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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 Ionization and Dissociative Ionization of Biomolecules

    NASA Technical Reports Server (NTRS)

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

    2006-01-01

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

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

    DTIC Science & Technology

    2006-02-01

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

  6. Electron-impact ionization and dissociative ionization of biomolecules

    NASA Astrophysics Data System (ADS)

    Huo, Winifred

    2006-05-01

    Oxidative damages by ionizing radiation are the source of radiation-induced damages to human health. It is recognized that secondary electrons play a role in the damage process, particularly important is the damage of DNA by electrons, potentially leading to mutagenesis. The damage can be direct, by creating a DNA lesion, or indirect, by producing radicals that attack the DNA. Molecular-level study of electron interaction with DNA provides information on the damage pathways and dominant mechanisms. This investigation focuses on ionization and dissociative ionization (DI) of DNA fragments by electron-impact. For ionization we use the improved binary-encounter dipole (iBED) model [W.M. Huo, Phys. Rev. A64, 042719-1 (2001)]. For DI it is assumed that electron motion is much faster than nuclear motion, allowing DI to be treated as a two-step process and the DI cross section given by the product of the ionization cross section and dissociation probability. The ionization study covers DNA bases, sugar phosphate backbone, and nucleotides. An additivity principle is observed. For example, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3'- and C5'-deoxyribose-phospate cross sections, differing by less than 5%. The result implies that certain properties of the DNA, like the total ionization cross section, are localized properties and an additivity principle may apply. This allows us to obtain properties of a larger molecular system built up from the results of smaller subsystem fragments. The DI of guanine and cytosine has been studied. For guanine, a proton is produced from the channel where the ionized electron originates from a molecular orbital with significant charge density along the N(1)-H bond. The interaction of the proton with cytosine was also studied.

  7. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

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

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

    SciTech Connect

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

    2011-09-15

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

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

    SciTech Connect

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

    2011-01-01

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

  14. 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.

  15. 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.

  16. 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.

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2007-10-01

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

  20. 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.

  1. 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.

  2. 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.

  3. Electron impact ionization of the gas-phase sorbitol

    NASA Astrophysics Data System (ADS)

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

    2015-03-01

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

  4. 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.

  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. Electron-impact ionization of W25+

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1993-01-01

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

  8. 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.

  9. Electron Impact Ionization of the Rare Gases

    NASA Astrophysics Data System (ADS)

    Lohmann, Birgit

    2008-10-01

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

  10. Electron impact ionization-excitation of Helium

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

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

    SciTech Connect

    Phaneuf, R.A.

    1985-01-01

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

  12. Electron-impact dissociation cross sections for CHF3 and C3F8

    NASA Astrophysics Data System (ADS)

    Baio, J. E.; Yu, H.; Flaherty, D. W.; Winters, H. F.; Graves, D. B.

    2007-11-01

    Absolute total dissociation cross sections, σt,diss, by electron-impact are reported for CHF3 and C3F8 from 10 to 300 eV using the chemical gettering technique described by Winters and Inokuti (1982 Phys. Rev. A 25 1420). Data are concentrated in the near-threshold region (10-30 eV). The thresholds for dissociation of CHF3 and C3F8 are determined to be 10.4 eV and 11.9 eV, respectively. Ionization thresholds occur at 16 eV for CHF3 and 16.2 eV for C3F8. Neutral dissociation cross sections of both CHF3 and C3F8 are obtained by subtracting the ionization cross sections, σt,ion, from the total dissociation cross sections, σt,diss.

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

    NASA Astrophysics Data System (ADS)

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

    2015-01-01

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

  14. Electron-impact ionization of ozone

    NASA Astrophysics Data System (ADS)

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

    1995-10-01

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

  15. Electron-Impact Dissociation of Hydrocarbon Molecular Ions

    SciTech Connect

    Bannister, Mark E; Schultz, David Robert

    2014-01-01

    Absolute cross sections for electron-impact dissociation of CH_x^+ (x=1,2,3) producing CH_y^+ (y=0,1,2) fragment ions were measured in the 3-100 eV range using a crossed electron-ion beams technique with total uncertainties of about 11% near the cross section peaks. For CH^+ dissociation, although the measured energy dependence agrees well with two sets of storage ring measurements, the magnitude of the present results lies about 15% to 25% below the other results at the cross section peak near 40 eV. For dissociation of CH_2^+, the cross sections are nearly identical for energies above 15 eV, but they are dramatically different at lower energies. The CH^+ channel exhibits a strong peak rising from an observed threshold of about 6 eV; the C^+ channel is relatively flat down to the lowest measured energy. For dissociation of CH_3^+ and CD_3^+, good agreement is found with other results reported for the CH^+ fragment, but some differences are found for the CD_2^+ and C^+ fragments. A pilot study has also been undertaken to assess the feasibility of applying a molecular dynamics approach to treat the full range of electron-hydrocarbon dissociation processes, especially for energies above a few eV, in order to provide an overarching theoretical model that can be readily applied. Comparison with the experimental data for CH^+ shows favorable agreement.

  16. Calculation of electron-impact ionization of potassium

    NASA Astrophysics Data System (ADS)

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

    2009-11-01

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

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

    SciTech Connect

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

    1986-01-01

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

  18. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-12-01

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

  20. 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.

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

    NASA Astrophysics Data System (ADS)

    Yun-fei, Yao; Zhang-jin, Chen

    1999-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

  3. Electron impact double ionization cross sections of light elements

    NASA Astrophysics Data System (ADS)

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

    2009-06-01

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

  4. 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.

  5. Electron-impact dissociation of CH{sup +} ions: Measurement of C{sup +} fragment ions

    SciTech Connect

    Bannister, M.E.; Krause, H.F.; Vane, C.R.; Djuric, N.; Popovic, D.B.; Stepanovic, M.; Dunn, G.H.; Chung, Y.-S.; Smith, A.C.H.; Wallbank, B.

    2003-10-01

    Absolute cross sections for electron-impact dissociation of CH{sup +} producing C{sup +} fragment ions were measured in the 3-100 eV range using a crossed electron-ion beams technique with total uncertainties of about 10% near the cross-section peak. Although the measured energy dependence agrees well with two sets of storage ring measurements, the magnitude of the present results lies about 15-25 % below the other results at the cross-section peak near 40 eV. Below 10 eV, the present data tend to exceed the storage ring data, consistent with the presence of excited states in the CH{sup +} ion beam. For energies above 29 eV, the cross sections should also include contributions from dissociative ionization, though no clear onset of this channel is evident in any of the three sets of measured data.

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

    NASA Astrophysics Data System (ADS)

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

    1998-12-01

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

  7. Kinetic-energy release of fragments from electron-impact dissociation of the molecular hydrogen ion and its isotopologues

    NASA Astrophysics Data System (ADS)

    Scarlett, Liam H.; Zammit, Mark C.; Fursa, Dmitry V.; Bray, Igor

    2017-08-01

    We calculate the kinetic-energy release distributions of fragments produced for electron-impact dissociation of the vibrationally excited molecular hydrogen ion H2 + and its isotopologues D2 + and T2 +. Here we apply the adiabatic-nuclei convergent close-coupling method and compare results with several different methods, including the δ approximation. Results are presented for a number of dissociative excitation transitions and dissociative ionization as a function of the initial vibrational state of the molecule. We confirm that the square root approximation is a good approximation for the adiabatic-nuclei kinetic-energy release cross sections of H2 +. Agreement with experiment, where available, is good.

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

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Ahmed, Mowfaq Jalil

    2017-09-01

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

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

    PubMed Central

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

    2002-01-01

    The Binary-Encounter-Bethe (BEB) model for electron-impact total ionization cross sections has been applied to CH2+, CH3+, CH4+, C2H2+, C2H4+, C2H6+ and H3O+. The cross sections for the hydrocarbon ions are needed for modeling cool plasmas in fusion devices. No experimental data are available for direct comparison. Molecular constants to generate total ionization cross sections at arbitrary incident electron energies using the BEB formula are presented. A recent experimental result on the ionization of H3O+ is found to be almost 1/20 of the present theory at the cross section peak. PMID:27446718

  11. 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.

  12. Electron impact ionization of highly charged lithiumlike ions

    SciTech Connect

    Wong, K L

    1992-10-01

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

  13. 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.

  14. 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.

  15. Electron impact ionization dynamics of para-benzoquinone

    NASA Astrophysics Data System (ADS)

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

    2016-10-01

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

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

    NASA Astrophysics Data System (ADS)

    Takayama, Mitsuo

    1995-06-01

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

  17. Electron Impact Ionization of He atom using screening potential

    NASA Astrophysics Data System (ADS)

    Saha, Hari P.

    2012-06-01

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

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

    PubMed

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

    2004-12-15

    An experimental study is reported on the electron-impact total ionization cross sections (TICSs) of CCl4, CCl3F, CCl2F2, and CClF3 molecules. The kinetic energy of the colliding electrons was in the 10-85 eV range. TICSs were obtained as the sum of the partial ionization cross sections of all fragment ions, measured and identified in a linear double focusing time-of-flight mass spectrometer. The resulting TICS profiles--as a function of the electron-impact energy--have been compared both with those computed by ab initio and (semi)empirical methods and with the available experimental data. The computational methods used include the binary-encounter-Bethe (BEB) modified to include atoms with principal quantum numbers n> or =3, the Deutsch and Märk (DM) formalism, and the modified additivity rule (MAR). It is concluded that both modified BEB and DM methods fit the experimental TICS for (CF4), CClF3, CCl2F2, CCl3F, and CCl4 to a high accuracy, in contrast with the poor accord of the MAR method. A discussion on the factors influencing the discrepancies of the fittings is presented. (c) 2004 American Institute of Physics

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

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

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

  20. 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.

  1. Electron Impact Ionization Cross Sections of n-decane

    NASA Astrophysics Data System (ADS)

    Jiao, Charles; Dejoseph, Charles; Garscadden, Alan

    2001-10-01

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

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2003-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2005-06-01

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

  5. 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.

  6. Electron impact excitation and dissociation of N2 via the b 1Pi(u) state

    NASA Technical Reports Server (NTRS)

    Ratliff, J. M.; James, G. K.; Trajmar, S.; Ajello, J. M.; Shemansky, D. E.

    1991-01-01

    Electron impact excitation of the b 1Pi(u) state in N2 plays a prominent role in the dissociation of the molecule and thus in the production of atomic nitrogen in planetary atmospheres. Electron impact excitation cross sections combined with electron-impact-induced fluorescence measurements can yield the corresponding dissociation cross sections. Serious discrepancies exist among excitation cross sections reported in the literature. To clarify the situation, these cross sections were measured at two impact energies using electron energy loss spectroscopy. The new results are in agreement with recent values deduced from optical measurements and fall midway between previous results which are too high or low by factors of 2.

  7. 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.

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

    PubMed Central

    2016-01-01

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

  9. 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.

  10. 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.

  11. Theoretical study of electron impact-ionization of molecules

    NASA Astrophysics Data System (ADS)

    Al-Hagan, Ola

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

  12. Electron Impact K-shell Ionization of Atomic Targets

    NASA Astrophysics Data System (ADS)

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

    2008-05-01

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

  13. R-matrix study of electron impact excitation and dissociation of CH+ ions

    NASA Astrophysics Data System (ADS)

    Chakrabarti, K.; Dora, A.; Ghosh, R.; Choudhury, B. S.; Tennyson, Jonathan

    2017-09-01

    Electron impact excitation and electron impact dissociation of CH+ ions are studied in the framework of the R-matrix method using the diatomic version of the UK molecular R-matrix codes. A configuration interaction calculation is first performed to yield the potential energy curves of the lowest eight singlet and triplet states of CH+. Scattering calculations are then performed to yield vibrationally-resolved electronic excitations to the lowest three bound states, namely the a {}3{{\\Pi }}, A {}1{{\\Pi }} and the b {}3{{{Σ }}}-. Electron impact dissociation cross sections are obtained from the assumption that all electronic excitations above the dissociation threshold result in dissociation. Bound states of CH and resonance positions and widths of Feshbach resonances in the e-CH+ system are also calculated at the CH+ equilibrium bond length 2.137 a0.

  14. 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

  15. 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.

  16. Electron-impact detachment and dissociation of C4- ions

    NASA Astrophysics Data System (ADS)

    Le Padellec, A.; Rabilloud, F.; Pegg, D.; Neau, A.; Hellberg, F.; Thomas, R.; Schmidt, H. T.; Larsson, M.; Danared, H.; Källberg, A.; Andersson, K.; Hanstorp, D.

    2001-12-01

    CRYRING was used to study collision processes between an electron and a negative ion cluster C4-. The total detachment cross sections for the production of the neutral 4C, 3C, 2C, and C fragments were measured. The cross sections for pure detachment, and for detachment plus dissociation leading to the production of C3+C, 2C2, and C2+2C were extracted using a grid. It was found that the pure detachment process overwhelmingly dominates all other fragmentation processes. The threshold location for the detachment channel is found to be around 6.0 eV. Although the doubly charged negative ion C42- has received little previous attention, a defined near-threshold resonance observed in the detachment cross section curve, has been associated with the short-lived state C42- (0.7 fs lifetime).

  17. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1991-09-01

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

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

    SciTech Connect

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

    1996-07-01

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

  20. On the dissociation of nitrogen by electron impact and by EUV photo-absorption. [in aurorqs

    NASA Technical Reports Server (NTRS)

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

    1978-01-01

    The dissociation of N2 by electron impact and by absorption of EUV photons was studied experimentally. It was shown that most of the N2 molecules excited to singlet states in the 12.5-14.86 eV range are depopulated by predissociation and not by the emission of EUV photons and that this is the principal mechanism by which N2 is dissociated by solar EUV absorption and by electron impact. The experiments provide a physical explanation for the near absence of N2 band radiation in airglow and auroral EUV spectra, and rule out the excitation of EUV radiation as a major factor in the overall energy economy of an auroral substorm.

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

    PubMed

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

    2008-09-01

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

  2. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-02-01

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

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

    NASA Technical Reports Server (NTRS)

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

    1975-01-01

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

  5. Electron-Impact Excitation and Ionization in Air

    DTIC Science & Technology

    2009-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-08-01

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

  7. 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.

  8. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  13. 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 of CO2. Absolute emission cross sections for these multiplets were measured from threshold to 350 eV. The electrostatically focussed electron gun used in this series of experiments is described in detail. The atomic multiplets which were produced by dissociative excitation of CO2 and the cross sections at 100 eV are given. The dependence of the excitation functions on electron energy shows that these multiplets are produced by electric-dipole-allowed transitions in CO2.

  14. 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.

  15. Linear momentum transfer effects in molecular dissociation produced by electron impact.

    NASA Technical Reports Server (NTRS)

    Misakian, M.; Pearl, J. C.; Mumma, M. J.

    1972-01-01

    In this study of molecular dissociation produced by electron impact, diatomic systems and polyatomic molecules are considered, and attention is given to the effects of thermal motion and of momentum transfer in the collision process. A procedure is described which makes it possible to 'construct' both the laboratory angular distribution and velocity distribution of the atomic fragments (or, alternatively, the time-of-flight distribution). The calculation assumes that s-wave electron scattering predominates, i.e., that excitation occurs near threshold. The computational procedure may also be reversed to allow construction of possible molecular models to fit given experimental angular and velocity distribution data.

  16. Dynamics of cluster dissociation following multiphoton ionization

    SciTech Connect

    Castleman, A.W.

    1986-01-01

    A major advance in the study of unimolecular dissociation and the spectroscopy of clusters has become available through the use of multiphoton ionization coupled with a reflectron introduced into the drift region of a time-of-flight mass spectrometer. Using single and two-color tunable pulsed lasers, the excess energy introduced into a cluster can be well controlled. The power of this method is demonstrated by the results of recent investigations of hydrogen-bonded clusters which, following ionization, lead to an internal ion-molecule reaction, and cluster fragmentation. The role of dissociation and the influence of the thermochemical stability of cluster ions in effecting the appearance of magic numbers in certain cluster distributions is discussed. The application of this method in determining ionization potentials of probe molecules following successive clustering with a solvent species is also presented.

  17. 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.

  18. Electron-impact excitation and ionization of boron

    NASA Astrophysics Data System (ADS)

    Wang, Kedong; Zatsarinny, Oleg; Bartschat, Klaus

    2016-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2001-08-01

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

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

    PubMed Central

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

    1997-01-01

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

  1. 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.

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

    SciTech Connect

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

    2016-05-14

    We analyzed calculated cross sections for K-, L-, and M-shell ionization by electron impact to determine the energy ranges over which these cross sections are consistent with the Bethe equation for inner-shell ionization. Our analysis was performed with K-shell ionization cross sections for 26 elements, with L-shell ionization cross sections for seven elements, L{sub 3}-subshell ionization cross sections for Xe, and M-shell ionization cross sections for three elements. The validity (or otherwise) of the Bethe equation could be checked with Fano plots based on a linearized form of the Bethe equation. Our Fano plots, which display theoretical cross sections and available measured cross sections, reveal two linear regions as predicted by de Heer and Inokuti [in Electron Impact Ionization, edited by T. D. Märk and G. H. Dunn, (Springer-Verlag, Vienna, 1985), Chap. 7, pp. 232–276]. For each region, we made linear fits and determined values of the two element-specific Bethe parameters. We found systematic variations of these parameters with atomic number for both the low- and the high-energy linear regions of the Fano plots. We also determined the energy ranges over which the Bethe equation can be used.

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

    SciTech Connect

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

    2015-09-11

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

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

    NASA Astrophysics Data System (ADS)

    Kumar, Neeraj; Pal, Satyendra

    2013-09-01

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

  5. 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}.

  6. Non-dissociative and dissociative ionization of a CO+ beam in intense ultrashort laser pulses

    NASA Astrophysics Data System (ADS)

    Gaire, B.; Ablikim, U.; Zohrabi, M.; Roland, S.; Carnes, K. D.; Ben-Itzhak, I.

