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Sample records for electron-impact dissociative ionization

  1. 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.

  2. 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.

  3. 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.

  4. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  6. 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.

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

    Demesh, Shandor Sh.; Remeta, Eugene Yu.

    2015-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-06-01

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

  11. 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.

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Lahmidi, N.; Joulakian, B.

    2005-01-01

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

  15. 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.

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

    SciTech Connect

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

    2011-10-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

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

  18. 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.

  19. Electron impact ionization of glycolaldehyde

    NASA Astrophysics Data System (ADS)

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

    2005-05-01

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

  20. Electron-Impact Ionization of Methane

    NASA Technical Reports Server (NTRS)

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

    2001-01-01

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

  1. 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.

  2. Electron-Impact Ionization Cross Section Database

    National Institute of Standards and Technology Data Gateway

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

  3. A new concept Tandem thermal dissociator/electron impact ion source for RIB generation

    SciTech Connect

    Alton, G.D.; Williams, C.

    1995-12-31

    An innovative thermal dissociation/electron impact ionization positive ion source is presently under design at the Oak Ridge National Laboratory for potential use for generating RIBs at the Holifield Radioactive Ion Beam Facility (HRIBF). Because of the low probability of simultaneously dissociating and efficiently ionizing the individual atomic constituents with conventional, hot-cathode, electron-impact ion sources, the ion beams extracted from these sources often appear as a mixture of several molecular sideband beams. In this way, the intensity of the species of interest is diluted. We have conceived an Ion source that combines the excellent molecular dissociation properties of a thermal dissociator and the high efficiency characteristics of an electron impact ionization source. If the concept proves to be a viable option, the source will be used as a complement to the electron beam plasma ion sources already in use at the HRIBF. The design features and principles of operation of the source are described in this article.

  4. Ionization of the glycerin molecule by the electron impact

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  5. 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}

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

    NASA Astrophysics Data System (ADS)

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

    2008-07-01

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

  7. VUV study of electron impact dissociative excitation of thymine

    NASA Astrophysics Data System (ADS)

    Tiessen, C. J.; Trocchi, J. A.; Hein, J. D.; Dech, J.; Kedzierski, W.; McConkey, J. W.

    2016-06-01

    Dissociative excitation of thymine following electron impact was studied in the energy range up to 430 eV. Emissions in the vacuum ultra-violet spectral region below 150 nm were studied and found to be dominated by the hydrogen Lyman series. Emission cross section data reveal that Lyman-α excitation displays a broad maximum at an electron impact energy of 160 eV. The probability of extracting other excited atoms from the parent molecule is found to be insignificant. Possible excitation and dissociation mechanisms in the parent molecule are discussed.

  8. Electron-impact ionization of W27 +

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  9. Single ionization of helium by electron impact

    SciTech Connect

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

    2010-06-15

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

  10. 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.

  11. Carbon monoxide dissociative attachment and resonant dissociation by electron-impact

    NASA Astrophysics Data System (ADS)

    Laporta, V.; Tennyson, J.; Celiberto, R.

    2016-02-01

    Low-energy dissociative electron attachment and resonant electron impact dissociation of CO molecule are considered. Ro-vibrationally resolved cross sections and rate coefficients for both the processes are calculated using an ab-initio model based on the low-lying \\text{X}{{}2}\\Pi resonance of CO-. Final results show that the cross sections increases very rapidly as a function of the ro-vibrational level; these cross sections should be useful for understanding kinetic dissociation of CO in strongly non-equilibrium plasmas.

  12. Rate coefficients for dissociative attachment and resonant electron-impact dissociation involving vibrationally excited O{sub 2} molecules

    SciTech Connect

    Laporta, V.; Celiberto, R.; Tennyson, J.

    2014-12-09

    Rate coefficients for dissociative electron attachment and electron-impact dissociation processes, involving vibrationally excited molecular oxygen, are presented. Analytical fits of the calculated numerical data, useful in the applications, are also provided.

  13. Electron impact multiple ionization cross sections of heavy ions

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

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

    SciTech Connect

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

    1994-07-01

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

  15. 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.

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

    SciTech Connect

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

    2010-04-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  18. Fast Nitrogen Atoms from Dissociative Excitation of N2 by Electron Impact

    NASA Technical Reports Server (NTRS)

    Ajello, Joseph M.; Ciocca, Marco

    1996-01-01

    The Doppler profiles of one of the fine structure lines of the N I (1200 A) g (sup 4)S(sup 0)-(sup 4)P multiplet and of the N II (1085 A) g (sup 3)p(sup O)-(sup 3)D multiplet have been measured. Excitation of the multiplets is produced by electron impact dissociative excitation of N2. The experimental line profiles are evaluated by fast Fourier transform (FFT) techniques and analysis of the profiles yields the kinetic energy distribution of fragments. The full width at half maximum (FWHM) of N I (1200 A) increases from 27+/-6 mA at 30 eV to 37+/-4 mA at 100 eV as the emission cross section of the dissociative ionization excitation process becomes more important relative to the dissociative excitation process. The FWHM of the N II (1085 A) line is 36+/-4 mA at 100 eV. For each multiplet the kinetic energy distribution function of each of the two fragment N atoms (ions) is much broader than thermal with a mean energy above 1.0 eV. The dissociation process with the largest cross section is predissociation and predominantly produces N atoms with kinetic energy distributions having mean energies above 0.5 eV. Dissociative processes can lead to a substantial escape flux of N I atoms from the satellites, Titan and Triton of the outer planets.

  19. 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.

  20. 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.

  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 Ionization Measurements Important for Solar Physics

    NASA Astrophysics Data System (ADS)

    Bannister, M. E.

    2004-05-01

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

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

    SciTech Connect

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

    2006-09-15

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

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

    NASA Astrophysics Data System (ADS)

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

    1994-02-01

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

  5. 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.

  6. Electron impact ionization of highly charged lithiumlike ions

    SciTech Connect

    Wong, K L

    1992-10-01

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

  7. Low-energy electron-impact ionization of helium

    SciTech Connect

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

    2005-12-15

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

  8. Electron-impact ionization of Li2 and Li2+

    NASA Astrophysics Data System (ADS)

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

    2008-10-01

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

  9. 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.

  10. 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.

  11. 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.

  12. Measurements of Electron-Impact Ionization Relevant for Astrophysics

    NASA Astrophysics Data System (ADS)

    Bannister, M. E.

    2005-05-01

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

  13. Dissociative Ionization of Aromatic and Heterocyclic Molecules

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.

    2003-01-01

    Space radiation poses a major health hazard to humans in space flight. The high-energy charged particles in space radiation ranging from protons to high atomic number, high-energy (HZE) particles, and the secondary species they produce, attack DNA, cells, and tissues. Of the potential hazards, long-term health effects such as carcinogenesis are likely linked to the DNA lesions caused by secondary electrons in the 1 - 30 eV range. Dissociative ionization (DI) is one of the electron collision processes that can damage the DNA, either directly by causing a DNA lesion, or indirectly by producing radicals and cations that attack the DNA. To understand this process, we have developed a theoretical model for DI. Our model makes use of the fact that electron motion is much faster than nuclear motion and assumes DI proceeds through a two-step process. The first step is electron-impact ionization resulting in a particular state of the molecular ion in the geometry of the neutral molecule. In the second step the ion undergoes unimolecular dissociation. Thus the DI cross section sigma(sup DI)(sub a) for channel a is given by sigma(sup DI)(sub a) = sigma(sup I)(sub a) P(sub D) with sigma(sup I)(sub a) the ionization cross section of channel a and P(sub D) the dissociation probability. This model has been applied to study the DI of H2O, NH3, and CH4, with results in good agreement with experiment. The ionization cross section sigma(sup I)(sub a) was calculated using the improved binary encounter-dipole model and the unimolecular dissociation probability P(sub D) obtained by following the minimum energy path determined by the gradients and Hessians of the electronic energy with respect to the nuclear coordinates of the ion. This model is used to study the DI from the low-lying channels of benzene and pyridine to understand the different product formation in aromatic and heterocyclic molecules. DI study of the DNA base thymine is underway. Solvent effects will also be discussed.

