pedersen, H. B.; Vejby-Christensen, L.; Djurić, N.

    1998-10-01

    Cross sections for electron-impact single and double detachment from B- have been measured from 0 to 200 eV. The single-detachment cross section peaks at 4-5 eV with a cross-section maximum of about 10-14 cm2. A (2p3) 4S state has recently been predicted to give rise to a resonance state in the H2- dianion [T. Sommerfeld et al., Phys. Rev. A 55 1903 (1997)]. We observe no resonances in the detachment cross section of B- and hence no sign of an equivalent shortlived B2-(2p3) state. The ratio of the double- to single-detachment cross section reaches a constant value of 3% at energies above 50 eV. A simple model relates this number to a shake-off probability of about 90%. The ratio between double and single ionization of neutral atomic targets at high energy is also discussed, and the model relates this ratio to the shake-off probability in the sudden approximation.

  9. Electron impact excitation of molecular hydrogen

    DOE PAGES

    Zammit, Mark Christian; Savage, Jeremy S.; Fursa, Dmitry V.; ...

    2017-02-06

    Here, we report the electron impact integrated and differential cross sections for excitation to the b 3Σmore » $$+\\atop{u}$$, a 3Σ$$+\\atop{g}$$, c 3Πu, B 1Σ$$+\\atop{u}$$, E, F 1Σ$$+\\atop{g}$$, C 1Πu, e 3Σ$$+\\atop{u}$$, h 3Σ $$+\\atop{g}$$, d 3Πu, B'' 1Σ$$+\\atop{u}$$ , D 1Πu, B'' 1Σ$$+\\atop{u}$$, and D' 1Πu states of molecular hydrogen in the energy range from 10 to 300 eV. Total scattering and total ionization cross sections are also presented. The calculations have been performed by using the convergent close-coupling method within the fixed-nuclei approximation. Detailed convergence studies have been performed with respect to the size of the close-coupling expansion and a set of recommended cross sections has been produced. Significant differences with previous calculations are found. Agreement with experiment is mixed, ranging from excellent to poor depending on the transition and incident energies.« less

  10. Electron-impact excitation of molecular hydrogen

    NASA Astrophysics Data System (ADS)

    Zammit, Mark C.; Savage, Jeremy S.; Fursa, Dmitry V.; Bray, Igor

    2017-02-01

    We report the electron impact integrated and differential cross sections for excitation to the b 3Σu+ , a 3Σg+ , c 3Πu , B 1Σu+ , E ,F 1Σg+ , C 1Πu , e 3Σu+ , h 3Σg+ , d 3Πu , B'1Σu+ , D 1Πu , B''1Σu+ , and D'1Πu states of molecular hydrogen in the energy range from 10 to 300 eV. Total scattering and total ionization cross sections are also presented. The calculations have been performed by using the convergent close-coupling method within the fixed-nuclei approximation. Detailed convergence studies have been performed with respect to the size of the close-coupling expansion and a set of recommended cross sections has been produced. Significant differences with previous calculations are found. Agreement with experiment is mixed, ranging from excellent to poor depending on the transition and incident energies.

  11. Static field ionization rates for multi-electron atoms and small molecules

    NASA Astrophysics Data System (ADS)

    Pramod Majety, Vinay; Scrinzi, Armin

    2015-12-01

    We present an application of the hybrid anti-symmetrized coupled channels approach to compute static field ionization rates for multi-electron atoms (He, Ne, Ar) and small molecules (H2, N2, CO). While inert gas atoms behave as effective single electron systems, molecules exhibit multi-electron effects in the form of core polarization. It is shown that at moderate field strengths, these effects can be modeled to about 10% accuracy using a few (5-6) channel ansatz. In the case of the CO molecule, description of core polarization is essential for the correct prediction of the maximum ionization direction and our converged results are in good agreement with the experimental measurements.

  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. 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.

  14. Role of direct laser acceleration of electrons in a laser wakefield accelerator with ionization injection

    NASA Astrophysics Data System (ADS)

    Shaw, Jessica; Lemos, Nuno; Amorim, Ligia Diana; Vafaei-Najafabadi, Navid; Marsh, Ken; Tsung, Frank; Froula, Dustin; Mori, Warren; Josh, Chan

    2016-10-01

    We show through experiments and supporting simulations the role of direct laser acceleration (DLA) of electrons in a laser wakefield accelerator when ionization injection of electrons is employed. The laser pulse is intense enough to create a nonlinear wakefield and long enough to overlap the electrons trapped in the first accelerating potential well (bucket) of the wakefield. The betatron oscillations of the trapped electrons in the plane of the laser polarization in the presence of an ion column lead to an energy transfer from the laser pulse to the electrons through DLA. We show that the produced electron beams exhibit characteristic features that are indicative of DLA as an additional acceleration mechanism when the laser pulse overlaps the trapped electrons. Experimental work supported by NSF Grant PHY-1415306 and DOE Grant DE-SC0010064. Simulation work done on the Fermi Cluster at Cineca.