    2011-05-01

    We have investigated the ionization of CO+ beams in intense ultrashort laser pulses. With the recent upgrades to our coincidence three-dimensional momentum imaging method we are able to measure both non-dissociative and dissociative ionization of the molecular-ion beam targets. Using CO+ as an example, we have found that non-dissociative ionization (leading to the metastable dication CO2+) involves a direct transition, i.e. the molecule is ionized with little or no internuclear distance stretch. Dissociative ionization (C+ + O+) occurs both directly and indirectly, stretching first and then ionizing. Our results show that the yield of dissociative ionization is higher than that of non-dissociative ionization and can be manipulated with the laser pulse duration by suppressing the indirect ionization path using ultrashort pulses (<=10 fs). Supported by the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy.

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

    NASA Astrophysics Data System (ADS)

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

    2006-08-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-07-01

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

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

    NASA Astrophysics Data System (ADS)

    Hahn, Yukap

    1980-07-01

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

  10. 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.

  11. 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.

  12. 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.

  13. 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.

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

    DOE PAGES

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

    2015-09-11

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

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

  17. Orientation dependence in multichannel dissociative ionization of OCS molecules

    NASA Astrophysics Data System (ADS)

    Sakemi, Yusuke; Minemoto, Shinichirou; Sakai, Hirofumi

    2017-07-01

    With 800-nm, 25-fs elliptically polarized ionization pulses, we observe molecular frame photoelectron angular distributions (MF-PADs) correlated with different dissociative ionization channels: OCS+→S+ +CO, CO++S, CS++O, and O++CS. We find that the asymmetry in the MF-PAD depends on the specific dissociation channel and the laser intensities. For the dissociation channel leading to the production of O+, the OCS molecules are more likely to be ionized when the electric field points toward the O atom, while for other dissociation channels, they are more likely to be ionized when the electric field points toward the S atom.

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

    NASA Astrophysics Data System (ADS)

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

    1999-02-01

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

  19. 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.

  20. 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.

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

    NASA Astrophysics Data System (ADS)

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

    1997-11-01

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

  2. 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.

  3. 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.

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

    SciTech Connect

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

    2015-11-01

    We have measured electron impact ionization for Fe{sup 7+} from the ionization threshold up to 1200 eV. The measurements were performed using the TSR heavy ion storage ring. The ions were stored long enough prior to measurements to remove most metastables, resulting in a beam of 94% ground-level ions. Comparing with the previously recommended atomic data, we find that the Arnaud and Raymond cross section is up to about 40% larger than our measurement, with the largest discrepancies below about 400 eV. The cross section of Dere agrees to within 10%, which is about the magnitude of the experimental uncertainties. The remaining discrepancies between our measurement and the Dere calculations are likely due to shortcomings in the theoretical treatment of the excitation-autoionization contribution.

  5. 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.

  6. 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.

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

    SciTech Connect

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

    2010-11-15

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

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

    SciTech Connect

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

    2016-05-06

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-11-01

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

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

    SciTech Connect

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

    2008-01-01

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

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

    NASA Astrophysics Data System (ADS)

    Pal, Satyendra; Kumar, Neeraj

    2013-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Dorn, Alexander

    2016-09-01

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

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

    SciTech Connect

    Amirav, A.; Dagan, S.

    1995-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1998-05-01

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

  16. Dissociative Ionization and Thermal Decomposition of Cyclopentanone.

    PubMed

    Pastoors, Johan I M; Bodi, Andras; Hemberger, Patrick; Bouwman, Jordy

    2017-09-21

    Despite the growing use of renewable and sustainable biofuels in transportation, their combustion chemistry is poorly understood, limiting our efforts to reduce harmful emissions. Here we report on the (dissociative) ionization and the thermal decomposition mechanism of cyclopentanone, studied using imaging photoelectron photoion coincidence spectroscopy. The fragmentation of the ions is dominated by loss of CO, C2 H4 , and C2 H5 , leading to daughter ions at m/z 56 and 55. Exploring the C5 H8 O(.)(+) potential energy surface reveals hydrogen tunneling to play an important role in low-energy decarbonylation and probably also in the ethene-loss processes, yielding 1-butene and methylketene cations, respectively. At higher energies, pathways without a reverse barrier open up to oxopropenyl and cyclopropanone cations by ethyl-radical loss and a second ethene-loss channel, respectively. A statistical Rice-Ramsperger-Kassel-Marcus model is employed to test the viability of this mechanism. The pyrolysis of cyclopentanone is studied at temperatures ranging from about 800 to 1100 K. Closed-shell pyrolysis products, namely 1,3-butadiene, ketene, propyne, allene, and ethene, are identified based on their photoion mass-selected threshold photoelectron spectrum. Furthermore, reactive radical species such as allyl, propargyl, and methyl are found. A reaction mechanism is derived incorporating both stable and reactive species, which were not predicted in prior computational studies. © 2017 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.

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

    SciTech Connect

    Shakeshaft, Robin

    2010-03-15

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

  18. 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.

  19. 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.

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

    SciTech Connect

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

    2007-07-15

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

  1. 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.

  2. 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.

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

    SciTech Connect

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

    2005-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2008-10-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-07-01

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

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

    PubMed

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

    2012-09-21

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

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

    NASA Astrophysics Data System (ADS)

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

    2012-09-01

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

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

    PubMed

    Ma, Yuning; Hites, Ronald A

    2013-08-01

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

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

    SciTech Connect

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

    2007-05-15

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

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

    NASA Astrophysics Data System (ADS)

    Granados-Castro, Carlos Mario; Ancarani, Lorenzo Ugo

    2017-03-01

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

  11. Near-Threshold Total Dissociation Electron Impact Cross Sections for C2F6, C3F8, and CHF3

    NASA Astrophysics Data System (ADS)

    Flaherty, David; Kasper, Michael; Graves, David; Winters, Harold

    2004-09-01

    Absolute total dissociation electron impact cross sections, σ _TD, are reported near threshold (8-30eV) for C_2F_6, C_3F_8, and CHF3 using the technique described by Winters and Inokuti [1]. Total neutral dissociation cross sections, σ _ND, are obtained by subtraction using total ionization cross sections, e.g. [2]. σ _ND for C_2F6 and C_3F8 are compared with values inferred from swarm data and to reported partial dissociation cross sections for production of CF3 and C_2F5 over the range of electron energies measured [3,4]. Work supported in part by the NSF/SRC ERC for Environmentally Benign Semiconductor Manufacturing. [1] H. Winters and M. Inokuti, Phys. Rev. A 25, 1420 (1982). [2] L. Christophorou and J. Olthoff, J. Phys. Chem. Ref. Data 28, 131, (1999) [3] S. Motlagh and J. Moore, J. Chem. Phys., Vol. 109 (2), 432, (1998) [4] Hayashi and Niwa, Gaseous Dielectrics V, Pergamon, New York, p. 27, (1987).

  12. An (e, 2e + ion) investigation of dissociative ionization of methane.

    PubMed

    Xu, Shenyue; Ma, Xinwen; Ren, Xueguang; Senftleben, Arne; Pflüger, Thomas; Yan, Shuncheng; Zhang, Pengju; Yang, Jie; Ullrich, Joachim; Dorn, Alexander

    2013-04-07

    We present in this paper an (e, 2e + ion) investigation of the dissociative ionization of methane by 54 eV electron impact employing the advanced reaction microscope. By measuring two electrons and the ion in the final state in triple coincidence, the species of the ions are identified and the energies deposited into the target are determined. The species and the kinetic energies of the fragmented ion show strong dependence on the intermediate states of the parent ion. Possible decay pathways for the production of different species of ions are analyzed.

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

    NASA Astrophysics Data System (ADS)

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

    2001-09-01

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

  14. Collisionally-activated dissociation in hyperthermal surface ionization of cholesterol

    NASA Astrophysics Data System (ADS)

    Dagan, Shai; Danon, Albert; Amirav, Aviv

    1992-03-01

    Cholesterol in a hydrogen-seeded supersonic molecular beam was scattered from a continuously oxidized rhenium foil. The hyperthermal surface scattering exhibited efficient molecular ionization with a controlled amount of molecular ion dissociation. At 5.3 eV incident molecular kinetic energy the hyperthermal surface ionization mass spectrum was dominated by the parent molecular ion. Upon the increase of the molecular kinetic energy, a gradual increase in the degree of ion dissociation was observed. At 22eV incident kinetic energy the parent ion was completely dissociated and the mass spectrum was dominated by an extensive consecutive fragmentation. An efficient kinetic-vibrational energy transfer was observed, and it is extimated to be over 18% of the available incident kinetic energy. The implication for surface collisionally-activated dissociation of polyatomic ions is discussed. Rhenium oxide is suggested as an optimal surface for this purpose, as well as for the hyperthermal surface ionization of neutral species.

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

    NASA Astrophysics Data System (ADS)

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

    2009-04-01

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

  16. 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.

  17. 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.

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

    SciTech Connect

    Winkler, C.; Maerk, T.D.

    1995-12-31

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

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

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

    NASA Astrophysics Data System (ADS)

    Bartschat, Klaus; Zatsarinny, Oleg

    2012-06-01

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

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

    NASA Astrophysics Data System (ADS)

    Colgan, James; Feagin, James; Pindzola, Michael

    2012-06-01

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

  2. 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.

  3. Theoretical resonant electron-impact vibrational excitation, dissociative recombination and dissociative excitation cross sections of ro-vibrationally excited BeH+ ion

    NASA Astrophysics Data System (ADS)

    Laporta, V.; Chakrabarti, K.; Celiberto, R.; Janev, R. K.; Mezei, J. Zs; Niyonzima, S.; Tennyson, J.; Schneider, I. F.

    2017-02-01

    A theoretical study of resonant vibrational excitation, dissociative recombination and dissociative excitation processes of the beryllium monohydride cation, BeH+, induced by electron impact, is reported. Full sets of ro-vibrationally-resolved cross sections and of the corresponding Maxwellian rate coefficients are presented for the three processes. Particular emphasis is given to the high-energy behaviour. Potential curves of {}2{{{Σ }}}+, {}2{{\\Pi }} and {}2{{Δ }} symmetries and the corresponding resonance widths, obtained from R-matrix calculations, provide the input for calculations which use a local complex-potential model for resonant collisions in each of the three symmetries. Rotational motion of nuclei and isotopic effects are also discussed. The relevant results are compared with those obtained using a multichannel quantum defect theory method. Full results are available from the Phys4Entry database.

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

    SciTech Connect

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

    2011-12-15

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

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

    NASA Astrophysics Data System (ADS)

    Savin, Daniel Wolf; Ciccarino, Christopher

    2017-06-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-06-01

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

  7. 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.

  8. 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.

  9. 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.

  10. 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

  11. Comparative dissociation of peptide polyanions by electron impact and photo-induced electron detachment.

    PubMed

    Larraillet, Vincent; Vorobyev, Aleksey; Brunet, Claire; Lemoine, Jérôme; Tsybin, Yury O; Antoine, Rodolphe; Dugourd, Philippe

    2010-04-01

    We compare product-ion mass spectra produced by electron detachment dissociation (EDD) and electron photodetachment dissociation (EPD) of multi-deprotonated peptides on a Fourier transform and a linear ion trap mass spectrometer, respectively. Both methods, EDD and EPD, involve the electron emission-induced formation of a radical oxidized species from a multi-deprotonated precursor peptide. Product-ion mass spectra display mainly fragment ions resulting from backbone cleavages of C(alpha)-C bond ruptures yielding a and x ions. Fragment ions originating from N-C(alpha) backbone bond cleavages are also observed, in particular by EPD. Although EDD and EPD methods involve the generation of a charge-reduced radical anion intermediate by electron emission, the product ion abundance distributions are drastically different. Both processes seem to be triggered by the location and the recombination of radicals (both neutral and cation radicals). Therefore, EPD product ions are predominantly formed near tryptophan and histidine residues, whereas in EDD the negative charge solvation sites on the backbone seem to be the most favorable for the nearby bond dissociation. 2010. Published by Elsevier Inc.

  12. Dissociation and dissociative ionization of H2+ using the time-dependent surface flux method

    NASA Astrophysics Data System (ADS)

    Yue, Lun; Madsen, Lars Bojer

    2013-12-01

    The time-dependent surface flux method developed for the description of electronic spectra L. Tao and A. Scrinzi, New J. Phys. 14, 013021 (2012), 10.1088/1367-2630/14/1/013021; A. Scrinzi, New J. Phys. 14, 085008 (2012), 10.1088/1367-2630/14/8/085008] is extended to treat dissociation and dissociative ionization processes of H2+ interacting with strong laser pulses. By dividing the simulation volume into proper spatial regions associated with the individual reaction channels and monitoring the probability flux, the joint energy spectrum for the dissociative ionization process and the energy spectrum for dissociation is obtained. The methodology is illustrated by solving the time-dependent Schrödinger equation for a collinear one-dimensional model of H2+ with electronic and nuclear motions treated exactly and validated by comparison with published results for dissociative ionization. The results for dissociation are qualitatively explained by analysis based on dressed diabatic Floquet potential energy curves, and the method is used to investigate the breakdown of the two-surface model.

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

    NASA Astrophysics Data System (ADS)

    Bhutadia, Harshad; Vinodkumar, Minaxi; Antony, Bobby

    2012-11-01

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

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

    NASA Astrophysics Data System (ADS)

    Bonhommeau, David; Halberstadt, Nadine; Viel, Alexandra

    2006-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  16. Dissociation dynamics of methanol clusters following multiphoton ionization

    SciTech Connect

    Morgan, S.; Castleman, A.W. Jr. )

    1989-06-01

    Following multiphoton ionization (MPI), neutral methanol clusters are found to undergo a well-known ion-molecule reaction which leads to the production of protonated clusters. Evaporative dissociation rates of the cluster ions are measured for sizes ranging from the dimer to the 21-mer following MPI. There is a general trend of the rates decreasing with time after the initial ionization event in accordance with the evaporative ensemble model. Rates measured at long times after ionization display a consistent trend of increasing with cluster size. These findings are shown to be in accord with statistical considerations of evaporative unimolecular dissociation. Collision-induced-dissociation cross sections are found to generally increase with size; the finding of a local minimum in the value for H{sup +}(CH{sub 3}OH){sub 3} is in agreement with predictions of its structure. Finally, through a combination of unimolecular evaporative and collision-induced-dissociation processes, as many as five methanol monomers are found to be lost from a cluster as small as H{sup +} (CH{sub 3}OH){sub 7}.

  17. Solvation and dissociation in weakly ionized polyelectrolytes.

    PubMed

    Onuki, Akira; Okamoto, Ryuichi

    2009-03-26

    We present a Ginzburg-Landau theory of inhomogeneous polyelectrolytes with a polar solvent. First, we take into account the molecular (solvation) interaction among the ions, the charged monomers, the uncharged monomers, and the solvent molecules, together with the electrostatic interaction with a composition-dependent dielectric constant. Second, we treat the degree of ionization as a fluctuating variable dependent on the local electric potential. With these two ingredients included, our results are as follows. (i) We derive a mass reaction law and a general expression for the surface tension. (ii) We calculate the structure factor of the composition fluctuations as a function of various parameters of the molecular interactions, which provides a general criterion of the formation of mesophases. (iii) We numerically examine some typical examples of interfaces and mesophase structures, which strongly depend on the molecular interaction parameters.

  18. 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.

  19. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2005-11-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

  2. 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)].

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

    SciTech Connect

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

    2001-08-24

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

  4. Dissociative recombination and electron-impact de-excitation in CH photon emission under ITER divertor-relevant plasma conditions

    NASA Astrophysics Data System (ADS)

    van Swaaij, G. A.; Bystrov, K.; Borodin, D.; Kirschner, A.; van der Vegt, L. B.; van Rooij, G. J.; De Temmerman, G.; Goedheer, W. J.

    2012-09-01

    For understanding carbon erosion and redeposition in nuclear fusion devices, it is important to understand the transport and chemical break-up of hydrocarbon molecules in edge plasmas, often diagnosed by emission of the CH A 2Δ-X 2Π Gerö band around 430 nm. The CH A-level can be excited either by electron-impact (EI) or by dissociative recombination (DR) of hydrocarbon ions. These processes were included in the 3D Monte Carlo impurity transport code ERO. A series of methane injection experiments was performed in the high-density, low-temperature linear plasma generator Pilot-PSI, and simulated emission intensity profiles were benchmarked against these experiments. It was confirmed that excitation by DR dominates at Te < 1.5 eV. The results indicate that the fraction of DR events that lead to a CH radical in the A-level and consequent photon emission is at least 10%. Additionally, quenching of the excited CH radicals by EI de-excitation was included in the modeling. This quenching is shown to be significant: depending on the electron density, it reduces the effective CH emission by a factor of 1.4 at ne = 1.3 × 1020 m-3, to 2.8 at ne = 9.3 × 1020 m-3. Its inclusion significantly improved agreement between experiment and modeling.

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

    SciTech Connect

    Stimson, Stephanie

    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 CH3SH+ by collisional activation: Observation of non-statistical behavior; High resolution vacuum ultraviolet pulsed field ionization photoelectron band for OCS+(X2π): An experimental and theoretical study; Rotationally resolved pulsed field ionization photoelectron bands of H2+2Σ+g, v+ = 0--18); and Rotationally resolved pulsed field ionization photoelectron bands of HD+2Σ+, v+ = 0--21).

  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. 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.

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

    PubMed

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

    2009-01-01

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

  9. 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.

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

    PubMed

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

    2005-12-21

    Electron impact (70 eV) mass spectra of a series of C1-C6 alcohols encased in large superfluid liquid helium nanodroplets (approximately 60,000 helium atoms) have been recorded. The presence of helium alters the fragmentation patterns when compared with the gas phase, with some ion product channels being more strongly affected than others, most notably cleavage of the C(alpha)-H bond in the parent ion to form the corresponding oxonium ion. Parent ion intensities are also enhanced by the helium, but only for the two cyclic alcohols studied, cyclopentanol and cyclohexanol, is this effect large enough to transform the parent ion from a minor product (in the gas phase) into the most abundant ion in the helium droplet experiments. To demonstrate that these findings are not unique to alcohols, we have also investigated several ethers. The results obtained for both alcohols and ethers are difficult to explain solely by rapid cooling of the excited parent ions by the surrounding superfluid helium, although this undoubtedly takes place. A second factor also seems to be involved, a cage effect which favors hydrogen atom loss over other fragmentation channels. The set of molecules explored in this work suggest that electron impact ionization of doped helium nanodroplets does not provide a sufficiently large softening effect to be useful in analytical mass spectrometry.