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

    NASA Astrophysics Data System (ADS)

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

    2013-10-01

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

  15. 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.

  16. Single electron impact ionization of the methane molecule

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  17. 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.

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

    PubMed

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

    2007-05-01

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

  19. Dissociative excitation of molecular hydrogen by electron impact.

    NASA Technical Reports Server (NTRS)

    Misakian, M.; Zorn, J. C.

    1972-01-01

    A pulsed electron beam was employed in the experiment to excite a diffuse gas of hydrogen molecules. The energy resolution of the electron gun permitted careful measurements of the thresholds for the production of slow and fast H(2s) atoms. The experiment was conducted in a vacuum system that facilitated a systematic study of the angular distribution of the fragments in the dissociative excitation process. The results permit the identification of the several excited states that are involved in the production of the H(2s) fragments.

  20. Dissociative excitation of NO2 by electron impact

    NASA Astrophysics Data System (ADS)

    Young, J. A.; Malone, C. P.; Johnson, P. V.; Liu, X.; Ajello, J. M.; Kanik, I.

    2009-09-01

    Electron-impact-induced vacuum ultraviolet emissions are measured for NO2, a species important to discharge phenomena and ozone decomposition in the Earth's atmosphere. A calibrated spectrum for 100 eV incident electrons is presented, along with cross sections for strong emission features between 80 and 160 nm. The dominant N i (2p3 4S°-3s 4P) emission at 120.1 nm is compared with that of N2 and used to provide an absolute calibration for all measured cross sections. In addition, 10-300 eV excitation functions for the N i (120.1 nm) and O i (130.4 nm) emissions are presented and interpreted. Comparisons are made with similar measurements of related species, in particular N2O and NO. Of interest, it was found that, on average, the variation in the intensity of oxygen and nitrogen emissions could be reasonably explained by the difference in the number of constituent oxygen and nitrogen atoms in each target.

  1. Theory of dissociative tunneling ionization

    NASA Astrophysics Data System (ADS)

    Svensmark, Jens; Tolstikhin, Oleg I.; Madsen, Lars Bojer

    2016-05-01

    We present a theoretical study of the dissociative tunneling ionization process. Analytic expressions for the nuclear kinetic energy distribution of the ionization rates are derived. A particularly simple expression for the spectrum is found by using the Born-Oppenheimer (BO) approximation in conjunction with the reflection principle. These spectra are compared to exact non-BO ab initio spectra obtained through model calculations with a quantum mechanical treatment of both the electronic and nuclear degrees of freedom. In the regime where the BO approximation is applicable, imaging of the BO nuclear wave function is demonstrated to be possible through reverse use of the reflection principle, when accounting appropriately for the electronic ionization rate. A qualitative difference between the exact and BO wave functions in the asymptotic region of large electronic distances is shown. Additionally, the behavior of the wave function across the turning line is seen to be reminiscent of light refraction. For weak fields, where the BO approximation does not apply, the weak-field asymptotic theory describes the spectrum accurately.

  2. Electron-Impact Dissociation of Ozone Cations O3+

    SciTech Connect

    Deng, Shihu; Vane, C Randy; Bannister, Mark E; FogleJr, Michael R

    2010-01-01

    Absolute cross sections for electron-impact dissociation of O3+ ions yielding O+ and O2+ fragment ions have been measured using a crossed electron-ion beams method for energies from about 3 eV to 100 eV. While the O2+ channel dominates the dissociation cross section over the measured energy range, a strong enhancement is observed in the O+ channel at low energy.

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

    NASA Astrophysics Data System (ADS)

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

    2004-03-01

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

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

    NASA Astrophysics Data System (ADS)

    He, Yunteng; Zhang, Jie; Kong, Wei

    2016-02-01

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

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

    PubMed

    He, Yunteng; Zhang, Jie; Kong, Wei

    2016-02-28

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

  6. 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

  7. Dissociative excitation of the N(+)(5S) state by electron impact on N2 - Excitation function and quenching

    NASA Technical Reports Server (NTRS)

    Erdman, P. W.; Zipf, E. C.

    1986-01-01

    Metastable N(+)(5S) ions were produced in the laboratory by dissociative excitation of N2 with energetic electrons. The resulting radiative decay of the N(+)(5S) state was observed with sufficient resolution to completely resolve the doublet from the nearby N2 molecular radiation. The excitation function was measured from threshold to 500 eV. The cross section peaks at a high electron energy and also exhibits a high threshold energy both of which are typical of dissociative excitation-ionization processes. This finding complicates the explanation of electron impact on N2 as the mechanism for the source of the 2145 A 'auroral mystery feature' by further increasing the required peak cross section. It is suggested that the apparent N(+)(5S) quenching in auroras may be an artifact due to the softening of the electron energy spectrum in the auroral E region.

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

    SciTech Connect

    Sampson, D.H.

    1989-11-15

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

  9. Electron-impact dissociation cross sections of vibrationally excited He_{2}^{+} molecular ion

    NASA Astrophysics Data System (ADS)

    Celiberto, R.; Baluja, K. L.; Janev, R. K.; Laporta, V.

    2016-01-01

    Electron-impact cross sections for the dissociation process of vibrationally excited He2+ molecular ion, as a function of the incident electron energy are calculated for the dissociative transition \\text{X}{{ }2}Σu+\\to \\text{A}{{ }2}Σg+ by using the R-matrix method in the adiabatic-nuclei approximation. The potential energy curves for the involved electronic states and transition dipole moment, also calculated with the R-matrix method, were found to be in good agreement with the results reported in literature. The vibrationally resolved dissociation cross sections of He2+(v) exhibit a resonant structure around 7 eV. The observed strong variation of the magnitude of this structure with the vibrational level is explained in terms of the overlap of initial and final (continuum) state wave functions in the Franck–Condon region.

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

    SciTech Connect

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

    1995-04-01

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

  11. 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.}

  12. Dissociative excitation of vacuum ultraviolet emission features by electron impact on molecular gases. 3: CO2

    NASA Technical Reports Server (NTRS)

    Mumma, M. J.; Borst, W. L.; Zipf, E. C.

    1972-01-01

    Vacuum ultraviolet multiplets of C I, C II, and O I were produced by electron impact on CO2. Absolute emission cross sections for these multiplets were measured from threshold to 350 eV. The electrostatically focused electron gun used is described in detail. The atomic multiplets which were produced by dissociative excitation of CO2 and the cross sections at 100 eV are presented. The dependence of the excitation functions on electron energy shows that these multiplets are produced by electric-dipole-allowed transitions in CO2.