  15. 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.

  16. Ionization-injected electron acceleration with sub-terawatt laser pulses

    NASA Astrophysics Data System (ADS)

    Feder, Linus; Goers, Andy; Hine, George; Miao, Bo; Salehi, Fatholah; Woodbury, Daniel; Milchberg, Howard

    2016-10-01

    The vast majority of laser wakefield acceleration (LWFA) experiments use drive lasers with peak powers >10 TW and repetition rates from 10 Hz to less than once an hour. However, it was recently demonstrated that by using a thin, high density gas target, LWFA can be driven by laser pulses well below a TW and with high repetition rates. We present experiments and particle-in-cell (PIC) simulations of the effect of doping the high density gas jet with higher Z molecules (here nitrogen). Our earlier experiments with low-Z gas relied on self-injection of electrons into the accelerating wake through wave-breaking. In ionization injection, the relativistically self-focused laser pulse ionizes the inner shell of the dopant inside the plasma wake. High energy electrons are then trapped by the wakefield in the earliest potential buckets, which overlap with the laser pulse. PIC simulations show acceleration of these electrons by LWFA and directly by the laser pulse, with the direct contribution significantly increasing the electron energy beyond the LWFA contribution alone. Additionally, ionization injection can be controlled to prevent dephasing of the electron beam, resulting in a narrower energy spectrum and lower spatial divergence. This research is supported by the Department of Energy and the National Science Foundation.

  17. Electronic dynamics of charge resonance enhanced ionization probed by laser-induced alignment in C2H2

    NASA Astrophysics Data System (ADS)

    Cornaggia, C.

    2016-10-01

    Although charge resonance enhanced ionization (CREI) be an ubiquitous effect in molecules in strong laser fields, the associated electron emission remains difficult to deal with. The main reason relies on the fact that CREI is part of an overall multielectron ionization, where the initial steps of single and dissociative ionization of neutral species dominate the electron spectrum. Using the rescattered electrons, we show that it is possible to address the electron signal from CREI without any contribution from other electron signals. The electrons from CREI are preferentially emitted when the molecular axis is parallel to the laser electric field as expected from its electronic dynamics. Acetylene is chosen for demonstration purpose because single ionization, which is not related to CREI, is more pronounced when the C2H2 molecular axis is perpendicular to the laser electric field.

  18. 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.

  19. Electron transfer, excitation, and ionization in {alpha}-H collisions studied with a Sturmian basis

    SciTech Connect

    Winter, Thomas G.

    2007-12-15

    Cross sections have been determined for electron transfer, direct excitation, and ionization in collisions between {alpha} particles and H(1s) atoms at {alpha} energies 3 keV-38.4 MeV, extending earlier work [Phys. Rev. A 25, 697 (1982)] restricted to total transfer at 20-200 keV. Transfer as well as excitation cross sections into individual states up to 3d have been determined with several coupled-Sturmian pseudostate bases, and tests of basis sensitivity have been carried out. These and ionization cross sections have been compared with existing experimental and other coupled-state results. Structure is observed in the lower-energy excitation cross sections, which is believed not to be an artifact of the bases used. Ionization and excitation cross sections have also been compared with corresponding Born results at higher energies.

  20. Influence of permanent dipole and dynamic core-electron polarization on tunneling ionization of polar molecules

    NASA Astrophysics Data System (ADS)

    Hoang, Van-Hung; Zhao, Song-Feng; Le, Van-Hoang; Le, Anh-Thu

    2017-02-01

    We present a detailed theoretical investigation on strong-field ionization of polar (CO and NO) as well as nonpolar molecules (N2, O2, and CO2). Our results indicate that accounting for the Stark correction in the molecular tunneling ionization theory leads to overall fairly good agreements with numerical solutions of the time-dependent Schrödinger equation. Furthermore, we show that the effect of dynamic core-electron polarization, in general, has a weak influence on the angle-dependent ionization probability. However, in the case of CO we confirm the recent finding by B. Zhang, J. Yuan, and Z. Zhao [Phys. Rev. Lett. 111, 163001 (2013), 10.1103/PhysRevLett.111.163001] that accounting for dynamic core-polarization is crucial to achieving an overall good agreement with experiments.