  11. 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).

  12. X-ray FEL induced multiphton ionization and molecular dissociation

    NASA Astrophysics Data System (ADS)

    Fang, Li

    2014-05-01

    X-ray Free electron lasers (FELs) enable multiphoton absorption at the core levels which is not possible with conventional light sources. Multiphoton ionization and the subsequent core-hole states relaxation lead to dramatic dynamics of the molecules. We present our experimental as well as theoretical results on multiphoton ionization and molecular fragmentation dynamics with the Linac Coherent Light Source (LCLS) at SLAC National Laboratory. We investigated simple diatomic system, N2 molecules, where we used multiphoton ionization as an internal clock for imaging the dynamics in time and the internuclear separation domain. We observed the modification of the ionization dynamic by varying the x-ray beam parameters and the effect of the spatial distribution on the ionization. We also investigated a complex system, C60, where we developed a full model to simulate the multiphoton ionization that results in various molecular ions and atomic carbon ions up to charge 6+. The calculation agrees well with our experimental results in ion kinetic energy distribution and charge state distribution. Moreover, our model provides further insights into the photoionization and dissociation dynamics as a function of time and molecular size. This work was supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Division of Chemical Sciences, Geosciences, and Biosciences. Thank T. Osipov, B. Murphy, Z. Jurek, S.-K. Son, R. Santra, and N. Berrah, M. Hoener, O. Gessner, F. Tarantelli, S.T. Pratt, O. Kornilov, C. Buth, M. Güehr, E. Kanter, C. Bostedt, J. D. Bozek, P. H. Bucksbaum, M. Chen, R. Coffee, J. Cryan, L. DiMauro, M. Glownia, E. Kukk, S.R. Leone, L. Avaldi, P. Bolognesi, J. Eland, J. Farrell, R. Feifel, L. Frasinski, D.T. Ha, K. Hoffmann, B. McFarland, C. Miron, M. Mucke, R. Squibb, K. Ueda for their contributions to this work.

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

    NASA Astrophysics Data System (ADS)

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

    1998-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-03-01

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

  15. 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

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

    NASA Astrophysics Data System (ADS)

    Zhang-jin, Chen; Ke-zun, Xu

    1999-05-01

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

  17. 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.

  18. 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.

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

    SciTech Connect

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

    2010-04-15

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-04-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2010-03-01

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

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

    PubMed

    Champion, C

    2010-01-07

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1998-02-01

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

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2013-05-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

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

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

    SciTech Connect

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

    1995-05-21

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

  14. Dissociative excitation of the B/sup 2/. sigma. /sup +//sub 1/2/ states of mercury monohalides by electron impact

    SciTech Connect

    Malinin, A.N.; Shuaibov, A.K.; Shevera, V.S.

    1983-07-01

    An investigation was made of the process of excitation of HgCl/sub 2/, HgBr/sub 2/, and HgI/sub 2/ molecules by electron impact producing B/sup 2/..sigma../sup +//sub 1/2/ states of HgCl*, HgBr*, and HgI*. The maximum values of the cross sections for dissociative excitation were found at low electron energies; the values of these cross sections were sigma = (6 +- 3) x 10/sup -18/, (7.5 +- 3) x 10/sup -17/, and (1.2 +- 0.6) x 10/sup -17/ cm/sup 2/ for HgCl*, HgBr*, and HgI*, respectively. The role of such dissociative excitation in lasing was analyzed.

  15. 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).

  16. IONIZATION AND COLLISION INDUCED DISSOCIATION OF STEROID BIS-GLUCURONIDES.

    PubMed

    Esquivel, Argitxu; Matabosch, Xavier; Kotronoulas, Aristotelis; Balcells, Georgina; Joglar, Jesús; Ventura, Rosa

    2017-07-21

    Studies on steroid metabolism are of utmost importance to improve the detection capabilities of anabolic androgenic steroids (AAS) misuse in sports drug testing. In humans, glucuronoconjugates are the most abundant phase II metabolites of AAS. Bis-glucuronidation is a reaction where two separated functional groups on the same molecule are conjugated with glucuronic acid. These metabolites have not been studied in depth for steroids and could be interesting markers for doping control. The aim of the present work was to study the ionization and collision induced dissociation of steroid bis-glucuronides to be able to develop mass spectrometric analytical strategies for their detection in urine samples after AAS administration. Since steroid bis-glucuronides are not commercially available, nineteen of them were qualitatively synthesized to study their mass spectrometric behavior. Bis-glucuronides ionized as [M+NH4 ](+) in positive mode, and as [M-H](-) and [M-2H](2-) in negative mode. The most specific product ions of steroid bis-glucuronides in positive mode resulted from the neutral losses of 387 and 405 Da (corresponding to [M+NH4 -NH3 -2gluc-H2 O](+) and [M+NH4 -NH3 -2gluc-2H2 O](+) , respectively, being 'gluc' a dehydrated glucuronide moiety) and, in negative mode, the fragmentation of [M-2H](2-) showed ion losses of m/z 175 and 75 (gluc(-) and HOCH2 CO2(-) , respectively). Based on the common behavior, a selected reaction monitoring method was developed to detect bis-glucuronide metabolites in urine samples. As a proof of concept, urines obtained after administration of norandrostenediol were studied, and a bis-glucuronide metabolite was detected in those urines. The results demonstrate the usefulness of the analytical strategy to detect bis-glucuronide metabolites in urine samples, and the formation of these metabolites after administration of AAS. This article is protected by copyright. All rights reserved.

  17. 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.

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

    PubMed

    Whitehead, Kenia; Hedges, John I

    2003-01-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2016-09-01

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

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

    PubMed

    Rahn, Anja K K; Yaylayan, Varoujan A

    2013-06-26

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

  1. 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.

  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

    2016-05-03

    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.

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

    NASA Astrophysics Data System (ADS)

    Aydinol, Mahmut

    2017-02-01

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

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

    NASA Astrophysics Data System (ADS)

    Aydinol, Mahmut

    2017-02-01

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

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

    SciTech Connect

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

    2005-09-15

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

  7. Multiphoton ionization of ammonia clusters and the dissociation dynamics of protonated cluster ions

    SciTech Connect

    Echt, O.; Dao, P.D.; Morgan, S.; Castleman A.W. Jr.

    1985-05-01

    Ammonia clusters, produced via supersonic expansion, are subjected to multiphoton ionization using a tunable pulsed laser. The products of ionization and subsequent dissociation processes are investigated using a time-of-flight mass spectrometer equipped with a reflectron (reflecting electric field). Cluster ions containing more than 65 ammonia molecules were formed via internal ion molecule reactions taking place within the initially ionized aggregate. The proton transfer reaction which ensues leads to substantial excess internal energy and subsequent cluster decomposition. Dissociation due to both collisional and unimolecular processes was identified in the field-free region. Studies of the dynamics of dissociation were made for species up to the protonated 16-mer; the loss of up to at least five monomer units following cluster ion formation was observed. Results of an investigation of the influence of laser fluence and the energy of the ionizing photons are also presented.

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

    SciTech Connect

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

    2006-07-15

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

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

    SciTech Connect

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

    2010-03-15

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

  10. Multiphoton ionization studies of xenon clusters

    SciTech Connect

    Echt, O.; Cook, M.C.; Castleman, A.W.

    1987-04-03

    Non-resonant multiphoton ionization of xenon clusters has revealed the same magic numbers as found in the case of electron-impact ionization. Large dissociation rates are found for the trimer through pentamer ion, measured on a time scale of approx 10/sup -7/ s after ionization.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

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

    NASA Astrophysics Data System (ADS)

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

    2014-07-01

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

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

    SciTech Connect

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

    2005-11-15

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

  14. Fully differential study on dissociative ionization dynamics of deuteron molecules in strong elliptical laser fields

    NASA Astrophysics Data System (ADS)

    Shao, Yun; He, Peilun; Liu, Ming-Ming; Sun, Xufei; Li, Min; Deng, Yongkai; Wu, Chengyin; He, Feng; Gong, Qihuang; Liu, Yunquan

    2017-03-01

    Deuteron momentum distributions from the dissociative ionization of D2 in intense elliptically polarized laser fields have been explored in a joint experimental and numerical study. The asymmetrical charge localization in the dissociative D2 + offers a large torque, and thus an elliptically polarized laser field efficiently rotates the molecular ion during its dissociation, resulting in the emission of deuterons finally deviating from the bond direction at the instant of tunneling ionization of D2. The rotating torque of the molecular ions increases with the field ellipticity, leading to an ellipticity-dependent tilt angle for the deuteron momentum distribution. Due to the notable rotation of D2 + during its dissociation, the photoelectron angular distributions in the laboratory frame and the molecular frame are distinct, which illustrates that the axial recoil approximation is broken for discussing the photoelectron angular distributions of molecules in elliptically polarized laser fields.

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

    SciTech Connect

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

    2011-05-15

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

  16. Experimental scaling of plane-Born cross sections and ab initio assignments for electron-impact excitation and dissociation of XF4 (X = C, Si, and Ge) molecules

    NASA Astrophysics Data System (ADS)

    Hoshino, M.; Duflot, D.; Limão-Vieira, P.; Ohtomi, S.; Tanaka, H.

    2017-04-01

    Electron energy loss spectra of carbon tetrafluoride, silicon tetrafluoride, and germanium tetrafluoride molecules (CF4, SiF4, and GeF4) have been measured for incident electron energies of 50-360 eV at 1.5°-15.5° and for 30 eV and 30° scattering angle, while sweeping the energy loss over the range 9.0-20.0 eV. Low-lying valence excited triplet and singlet states are investigated by quantum chemical ab initio calculations. The Rydberg series converging to the (lowest) ionisation energy limits of XF4 (X = C, Si, Ge) are also identified and classified using the systematic behaviour according to the magnitude of the quantum defects. A generalized oscillator strength analysis is employed to derive oscillator strength f0 value and the apparent Born integral cross sections from the corresponding differential cross sections by using the Vriens formula for the optically allowed transitions. The f0 value is compared with the optical oscillator strength of the photoabsorption, pseudo-photon measurements, and theoretical values. The binary-encounter and f-scaled Born cross sections of the most intense optically allowed transitions have been also derived from the excitation threshold to the high energy region where the Born approximation is valid. Potential energy curves were obtained along the XF3 + F coordinate with two different basis sets to lend support on electron impact dissociation processes yielding radical formation. We found that in CF4, the lowest-lying dissociative character is due to intramolecular conversion from Rydberg 3s to valence character (σ*(C-F)), whereas in SiF4 and GeF4, an antibonding behaviour prevails.

  17. Strong field dissociative ionization of the D2+: Nuclear wave packet analysis

    NASA Astrophysics Data System (ADS)

    Tóth, A.; Borbély, S.; Halász, G. J.; Vibók, Á.

    2017-09-01

    Theoretical ab initio investigation of strong field dissociative ionization of the D2+ molecule in the multiphoton regime is reported. The dynamics is initiated by ultrashort laser pulses for fixed molecular axis orientations. Nuclear wave packet calculations are performed to provide the joint energy spectra (JES): ionization-dissociation probability density via electron (Ee) and nuclear (En) kinetic energy. Analyzing the time-dependent nuclear wave packet densities we have successfully identified the exact path followed by the D2+ target for each multiphoton peak.

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

    NASA Astrophysics Data System (ADS)

    Bruhwiler, David

    2002-11-01

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

  19. Ultrafast molecular dynamics of dissociative ionization in OCS probed by soft x-ray synchrotron radiation

    NASA Astrophysics Data System (ADS)

    Ramadhan, Ali; Wales, Benji; Karimi, Reza; Gauthier, Isabelle; MacDonald, Michael; Zuin, Lucia; Sanderson, Joe

    2016-11-01

    Soft x-rays (90-173 eV) from the 3rd generation Canadian Light Source have been used in conjunction with a multi coincidence time and position sensitive detection apparatus to observe the dissociative ionization of OCS. By varying the x-ray energy we can compare dynamics from direct and Auger ionization processes, and access ionization channels which result in two or three body breakup, from 2+ to 4+ ionization states. We make several new observations for the 3+ state such as kinetic energy release limited by photon energy, and using Dalitz plots we can see evidence of timescale effects between the direct and Auger ionization process for the first time. Finally, using Dalitz plots for OCS4+ we observe for the first time that breakup involving an O2+ ion can only proceed from out of equilibrium nuclear arrangement for S(2p) Auger ionization.

  20. 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.

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

    DTIC Science & Technology

    1980-03-01

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

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

    PubMed

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

    2014-02-14

    Strong-field induced ionization and dissociation dynamics of vinyl bromide, CH2=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 C2H3Br, the formation of C2H3Br(+) ions in their ground (X̃) and first excited (Ã) states, the production of C2H3Br(++) ions, and the appearance of neutral Br ((2)P3/2) atoms by dissociative ionization. The formation of free Br ((2)P3/2) atoms occurs on a timescale of 330 ± 150 fs. The ionic à 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 à state as a function of NIR peak intensity. The observations suggest that a fraction of vibrationally excited C2H3Br(+) (Ã) ions undergoes intramolecular vibrational energy redistribution followed by the C-Br bond dissociation. The C2H3Br(+) (X̃) products and the majority of the C2H3Br(++) 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.

  3. 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.

  4. 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.

  5. Dissociative double ionization of CO in orthogonal two-color laser fields

    NASA Astrophysics Data System (ADS)

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

    2017-01-01

    We experimentally investigate dissociative double ionization of CO by a phase-controlled orthogonal two-color (OTC) laser pulse. Directional breaking of doubly ionized CO as a function of both kinetic energy and emission direction of the nuclear fragments is observed in the polarization plane steered by the laser phase. It is attributed to the dominating sequential double ionization at the maximum strength and nonsequential double ionization at a relatively weak strength of the spatiotemporally shaped oscillating laser field pointing to various directions. Our results are interesting not only for two-dimensional control of directional bond breaking, but also strengthen our understanding of strong-field sequential and nonsequential double ionization of molecules which are spatiotemporally streaked to various directions and kinetic energies by an OTC laser pulse.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

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

    SciTech Connect

    Ayinol, M.; Aydeniz, D.

    2016-03-25

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

  8. 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

  9. 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.

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

    NASA Astrophysics Data System (ADS)

    Wang, Yang; Zatsarinny, Oleg; Bartschat, Klaus

    2014-06-01

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

  11. 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.

  12. Dissociative ionization of acetonitrile in intense femtosecond laser fields

    NASA Astrophysics Data System (ADS)

    Boran, Y.; Kolomenskii, A. A.; Sayrac, M.; Kaya, N.; Schuessler, H. A.; Strohaber, J.

    2017-07-01

    We investigate the formation of positively charged fragments of acetonitrile (CH3CN) in intense 800 nm, 50 fs pulses of radiation using a reflectron time-of-flight (TOF) ion mass spectrometer. Singly-charged ions of CHnCN+ (n={0-3}), HCN+, CN+, {{{{CH}}}3}+, {{{{CH}}}2}+, CH+, C+ and H+; and the multiply charged ions of C2+, C3+, {{{{CH}}}2}2+, and {{{{CH}}}2}3+ were observed in the mass spectra. Quantum chemical calculations with GAMESS (General Atomic and Molecular Electronic Structure System) of appearance energies for the parent molecule and daughter fragments have been carried out. Intensity dependent ion yields were measured for intensities between 4.4× {10}13 {{W}} {{{cm}}}-2 and 3.3× {10}14 {{W}} {{{cm}}}-2. Angular distributions of most fragment ions were found to peak when the laser radiation was polarized parallel to the TOF axis, while the carbon ions, C+ and C2+, were found to have maxima for both polarizations parallel and perpendicular to this axis. Kinetic energies of H+ fragments were experimentally measured and three different photo dissociation mechanisms were identified.

  13. 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.

  14. 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.

  15. Attosecond control of dissociative ionization of O{sub 2} molecules

    SciTech Connect

    Siu, W.; Kelkensberg, F.; Gademann, G.; Rouzee, A.; Vrakking, M. J. J.; Johnsson, P.; Dowek, D.; Lucchini, M.; Calegari, F.; De Giovannini, U.; Rubio, A.; Lucchese, R. R.; Kono, H.; Lepine, F.

    2011-12-15

    We demonstrate that dissociative ionization of O{sub 2} can be controlled by the relative delay between an attosecond pulse train (APT) and a copropagating infrared (IR) field. Our experiments reveal a dependence of both the branching ratios between a range of electronic states and the fragment angular distributions on the extreme ultraviolet (XUV) to IR time delay. The observations go beyond adiabatic propagation of dissociative wave packets on IR-induced quasistatic potential energy curves and are understood in terms of an IR-induced coupling between electronic states in the molecular ion.

  16. 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.

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

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

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

    PubMed

    Dayhuff, Le-Ellen; Wells, Martha J M

    2005-12-09

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

  20. Structure and hydration of the C4H4•+ ion formed by electron impact ionization of acetylene clusters

    NASA Astrophysics Data System (ADS)

    Momoh, Paul O.; Hamid, Ahmed M.; Abrash, Samuel A.; Samy El-Shall, M.