  13. On the excitation of Lyman beta and Balmer alpha radiation by electron-impact dissociation of methane

    NASA Technical Reports Server (NTRS)

    Mclaughlin, R. W.; Zipf, E. C.

    1978-01-01

    The cross sections for the excitation of Ly-beta and H-alpha when methane is dissociated by electron impact have values of 17.1 by 10 to the -19th power sq cm and 26.0 by 10 to the -19th power sq cm, respectively, at an electron impact energy of 100 eV. These results are in disagreement with the implications of recent polarization measurements of H-alpha radiation that suggest negligible H(3p) excitation in the dissociation of CH4 by electron impact.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-05-01

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

  16. 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.

  17. 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.

  18. 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.

  19. 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.

  20. Ionization yield in xenon due to electron impact

    NASA Astrophysics Data System (ADS)

    Dayashankar

    1982-04-01

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

  1. VUV fluorescence following electron-impact dissociative excitation of CS{sub 2}

    SciTech Connect

    Brotton, S. J.; McConkey, J. W.

    2011-01-15

    Electron-impact dissociation of CS{sub 2} has been studied by observation of the atomic spectral emission features in the range 115-170 nm. Absolute photoemission cross sections are presented over the complete wavelength range for an incident electron energy of 100 eV. As an example, the measured cross section of the strong C i emission at 165.7 nm, which is a prominent feature in many solar and other extraterrestrial spectra, is (1.45{+-}0.19)x10{sup -18} cm{sup 2}. Comparison with earlier cross-sectional measurements suggest that these were too high by a factor of more than three. Excitation functions of the dominant C i (156.1 nm) and S i (147.4 nm) emission lines have been measured for electron-impact energies from threshold to 360 eV. From appearance energy measurements in the near-threshold region, likely fragmentation channels are identified which involve both two-fragment breakup and total fragmentation of the parent CS{sub 2}.

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

    SciTech Connect

    Ellis, Andrew M.; Yang Shengfu

    2007-09-15

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

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

    SciTech Connect

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

    1997-10-01

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

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

    SciTech Connect

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

    1997-08-01

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

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

    SciTech Connect

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

    1995-04-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2002-01-01

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

  7. 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.

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

    NASA Astrophysics Data System (ADS)

    Opitz, Joachim

    2007-08-01

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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2002-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

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

    SciTech Connect

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

    1981-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Madison, Don

    2015-09-01

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

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  1. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

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

    SciTech Connect

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

    1991-10-01

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

  4. 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.

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

    PubMed Central

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

    2016-01-01

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

  6. 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.

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

    NASA Technical Reports Server (NTRS)

    Lee, Long C.; Srivastava, Santosh K.

    1990-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1990-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

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

  12. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

  14. 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.

  15. 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.

  16. 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.

  17. 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.

  18. 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.

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

    SciTech Connect

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

    2003-05-01

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

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

    SciTech Connect

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

    1988-03-24

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

  1. Dissociation of CH4 by electron impact: Production of metastable hydrogen and carbon fragments

    NASA Technical Reports Server (NTRS)

    Finn, T. G.; Carnahan, B. L.; Zipf, E. C.

    1974-01-01

    Metastable fragments produced by electron impact excitation of CH4 have been investigated for incident electron energies from threshold to 300 eV. Only metastable hydrogen and carbon atoms were observed. Onset energies for the production of metastable hydrogen atoms were observed at electron impact energies of 22.0 + or - .5 eV, 25.5 + or - .6 eV, 36.7 + or - .6 eV and 66 + or - 3 eV, and at 26.6 + or - .6 eV for the production of metastable carbon atoms. Most of the fragments appear to have been formed in high-lying Rydberg states. The total metastable hydrogen cross section reaches a maximum value of approximately 1 X 10 to the minus 18th power sq cm at 100 eV. At the same energy, the metastable carbon cross section is 2 x 10 to the minus 19th power sq cm.

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

    SciTech Connect

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

    2014-03-20

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

  3. 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.

  4. 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.

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

    PubMed

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

    2016-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  11. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-09-01

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

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

    SciTech Connect

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

    2005-09-15

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

  14. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1995-01-01

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

  16. Electron ionization and dissociation of aliphatic amino acids

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2013-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

  19. 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.

  20. 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.

  1. 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).

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

    NASA Astrophysics Data System (ADS)

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

    2011-05-01

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

  3. 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).

  4. Dissociative ionization of sodium molecules via repulsive Rydberg states

    NASA Astrophysics Data System (ADS)

    Chen, Hong

    In this thesis, an investigation of two color resonance multiphoton ionization (REMPI) and fragmentation processes in Na2 has been performed in combination with Linear Time-of-Flight Mass Spectrometry technique. The ionization and dissociative ionizations channels in the energy range up to 2500cm -1 above the dissociative ionization threshold into Na(3s)+Na ++e have been studied. After a mild supersonic expansion from the beam source, neutral sodium dimers in the ground state have been produced. Two tunable, pulsed lasers excite Na2 molecules via the intermediate A1S+u state to a single ro-vibrational level of the second intermediate 21pig state. Following absorption of a third photon, the total energy is above the dissociation limit into Na(3s) + Na+ + e. Typically, a small portion of atomic ions is produced under our experimental conditions. By varying the total available energy below and through the doubly excited states correlating with the Na(3p)+Na(4s) atom pair, there is no evidence that the doubly excited states positioned in the ionic continuum get involved. By calculation of the expected transition probabilities for all possible channels which can decay directly and indirectly into atomic ions, I find that direct dissociative ionization via 12S+u is impossible. The transition probabilities for dissociative ionization via the repulsive Rydberg states with principal quantum numbers n from 5˜12 converging toward the 12S+u state are three to four orders of magnitude larger than those for direct ionization into the continuum of the X2S+g ground state. These repulsive Rydberg states are much more likely to play a role in the photo-ionization through the intermediate 21Pg state. A semi-classical model which was originally developed for negative ion dissociative attachment (O'MAL'67) describes how dissociative ionization occurs along the repulsive Rydberg states. Its prediction concerning the ratio of atomic to molecular ion production as a function of initial

  5. Ionization and dissociation dynamics of molecules in strong laser fields

    NASA Astrophysics Data System (ADS)

    Lai, Wei

    The fast advancement of ultrashort-pulsed high-intensity laser technology allows for generating an electric field equivalent to the Coulomb field inside an atom or a molecule (e.g., EC=5.14x109 V/cm at the 1s orbit radius a0=0.0529 nm of the hydrogen atom, which corresponds to an intensity of 3.54x1016 W/cm2). Atoms and molecules exposed in such a field will easily be ionized, as the external field is strong enough to remove the electrons from the core. This is usually referred to "strong field". Strong fields provide a new tool for studying the interaction of atoms and molecules with light in the nonlinear nonperturbative regime. During the past three decades, significant progress has been made in the strong field science. Today, most phenomena involving atoms in strong fields have been relatively well understood by the single-active-electron (SAE) approximation. However, the interpretation of these responses in molecules has encountered great difficulties. Not like atoms that only undergo excitation and ionization, various dissociation channels accompanying excitation and ionization can occur in molecules during the laser pulse interaction, which imparts further complexity to the study of molecules in strong fields. Previous studies have shown that molecules can behave significantly different from rare gas atoms in phenomena as simple as single and double ionization. Molecular dissociation following ionization also presents challenges in strong fields compared to what we have learned in the weak-field regime. This dissertation focuses on experimental studies on ionization and dissociation of some commonly-seen small molecules in strong laser fields. Previous work of molecules in strong fields will be briefly reviewed, particularly on some open questions about multiple dissociation channels, nonsequential double ionization, enhanced ionization and molecular alignment. The identification of various molecular dissociation channels by recent experimental technical