    2011-05-01

    Here we report ion mobility experiments and theoretical studies aimed at elucidating the identity of the acetylene dimer cation and its hydrated structures. The mobility measurement indicates the presence of more than one isomer for the C4H4•+ ion in the cluster beam. The measured average collision cross section of the C4H4•+ isomers in helium (38.9 ± 1 Å2) is consistent with the calculated cross sections of the four most stable covalent structures calculated for the C4H4•+ ion [methylenecyclopropene (39.9 Å2), 1,2,3-butatriene (41.1 Å2), cyclobutadiene (38.6 Å2), and vinyl acetylene (41.1 Å2)]. However, none of the single isomers is able to reproduce the experimental arrival time distribution of the C4H4•+ ion. Combinations of cyclobutadiene and vinyl acetylene isomers show excellent agreement with the experimental mobility profile and the measured collision cross section. The fragment ions obtained by the dissociation of the C4H4•+ ion are consistent with the cyclobutadiene structure in agreement with the vibrational predissociation spectrum of the acetylene dimer cation (C2H2)2•+ [R. A. Relph, J. C. Bopp, J. R. Roscioli, and M. A. Johnson, J. Chem. Phys. 131, 114305 (2009)], 10.1063/1.3212595. The stepwise hydration experiments show that dissociative proton transfer reactions occur within the C4H4•+(H2O)n clusters with n ≥ 3 resulting in the formation of protonated water clusters. The measured binding energy of the C4H4•+H2O cluster, 38.7 ± 4 kJ/mol, is in excellent agreement with the G3(MP2) calculated binding energy of cyclobutadiene•+.H2O cluster (41 kJ/mol). The binding energies of the C4H4•+(H2O)n clusters change little from n = 1 to 5 (39-48 kJ/mol) suggesting the presence of multiple binding sites with comparable energies for the water-C4H4•+ and water-water interactions. A significant entropy loss is measured for the addition of the fifth water molecule suggesting a structure with restrained water molecules, probably a

  1. Structure and hydration of the C4H4●+ ion formed by electron impact ionization of acetylene clusters.

    PubMed

    Momoh, Paul O; Hamid, Ahmed M; Abrash, Samuel A; El-Shall, M Samy

    2011-05-28

    Here we report ion mobility experiments and theoretical studies aimed at elucidating the identity of the acetylene dimer cation and its hydrated structures. The mobility measurement indicates the presence of more than one isomer for the C(4)H(4)(●+) ion in the cluster beam. The measured average collision cross section of the C(4)H(4)(●+) isomers in helium (38.9 ± 1 Å(2)) is consistent with the calculated cross sections of the four most stable covalent structures calculated for the C(4)H(4)(●+) ion [methylenecyclopropene (39.9 Å(2)), 1,2,3-butatriene (41.1 Å(2)), cyclobutadiene (38.6 Å(2)), and vinyl acetylene (41.1 Å(2))]. However, none of the single isomers is able to reproduce the experimental arrival time distribution of the C(4)H(4)(●+) ion. Combinations of cyclobutadiene and vinyl acetylene isomers show excellent agreement with the experimental mobility profile and the measured collision cross section. The fragment ions obtained by the dissociation of the C(4)H(4)(●+) ion are consistent with the cyclobutadiene structure in agreement with the vibrational predissociation spectrum of the acetylene dimer cation (C(2)H(2))(2)(●+) [R. A. Relph, J. C. Bopp, J. R. Roscioli, and M. A. Johnson, J. Chem. Phys. 131, 114305 (2009)]. The stepwise hydration experiments show that dissociative proton transfer reactions occur within the C(4)H(4)(●+)(H(2)O)(n) clusters with n ≥ 3 resulting in the formation of protonated water clusters. The measured binding energy of the C(4)H(4)(●+)H(2)O cluster, 38.7 ± 4 kJ/mol, is in excellent agreement with the G3(MP2) calculated binding energy of cyclobutadiene(●+)·H(2)O cluster (41 kJ/mol). The binding energies of the C(4)H(4)(●+)(H(2)O)(n) clusters change little from n = 1 to 5 (39-48 kJ/mol) suggesting the presence of multiple binding sites with comparable energies for the water-C(4)H(4)(●+) and water-water interactions. A significant entropy loss is measured for the addition of the fifth water

  2. Monte Carlo wave packet approach to dissociative multiple ionization in diatomic molecules

    NASA Astrophysics Data System (ADS)

    Leth, Henriette Astrup; Madsen, Lars Bojer; Mølmer, Klaus

    2010-05-01

    A detailed description of the Monte Carlo wave packet technique applied to dissociative multiple ionization of diatomic molecules in short intense laser pulses is presented. The Monte Carlo wave packet technique relies on the Born-Oppenheimer separation of electronic and nuclear dynamics and provides a consistent theoretical framework for treating simultaneously both ionization and dissociation. By simulating the detection of continuum electrons and collapsing the system onto either the neutral, singly ionized or doubly ionized states in every time step the nuclear dynamics can be solved separately for each molecular charge state. Our model circumvents the solution of a multiparticle Schrödinger equation and makes it possible to extract the kinetic energy release spectrum via the Coulomb explosion channel as well as the physical origin of the different structures in the spectrum. The computational effort is restricted and the model is applicable to any molecular system where electronic Born-Oppenheimer curves, dipole moment functions, and ionization rates as a function of nuclear coordinates can be determined.

  3. Ellipticity-dependent ionization/dissociation of carbon dioxide in strong laser fields

    NASA Astrophysics Data System (ADS)

    Zhang, Jun-Feng; Ma, Ri; Zuo, Wan-Long; Lv, Hang; Huang, Hong-Wei; Xu, Hai-Feng; Jin, Ming-Xing; Ding, Da-Jun

    2015-03-01

    Ionization and dissociation of linear triatomic molecules, carbon dioxide, are studied in 50-fs 800-nm strong laser fields using time-of-flight mass spectrometer. The yields of double charged ions and various fragment ions (CO+, On+, and Cn+ (n = 1, 2)) are measured as a function of ellipticity of laser polarization in the intensity range from 5.0 × 1013 W/cm2 to 6.0 × 1014 W/cm2. The results demonstrate that non-sequential double ionization, which is induced by laser-driven electron recollision, dominates double ionization of CO2 in the strong IR laser field with intensity lower than 2.0 × 1014 W/cm2. The electron recollision could also have contribution in strong-field multiple ionization and formation of fragments of CO2 molecules. The present study indicates that the intensity and ellipticity dependence of ions yields can be used to probe the complex dynamics of strong-field ionization/dissociation of polyatomic molecules. Project supported by the National Basic Research Program of China (Grant No. 2013CB922200) and the National Natural Science Foundation of China (Grant Nos. 11034003 and 11274140).

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

    NASA Astrophysics Data System (ADS)

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

    2015-09-01

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

  5. 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.

  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. 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.

  8. Photon-number-resolved asymmetric dissociative single ionization of H2

    NASA Astrophysics Data System (ADS)

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

    2017-09-01

    The electron-nuclear joint energy spectrum allows one to unambiguously count the total number of photons absorbed by the electrons and nuclei of a molecule. Driven by phase-controlled, linearly polarized two-color femtosecond laser pulses, we experimentally demonstrate that the asymmetric bond breaking of a singly ionized H2 depends on the total number of photons absorbed by the molecule in the ionization and dissociation processes. The accessibilities of different dissociation pathways and their interference-induced asymmetric electron localization as a function of the absorbed photons are retrieved. Our results strengthen the understanding of the directional bond breaking of a molecule from the aspect of the correlated electron-nuclear dynamics.

  9. 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.

  10. 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.

  11. 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.

  12. Multielectron dissociative ionization of methane and formaldehyde molecules with optimally tailored intense femtosecond laser pulses

    NASA Astrophysics Data System (ADS)

    Irani, E.; Anvari, A.; Sadighi-Bonabi, R.; Monfared, M.

    2017-10-01

    The multielectron dissociative ionization of CH4 and CH2O molecules has been investigated using optimum convolution of different dual tailored short laser pulses. Based on three dimensional molecular dynamics simulations and TDDFT approach, the dissociation probability is enhanced by designing the dual chirped-chirped laser pulses and chirped-ordinary laser pulses for formaldehyde molecule. However, it is interesting to notice that the sensitivity of enhanced dissociation probability into different tailored laser pulses is not significant for methane molecule. In this presented modifications, time variation of bond length, velocity, time dependent electron localization function and evolution of the efficient occupation states are presented to analyze the time evolution of molecular dynamics. This work is proved to be a potential way to reduce the controlling costs with a currently available pulse shaping technology.

  13. Potential Energy Surfaces of Core-Hole and Shake-Up States for Dissociative Ionization Studies.

    PubMed

    Corral, Inés; González-Vázquez, Jesús; Martín, Fernando

    2017-04-11

    The theoretical description of core-hole and core-hole excited (shake-up) states resulting from the interaction of a molecule with X-ray free-electron lasers, attosecond pulses, and synchrotron radiation is a challenging task, as these states lie in the ionization continuum and, therefore, are subject to variational collapse. Although much effort has been devoted in the past to describe core-hole states in the Franck-Condon (FC) region, very few attempts, even less for shake-up states, have been reported near the dissociation threshold, where multistate degeneracy introduces additional complications. Knowledge of the whole potential energy surface (PES) is, however, essential when dissociative ionization resulting from the interaction with XUV or X-ray light occurs. In this work, we gauge the accuracy of two widely used multiconfigurational methods, CASSCF and MRCI, to obtain the potential energy curves of core-hole states of CO, N2, and the small polyatomic molecule BF3, from the FC region up to the dissociation limit, and show that CASSCF in combination with a triple-ζ basis set provides a very reasonable compromise between accuracy and computational cost to correctly describe core-hole and shake-up states in the entire PES. Besides providing the vibrational spectroscopic constants associated with these states, we also analyze the corresponding bonding and dissociation properties, which, in some cases, are counterintuitive and significantly different from those of bound states.

  14. Electron Transfer Reagent Anion Formation via Electrospray Ionization and Collision-induced Dissociation

    PubMed Central

    Huang, Teng-Yi; Emory, Joshua F.; O’Hair, Richard A.J.; McLuckey, Scott A.

    2011-01-01

    A strategy is described and demonstrated for the formation of reagent anions via electrospray ionization (ESI) for electron transfer dissociation (ETD). To circumvent difficulties associated with formation of high mass-to-charge ratio (m/z) reagent anions, it is desirable to form ETD reagents via means other than those that require reagent molecule vaporization. ESI is a candidate method but anions that are generally generated efficiently by ESI tend to react with multiply protonated polypeptides via proton transfer. The strategy described herein involves the use of a precursor reagent molecule that ionizes efficiently via electrospray ionization and that can subsequently be converted to an ETD reagent via gas-phase dissociation. The approach is demonstrated with arene carboxylic acids that yield strong signals associated with the deprotonated molecule and that subsequently undergo collision-induced dissociation (CID) by loss of CO2. In the present work, triply protonated KGAILKGAILR served as a test substrate for the CID product ions to give rise to ETD. Several precursor molecules were shown to be capable of generating ETD reagents via ESI followed by CID. These included 9-anthracenecarboxylic acid, 2-fluoro-5-iodobenzoic acid, and 2-(fluoranthene-8-carbonyl)-benzoic acid. The latter molecule has the most attractive set of characteristics as a precursor for a relatively high m/z ratio ETD reagent. PMID:17073403

  15. Gas chromatography/chemical ionization triple quadrupole mass spectrometry analysis of anabolic steroids: ionization and collision-induced dissociation behavior.

    PubMed

    Polet, Michael; Van Gansbeke, Wim; Van Eenoo, Peter; Deventer, Koen

    2016-02-28

    The detection of new anabolic steroid metabolites and new designer steroids is a challenging task in doping analysis. Switching from electron ionization gas chromatography triple quadrupole mass spectrometry (GC/EI-MS/MS) to chemical ionization (CI) has proven to be an efficient way to increase the sensitivity of GC/MS/MS analyses and facilitate the detection of anabolic steroids. CI also extends the possibilities of GC/MS/MS analyses as the molecular ion is retained in its protonated form due to the softer ionization. In EI it can be difficult to find previously unknown but expected metabolites due to the low abundance or absence of the molecular ion and the extensive (and to a large extent unpredictable) fragmentation. The main aim of this work was to study the CI and collision-induced dissociation (CID) behavior of a large number of anabolic androgenic steroids (AAS) as their trimethylsilyl derivatives in order to determine correlations between structures and CID fragmentation. Clarification of these correlations is needed for the elucidation of structures of unknown steroids and new metabolites. The ionization and CID behavior of 65 AAS have been studied using GC/CI-MS/MS with ammonia as the reagent gas. Glucuronidated AAS reference standards were first hydrolyzed to obtain their free forms. Afterwards, all the standards were derivatized to their trimethylsilyl forms. Full scan and product ion scan analyses were used to examine the ionization and CID behavior. Full scan and product ion scan analyses revealed clear correlations between AAS structure and the obtained mass spectra. These correlations were confirmed by analysis of multiple hydroxylated, methylated, chlorinated and deuterated analogs. AAS have been divided into three groups according to their ionization behavior and into seven groups according to their CID behavior. Correlations between fragmentation and structure were revealed and fragmentation pathways were postulated. Copyright © 2016 John Wiley

  16. 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.

  17. Glycerol Carbonate: A Novel Biosolvent with Strong Ionizing and Dissociating Powers

    PubMed Central

    Ou, Guangnan; He, Biyan; Li, Xuejing; Lei, Jianhui

    2012-01-01

    The activity of biocatalysts in nonaqueous solvents is related to the interaction of organic solvents with cells or enzymes. The behavior of proteins is strongly dependent on the protonation state of their ionizable groups, which ionization constants are greatly affected by the solvent. Due to the weak ionizing and dissociating powers of common organic solvents, the charge of the protein will change significantly when the protein is transferred from water to common organic solvents, resulting in protein denaturation. In this work, glycerol carbonate (GC) was synthesized, which ionizing and dissociating abilities were very close to those of water. Transesterification activities of Candida antarctica lipase B (CALB) in GC were comparable to those in water and remained constant during 4-week storage. Bacillus subtilis and Saccharomyecs cerevisiae were cultured in liquid media containing GC with test tubes. In the medium containing low GC concentration, Bacillus subtilis and Saccharomyecs cerevisiae grew well as in a medium containing no organic solvent, but, in the medium containing high GC concentration, the growth of Bacillus subtilis and Saccharomyecs cerevisiae was suppressed. The results suggested that GC is a potential biosolvent, which has great significance to biocatalysis in nonaqueous solvents. PMID:22629185

  18. Glycerol carbonate: a novel biosolvent with strong ionizing and dissociating powers.

    PubMed

    Ou, Guangnan; He, Biyan; Li, Xuejing; Lei, Jianhui

    2012-01-01

    The activity of biocatalysts in nonaqueous solvents is related to the interaction of organic solvents with cells or enzymes. The behavior of proteins is strongly dependent on the protonation state of their ionizable groups, which ionization constants are greatly affected by the solvent. Due to the weak ionizing and dissociating powers of common organic solvents, the charge of the protein will change significantly when the protein is transferred from water to common organic solvents, resulting in protein denaturation. In this work, glycerol carbonate (GC) was synthesized, which ionizing and dissociating abilities were very close to those of water. Transesterification activities of Candida antarctica lipase B (CALB) in GC were comparable to those in water and remained constant during 4-week storage. Bacillus subtilis and Saccharomyecs cerevisiae were cultured in liquid media containing GC with test tubes. In the medium containing low GC concentration, Bacillus subtilis and Saccharomyecs cerevisiae grew well as in a medium containing no organic solvent, but, in the medium containing high GC concentration, the growth of Bacillus subtilis and Saccharomyecs cerevisiae was suppressed. The results suggested that GC is a potential biosolvent, which has great significance to biocatalysis in nonaqueous solvents.

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

    NASA Astrophysics Data System (ADS)

    Lai, Wei; Guo, Chunlei

    2016-11-01

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

  20. Ionization and dissociation of CH3I in intense laser field

    NASA Astrophysics Data System (ADS)

    Liu, Hongtao; Yang, Zheng; Gao, Zhen; Tang, Zichao

    2007-01-01

    The ionization-dissociation of methyl iodide in intense laser field has been studied using a reflection time-of-flight mass spectrometry (RTOF-MS), at a laser intensity of ⩽6.6×1014W/cm2, λ =798nm, and a pulse width of 180fs. With the high resolution of RTOF-MS, the fragment ions with the same M /z but from different dissociation channels are resolved in the mass spectra, and the kinetic energy releases (KERs) of the fragment ions such as Iq + (q=1-6), CHm+ (m =0-3), C2+, and C3+ are measured. It is found that the KERs of the fragment ions are independent of the laser intensity. The fragments CH3+ and I + with very low KERs (<1eV for CH3+ and <0.07eV for I +) are assigned to be produced by the multiphoton dissociation of CH3I +. For the fragments CH3+ and I + from CH3I2+, they are produced by the Coulomb explosion of CH3I2+ with the interaction from the covalent force of the remaining valence electrons. The split of the KER of the fragments produced from CH3I2+ dissociation is observed experimentally and explained with the energy split of I +(P23) and I+(P0,13). The dissociation CH3I3+→CH3++I2+ is caused by Coulomb explosion. The valid charge distance Rc between I2+ and CH3+, at which enhanced ionization of methyl iodide occurs, is obtained to be 3.7Å by the measurements of the KERs of the fragments CH3+ and I2+. For the CH3In + (n⩾3), the KERs of the fragment ions CH3p + and Iq + are attributed to the Coulomb repulsion between CH3p + and Iq + from Rc≈3.7Å. The dissociation of the fragment CH3+ is also discussed. By the enhanced ionization mechanism and using the measured KER of Iq +, all the possible Coulomb explosion channels are identified. By comparing the abundance of fragment ions in mass spectrum, it is found that the asymmetric dissociation channels with more charges on iodine, q >p, are the dominant channels.

  1. Dissociative ionization of CH2Br2 in 800 and 400 nm femtosecond laser fields

    NASA Astrophysics Data System (ADS)

    Zhang, Jian; Yang, Yan; Li, Zhipeng; Sun, Zhenrong

    2017-10-01

    We experimentally demonstrate the dissociative ionization of CH2Br2 molecules irritated by 800 and 400 nm femtosecond laser fields using time-of-flight mass spectra and dc-sliced ion imaging technology. Our results show that in both laser fields, CH2Br2 can ionize to CH2Br2+, then CH2Br2+ break one Csbnd Br bond to produce fragments CH2Br(+) and Br(+). The charge assignment is determined by the ionization energy of the fragments. Additionally, in 400 nm laser fields, the CH2Br2+ can overpass a transition state to form an intermediate CH2Brsbnd Br+, then the intermediate break Csbnd Br bond to produce Br2 or Br2+ via elimination channel.

  2. VUV excitation of a vibrational wavepacket in D2 measured through strong-field dissociative ionization

    NASA Astrophysics Data System (ADS)

    Bainbridge, A. R.; Harrington, J.; Kirrander, A.; Cacho, C.; Springate, E.; Bryan, W. A.; Minns, R. S.

    2015-10-01

    Femtosecond vacuum ultraviolet pulses from a monochromated high harmonic generation source excite vibrational wavepackets in the {B}1{{{Σ }}}{{g}}+ state of D2. The wavepacket motion is measured through strong field ionization into bound and dissociative ion states yielding {{{D}}}2+ and D+ products. The time dependence of the {{{D}}}2+ and D+ ion signals provides a sensitive fingerprint of the quantum nuclear wavepacket, due to the different ionization rates for the two channels. The experiments are modelled with excitation and ionization processes included explicitly, with the results of the model showing a very good agreement with the experimental observations. The experiment demonstrates the level of detail attainable when studying ultrafast quantum nuclear dynamics using high harmonic sources.

  3. Formation of protons from dissociative ionization of methane induced by 54 eV electrons

    SciTech Connect

    Xu, S.; Ma, X.; Ren, X.; Senftleben, A.; Pflueger, T.; Dorn, A.; Ullrich, J.

    2011-05-15

    The production mechanisms of protons in dissociation of methane by 54 eV electron impact is investigated using the reaction microscope. By measuring all three charged particles in the final state in triple coincidence, the energy deposited in the target is determined. It is found that the (2a{sub 1}){sup -1}(npt{sub 2}){sup 1}, (2a{sub 1}){sup -1}, (1t{sub 2}){sup -2}(3a{sub 1}){sup 1}, and (2a{sub 1}){sup -2}(3a{sub 1}){sup 1} states of the intermediate CH{sub 4}{sup +} make the major contributions to the formation of protons at this incident energy. The decay of each state results in a different kinetic energy distribution of protons. Possible decay mechanisms of these states are analyzed.

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

    SciTech Connect

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

    2014-10-07

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

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

    PubMed

    Dallakian, P; Budzikiewicz, H; Brzezinka, H

    1996-01-01

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

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

    PubMed

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

    2014-10-07

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

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

    SciTech Connect

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

    2015-09-15

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

  8. 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)

  9. A semi-classical model of attosecond electron localization in dissociative ionization of hydrogen.

    PubMed

    Kelkensberg, Freek; Sansone, Giuseppe; Ivanov, Misha Y; Vrakking, Marc

    2011-05-21

    In the development of attosecond molecular science, a series of experiments have recently been performed where ionic fragment asymmetries in the dissociative ionization of H(2) into H(+) + H and that of D(2) into D(+) + D were used to uncover electron localization processes that occur on the attosecond and few-femtosecond timescale. Electron localization was observed both in strong-field dissociative ionization using carrier envelope phase-stable few-cycle laser pulses [Kling et al., Science, 2006, 312, 246] and in a two-color extreme ultra-violet + infrared attosecond pump-probe experiment [Sansone et al., Nature, 2010, 465, 763]. Here we show that the observed electron localization can be well understood using a semi-classical model that describes the dynamics in terms of quasi-static states that take the interaction of the molecule with the laser field instantaneously into account. The electron localization is shown to be determined by the passage of the dissociating molecule through a regime where the laser-molecule interaction is neither diabatic nor adiabatic.

  10. Dissociation and Ionization of Quasi-Periodically Vibrating H2+ in Intense Few-Cycle Mid-Infrared Laser Fields

    PubMed Central

    Jiang, Shicheng; Yu, Chao; Yuan, Guanglu; Wu, Tong; Lu, Ruifeng

    2017-01-01

    Using quantum mechanics calculations, we theoretically study the dissociation and ionization dynamics of the hydrogen-molecule ion in strong laser fields. Having prepared the nuclear wave packet of H2+ in a specific vibrational state, a pump laser is used to produce a vibrational excitation, leading to quasi-periodical vibration without ionization. Then, a time-delayed few-cycle laser is applied to trigger the dissociation or ionization of H2+. Both the time delay and the intensity of the probe laser alter the competition between dissociation and ionization. We also explore the dependence of kinetic-energy release spectra of fragments on the time delay, showing that the channels of above-threshold dissociation and below-threshold dissociation are opened and closed periodically. Also, dissociation from different channels is influenced by nuclear motion. The dissociation mechanism has been described in detail using the Floquet picture. This work provides a useful method for steering the electronic and nuclear dynamics of diatomic molecules in intense laser fields. PMID:28165034

  11. Dissociation and Ionization of Quasi-Periodically Vibrating H2+ in Intense Few-Cycle Mid-Infrared Laser Fields

    NASA Astrophysics Data System (ADS)

    Jiang, Shicheng; Yu, Chao; Yuan, Guanglu; Wu, Tong; Lu, Ruifeng

    2017-02-01

    Using quantum mechanics calculations, we theoretically study the dissociation and ionization dynamics of the hydrogen-molecule ion in strong laser fields. Having prepared the nuclear wave packet of H2+ in a specific vibrational state, a pump laser is used to produce a vibrational excitation, leading to quasi-periodical vibration without ionization. Then, a time-delayed few-cycle laser is applied to trigger the dissociation or ionization of H2+. Both the time delay and the intensity of the probe laser alter the competition between dissociation and ionization. We also explore the dependence of kinetic-energy release spectra of fragments on the time delay, showing that the channels of above-threshold dissociation and below-threshold dissociation are opened and closed periodically. Also, dissociation from different channels is influenced by nuclear motion. The dissociation mechanism has been described in detail using the Floquet picture. This work provides a useful method for steering the electronic and nuclear dynamics of diatomic molecules in intense laser fields.

  12. 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.

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

    PubMed

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

    2007-11-01

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

  14. Electron Impact Fragmentation of CH4 Molecules

    NASA Astrophysics Data System (ADS)

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

    2004-09-01

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

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

    NASA Astrophysics Data System (ADS)

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

    1998-12-01

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

  16. Dissociative ionization and Coulomb explosion of CH3I in intense femto second laser fields

    NASA Astrophysics Data System (ADS)

    Zhang, Dongdong; Luo, Sizuo; Xu, Haifeng; Jin, Mingxing; Liu, Fuchun; Yan, Bing; Wang, Zhigang; Liu, Hang; Jiang, Dianwu; Eppink, André; Roeterdink, Wim; Stolte, Steven; Ding, Dajun

    2017-06-01

    The interaction of CH3I molecules with 100 fs 800 nm linearly polarized laser fields has been investigated at the intensity region from 2.6 × 1014 to 5.8 × 1014 W/cm2 by means of a velocity map imaging method. The kinetic energy distribution of the various atomic fragment ions I q+ ( q = 1-3) has been measured and reproduced by a fit of multiple Gaussian functions. Several dissociative ionization and Coulomb explosion channels were identified for I q+ ( q = 1-3). As expected for a geometric alignment dominated interaction process the anisotropic angular recoil distributions of the atomic ion fragments are peaked in the laser polarization direction. The kinetic energy release (KER) of I q+ ( q = 1-3) depending upon the laser intensity has been investigated. The relative weight of the various contributions from the identified dissociative ionization (DI) and Coulomb explosion (CE) channels is found to depend strongly on the laser intensity.

  17. Multiphoton ionization/dissociation dynamics of formyl fluoride by velocity mapping ion imaging.

    PubMed

    Wang, Fengyan; Zhang, Yongwei; Wang, Hua; Liu, Jie; Jiang, Bo; Wang, Xiuyan; Yang, Xueming

    2009-10-21

    The dissociation dynamics of HFCO(+) ion has been studied using the velocity map ion imaging technique. The HFCO(+) ion is prepared by one-photon resonant three-photon ionization in the region of 43100-43860 cm(-1) excitation energy. The HFCO(+) ions, produced by multiphoton ionization, have sufficient internal energy to dissociate into the F and HCO(+) fragments without further absorption of another photon. Images of HCO(+) have been recorded at various excitation energies. It is noticed that the angular distributions of HCO(+) change dramatically from parallel distribution to perpendicular distribution and then back to parallel distribution in a very narrow excitation energy region of 43 473-43 500 cm(-1). Analysis of anisotropy parameters of beta(n) (n = 2, 4 and 6) reveals that the electronic states in the three-photon excitation of HFCO are mainly: HFCO(X(1)A') --> HFCO(A(1)A'') --> HFCO(A') --> HFCO(+)(A(2)A'';B(2)A'). The purely perpendicular resonant transitions are likely responsible for the perpendicular angular distribution of the HCO(+) ion fragment.

  18. Universal imaging: Dissociative ionization of polyatomic molecules, chemical dynamics beamline 9.0.2

    SciTech Connect

    Ahmed, M.; Chen, D.; Suits, A.G.

    1997-04-01

    A third endstation was recently added to the Chemical Dynamics beamline, designed to exploit the high flux broadband undulator light for a range of studies of reactive scattering, photochemistry and photoionization processes using time-of-flight mass spectroscopy coupled with position-sensitive detection. Two molecular beam sources are fixed at right angles, with the undulator light, or laser beams, intersecting the molecular beams at 45{degrees}. To date, beamline experiments have included a study of dissociative photoionization of a variety of molecules including N{sub 2}O and SF{sub 6}. In this mode, a single molecular beam source is used, with the tunable undulator light inducing, in SF{sub 6} for example, the process SF{sub 6} {r_arrow} SF{sub 6}{sup +} + e{sup {minus}} {r_arrow} SF{sub 5}{sup +} + F + e{sup {minus}}. The SF{sub 5}{sup +} ions are accelerated up the flight tube, mass selected and detected as a function of position on a phosphor screen viewed by a CCD camera. The position directly reveals the recoil speed (or translational energy release) and angular distribution for the dissociative ionization process. Furthermore, this measurement is obtained for all recoil speeds and angles simultaneously. Such detailed angular information has not previously been obtained for dissociative ionization processes; typically ion time-of-flight profiles are deconvoluted to yield rough insight into the angular distributions. The recorded image is actually a 2-dimensional projection of the nascent 3-dimensional velocity distribution, but established tomographic techniques enable the authors to reconstruct the 3-D distribution.

  19. Cross sections for radicals from electron impact on methane and fluoroalkanes

    NASA Astrophysics Data System (ADS)

    Motlagh, Safa; Moore, John H.

    1998-07-01

    Molecular and atomic radicals from electron-impact dissociation of methane and a variety of fluoroalkanes are detected mass spectometrically as organotellurides produced by the reaction of the radicals at the surface of a tellurium mirror. The radicals detected include CH3 from CH4; CF3 from CF4 and CHF3; CHF2 from CHF3 and CH2F2; CH2F from CH3F; and CF3 and C2F5 from C2F6 and C3F8 produced by electron impact at energies between 10 eV and 500 eV. Relative cross sections are measured. These are placed on an absolute scale by comparison with related measurements. For the collision energies relevant to processing plasmas, 10-30 eV, it is shown that dissociation into neutrals rather than dissociative ionization is mainly responsible for the production of molecular radicals.

  20. One-color two-photon mass-analyzed threshold ionization spectroscopy of ethyl bromide through a dissociative intermediate state

    NASA Astrophysics Data System (ADS)

    Tang, Bifeng; Zhang, Song; Wang, Yanmei; Tang, Ying; Zhang, Bing

    2005-10-01

    Mass-analyzed threshold ionization (MATI) spectra of ethyl bromide were obtained using one-color two-photon ionization through a dissociative intermediate state. Accurate values for the adiabatic ionization energy have been obtained, 83099±5 and 85454±5cm-1 for the X˜1E2 and X˜2E2 states of the ethyl bromide cation, respectively, giving a splitting of 2355±10cm-1. Compared with conventional photoelectron data, the two-photon MATI spectrum exhibited a more extensive vibrational structure with a higher resolution, mainly containing the modes involving the dissociation coordinate. The observed modes were analyzed and discussed in terms of wave packet evolving on the potential-energy surface of the dissociative state.

  1. Photo-Ionization and Photo-Dissociation of Trapped PAH Cations

    NASA Astrophysics Data System (ADS)

    Joblin, Christine; Zhen, Junfeng; Rodriguez Castillo, Sarah; Mulas, Giacomo; Sabbah, Hassan; Simon, Aude; Giuliani, Alexandre; Nahon, Laurent; Martin, Serge; Champeaux, Jean-Philippe; Mayer, Paul M.

    2016-06-01

    In astrophysical environments, polycyclic aromatic hydrocarbons (PAHs) are submitted to VUV photons of energy up to ˜20 eV. In the laboratory, photoelectron-photoion spectroscopy is usually performed using VUV synchrotron radiation, in which the same photon (15-25 eV), is used to ionize and dissociate PAHs. These experiments explore specific conditions and complementary studies in ion traps are required for a wider investigation of interstellar conditions. We have used the LTQ linear ion trap available on the DESIRS VUV beamline at SOLEIL to study the interaction of PAH cations with photons in the 7-20 eV range. We recorded by action spectroscopy the relative intensities of photo-fragmentation and photo-ionization of eight PAH cations ranging in size from 14 to 24 carbon atoms and with different structures. We found that, at photon energies below ˜13.6 eV, fragmentation dominates for the smaller species, while for larger species ionization is competitive immediately above the second ionization potential. At higher photon energies, all species behave similarly, the ionization yield gradually increases, levelling off between 0.8 and 0.9 at ˜18 eV. We have also recorded the competition between the different dissociation channels as a function of the VUV photon energy, such as the C_2H_2 versus H/H_2 loss. We will discuss how these data can be compared to results of photoelectron spectroscopy performed on neutral PAHs at the VUV beamline at the Swiss Light Source. H.W. Jochims et al., Astron. & Astrophys. 420 (1994), 307-317; P. M. Mayer et al., J. Chem. Phys. 134 (2011), 244312-244312-8 J. Zhen et al., Astron. & Astrophys. (2016), in press B. West et al., J. Phys. Chem. A 118 (2014), 7824-7831; B. West et al., J. Phys. Chem. A 118 (2014), 9870-9878 Acknowledgments: European Research Council grant ERC-2013-SyG, Grant Agreement n. 610256 NANOCOSMOS.

  2. Dissociation and multiple ionization energies for five polycyclic aromatic hydrocarbon molecules

    NASA Astrophysics Data System (ADS)

    Holm, A. I. S.; Johansson, H. A. B.; Cederquist, H.; Zettergren, H.

    2011-01-01

    We have performed density functional theory calculations for a range of neutral, singly, and multiply charged polycyclic aromatic hydrocarbons (PAHs), and their fragmentation products for H-, H^+-, C_2H_2-, and C_2H_2^+-emissions. The adiabatic and vertical ionization energies follow linear dependencies as functions of charge state for all five intact PAHs (naphthalene, biphenylene, anthracene, pyrene, and coronene). First estimates of the total ionization and fragmentation cross sections in ion-PAH collisions display markedly different size dependencies for pericondensed and catacondensed PAH species, reflecting differences in their first ionization energies. The dissociation energies show that the PAH^{q+}-molecules are thermodynamically stable for q ⩽ 2 (naphthalene, biphenylene, and anthracene), q ⩽ 3 (pyrene), and q ⩽ 4 (coronene). PAHs in charge states above these limits may also survive experimental time scales due to the presence of reaction barriers as deduced from explorations of the potential energy surface regions for H^+-emissions from all five PAHs and for C_2H_2+-emission from naphthalene - the smallest PAH.

  3. A combined electron-ion spectrometer for studying complete kinematics of molecular dissociation upon shell selective ionization

    SciTech Connect

    Saha, K.; Banerjee, S. B.; Bapat, B.

    2013-07-15

    A combined electron-ion spectrometer has been built to study dissociation kinematics of molecular ions upon various electronic decay processes ensuing from ionization of neutral molecules. The apparatus can be used with various ionization agents. Ion time-of-flight (ToF) spectra arising from various electronic decay processes are acquired by triggering the ToF measurement in coincidence with energy analyzed electrons. The design and the performance of the spectrometer in a photoionization experiment is presented in detail. Electron spectra and ion time of flight spectra resulting from valence and 2p{sub 1/2} ionization of Argon and those from valence ionization of CO are presented to demonstrate the capability of the instrument. The fragment ion spectra show remarkable differences (both kinematic and cross sectional) dependent on the energy of the ejected electron, corresponding to various electron loss and decay mechanisms in dissociative photoionization of molecules.

  4. Energy and momentum correlation in dissociative ionization D2 by 1 MeV/u F^8+ ions*

    NASA Astrophysics Data System (ADS)

    Landers, A. L.; Robison, A.; Naser, A. Al; Tanis, J. A.; Wells, E.; Osipov, T.; Carnes, K. D.; Ben-Itzhak, I.; Cocke, C. L.

    2003-05-01

    Dissociative ionization of D2 molecules by 19 MeV F^8+ ions was studied using an imaging technique. We have measured in coincidence the vector momentum of at least one molecule fragment and one electron produced in these ionizing collisions. Measurement of the molecule fragment(s) yields both the alignment at the time of the collision and the final dissociation energy. In addition to previous results that indicate the double-ionization cross section has an unexpectedly strong dependence on molecular orientation, we have new evidence of states populated by double excitation which ultimately decay to the disscociative single ionization channel. Further investigations include the dependence of this doubly excited state upon molecule orientation and electron emission in the fixed molecule frame. *Supported by U.S. Department of Energy

  5. The Effect of the Argon Carrier Gas in the Multiphoton Dissociation-Ionization of Tetracene

    PubMed Central

    Poveda, Juan Carlos; Román, Alejandro San; Guerrero, Alfonso; Álvarez, Ignacio; Cisneros, Carmen

    2008-01-01

    The multiphoton dissociation-ionization of tetracene at 355 nm using 6.5 nanosecond laser pulses, with and without argon as a carrier gas (CG), has been studied and compared. Ion fragments were analyzed in a time-of-flight mass spectrometer and separated according to their mass-to-charge ratio (m/z). The results show that the dynamic of photodissociation at ∼1010 W cm−2 intensities is strongly influenced by the CG. The suppression of fragmentation channels primarily those relating to the formation of the CHm+ (m = 2, 4), C2H4+ and C5H4+2 ions. CH5+ and CH6+ were observed which have not been reported before in photodissociation tetracene experiments. PMID:19325732

  6. Three-body neutral dissociations of a multiply excited water molecule around the double ionization potential

    NASA Astrophysics Data System (ADS)

    Odagiri, Takeshi; Nakano, Motoyoshi; Tanabe, Takehiko; Kumagai, Yoshiaki; Suzuki, Isao H.; Kitajima, Masashi; Kouchi, Noriyuki

    2012-11-01

    The cross sections for emission of two fluorescence photons from a pair of excited fragments in photoexcitation of H2O have been measured as a function of the incident photon energy using the photon-photon coincidence technique. The cross section increased in the range 30-45 eV, i.e. in the vicinity of the double ionization potential of H2O. The increase of the cross section was attributed to three-body neutral dissociations of a water molecule via multiply excited states: H2O** → H(2p) + OH** → H(2p) + H(2p) + O(3P). Some multiply excited states of H2O were also found in the cross section curve around 65 eV.