  6. Control of ionization and dissociation by optical pulse trains.

    PubMed

    Kirrander, A; Jungen, Ch; Fielding, H H

    2010-08-21

    Ever since the first lasers were built over 40 years ago, chemists and physicists have been attempting to exploit them as tools for controlling the outcome of chemical reactions. Over the last decade this dream has become a reality. The most successful approaches have employed learning algorithms to shape femtosecond laser pulses; however, in these experiments, the laser light effectively learns for itself what pulse shape is required to generate a specific product and it is not always easy to unravel the underlying physics of the control process. In this theoretical investigation we unravel the mechanism of ionisation/dissociation control in the prototypical H(2) molecule. We track the excited state molecular dynamics from the moment of interaction with the laser field to ionization and dissociation, and determine how sequences of carefully tuned laser pulses are able to change the ionization/dissociation branching ratio. PMID:20532353

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

    PubMed

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

    2010-03-01

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

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

    SciTech Connect

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

    1993-07-01

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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  11. Nuclear-Electronic Coherence in Strong-Field Dissociative Ionization

    NASA Astrophysics Data System (ADS)

    Yu, Youliang; Wang, Yujun; Zeng, Shuo; Esry, B. D.

    2015-05-01

    In strong-field dissociative ionization of molecules, the ionization step is usually modeled since direct calculation is very challenging. In most of the models used to date, ionization is assumed to occur at several well-defined times accompanied by promotion of a nuclear wave packet to the ionic Born-Oppenheimer potential. Whether these nuclear wave packets should add coherently or incoherently in general is an open question. To answer it, we solve the time-dependent Schrödinger equation for one-dimensional H2+,where ionization is included naturally, and compare the observables, such as the kinetic energy release spectrum, with those from an ionization model. We then examine the validity of such models in strong-field dissociative ionization of H2+with reduced dimensionality. We do not, however, expect this physics to depend sensitively on the dimensionality. Supported by the Chemical Sciences, Geosciences, and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

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

    NASA Astrophysics Data System (ADS)

    Hahn, M.; Savin, D. W.

    2015-02-01

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

  13. 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.

  14. 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.

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

    NASA Astrophysics Data System (ADS)

    Vallance, Claire; Harland, Peter W.

    2005-04-01

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

  16. Nonthermal rotational distribution of CO/A 1Pi/ fragments produced by dissociative excitation of CO2 by electron impact. [in Mars atmosphere

    NASA Technical Reports Server (NTRS)

    Mumma, M. J.; Stone, E. J.; Zipf, E. C.

    1975-01-01

    Measurements were made of the rotational profiles of specific bands of the CO fourth-positive group (4PG). The CO 4PG bands were excited by electron impact dissociative excitation of CO2. The results are applicable to analysis of the Mariner observations of the CO 4PG in the dayglow of Mars. The results indicate that dissociative excitation of CO2 by electron impact leads to CO(A 1Pi) fragments with a rotational distribution that is highly nonthermal. The parent CO2 temperature was about 300 K in the experiment, while the fragment CO(A 1Pi) showed emission band profiles consistent with a rotational temperature greater than about 1500 K. Laboratory measurement of the reduced transmission of the hot bands by thermal CO appears to be the most direct way of determining the column density responsible for the CO(v',0) absorption of Mars.

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    SciTech Connect

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

    2013-12-15

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

  19. Collision-induced dissociation reactions and pulsed field ionization photoelectron

    SciTech Connect

    Stimson, S.

    1999-02-12

    This report summarized the four parts of the research study and describes the general conclusions. Individual chapters have been removed for separate processing. The chapter titles are: A study of the dissociation of CH{sub 3}SH{sup +} by collisional activation: Observation of non-statistical behavior; High resolution vacuum ultraviolet pulsed field ionization photoelectron band for OCS{sup +}(X{sup 2}{Pi}): An experimental and theoretical study; Rotationally resolved pulsed field ionization photoelectron bands of H{sub 2}{sup +} ({Chi}{sup 2}{Sigma}{sup +}{sub g}, v{sup +} = 0--18); and Rotationally resolved pulsed field ionization photoelectron bands of HD{sup +} ({Chi}{sup 2}{Sigma}{sup +}, v{sup +} = 0--21).

  20. 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.

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

    SciTech Connect

    Colgan, J.; Pindzola, M. S.

    2002-12-01

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

  2. 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.

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

    SciTech Connect

    Konovalov, D. A.; Bray, I.

    2010-08-15

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

  4. 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)].

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

    NASA Astrophysics Data System (ADS)

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

    2013-09-01

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

  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. Photoinduced ionization and dissociation of aniline-(methanol)n clusters

    NASA Astrophysics Data System (ADS)

    Park, Hye Sun; Nam, Sang Hwan; Song, Jae Kyu; Park, Seung Min

    2007-04-01

    A linear tandem-type time-of-flight mass spectrometer was employed to study unimolecular dissociation of metastable aniline+-(methanol)n (An+-(CH3OH)n, n = 2-9) cluster cations formed by two-photon ionization of neutral clusters. The dominant dissociation channel was to liberate a single methanol molecule, namely, An+-(CH3OH)n --> An+-(CH3OH)n-1 + CH3OH. The decay time constant of the ions ranged from 65 to 460 [mu]s and turned out to be highly dependent on the cluster size. Also, hydrogen transfer mechanism in the formation of An+-(CH3OH)nH was examined by analyzing experimental results from isotopomers, such as deuterated An-d7+-(CH3OD) and An-d7+-(CD3OD) cluster ions. Density functional theory calculations were carried out to obtain optimized structures for neutral and ionic clusters and to support mechanisms related to the hydrogen transfer and unimolecular dissociation reaction.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2007-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-11-01

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

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

    PubMed

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

    2013-09-01

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

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

    SciTech Connect

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

    1985-09-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Lillis, Robert J.; Fang, Xiaohua

    2015-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2002-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2002-07-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  19. Electron-induced ionization and dissociative ionization of iron pentacarbonyl molecules

    NASA Astrophysics Data System (ADS)

    Lacko, Michal; Papp, Peter; Wnorowski, Karol; Matejčík, Štefan

    2015-03-01

    Electron ionization (EI) and dissociative ionization (DI) of Iron pentacarbonyl molecule (Fe(CO)5) was studied using a crossed molecular and electron beam mass spectrometry technique. Positive ions FeO(CO)+, FeC(CO)2+ and CO+ of Fe(CO)5 were detected for the first time. We have determined the experimental appearance energies of positive ions, the thresholds for dissociative reactions, the experimental bond dissociation energies for (CO)nFe+-CO bond breaks (for n = 4,..., 0) and their average value for Fe-C bond energy 1.25 eV in Fe(CO)5+. We have performed extensive density functional theory (DFT) studies of the ground states of neutral molecule and fragments 1 A1' Fe(CO)5, 3B1 Fe(CO)4, 3A1Fe(CO)3, 3∑g Fe(CO)2, 3 ∑FeCO as well as positive ions 2A1 Fe(CO)5+, 4A1 Fe(CO)4+, 4A1 Fe(CO)3+, 4∑g Fe(CO)2+ and 4 ∑ FeCO+. The structures and energies of the states have beendetermined and the calculated bond dissociation energies (BDEs) were compared with present experiments as well as with previous works. Contribution to the Topical Issue "Elementary Processes with Atoms and Molecules in Isolated and Aggregated States", edited by Friedrich Aumayr, Bratislav Marinkovic, Stefan Matejick, John Tanis and Kurt H. Becker.