  7. LETTER TO THE EDITOR: H2+ in intense laser field pulses: ionization versus dissociation within moving nucleus simulations

    NASA Astrophysics Data System (ADS)

    Rotenberg, Benjamin; Taïeb, Richard; Véniard, Valérie; Maquet, Alfred

    2002-09-01

    The theory of the interaction of the H2+ molecular ion with an intense short laser pulse is modelled by solving the time-dependent Schrödinger equation for the electronic degree of freedom while the nuclear motion is described classically. This method allows us to discuss the influence of the pulse duration on the respective weights of ionization and dissociation.

  8. Comparative Study of the Dissociative Ionization of 1,1,1-Trichloroethane Using Nanosecond and Femtosecond Laser Pulses

    PubMed Central

    du Plessis, Anton; Strydom, Christien; Botha, Lourens

    2010-01-01

    Changes in the laser induced molecular dissociation of 1,1,1-trichloroethane (TCE) were studied using a range of intensities and standard laser wavelengths with nanosecond and femtosecond pulse durations. TCE contains C-H, C-C and C-Cl bonds and selective bond breakage of one or more of these bonds is of scientific interest. Using laser ionization time of flight mass spectrometry, it was found that considerable variation of fragment ion peak heights as well as changes in relative peak ratios is possible by varying the laser intensity (by attenuation), wavelength and pulse duration using standard laser sources. The nanosecond laser dissociation seems to occur via C-Cl bond breakage, with significant fragmentation and only a few large mass ion peaks observed. In contrast, femtosecond laser dissociative ionization results in many large mass ion peaks. Evidence is found for various competing dissociation and ionization pathways. Variation of the nanosecond laser intensity does not change the fragmentation pattern, while at high femtosecond intensities large changes are observed in relative ion peak sizes. The total ionization yield and fragmentation ratios are presented for a range of wavelengths and intensities, and compared to the changes observed due to a linear chirp variation. PMID:20480004

  9. Formation of negative ions by electron impact on SiF4 and CF4

    NASA Technical Reports Server (NTRS)

    Iga, I.; Rao, M. V. V. S.; Srivastava, S. K.; Nogueira, J. C.

    1992-01-01

    First measurements of cross sections for the formation of negative ions by electron attachment to SiF4 and CF4 are reported for an electron impact energy range of 0 to 50 eV. The energies at which the various ions appear and the positions at which the ionization efficiency curves peak have been obtained and compared with previous measurements. Thermochemical data have been used to predict and identify the various channels of dissociation. Cross sections for the production of ion pairs through the process of polar dissociation have also been measured.

  10. Formation of negative ions by electron impact on SiF4 and CF4

    NASA Technical Reports Server (NTRS)

    Iga, I.; Rao, M. V. V. S.; Srivastava, S. K.; Nogueira, J. C.

    1992-01-01

    First measurements of cross sections for the formation of negative ions by electron attachment to SiF4 and CF4 are reported for an electron impact energy range of 0 to 50 eV. The energies at which the various ions appear and the positions at which the ionization efficiency curves peak have been obtained and compared with previous measurements. Thermochemical data have been used to predict and identify the various channels of dissociation. Cross sections for the production of ion pairs through the process of polar dissociation have also been measured.

  11. Sub-cycle directional control of the dissociative ionization of H2 in tailored femtosecond laser fields

    NASA Astrophysics Data System (ADS)

    Li, H.; Gong, X.; Lin, K.; de Vivie-Riedle, R.; Tong, X. M.; Wu, J.; Kling, M. F.

    2017-09-01

    Being the simplest molecule on the planet, H2, as well as its isotopes, have been the prototype systems for strong-field molecular physics for decades. Photoionization and dissociation of H2 have been extensively investigated. After single ionization, the electron left in the molecular ion and its microscopic localization around the two dissociating nuclei can be effectively manipulated using intense femtosecond laser fields with broken symmetry. In this paper, we review the recent progress made on the sub-cycle directional control of the dissociative ionization of hydrogen molecules by tailoring the waveform of femtosecond laser fields, including few-cycle pulses and 2-color fields polarized along the same direction (one-dimension) or different directions (two-dimension).

  12. VUV dissociative excitation cross sections of H2O, NH3, and CH4 by electron impact. [Vacuum Ultra-Violet

    NASA Technical Reports Server (NTRS)

    Morgan, H. D.; Mentall, J. E.

    1974-01-01

    Absolute excitation functions for excited fragments resulting from electron bombardment of H2O, NH3, and CH4 by low-energy electrons (0 to 300 eV) have been measured in the vacuum ultraviolet (1100 to 1950 A). The predominant emission for each molecule was the H Lyman-alpha line, while the O I, N I, C I, and C II emissions were at least an order of magnitude weaker. Absolute cross sections at 100 eV are given along with the appearance potential of the various processes and the possible dissociative-excitation channels through which such processes proceed.

  13. VUV dissociative excitation cross sections of H2O, NH3, and CH4 by electron impact. [Vacuum Ultra-Violet

    NASA Technical Reports Server (NTRS)

    Morgan, H. D.; Mentall, J. E.

    1974-01-01

    Absolute excitation functions for excited fragments resulting from electron bombardment of H2O, NH3, and CH4 by low-energy electrons (0 to 300 eV) have been measured in the vacuum ultraviolet (1100 to 1950 A). The predominant emission for each molecule was the H Lyman-alpha line, while the O I, N I, C I, and C II emissions were at least an order of magnitude weaker. Absolute cross sections at 100 eV are given along with the appearance potential of the various processes and the possible dissociative-excitation channels through which such processes proceed.

  14. β-Methylphenylethylamines: common fragmentation pathways with amphetamines in electrospray ionization collision-induced dissociation.

    PubMed

    Brown, David H; Hansson, Robert; Oosthuizen, Francois; Sumner, Nathan

    2016-01-01

    β-Methylphenylethylamines are positional isomers of amphetamines and have been discovered in sporting supplements. Although the fragmentation of the β-methylphenylethylamine and N-methyl-β-methylphenylethylamine in gas chromatography-electron ionization-mass spectrometry (GC-EI-MS) systems is significantly different to their amphetamine and methylamphetamine isomers, under electrospray ionization commonly used in liquid chromatography-mass spectrometry (LC-MS) systems, the fragmentation of each of the isomeric pairs is almost identical. The similarities in fragmentation make it possible for the misidentification of the β-methylphenylethylamines as the illicit amphetamines. It is proposed that the similarities are due to a fragmentation pathway involving a common phenonium ion intermediate. By careful control of fragmentation energies in liquid chromatography-tandem mass spectrometry (LC-MS/MS) systems and/or close examination of the relative abundances of product ions formed by collision-induced dissociation (qualifier ratios), it is possible to distinguish the β-methylphenylethylamines from the amphetamines, even if significant retention time separation is not achieved. In liquid chromatography-electrospray ionization-quadrupole time of flight (LC-ESI-QTOF) systems the mass spectra of the β-methylphenylethylamines are identical to their amphetamine isomers. In such systems, retention time separation of the isomers is critical to avoid misidentification. During this study β-methylphenylethylamine and N-methyl-β-methylphenylethylamine have been identified in commercially available sporting supplements and oral fluid samples taken during the course of road-side drugs-in-drivers and workplace testing programmes. Copyright © 2015 John Wiley & Sons, Ltd.

  15. A generalized version of the Rankine-Hugoniot relations including ionization, dissociation and related phenomena

    NASA Technical Reports Server (NTRS)

    Nieuwenhuijzen, H.; De Jager, C.; Cuntz, M.; Lobel, A.; Achmad, L.

    1993-01-01

    For purposes of computing shocks in stellars atmospheres and winds we have developed a generalized version of the Rankine-Hugoniot relations including ionization, dissociation, radiation and related phenomena such as excitation, rotation and vibration of molecules. The new equations are given in analytical form. They are valid as long as the internal energy E, the total pressure P, and the first adiabatic coefficient gamma(sub 1) can be evaluated. However, we have not treated shock structures. In the case of non-LTE we have to employ an approximation for gamma(sub 1) because in that case no definition exists. Our new version of the Rankine-Hugoniot relations can easily be used for many purposes including ab-initio modeling. In our derivation we introduce a parameter gamma(sub H), which is definded as the ratio of the enthalpy H (sometimes called heat function w) to the internal energy E (sometimes called U). Using this parameter we solve the equations for changing mu and (d(natural log P)/d(natural log rho))(sub ad) identically equal to gamma(sub 1) on both sides of the shock. Both gamma(sub H) and gamma(sub 1), and also mu are functions of pressure P and temperature T. We present: (1) the derivation, (2) examples of gamma(sub 1) (P,T) and gamma(sub H) (P,T) which include/exclude ionization and radiation, and (3) as an example the differences in post-shock parameters as function of the pre-shock temperature for the case with ionization and without radiation.

  16. Effective novel dissociation methods for intact protein: heat-assisted nozzle-skimmer collisionally induced dissociation and infrared multiphoton dissociation using a Fourier transform ion cyclotron resonance mass spectrometer equipped with a micrometal electrospray ionization emitter.

    PubMed

    Yamada, Naoyuki; Suzuki, Ei-Ichiro; Hirayama, Kazuo

    2006-01-01

    Heating of a nano-electrospray ionization (nanoESI) source can improve the dissociation efficiency of collisionally induced dissociation (CID) methods, such as nozzle-skimmer CID (NS-CID) and infrared multiphoton dissociation (IRMPD), for large biomolecule fragmentation. A metal nanoESI emitter was used due to its resistance to heating above 250 degrees C. This novel method for the dissociation of large biomolecular ions is termed "heat-assisted NS-CID" (HANS-CID) or "heat-assisted IRMPD" (HA-IRMPD). Multiple charged nonreduced protein ions (8.6 Da ubiquitin, 14 kDa lysozyme, and 67 kDa bovine serum albumin) were directly dissociated by HANS-CID and HA-IRMPD to effectively yield fragment ions that could be assigned. The fragment ions of ubiquitin by HANS-CID can be analyzed by tandem mass spectrometry (MS/MS) using sustained off-resonance irradiation CID (SORI-CID) and IRMPD. In addition, a native large protein, immunoglobulin G (IgG, 150 kDa), was efficiently dissociated by HA-IRMPD. The product ions that were obtained reflected the domain structure of IgG. However, these product ions of IgG and lysozyme were not dissociated by MS/MS using the same heating energetic methods such as IRMPD and SORI-CID.

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

    SciTech Connect

    Aydinol, M.; Aydeniz, D.

    2016-03-25

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

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

    NASA Astrophysics Data System (ADS)

    Aydinol, M.; Aydeniz, D.

    2016-03-01

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

  19. Structural Characterization of Native Proteins and Protein Complexes by Electron Ionization Dissociation-Mass Spectrometry.

    PubMed

    Li, Huilin; Sheng, Yuewei; McGee, William; Cammarata, Michael; Holden, Dustin; Loo, Joseph A

    2017-03-07

    Mass spectrometry (MS) has played an increasingly important role in the identification and structural and functional characterization of proteins. In particular, the use of tandem mass spectrometry has afforded one of the most versatile methods to acquire structural information for proteins and protein complexes. The unique nature of electron capture dissociation (ECD) for cleaving protein backbone bonds while preserving noncovalent interactions has made it especially suitable for the study of native protein structures. However, the intra- and intermolecular interactions stabilized by hydrogen bonds and salt bridges can hinder the separation of fragments even with preactivation, which has become particularly problematic for the study of large macromolecular proteins and protein complexes. Here, we describe the capabilities of another activation method, 30 eV electron ionization dissociation (EID), for the top-down MS characterization of native protein-ligand and protein-protein complexes. Rich structural information that cannot be delivered by ECD can be generated by EID. EID allowed for the comparison of the gas-phase and the solution-phase structural stability and unfolding process of human carbonic anhydrase I (HCA-I). In addition, the EID fragmentation patterns reflect the structural similarities and differences among apo-, Zn-, and Cu,Zn-superoxide dismutase (SOD1) dimers. In particular, the structural changes due to Cu-binding and a point mutation (G41D) were revealed by EID-MS. The performance of EID was also compared to that of 193 nm ultraviolet photodissociation (UVPD), which allowed us to explore their qualitative similarities and differences as potential valuable tools for the MS study of native proteins and protein complexes.

  20. Strong-Field Induced Dissociative Ionization of Vinyl Bromide Probed by Femtosecond Extreme Ultraviolet (xuv) Transient Absorption Spectroscopy

    NASA Astrophysics Data System (ADS)

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

    2014-06-01

    A table-top high harmonic XUV light source (50 eV to 70 eV) has been successfully utilized to explore the ultrafast dynamics of vinyl bromide (CH2=CHBr) with electronic state specificity and elemental sensitivity. Strong-field ionization (SFI) provides a method to produce ions in different ionic states. The production and dissociation dynamics of these ionic states are investigated by femtosecond XUV transient absorption spectroscopy. The XUV photons probe the time-dependent spectroscopic features associated with transitions of the Br (3d) inner-shell electrons to vacancies in molecular and atomic valence orbitals. The experimental observation shows that two ionic states are produced by SFI. The first ionic excited state is dissociative, leading to C-Br bond dissociation which is observed in real time as a shift in the absorption energy. 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.

  1. Laser-induced dissociative ionization of H2 from the near-infrared to the mid-infrared regime

    NASA Astrophysics Data System (ADS)

    Jing, Qingli; Madsen, Lars Bojer

    2016-12-01

    We apply the Monte Carlo wave packet (MCWP) approach to investigate the kinetic energy release (KER) spectra of the protons following double ionization in H2 when interacting with laser pulses with central wavelengths ranging from the near-infrared (IR) (800 nm) to the mid-IR (6400 nm) regions and with durations of 3-21 laser cycles. We uncover the physical origins of the peaks in the nuclear KER spectra and ascribe them to mechanisms such as ionization following a resonant dipole transition, charge-resonance-enhanced ionization, and ionization in the dissociative limit of large internuclear distances. For relatively large pulse durations, i.e., for 15 or more laser cycles at 3200 nm and 10 or more at 6400 nm, it is possible for the nuclear wave packet in H2+ to reach very large separations. Ionization of this part of the wave packet results in peaks in the KER spectra with very low energies. These peaks give direct information about the dissociative energy in the 2 p σu potential energy curve of H2+ at the one- and three-photon resonances between the 2 p σu and 1 s σg curves in H2+ . With the MCWP approach, we perform a trajectory analysis of the contributions to the KER peaks and identify the dominant ionization pathways. Finally, we consider a pump-probe scheme by applying two delayed pulses to track the nuclear dynamics in a time-resolved setting. Low-energy peaks appear for large delays and these are used to obtain the 2 p σu dissociative energy values at the one-photon resonance between the 2 p σu and 1 s σg curves in H2+ for different wavelengths.

  2. Low energy (0-4 eV) electron impact to N{sub 2}O clusters: Dissociative electron attachment, ion-molecule reactions, and vibrational Feshbach resonances

    SciTech Connect

    Vizcaino, Violaine; Denifl, Stephan; Maerk, Tilmann D.; Scheier, Paul; Illenberger, Eugen

    2010-10-21

    Electron attachment to clusters of N{sub 2}O in the energy range of 0-4 eV yields the ionic complexes [(N{sub 2}O){sub n}O]{sup -}, [(N{sub 2}O){sub n}NO]{sup -}, and (N{sub 2}O){sub n}{sup -} . The shape of the ion yields of the three homologous series differs substantially reflecting the different formation mechanisms. While the generation of [(N{sub 2}O){sub n}O]{sup -} can be assigned to dissociative electron attachment (DEA) of an individual N{sub 2}O molecule in the target cluster, the formation of [(N{sub 2}O){sub n}NO]{sup -} is interpreted via a sequence of ion molecule reactions involving the formation of O{sup -} via DEA in the first step. The nondecomposed complexes (N{sub 2}O){sub n}{sup -} are preferentially formed at very low energies (below 0.5 eV) as a result of intramolecular stabilization of a diffuse molecular anion at low energy. The ion yields of [(N{sub 2}O){sub n}O]{sup -} and (N{sub 2}O){sub n}{sup -} versus electron energy show sharp peaks at the threshold region, which can be assigned to vibrational Feshbach resonances mediated by the diffuse anion state as already observed in an ultrahigh resolution electron attachment study of N{sub 2}O clusters [E. Leber, S. Barsotti, J. Boemmels, J. M. Weber, I. I. Fabrikant, M.-W. Ruf, and H. Hotop, Chem. Phys. Lett. 325, 345 (2000)].

  3. Assessment of two-temperature kinetic model for dissociating and weakly-ionizing nitrogen

    NASA Technical Reports Server (NTRS)

    Park, C.

    1986-01-01

    The validity of the author's two-temperature, chemical/kinetic model which the author has recently improved is assessed by comparing the calculated results with the existing experimental data for nitrogen in the dissociating and weakly ionizing regime produced behind a normal shock wave. The computer program Shock Tube Radiation Program (STRAP) based on the two-temperature model is used in calculating the flow properties behind the shock wave and the Nonequilibrium Air Radiation (NEQAIR) program, in determining the radiative characteristics of the flow. Both programs were developed earlier. Comparison is made between the calculated and the existing shock tube data on (1) spectra in the equilibrium region, (2) rotational temperature of the N2(+) B state, (3) vibrational temperature of the N2(+) B state, (4) electronic excitation temperature of the N2 B state, (5) the shape of time-variation of radiation intensities, (6) the times to reach the peak in radiation intensity and equilibrium, and (7) the ratio of nonequilibrium to equilibrium radiative heat fluxes. Good agreement is seen between the experimental data and the present calculation except for the vibrational temperature. A possible reason for the discrepancy is given.