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

    SciTech Connect

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

    1995-01-01

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

  1. 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).

  2. Dissociation of CH4 and CD4 by electron impact - Production of metastable and high-Rydberg hydrogen and carbon fragments

    NASA Technical Reports Server (NTRS)

    Finn, T. G.; Carnahan, B. L.; Wells, W. C.; Zipf, E. C.

    1975-01-01

    Production of hydrogen and carbon atoms in metastable and high-lying Rydberg states by electron-impact dissociation of methane and deuterated methane is investigated for incident electron energies ranging from threshold values to 300 eV. Threshold energies for five different processes resulting in metastable hydrogen and carbon atoms are determined in the energy range from 20 to 70 eV, and it is shown that metastable hydrogen atoms are produced in four of these collisional processes while metastable carbon atoms are produced in the other. The nature of each collisional process is described, differential cross sections are derived for the dissociative excitation of both types of atoms to metastable and high-Rydberg states at 100 eV, and the onset energy for UV photon production is measured. Much of the data is interpreted in terms of the ion core model suggested by Kupriyanov (1968) and developed by Freund (1971).

  3. 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.

  4. 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

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

    SciTech Connect

    Sampson, D.H.

    1992-04-15

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

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

    SciTech Connect

    Sampson, D.H.

    1992-04-15

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

  7. 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.

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

    NASA Astrophysics Data System (ADS)

    Harrison, Alex G.; Malat, Jan

    1997-11-01

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

  9. A comparative study of Dissociative Ionization of N2 and CO

    NASA Astrophysics Data System (ADS)

    Pandey, Amrendra; Bapat, B.; Shamsundar, K. R.

    2014-04-01

    A comparative study on the properties of charge symmetric dissociation (CSD) and charge asymmetric dissociation (CAD) of doubly ionized N2 and CO is performed. Kinetic energy release (KER) distributions resulting from the dissociation of doubly charged molecular ions are explained on the basis of calculated potential energy curves.

  10. Exploration of the Dissociative Recombination following DNA ionization to DNA+ due to ionizing radiation

    NASA Astrophysics Data System (ADS)

    Strom, Richard A.; Zimmerly, Andrew T.; Andrianarijaona, Vola M.

    2014-05-01

    It is known that ionizing radiation generates low-energy secondary electrons, which may interact with the surrounding area, including biomolecules, such as triggering DNA single strand and double strand breaks as demonstrated by Sanche and coworkers (Radiat. Res. 157, 227(2002)). The bio-effects of low-energy electrons are currently a topic of high interest. Most of the studies are dedicated to dissociative electron attachments; however, the area is still mostly unexplored and still not well understood. We are computationally investigating the effect of ionizing radiation on DNA, such as its ionization to DNA+. More specifically, we are exploring the possibility of the dissociative recombination of the temporary DNA+ with one of the low-energy secondary electrons, produced by the ionizing radiation, to be another process of DNA strand breaks. Our preliminary results, which are performed with the binaries of ORCA, will be presented. Authors wish to give special thanks to Pacific Union College Student Senate in Angwin, California, for their financial support.

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

    SciTech Connect

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

    2004-09-15

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

  12. 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.

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

    NASA Astrophysics Data System (ADS)

    Wang, Kedong; Zatsarinny, Oleg; Bartschat, Klaus

    2016-05-01

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

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

    PubMed

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

    2016-04-28

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

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

    PubMed

    Sakai, Masamichi; Okada, Kazumasa

    2011-07-01

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

  16. 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.

  17. 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.

  18. Optical phase and the ionization-dissociation dynamics of excited H{sub 2}

    SciTech Connect

    Kirrander, A.; Fielding, H. H.; Jungen, Ch.

    2010-01-14

    We investigate the influence of optical phase on the dynamics of hydrogen molecules excited to a spectral region with competition between predominantly rotational ionization, and dissociation. We show that an appropriate choice of optical phase changes the relative timing of the ionization and dissociation. Furthermore, the temporal width of the ionization and dissociation fluxes can also be controlled, in a matter-wave analogy of transform-limited optical pulses. The close link between the optical phase and the photoinduced electronic and molecular dynamics has important implications for femtochemistry.

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

    SciTech Connect

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

    2005-05-15

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

  20. 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.

  1. LETTER TO THE EDITOR: Distortion of molecular electron density distributions by an intense laser field: dissociative ionization of ?

    NASA Astrophysics Data System (ADS)

    Vijayalakshmi, K.; Bhardwaj, V. R.; Safvan, C. P.; Mathur, D.

    1997-05-01

    The interaction of a tetrahedral molecule (carbon tetrachloride) with intense, 532 nm, 35 ps, 0953-4075/30/10/003/img2 linearly polarized, laser fields is explored theoretically and experimentally. Distortions caused by the laser field in the molecular electron density distributions are computed in an approximate fashion using quantum-chemical techniques. A comparative experimental study is performed of the dissociative ionization of 0953-4075/30/10/003/img3 in such an intense laser field and also by electron impact. Significant differences are observed and attempts are made to explore the possibility that these can be explained using field-distorted electron density distributions. Angular distributions of the 0953-4075/30/10/003/img4 fragment ion have also been measured and show a pronounced anisotropy with the ion signal being detected mainly along the direction of the laser's polarization axis.

  2. 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.

  3. Capillary Dielectric Barrier Discharge: Transition from Soft Ionization to Dissociative Plasma.

    PubMed

    Klute, Felix David; Michels, Antje; Schütz, Alexander; Vadla, Cedomil; Horvatic, Vlasta; Franzke, Joachim

    2016-05-01

    A capillary He dielectric barrier discharge was investigated with respect to its performance as a soft or dissociative ionization source. Spatiotemporal measurements of the plasma emission showed that in one voltage duty cycle the plasma evolved from a soft to dissociative ionization source. At the earliest time, the soft plasma was generated between the electrodes as well as outside the capillary forming the plasma jet. It was characterized by significant radiation arising only from He and N2(+), which are known to be important in the process of the soft ionization of the analyte. Later in time, the plasma capable of dissociating molecules develops. It is characterized by appreciable radiation from analyte dissociation products and is restricted to the interelectrode region in the capillary. Thus, for the soft ionization purposes, it is feasible to introduce the analyte exclusively in the plasma jet. For elemental analysis, the interelectrode plasma is appropriate. PMID:27032869

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

    SciTech Connect

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

    1995-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

  7. Pathways and dynamics of dissociation of ionized (H{sub 2}O){sub 2}

    SciTech Connect

    Barnett, R.N.; Landman, U.

    1995-11-30

    The energetics, geometrical and electronic structure, ionization processes, dynamics, and dissociation pathways of natural and singly and doubly ionized water dimers are investigated with simulations employing the Born-Oppenheimer local-spin-density functional molecular dynamics (BO-LSD-MD) method. Vertical and adiabatic ionization potentials and dissociation energies and barriers are calculated for various dissociation channels of the singly and doubly ionized dimer. A new bound ground-state, (H{sub 2}O){sub 2} {sup +}(a), with a hydrazine-like configuration, whose energy is lower by 0.22 eV than that of the disproportionated-ion isomer, (OH)(H{sub 3}O){sup +}, is found for the singly charged dimer cation. A state with a similar geometry is found for a bound metastable state of the doubly ionized water dimer, whose dissociation into 2(H{sub 2}O{sup +}) involves a barrier of {approx}0.68 eV. The dissociation pathways of the singly ionized dimer depend on the internal energy of the parent neutral and on the excited energy, with the OH + H{sub 2}O{sup +} channel dominating at low energies. 45 refs., 5 figs., 3 tabs.

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

    SciTech Connect

    Serov, Vladislav V.; Joulakian, Boghos B.

    2010-08-15

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

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

    SciTech Connect

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

    1988-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2003-07-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1986-01-01

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

  12. Multiphoton ionization/dissociation of cyclopentanone at the lower Rydberg states

    NASA Astrophysics Data System (ADS)

    Philis, John G.; Kosmidis, Constantine; Tzallas, Paraskevas

    1998-12-01

    The 2-photon excitation of the 3p and 3d Rydberg states in jet-cooled cyclopentanone has been investigated by resonance enhanced multiphoton ionization (REMPI) in a time of flight mass spectrometer. The three 3px,y,z components are clearly resolved while the case for the 3di excitations is obscure due to the S1 one-photon resonance. The ns laser induced mass spectra are characteristic of hard ionization while the fs laser induced mass spectrum is very similar to the Electron Impact one.

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

    SciTech Connect

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

    1990-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-02-01

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

  16. THERMOSPRAY IONIZATION WITH REPELLER-INDUCED COLLISIONALLY ACTIVATED DISSOCIATION OF DYES

    EPA Science Inventory

    Thermospray ionization with repeller-induced collisionally activated dissociation (repeller-CAD) has been used to acquire mass spectra of a series of dyes. hese were obtained by applying a voltage of 400 V on the wire repeller. he mass spectra contained arge number of fragment io...

  17. Electron-nuclear energy sharing in above-threshold multiphoton dissociative ionization of H2.

    PubMed

    Wu, J; Kunitski, M; Pitzer, M; Trinter, F; Schmidt, L Ph H; Jahnke, T; Magrakvelidze, M; Madsen, C B; Madsen, L B; Thumm, U; Dörner, R

    2013-07-12

    We report experimental observation of the energy sharing between electron and nuclei in above-threshold multiphoton dissociative ionization of H2 by strong laser fields. The absorbed photon energy is shared between the ejected electron and nuclei in a correlated fashion, resulting in multiple diagonal lines in their joint energy spectrum governed by the energy conservation of all fragment particles. PMID:23889391

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

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  19. 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.

  20. Projectile charge dependence of ionization and dissociation of CO in fast collisions

    NASA Astrophysics Data System (ADS)

    Krishnamurthi, Vidhya; Ben-Itzhak, I.; Carnes, K. D.

    1997-02-01

    Experiments have been carried out to study how changes in the interaction strength (defined as q/vb) of a fast ion-molecule colision affect the ionization and dissociation of the molecular target, in this case CO. The coincidence time-of-flight technique was used for collisions at fixed velocity (energy of 1 MeV/amu). The interaction strength was changed by varying the charge of the projectile ion. The cross sections for single and multiple ionization of CO increase rapidly for small q, approximately as q2n (where n is the number of ionized electrons), and more slowly for larger values of q. A rather simple theoretical model based on the independent electron approximation and perturbation theory is in good agreement with the data [1]. The dissociation patterns of the transient COQ+ molecular ions also exhibit a dependence on the projectile charge which is qualitatively explained by the same model.

  1. Virtual detector methods for efficiently computing momentum-resolved dissociation and ionization spectra

    NASA Astrophysics Data System (ADS)

    Kramer, Alex; Thumm, Uwe

    2016-05-01

    We discuss a class of window-transform-based ``virtual detector'' methods for computing momentum-resolved dissociation and ionization spectra by numerically analyzing the motion of nuclear or electronic quantum-mechanical wavepackets at the periphery of their numerical grids. While prior applications of such surface-flux methods considered semi-classical limits to derive ionization and dissociation spectra, we systematically include quantum-mechanical corrections and extensions to higher dimensions, discussing numerical convergence properties and the computational efficiency of our method in comparison with alternative schemes for obtaining momentum distributions. Using the example of atomic ionization by co- and counter-rotating circularly polarized laser pulses, we scrutinize the efficiency of common finite-difference schemes for solving the time-dependent Schrödinger equation in virtual detection and standard Fourier-transformation methods for extracting momentum spectra. Supported by the DoE, NSF, and Alexander von Humboldt foundation.

  2. Cross sections for the production of energetic cations by electron impact on N2 and CO2

    NASA Technical Reports Server (NTRS)

    Iga, I.; Srivastava, S. K.; Rao, M. V. V. S.; Katayama, D. H.

    1995-01-01

    Dissociative ionization cross sections for the production of singly charged energetic ions by electron impact on N2 and CO2 have been measured. The ions were divided into two groups: one with energies less than 1 eV and the other with energies greater than 1 eV. The ions detected were N+ from N2 and C+, O+, and CO+ from CO2. The electron impact energy range, and cross section data on ions is given.

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

    NASA Astrophysics Data System (ADS)

    Ayinol, M.; Aydeniz, D.

    2016-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-06-01

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

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

    PubMed

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

    2006-02-10

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

  6. Dissociation and ionization of molecular gas in the spiral arms of M51

    NASA Technical Reports Server (NTRS)

    Lees, J. F.; Lo, K. Y.

    1990-01-01

    Researchers derive the star formation rate and efficiency in the arm and interarm regions of M51 from observations of the molecular (Lo et al. 1987) and ionized (van der Hulst et al. 1988) phases of the interstellar medium, and show that the HI observations of Tilanus and Allen (1989) are consistent with dissociation of molecular gas by these young, massive stars if n sub H greater than or equal to 200 cm (-2). However, these stars are not able to dissociate or ionize all the gas, and at least 60 percent must remain molecular in the interarm regions. The efficiency of star formation in M51 seems to be similar to that in the Galaxy, and does not appear to be enhanced in the spiral arms. Therefore, the effect of the strong density wave may be only to concentrate the gas, and hence the young stars, to the arm regions.

  7. Exploring the parameter space for ionization and dissociation of H2^+ in an intense laser pulse

    NASA Astrophysics Data System (ADS)

    Roudnev, Vladimir

    2005-05-01

    We explore the dissociation and ionization of H2^+ ions aligned with a 790 nm laser field of peak intensity in the range 1.0x10^13 to 7.0x10^14 W/cm ^2 . Calculated dissociation and ionization probabilities are reported for different initial vibrational states and for the initial state averaged over the Franck-Condon distribution. The dependence on the carrier-envelope phase difference for different initial states and for pulse durations from 5 to 30 fs FWHM is presented. These results --- from direct solution of the time-dependent Schr"odinger equation --- are compared with solutions in the Born-Oppenheimer representation with two-channels for low peak laser intensities.

  8. Dissociation and ionization equilibria of deuterium fluid over a wide range of temperatures and densities

    SciTech Connect

    Zaghloul, Mofreh R.