  4. Dissociation and ionization in capture of antiprotons by the hydrogen molecular ion

    NASA Astrophysics Data System (ADS)

    Cohen, James S.

    2005-05-01

    Antiprotonic atoms and anti-hydrogen are hot areas of current experimental research. Cross sections for antiproton capture will soon be measured directly for the first time by the ASACUSA collaboration at the CERN antiproton decelerator and trap. In the present work [1], cross sections and initial quantum number distributions are calculated for capture of the antiproton (p) and the negative muon (^-) by the hydrogen molecular ion H2^+ using the fermion molecular dynamics (FMD) method. The capture of p is found to be almost entirely adiabatic, occurring via target dissociation without ionization, but nonadiabatic effects are found to play a significant role in the capture of ^-, especially at the higher capture energies. Generally good agreement is obtained with the recent adiabatic classical-trajectory Monte Carlo (CTMC-a) calculation of Sakimoto [2]. The capture properties of H2^+ are shown to be completely different from those previously calculated for both the H atom and neutral H2 molecule. Proposed experiments [3] on p capture by H, H2 and H2^+, at the same relative collision energies, will provide a major test of our theoretical understanding [4].[1] J.S. Cohen, J. Phys. B (to be published).[2] K. Sakimoto, J. Phys. B 37, 2255 (2004).[3] Y. Yamazaki et al., Nucl. Instrum. Methods B 154, 174 (1999); 214, 196 (2004); Hyperfine Interact. 138, 141 (2001).[4] J.S. Cohen, Rep. Prog. Phys. 67, 1769 (2004).

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

    NASA Astrophysics Data System (ADS)

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

    2008-07-01

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

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

    PubMed

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

    2008-07-15

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

  7. Calculation of laser induced impulse based on the laser supported detonation wave model with dissociation, ionization and radiation

    NASA Astrophysics Data System (ADS)

    Gan, Li; Mousen, Cheng; Xiaokang, Li

    2014-03-01

    In the laser intensity range that the laser supported detonation (LSD) wave can be maintained, dissociation, ionization and radiation take a substantial part of the incidence laser energy. There is little treatment on the phenomenon in the existing models, which brings obvious discrepancies between their predictions and the experiment results. Taking into account the impact of dissociation, ionization and radiation in the conservations of mass, momentum and energy, a modified LSD wave model is developed which fits the experimental data more effectively rather than the existing models. Taking into consideration the pressure decay of the normal and the radial rarefaction, the laser induced impulse that is delivered to the target surface is calculated in the air; and the dependencies of impulse performance on laser intensity, pulse width, ambient pressure and spot size are indicated. The results confirm that the dissociation is the pivotal factor of the appearance of the momentum coupling coefficient extremum. This study focuses on a more thorough understanding of LSD and the interaction between laser and matter.

  8. Identification of a Previously Unobserved Dissociative Ionization Pathway in Time-Resolved Photospectroscopy of the Deuterium Molecule

    NASA Astrophysics Data System (ADS)

    Cao, Wei; Laurent, Guillaume; Ben-Itzhak, Itzik; Cocke, C. Lewis

    2015-03-01

    A femtosecond vacuum ultraviolet (VUV) pulse with high spectral resolution (<200 meV ) is selected from the laser-driven high order harmonics. This ultrafast VUV pulse is synchronized with an infrared (IR) laser pulse to study dissociative ionization in deuterium molecules. At a VUV photon energy of 16.95 eV, a previously unobserved bond-breaking pathway is found in which the dissociation direction does not follow the IR polarization. We interpret it as corresponding to molecules predissociating into two separated atoms, one of which is photoionized by the following IR pulse. A time resolved study allows us to determine the lifetime of the intermediate predissociation process to be about 1 ps. Additionally, the dissociative ionization pathways show high sensitivity to the VUV photon energy. As the VUV photon energy is blueshifted to 17.45 eV, the more familiar bond-softening channel is opened to compete with the newly discovered pathway. The interpretation of different pathways is supported by the energy sharing between the electron and nuclei.

  9. Calculation of laser induced impulse based on the laser supported detonation wave model with dissociation, ionization and radiation

    SciTech Connect

    Gan, Li Mousen, Cheng; Xiaokang, Li

    2014-03-15

    In the laser intensity range that the laser supported detonation (LSD) wave can be maintained, dissociation, ionization and radiation take a substantial part of the incidence laser energy. There is little treatment on the phenomenon in the existing models, which brings obvious discrepancies between their predictions and the experiment results. Taking into account the impact of dissociation, ionization and radiation in the conservations of mass, momentum and energy, a modified LSD wave model is developed which fits the experimental data more effectively rather than the existing models. Taking into consideration the pressure decay of the normal and the radial rarefaction, the laser induced impulse that is delivered to the target surface is calculated in the air; and the dependencies of impulse performance on laser intensity, pulse width, ambient pressure and spot size are indicated. The results confirm that the dissociation is the pivotal factor of the appearance of the momentum coupling coefficient extremum. This study focuses on a more thorough understanding of LSD and the interaction between laser and matter.

  10. Dissociative Ionization Mechanism and Appearance Energies in Adipic Acid Revealed by Imaging Photoelectron Photoion Coincidence, Selective Deuteration, and Calculations.

    PubMed

    Heringa, Maarten F; Slowik, Jay G; Prévôt, André S H; Baltensperger, Urs; Hemberger, Patrick; Bodi, Andras

    2016-05-26

    Adipic acid, a model compound for oxygenated organic aerosol, has been studied at the VUV beamline of the Swiss Light Source. Internal energy selected cations were prepared by threshold photoionization using vacuum ultraviolet synchrotron radiation and imaging photoelectron photoion coincidence spectroscopy (iPEPICO). The threshold photoelectron spectrum yields a vertical ionization energy (IE) of 10.5 eV, significantly above the calculated adiabatic IE of 8.6 eV. The cationic minimum is accessible after vertical ionization by H-transfer from one of the γ-carbons to a carbonyl oxygen and is sufficiently energetic to decay by water loss at the ionization onset. The slope of the breakdown curves, quantum chemical calculations, and selective deuteration of the carboxylic hydrogens establish the dissociative photoionization mechanism. After ionization, one γ-methylene hydrogen and the two carboxylic hydrogens are randomized prior to H2O loss. On the basis of the deuteration degree in the H2O + CO-loss product at higher energies, a direct water-loss channel without complete randomization also exists. The breakdown diagram and center of gravity of the H2O + CO-loss peak were modeled to obtain 0 K appearance energies of 10.77, 10.32, and 11.53 eV for H2O + CO loss, CH2COOH loss, and H2O + CH2COOH loss from adipic acid. These agree well with the CBS-QB3 calculated values of 10.68, 10.45, and 11.57 eV, respectively, which shows that threshold photoionization can yield energetics data as long as the dissociation is statistical, even when the parent ion cannot be observed. The results can be used as a starting point for a deeper understanding of the ionization and low-energy fragmentation of organic aerosol components.

  11. Velocity map imaging of dissociative ionization and coulomb explosion of CH3I induced by a femtosecond laser.

    PubMed

    Wang, Yanmei; Zhang, Song; Wei, Zhengrong; Zhang, Bing

    2008-05-01

    The dissociative ionization and the Coulomb explosion of CH3I irradiated by a 35 fs 800 nm laser with a laser intensity of 4 x 10(13) to 6 x 10(14) W/cm2 was studied. In a relatively weak laser field (about 10(13) W/cm2), the dissociative ionization of CH3I took place. The speed distributions of the CH3+ and I+ fragments were measured and fitted using multiple Gaussian functions. Different product channels were found for CH3+ and I+, respectively. In a strong laser field (about 10(14) W/cm2), the multiply ionized fragment ions of Iq+ (q

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

    NASA Astrophysics Data System (ADS)

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

    2017-05-01

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

  13. Following Ultrafast Radiationless Relaxation Dynamics With Strong Field Dissociative Ionization: A Comparison Between Adenine, Uracil, and Cytosine

    SciTech Connect

    Kotur, Marija; Weinacht, Thomas C.; Zhou, Congyi; Matsika, Spiridoula

    2011-03-22

    We present the application of ultrafast time- and mass-resolved ion yield laser spectroscopy in conjunction with ab initio electronic structure calculations to track molecular excited-state dynamics. We discuss how molecular fragment ions can be associated with conformations the molecule assumes during its relaxation, and how various features of the pump-probe signal for those fragments can be used to infer details of the excited state dynamics. We present results for radiationless relaxation in DNA and RNA bases adenine, cytosine, and uracil in the gas phase, pumped near a one-photon resonance transition to an excited state, and probed via strong-field near-IR dissociative ionization.

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

    PubMed

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

    2006-02-01

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

  15. Carbon dioxide ion dissociations after inner shell excitation and ionization: The origin of site-specific effects

    SciTech Connect

    Eland, J. H. D.; Zagorodskikh, S.; Mucke, M.; Squibb, R. J.; Feifel, R.; Sorensen, S. L.

    2014-05-14

    Multi-coincidence experiments with detection of both electrons and ions from decay of core-excited and core-ionized states of CO{sub 2} confirm that O{sub 2}{sup +} is formed specifically in Auger decay from the C1s-π* and O1s-π* resonances. Molecular rearrangement occurs by bending in the resonant states, and O{sub 2}{sup +} is produced by both single and double Auger decay. It is suggested that electron capture by C{sup +} after partial dissociation in the doubly ionized core of excited CO{sub 2}{sup +}, formed by shake-up in spectator resonant Auger decay, accounts for high kinetic energy and high internal energy in some C + O{sub 2}{sup +} fragments.

  16. Time-dependent coupling of electron energy distribution function, vibrational kinetics of the asymmetric mode of CO2 and dissociation, ionization and electronic excitation kinetics under discharge and post-discharge conditions

    NASA Astrophysics Data System (ADS)

    Pietanza, L. D.; Colonna, G.; D'Ammando, G.; Capitelli, M.

    2017-01-01

    A time-dependent self-consistent model based on the coupling of the Boltzmann equation for the electron energy distribution function (EEDF) with the non-equilibrium vibrational kinetics of the asymmetric mode, as well as a simplified global model, have been implemented for a pure CO2 plasma. The simplified time-dependent global model takes into account dissociation and ionization as well as the reverse of these processes. It also takes into account the excitation/de-excitation of an electronic excited state at 10.5 eV. The model has been applied to describe the discharge and post-discharge conditions typically met in an atmospheric-pressure dielectric barrier discharge (DBD) and in a moderate-pressure microwave discharge. The reported results show the strong coupling between the excited state and the electron energy distribution kinetics due to superelastic (vibrational and electronic) collisions. Moreover, the dissociation rate from a pure vibrational mechanism can become competitive with the corresponding rate from the direct electron impact mechanism at high values of vibrational temperature.

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

    PubMed

    Eustergerling, Brett; Hèden, Martin; Shi, Yujun

    2007-11-01

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

  18. Optimization of Electrospray Ionization by Statistical Design of Experiments and Response Surface Methodology: Protein-Ligand Equilibrium Dissociation Constant Determinations

    NASA Astrophysics Data System (ADS)

    Pedro, Liliana; Van Voorhis, Wesley C.; Quinn, Ronald J.

    2016-09-01

    Electrospray ionization mass spectrometry (ESI-MS) binding studies between proteins and ligands under native conditions require that instrumental ESI source conditions are optimized if relative solution-phase equilibrium concentrations between the protein-ligand complex and free protein are to be retained. Instrumental ESI source conditions that simultaneously maximize the relative ionization efficiency of the protein-ligand complex over free protein and minimize the protein-ligand complex dissociation during the ESI process and the transfer from atmospheric pressure to vacuum are generally specific for each protein-ligand system and should be established when an accurate equilibrium dissociation constant (KD) is to be determined via titration. In this paper, a straightforward and systematic approach for ESI source optimization is presented. The method uses statistical design of experiments (DOE) in conjunction with response surface methodology (RSM) and is demonstrated for the complexes between Plasmodium vivax guanylate kinase ( PvGK) and two ligands: 5'-guanosine monophosphate (GMP) and 5'-guanosine diphosphate (GDP). It was verified that even though the ligands are structurally similar, the most appropriate ESI conditions for KD determination by titration are different for each.

  19. Optimization of Electrospray Ionization by Statistical Design of Experiments and Response Surface Methodology: Protein-Ligand Equilibrium Dissociation Constant Determinations.

    PubMed

    Pedro, Liliana; Van Voorhis, Wesley C; Quinn, Ronald J

    2016-09-01

    Electrospray ionization mass spectrometry (ESI-MS) binding studies between proteins and ligands under native conditions require that instrumental ESI source conditions are optimized if relative solution-phase equilibrium concentrations between the protein-ligand complex and free protein are to be retained. Instrumental ESI source conditions that simultaneously maximize the relative ionization efficiency of the protein-ligand complex over free protein and minimize the protein-ligand complex dissociation during the ESI process and the transfer from atmospheric pressure to vacuum are generally specific for each protein-ligand system and should be established when an accurate equilibrium dissociation constant (KD) is to be determined via titration. In this paper, a straightforward and systematic approach for ESI source optimization is presented. The method uses statistical design of experiments (DOE) in conjunction with response surface methodology (RSM) and is demonstrated for the complexes between Plasmodium vivax guanylate kinase (PvGK) and two ligands: 5'-guanosine monophosphate (GMP) and 5'-guanosine diphosphate (GDP). It was verified that even though the ligands are structurally similar, the most appropriate ESI conditions for KD determination by titration are different for each. Graphical Abstract ᅟ.

  20. Three products are better than two: entropic advantages in the competing dissociation reactions of ionized azo-t-butane.

    PubMed

    Rabaev, Madlena; Boulanger, Anne-Marie; Holland, David M P; Shaw, David A; Mayer, Paul M

    2009-02-26

    Ionized azo-t-butane (m/z 142) undergoes three dissociation reactions: competitive cleavage of the N-C bond to form (1) the t-butyl cation ((CH(3))(3)C(+), m/z 57) plus a neutral that is nominally (CH(3))(3)CN(2)(*) (85 Da); (2) m/z 85 cation, (CH(3))(3)CN(2)(+), plus the neutral t-butyl radical; and (3) a minor rearrangement reaction leading to ionized butene. The competition between channels (1) and (2) is governed by both energetic and entropic considerations as the 85 Da neutral lies in a 1 kJ mol(-1) potential energy well and when formed dissociates into the t-butyl radical and N(2). This gives channel 1 an entropic advantage over channel 2, as long as the transition states for these processes reside close to products, a conclusion supported by threshold photoelectron photoion coincidence spectroscopy, tandem mass spectrometry, and ab initio calculations.

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

    PubMed

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

    2004-10-01

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

  2. Self-consistent time dependent vibrational and free electron kinetics for CO2 dissociation and ionization in cold plasmas

    NASA Astrophysics Data System (ADS)

    Capitelli, M.; Colonna, G.; D'Ammando, G.; Pietanza, L. D.

    2017-05-01

    A self-consistent time dependent model, based on the coupling between the Boltzmann equation for free electrons, the non equilibrium vibrational kinetics for the asymmetric mode of CO2 and simplified global models for the dissociation and ionization plasma chemistry, has been applied to conditions which can be met under pulsed microwave (MW), dielectric barrier discharge (DBD) and nanosecond pulsed discharges (NPD). Under MW discharge type conditions, the selected pulse duration generates large concentration of vibrational excited states, which affects the electron energy distribution function (eedf) through the superelastic vibrational collisions. Moreover, in discharge conditions, plateaux appear in the vibrational distribution function (vdf) through the vibrational-vibrational up pumping mechanism, persisting also in the post discharge. In post discharge conditions, also the eedf is characterized by plateaux due to the superelastic collisions between cold electrons and the CO2 electronic state at 10.5 eV. The plateau in vdf increases the dissociation of pure vibrational mechanism (PVM), which can become competitive with the dissociation mechanism induced by electron molecule collisions. The PVM rates increase with the decrease of gas temperature, generating a non-Arrhenius behaviour. The situation completely changes under DBD and NPD type conditions characterized by shorter pulse duration and higher applied E/N values. Under discharge conditions, both vdf and eedf plateaux disappear, reappering in the afterglow.

  3. Selective photo-dissociative ionization of methane molecule with TDDFT study

    NASA Astrophysics Data System (ADS)

    Irani, E.; Anvari, A.; Sadighi-Bonabi, R.

    2017-01-01

    Three dimensional calculation of control dynamics for finding the optimized laser filed is formulated using an iterative method and time-dependent density functional approach. An appropriate laser pulse is designed to control the desired products in the dissociation of methane molecule. The tailored laser pulse profile, eigenstate distributions and evolution of the efficient occupation numbers are predicted and exact energy levels of this five-atomic molecule is obtained. Dissociation rates of up to 78%, 80%, 90%, and 82% for CH2+, CH+, C+ and C++ are achieved. Based on the present approach one can reduce the controlling costs.

  4. Non-Franck-Condon electron-impact dissociative-excitation cross sections of molecular hydrogen producing H(1s)+H(2l) through X 1Σ+g(v=0)-->\\{B 1Σ+u, B' 1Σ+u, C 1Πu\\}

    NASA Astrophysics Data System (ADS)

    Borges, Itamar, Jr.; Jalbert, Ginette; Bielschowsky, Carlos Eduardo

    1998-02-01

    Dissociation cross sections of H2 for high-energy electron impact (100-1000 eV) producing H(1s), H(2s), and H(2p) for excitation from the ground vibrational state (v=0) to the continuum of the B1Σ+u, B' 1Σ+u, and C 1Πu states were computed in the first Born approximation. Configuration-interaction electronic wave functions were used and vibrational degrees of freedom taken in account. The dissociative excitation cross sections as a function of the continuum energy for each final state were presented, and the accuracy of the wave function, including the importance of relaxation effects and the validity of the Franck-Condon approximation, is analyzed in comparison to available previous theoretical results. The computed dissociation cross sections were compared to experimental results making use of the separation of the various breakup channels proposed by Ajello, Shemansky, and James [Astrophys. J. 371, 422 (1991)]. The obtained cross sections to produce H(2p)+H(1s) fragments via dissociative excitation to the B and C states have agreed well with the decomposed experimental results within the error bars. The dissociation cross sections to produce H(2s)+H(1s) through the B' state were in most cases somewhat larger than the reported experimental error bars. In the most favorable case our theoretical B' dissociation cross section was 3.1% within the reported error bar at 300 eV electron impact energy. A possible experimental reason for this discrepancy was raised.