    2015-06-15

    We investigate the dissociation and ionization equilibria of deuterium fluid over a wide range of temperatures and densities. The partition functions for molecular and atomic species are evaluated, in a statistical-mechanically consistent way, implementing recent developments in the literature and taking high-density effects into account. A new chemical model (free energy function) is introduced in which the fluid is considered as a mixture of diatomic molecules, atoms, ions, and free electrons. Intensive short range hard core repulsion is taken into account together with partial degeneracy of free electrons and Coulomb interactions among charged particles. Samples of computational results are presented as a set of isotherms for the degree of ionization, dissociated fraction of molecules, pressure, and specific internal energy for a wide range of densities and temperatures. Predictions from the present model calculations show an improved and sensible physical behavior compared to other results in the literature.

  9. Competing decay-channel fluorescence, dissociation, and ionization in superexcited levels of H{sub 2}

    SciTech Connect

    Glass-Maujean, M.; Jungen, Ch.; Reichardt, G.; Balzer, A.; Schmoranzer, H.; Ehresmann, A.; Haar, I.; Reiss, P.

    2010-12-15

    The absolute cross sections for the competing decay-channel fluorescence, dissociation, and ionization of photoexcited long-lived superexcited H{sub 2} molecular levels have been measured from the ionization threshold of H{sub 2} up to the H(1s) + H(n=3) dissociation limit. The total and partial natural widths of these levels have been determined. Good agreement is found with first principles calculations carried out with the multichannel quantum defect theory for excited levels of {sup 1{Pi}}{sub u}{sup -} symmetry, which represent 70% of the levels studied experimentally. The calculations reproduce the balance between the competing decay processes as well as its substantial evolution from level to level.

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

    NASA Astrophysics Data System (ADS)

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

    2006-03-01

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

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

    SciTech Connect

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

    2010-03-15

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

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

    SciTech Connect

    Serov, Vladislav V.

    2011-12-15

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

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

    SciTech Connect

    Toth, A.; Nagy, L.

    2011-10-03

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

  14. Ultraintense X-Ray Induced Ionization, Dissociation, and Frustrated Absorption in Molecular Nitrogen

    SciTech Connect

    Hoener, M.; Fang, L.; Murphy, B.; Berrah, N.; Kornilov, O.; Gessner, O.; Pratt, S. T.; Kanter, E. P.; Guehr, M.; Bucksbaum, P. H.; Cryan, J.; Glownia, M.; McFarland, B.; Petrovic, V.; Blaga, C.; DiMauro, L.; Bostedt, C.; Bozek, J. D.; Coffee, R.; Messerschmidt, M.

    2010-06-25

    Sequential multiple photoionization of the prototypical molecule N{sub 2} is studied with femtosecond time resolution using the Linac Coherent Light Source (LCLS). A detailed picture of intense x-ray induced ionization and dissociation dynamics is revealed, including a molecular mechanism of frustrated absorption that suppresses the formation of high charge states at short pulse durations. The inverse scaling of the average target charge state with x-ray peak brightness has possible implications for single-pulse imaging applications.

  15. Ultraintense x-ray induced ionization, dissociation and frustrated absorption in molecular nitrogen.

    SciTech Connect

    Hoener, M.; Fang, L.; Kornilov, O.; Gessner, O.; Pratt, S. T.; Guhr, M.; Kanter, E. P.; Blaga, C.; Bostedt, C.; Bozek, J. D.; Bucksbaum, P. H.; Buth, C.; Chen, M.; Coffee, R.; Cryan, J.; DiMauro, L.; Glownia, M.; Hosler, E.; Kukk, E.; Leone, S. R.; McFarland, B.; Messerschmidt, M.; Murphy, B.; Petrovic, V.; Rolles, D.; Berrah, N.; Chemical Sciences and Engineering Division; Western Michigan Univ.; LBNL; Ohio State Univ.; Louisiana State Univ.; LLNL; Univ. of Turku; Univ. of California at Berkeley; Max Planck Advanced Study Group, CFEL; LCLS

    2010-06-23

    Sequential multiple photoionization of the prototypical molecule N2 is studied with femtosecond time resolution using the Linac Coherent Light Source (LCLS). A detailed picture of intense x-ray induced ionization and dissociation dynamics is revealed, including a molecular mechanism of frustrated absorption that suppresses the formation of high charge states at short pulse durations. The inverse scaling of the average target charge state with x-ray peak brightness has possible implications for single-pulse imaging applications.

  16. 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.

  17. Ionization and dissociation dynamics of vinyl bromide probed by femtosecond extreme ultraviolet transient absorption spectroscopy

    SciTech Connect

    Lin, Ming-Fu; Neumark, Daniel M.; Gessner, Oliver; Leone, Stephen R.

    2014-02-14

    Strong-field induced ionization and dissociation dynamics of vinyl bromide, CH{sub 2}=CHBr, are probed using femtosecond extreme ultraviolet (XUV) transient absorption spectroscopy. Strong-field ionization is initiated with an intense femtosecond, near infrared (NIR, 775 nm) laser field. Femtosecond XUV pulses covering the photon energy range of 50-72 eV probe the subsequent dynamics by measuring the time-dependent spectroscopic features associated with transitions of the Br (3d) inner-shell electrons to vacancies in molecular and atomic valence orbitals. Spectral signatures are observed for the depletion of neutral C{sub 2}H{sub 3}Br, the formation of C{sub 2}H{sub 3}Br{sup +} ions in their ground (X{sup ~}) and first excited (A{sup ~}) states, the production of C{sub 2}H{sub 3}Br{sup ++} ions, and the appearance of neutral Br ({sup 2}P{sub 3/2}) atoms by dissociative ionization. The formation of free Br ({sup 2}P{sub 3/2}) atoms occurs on a timescale of 330 ± 150 fs. The ionic A{sup ~} state exhibits a time-dependent XUV absorption energy shift of ∼0.4 eV within the time window of the atomic Br formation. The yield of Br atoms correlates with the yield of parent ions in the A{sup ~} state as a function of NIR peak intensity. The observations suggest that a fraction of vibrationally excited C{sub 2}H{sub 3}Br{sup +} (A{sup ~}) ions undergoes intramolecular vibrational energy redistribution followed by the C–Br bond dissociation. The C{sub 2}H{sub 3}Br{sup +} (X{sup ~}) products and the majority of the C{sub 2}H{sub 3}Br{sup ++} ions are relatively stable due to a deeper potential well and a high dissociation barrier, respectively. The results offer powerful new insights about orbital-specific electronic processes in high field ionization, coupled vibrational relaxation and dissociation dynamics, and the correlation of valence hole-state location and dissociation in polyatomic molecules, all probed simultaneously by ultrafast table-top XUV spectroscopy.

  18. 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

  19. UV laser multiphoton ionization--dissociation of phenylsilane and its homogeneous dimers

    NASA Astrophysics Data System (ADS)

    Kosmidis, Constantine; Philis, John G.

    1998-01-01

    Homogeneous dimers of phenylsilane, formed in a rare-gas seeded supersonic expansion have been studied by laser resonant two-photon ionization combined with a time-of-flight mass spectrometer. The resonant intermediate states are the S1 (270 nm) and S2 (210 nm) ones. The ionization of phenylsilane monomer is inefficient at 210 nm whereas phenylsilane homo-dimers are resonantly ionized with high efficiency at this wavelength region. The wavelength dependence of the dimer at S1<-- S0 origin region implies the existence of at least two, almost isoenergetic, dimer conformers in the molecular beam. Photoionization of phenylsilane dimer induces chemical reactions within the dimer. The detected dissociation channels have to do with -SiH3 and -C6H6 loss and proton-transfer. Van der Waals fragmentation (evaporation of a neutral phenylsilane) is also taking place.

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

    PubMed

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

    2013-04-12

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

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

    NASA Astrophysics Data System (ADS)

    Zatsarinny, Oleg

    2013-09-01

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

  2. 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.

  3. Precision Measurement of the Ionization and Dissociation Energies of H_2, HD and D_2

    NASA Astrophysics Data System (ADS)

    Sprecher, Daniel; Liu, Jinjun; Merkt, Frédéric; Jungen, Christian; Ubachs, Wim

    2010-06-01

    The ionization and dissociation energies of H_2, HD and D_2 are benchmark quantities in molecular quantum mechanics. Comparison between experimental and theoretical values for these quantities has a long history starting with the early measurement of Beutler and the calculations of James and Coolidge. Transition wave numbers from the EF ^1Σ g^+ (v=0,N=0,1) state to selected np Rydberg states (n ≈ 60) below the X+ ^2Σ^+u (v^+=0,N^+=0,1)} ionization threshold have been measured in H_2, HD and D_2 at a precision better than 10 MHz (0.0003 cm-1). Combining the results with previous experimental and theoretical data for other energy level intervals, the ionization and dissociation energies of H_2, HD and D_2 could be determined at an absolute accuracy of better than 20 MHz. These new results represent an improvement over previous experimental results by more than one order of magnitude and the most precise values of dissociation and ionization energies measured to date in a molecular system. The results therefore offer the opportunity of a comparison with theoretical values. In particular they will be compared to the latest ab initio calculations which include nonadiabatic, relativistic and radiative effects. The comparison indicates that relativistic and radiative quantum electrodynamics corrections of order up to α^4 are needed to account for the experimental results. H. Beutler, Z. Phys. Chem. 29, 315 (1935) H. M. James and A. S. Coolidge, J. Chem. Phys. 1, 825 (1933) J. Liu, E. J. Salumbides, U. Hollenstein, J. C. J. Koelemeij, K. S. E. Eikema, W. Ubachs, and F. Merkt, J. Chem. Phys. 130, 174306 (2009) J. Liu, D. Sprecher, Ch. Jungen, W. Ubachs, and F. Merkt, submitted to J. Chem. Phys. K. Piszczatowski, G. Łach, M. Przybytek, J. Komasa, K. Pachucki, and B. Jeziorski, J. Chem. Theory Comput. 5, 3039 (2009)

  4. Floquet surface hopping: Laser-driven dissociation and ionization dynamics of H2 +

    NASA Astrophysics Data System (ADS)

    Fiedlschuster, T.; Handt, J.; Schmidt, R.

    2016-05-01

    A quantum-classical approach is developed to describe the strong-field molecular dynamics of H2 +, taking into account all degrees of freedom and simultaneously dissociation as well as ionization. The electron and nuclei are treated correlated, by propagating the nuclei stochastically on potential energy surfaces. It is demonstrated that Floquet surface hopping (FSH) is particularly well suited to describe the laser-driven dynamics. The method is tested against exact solutions of the time-dependent Schrödinger equation, where available. In addition, the FSH results are in excellent agreement with recent experimental data of the dissociation and ionization dynamics of H2 +. As an additional issue of this work, the primary importance of the focal volume average is worked out for the understanding of experimental results. It determines the gross features of the experimental spectra and provides also a natural explanation of the puzzling saturation effect in the dissociation spectra, observed experimentally. Future applications and further extensions of the method are discussed.

  5. Intensity dependence of the attosecond control of the dissociative ionization of D2

    NASA Astrophysics Data System (ADS)

    Li, H.; Alnaser, A. S.; Tong, X. M.; Betsch, K. J.; Kübel, M.; Pischke, T.; Förg, B.; Schötz, J.; Süßmann, F.; Zherebtsov, S.; Bergues, B.; Kessel, A.; Trushin, S. A.; Azzeer, A. M.; Kling, M. F.

    2014-06-01

    Light-field driven electron localization in deuterium molecules in intense near single-cycle laser fields is studied as a function of the laser intensity. The emission of D+ ions from the dissociative ionization of D2 is interrogated with single-shot carrier-envelope phase (CEP)-tagged velocity map imaging. We explore the reaction for an intensity range of (1.0-2.8) × 1014 W cm-2, where laser-driven electron recollision leads to the population of excited states of D2+. Within this range we find the onset of dissociation from 3σ states of D2+ by comparing the experimental data to quantum dynamical simulations including the first eight states of D2+. We find that dissociation from the 3σ states yields D+ ions with kinetic energies above 8 eV. Electron localization in the dissociating molecule is identified through an asymmetry in the emission of D+ ions with respect to the laser polarization axis. The observed CEP-dependent asymmetry indicates two mechanisms for the population of 3σ states: (1) excitation by electron recollision to the lower excited states, followed by laser-field excitation to the 3σ states, dominating at low intensities, and (2) direct excitation to the 3σ states by electron recollision, playing a role at higher intensities.

  6. Dissociative ionization at high laser intensities: importance of resonances and relaxation for fragmentation

    NASA Astrophysics Data System (ADS)

    Trushin, S. A.; Fuß, W.; Schmid, W. E.

    2004-10-01

    We investigated dissociative single and double ionization of the metal carbonyls Ni(CO)4, Fe(CO)5 and Cr(CO)6 in the gas phase by means of laser pulses of different durations (30-110 fs) and wavelengths (0.8 and 1.35 µm) at intensities of 2 × 1012-2 × 1014 W cm-2. The mass spectra show striking differences: for example, Fe(CO)5 strongly fragments at 0.8 µm but little at 1.35 µm, whereas for Ni(CO)4 fragmentation is higher at 1.35 µm than at 0.8 µm chromium carbonyl shows little fragmentation at both wavelengths. In other cases, fragmentation first decreases and then increases again with intensity. These and other phenomena, also published ones, can readily be understood from long-known principles, namely resonances in the parent ions, sometimes also in the neutral molecules, in particular if relaxations are also taken into account. We emphasize that fragmentation and ionization are two separate processes. We also point out that in the process of dissociative ionization in intense laser radiation, one should generally consider intermediate states, even if there is no one-photon resonance.

  7. Two-dimensional directional proton emission in dissociative ionization of H(2).

    PubMed

    Gong, Xiaochun; He, Peilun; Song, Qiying; Ji, Qinying; Pan, Haifeng; Ding, Jingxin; He, Feng; Zeng, Heping; Wu, Jian

    2014-11-14

    An intense phase-controlled orthogonally polarized two-color ultrashort laser pulse is used to singly ionize and dissociate H_{2} into a neutral hydrogen atom and a proton. Emission-direction and kinetic-energy dependent asymmetric dissociation of H_{2} is observed as a function of the relative phase of the orthogonally polarized two-color pulse. Significant asymmetric proton emission is measured in the direction between two polarization axes. Our numerical simulations of the time-dependent Schrödinger equation reproduce many of the observed features. The asymmetry is attributed to the coherent superposition of two-dimensional nuclear wave packets with opposite parities, which have the same energies and overlap in the same emission directions. PMID:25432039

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

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

    PubMed

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

    2014-10-01

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

  10. 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)