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

    NASA Astrophysics Data System (ADS)

    Schippers, Stefan

    2010-03-01

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

  6. Mass-analyzed threshold ionization spectroscopy of 1-bromopropane through dissociative intermediate states

    NASA Astrophysics Data System (ADS)

    Zhang, Song; Wang, Yanmei; Tang, Bifeng; Zheng, Qiusha; Zhang, Bing

    2006-02-01

    One-color two-photon ionization of 1-bromopropane, resulting in the 1-C 3H 7Br + ions in the X2E and X2E electronic states, is investigated using mass-analyzed threshold ionization (MATI) spectroscopy. The adiabatic ionization energies of two spin states are found to be 82 257 ± 5 and 84 823 ± 5 cm -1, respectively. The two-photon MATI spectrum exhibits an extensive vibrational structure. The active modes, including the C-Br stretching, the CH 2-Br wagging, the CH 2 and the CH 3 rocking modes, are observed and reliable values for these vibrational frequencies are obtained. We have also performed ab initio and density functional calculations, which provide interpretation for our experimental finding.

  7. On the ionization and dissociative photoionization of iodomethane: a definitive experimental enthalpy of formation of CH3I.

    PubMed

    Bodi, Andras; Shuman, Nicholas S; Baer, Tomas

    2009-12-14

    The dissociative photoionization onset energy of the CH(3)I --> CH(3)(+) + I reaction was studied at the vacuum ultraviolet (VUV) beamline of the Swiss Light Source (SLS) using a new imaging photoelectron photoion coincidence (iPEPICO) apparatus operating with a photon resolution of 2 meV and a threshold electron kinetic energy resolution of about 1 meV. Three previous attempts at establishing this value accurately, namely a pulsed field ionization (PFI)-PEPICO measurement, ab initio calculations and a mass-analyzed threshold ionization (MATI) experiment, in which the onset energy was bracketed by state-selected excitation to vibrationally excited (2)A(1) A states of the parent ion, have yielded contradictory results. It is shown that dimers and adducts formed in the supersonic molecular beam affected the PFI-PEPICO onset energy. The room temperature iPEPICO experiment yields an accurate 0 K onset of 12.248 +/- 0.003 eV, from which we derive a Delta(f)H(o)(298 K)(CH(3)I) = 15.23 +/- 0.3 kJ mol(-1), and the C-I bond energy in CH(3)I is 232.4 +/- 0.4 kJ mol(-1). The room temperature breakdown diagram shows a fine structure that corresponds to the threshold photoelectron spectrum (TPES) of the A state. Low internal energy neutrals seem to be preferentially ionized in the A state when compared with the X state, and A state peaks in the TPES are Stark-shifted as a function of the DC field, whereas the dissociative photoionization of X state ions is not affected. This suggests that there are different competing mechanisms at play to produce ions in the A state vs. ions in the X state. The competition between field ionization and autoionization in CH(3)I is compared with that in Ar, N(2) and in the H-atom loss energy region in CH(4)(+). The binding energies of the neutral and ionic Ar-CH(3)I clusters were found to be 26 and 66 meV, respectively.

  8. Dissociative ionization of the H 2O molecule induced by medium-energy singly charged projectiles

    NASA Astrophysics Data System (ADS)

    Kovács, S. T. S.; Herczku, P.; Juhász, Z.; Sarkadi, L.; Gulyás, L.; Sulik, B.

    2017-09-01

    We report on the fragmentation of the water molecule by 1 MeV H+ and He+ and 650 keV N+ ion impact. The fragment-ion energy spectra were measured by an electrostatic spectrometer at different observation angles. The obtained double-differential fragmentation cross sections for N+ are found to be more than an order of magnitude higher than that for H+. The relative ratios of the fragmentation channels are also different for the three projectiles. Additional fragmentation channels were observed in the spectra for He+ and for N+ impact, which are missing in the case of H+. From the analysis of the kinetic energy of the fragments, the maximum observed degree of ionization was found to be qmax=3 , 4, and 5 for H + , He + , and N + impact, respectively. Absolute multiple-ionization cross sections have been determined. They are compared with the predictions of the classical trajectory Monte Carlo and continuum-distorted-wave eikonal-initial-state theories. At lower degrees of ionization, theories provide reasonable agreement with experiment. The systematic overestimation of the cross section by the theories towards higher degrees of ionization indicates the failure of the independent particle model.

  9. Coherent control of D2/H2 dissociative ionization by a mid-infrared two-color laser field

    NASA Astrophysics Data System (ADS)

    Wanie, Vincent; Ibrahim, Heide; Beaulieu, Samuel; Thiré, Nicolas; Schmidt, Bruno E.; Deng, Yunpei; Alnaser, Ali S.; Litvinyuk, Igor V.; Tong, Xiao-Min; Légaré, François

    2016-01-01

    Steering the electrons during an ultrafast photo-induced process in a molecule influences the chemical behavior of the system, opening the door to the control of photochemical reactions and photobiological processes. Electrons can be efficiently localized using a strong laser field with a well-designed temporal shape of the electric component. Consequently, many experiments have been performed with laser sources in the near-infrared region (800 nm) in the interest of studying and enhancing the electron localization. However, due to its limited accessibility, the mid-infrared (MIR) range has barely been investigated, although it allows to efficiently control small molecules and even more complex systems. To push further the manipulation of basic chemical mechanisms, we used a MIR two-color (1800 and 900 nm) laser field to ionize H2 and D2 molecules and to steer the remaining electron during the photo-induced dissociation. The study of this prototype reaction led to the simultaneous control of four fragmentation channels. The results are well reproduced by a theoretical model solving the time-dependent Schrödinger equation for the molecular ion, identifying the involved dissociation mechanisms. By varying the relative phase between the two colors, asymmetries (i.e., electron localization selectivity) of up to 65% were obtained, corresponding to enhanced or equivalent levels of control compared to previous experiments. Experimentally easier to implement, the use of a two-color laser field leads to a better electron localization than carrier-envelope phase stabilized pulses and applying the technique in the MIR range reveals more dissociation channels than at 800 nm.

  10. Numerical simulation of the kinetics of dissociation and ionization of molecular hydrogen in the penning discharge plasma with the use of the reduced kinetic model

    NASA Astrophysics Data System (ADS)

    Storozhev, D. A.; E Kuratov, S.

    2017-02-01

    A simplified kinetic scheme for describing the kinetics of ionization and dissociation of hydrogen in the Penning discharge plasma is developed. The calculations of the component composition of the Penning discharge plasma are performed. Numerical simulation results are compared with the results provided by the detailed state-to-state kinetic scheme.

  11. The importance of Rydberg orbitals in dissociative ionization of small hydrocarbon molecules in intense few-cycle laser pulses

    NASA Astrophysics Data System (ADS)

    Wells, E.; Voznyuk, A.; Mahowald, J. B.; Schmitz, D. G.; Burwitz, T. G.; Jochim, B.; Zohrabi, M.; Betsch, K. J.; Severt, T.; Berry, B.; Kling, N. G.; Ablikim, U.; Carnes, K. D.; Ben-Itzhak, I.; Siemering, R.; Kling, M. F.; de Vivie-Riedle, R.

    2015-05-01

    Much of our intuition about strong-field processes is built upon studies of diatomic molecules, which have relatively well separated electronic states. In polyatomic molecules, however, the electronic states are closer together, leading to more complex interactions. A combined experimental and theoretical investigation of strong-field ionization followed by hydrogen elimination in the hydrocarbon series C2D2, C2D4, and C2D6 reveals that the photofragment angular distributions can only be understood when ionization from Rydberg orbitals is considered. These commonly neglected Rydberg orbitals are readily populated for some orientations of the molecule relative to the laser polarization, leading to dissociation patterns and an intensity dependence consistent with significant Rydberg orbital influence. Our results suggest that Rydberg states should be routinely considered when studying polyatomic molecules in intense laser fields. Funding provided by National Science Foundation grant 1404185, the Chemical Sciences, Geosciences and Biosciences Division, Office of Basic Energy Sciences, Office of Science, U.S. Department of Energy, and the DFG.

  12. Mapping the Dissociative Ionization Dynamics of Molecular Nitrogen with Attosecond Time Resolution

    NASA Astrophysics Data System (ADS)

    Trabattoni, A.; Klinker, M.; González-Vázquez, J.; Liu, C.; Sansone, G.; Linguerri, R.; Hochlaf, M.; Klei, J.; Vrakking, M. J. J.; Martín, F.; Nisoli, M.; Calegari, F.

    2015-10-01

    Studying the interaction of molecular nitrogen with extreme ultraviolet (XUV) radiation is of prime importance to understand radiation-induced processes occurring in Earth's upper atmosphere. In particular, photoinduced dissociation dynamics involving excited states of N2 + leads to N and N+ atomic species that are relevant in atmospheric photochemical processes. However, tracking the relaxation dynamics of highly excited states of N2 + is difficult to achieve, and its theoretical modeling is notoriously complex. Here, we report on an experimental and theoretical investigation of the dissociation dynamics of N2+ induced by isolated attosecond XUV pulses in combination with few-optical-cycle near-infrared/visible (NIR/VIS) pulses. The momentum distribution of the produced N+ fragments is measured as a function of pump-probe delay with subfemtosecond resolution using a velocity map imaging spectrometer. The time-dependent measurements reveal the presence of NIR/VIS-induced transitions between N2 + states together with an interference pattern that carries the signature of the potential energy curves activated by the XUV pulse. We show that the subfemtosecond characterization of the interference pattern is essential for a semiquantitative determination of the repulsive part of these curves.

  13. Electron-impact ionization of atomic hydrogen

    SciTech Connect

    Baertschy, Mark D.

    2000-02-01

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

  14. Electron impact ionization at relativistic energies

    NASA Astrophysics Data System (ADS)

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

    2004-05-01

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

  15. Charge transfer in dissociating iodomethane and fluoromethane molecules ionized by intense femtosecond X-ray pulses

    PubMed Central

    Boll, Rebecca; Erk, Benjamin; Coffee, Ryan; Trippel, Sebastian; Kierspel, Thomas; Bomme, Cédric; Bozek, John D.; Burkett, Mitchell; Carron, Sebastian; Ferguson, Ken R.; Foucar, Lutz; Küpper, Jochen; Marchenko, Tatiana; Miron, Catalin; Patanen, Minna; Osipov, Timur; Schorb, Sebastian; Simon, Marc; Swiggers, Michelle; Techert, Simone; Ueda, Kiyoshi; Bostedt, Christoph; Rolles, Daniel; Rudenko, Artem

    2016-01-01

    Ultrafast electron transfer in dissociating iodomethane and fluoromethane molecules was studied at the Linac Coherent Light Source free-electron laser using an ultraviolet-pump, X-ray-probe scheme. The results for both molecules are discussed with respect to the nature of their UV excitation and different chemical properties. Signatures of long-distance intramolecular charge transfer are observed for both species, and a quantitative analysis of its distance dependence in iodomethane is carried out for charge states up to I21+. The reconstructed critical distances for electron transfer are in good agreement with a classical over-the-barrier model and with an earlier experiment employing a near-infrared pump pulse. PMID:27051675

  16. Electron impact excitation coefficients for laboratory and astrophysical plasmas

    NASA Technical Reports Server (NTRS)

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

    1976-01-01

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

  17. Threshold behavior in metastable dissociation of multi-photon ionized thymine and uracil

    NASA Astrophysics Data System (ADS)

    Pandey, R.; Ryszka, M.; da Fonseca Cunha, T.; Lalande, M.; Dampc, M.; Limão-Vieira, P.; Mason, N. J.; Poully, J. C.; Eden, S.

    2017-09-01

    Microsecond-timescale HNCO loss has been observed from single-color multi-photon ionized pyrimidine nucleobases in the gas phase. Photon energy thresholds for the metastable channels have been measured at 5.55 ± 0.02 eV for thymine and 5.57 ± 0.02 eV for uracil. We argue that these results can be attributed to accessing the molecules' S1 states with additional vibrational energy matching the threshold energy for HNCO loss from the radical cation. Combined with previous photoionization energies, this enables the S1 adiabatic energies to be deduced: 3.67 ± 0.07 eV for thymine and 3.77 ± 0.07 eV for uracil. These values are consistent with recent calculations.

  18. A parametric study of dissociation and ionization models at 12 km/sec

    NASA Technical Reports Server (NTRS)

    Mitcheltree, R. A.

    1991-01-01

    Thermochemical nonequilibrium-solution dependence on available models for the chemical reaction rates is examined. Solutions from the Kang and Dunn (1973) reaction-rate set, the Park rate set of 1987, and the Park rate set of 1991 are compared. The blunt-nosed, axisymmetric geometry considered is a 60-deg sphere cone with nose radius of 1.07 m and cicular aft skirt. The nonequilibrium test case is 12 km/sec entry into the earth's atmosphere at 80 km altitude. The model variations are implemented into the Langley aerothermodynamics upwind relaxation algorithm code. While variations in the reaction rates have no effect on the surface pressure distribution and little effect on the convective heating, the effect on degree of ionization and radiative heating can be a factor of three.

  19. Internal energy distribution of peptides in electrospray ionization : ESI and collision-induced dissociation spectra calculation.

    PubMed

    Pak, Alireza; Lesage, Denis; Gimbert, Yves; Vékey, Károly; Tabet, Jean-Claude

    2008-04-01

    The internal energy of ions and the timescale play fundamental roles in mass spectrometry. The main objective of this study is to estimate and compare the internal energy distributions of different ions (different nature, degree of freedom 'DOF' and fragmentations) produced in an electrospray source (ESI) of a triple-quadrupole instrument (Quattro I Micromass). These measurements were performed using both the Survival Yield method (as proposed by De Pauw) and the MassKinetics software (kinetic model introduced by Vékey). The internal energy calibration is the preliminary step for ESI and collision-induced dissociation (CID) spectra calculation. meta-Methyl-benzylpyridinium ion and four protonated peptides (YGGFL, LDIFSDF, LDIFSDFR and RLDIFSDF) were produced using an electrospray source. These ions were used as thermometer probe compounds. Cone voltages (V(c)) were linearly correlated with the mean internal energy values () carried by desolvated ions. These mean internal energy values seem to be slightly dependent on the size of the studied ion. ESI mass spectra and CID spectra were then simulated using the MassKinetics software to propose an empirical equation for the mean internal energy () versus cone voltage (V(c)) for different source temperatures (T): < E(int) > = [405 x 10(-6) - 480 x 10(-9) (DOF)] V(c)T + E(therm)(T). In this equation, the E(therm)(T) parameter is the mean internal energy due to the source temperature at 0 V(c).

  20. A Survey of Electron Impact Cross-Sections for Halogens and Halogen Compounds of Interest to Plasma Processing

    NASA Technical Reports Server (NTRS)

    Sharma, S. P.; Rao, M. V. V. S.; Arnold, James O. (Technical Monitor)

    1998-01-01

    Published electron impact cross section data on halogens Cl2, F2, and halogen containing compounds such as Cx Fy, HCl, Cx Cly Fz are reviewed and critically evaluated based on the information provided by various researchers. The present work reports data on electron impact excitation, ionization, dissociation, electron attachment, electron detachment, and photo detachment. Elastic scattering cross sections and data on bulk properties such as diffusion coefficients in various background gases are also evaluated. Since some of the cross sectional data is derived from indirect measurements such as drift velocity, care has been taken to reconcile the differences among the reported data with due attention to the measurement technique. In conclusion, the processes with no or very limited amount of data and questionable set of data are identified and recommendation for further research direction is made.

  1. A Survey of Electron Impact Cross-Sections for Halogens and Halogen Compounds of Interest to Plasma Processing

    NASA Technical Reports Server (NTRS)

    Sharma, S. P.; Rao, M. V. V. S.; Arnold, James O. (Technical Monitor)

    1998-01-01

    Published electron impact cross section data on halogens Cl2, F2, and halogen containing compounds such as Cx Fy, HCl, Cx Cly Fz are reviewed and critically evaluated based on the information provided by various researchers. The present work reports data on electron impact excitation, ionization, dissociation, electron attachment, electron detachment, and photo detachment. Elastic scattering cross sections and data on bulk properties such as diffusion coefficients in various background gases are also evaluated. Since some of the cross sectional data is derived from indirect measurements such as drift velocity, care has been taken to reconcile the differences among the reported data with due attention to the measurement technique. In conclusion, the processes with no or very limited amount of data and questionable set of data are identified and recommendation for further research direction is made.

  2. Electrospray ionization collision-induced dissociation tandem mass spectrometry of amoxicillin and ampicillin and their degradation products.

    PubMed

    Frański, Rafał; Czerniel, Joanna; Kowalska, Marta; Frańska, Magdalena

    2014-04-15

    Detailed analysis of the literature results on the electrospray ionization mass spectrometry (ESI-MS) fragmentation of amoxicillin and ampicillin, and their comparison with our results, have revealed some incorrect suggestions or incomplete interpretations of mass spectra of these compounds. Therefore, this paper contains a comprehensive discussion devoted to the ESI-MS/MS of ampicillin and amoxicillin as well as their degradation products, namely products of hydrolysis and methanolysis. Electrospray ionization collision-induced dissociation tandem mass (ESI-CID-MS/MS) spectra and accurate mass measurements were made on a quadrupole time-of-flight (Q-tof) mass spectrometer. Hydrolysis of the antibiotics was performed by heating, for a few hours, their aqueous solutions adjusted to pH 10. Methanolysis of the antibiotics was performed by heating their methanol solutions for a few minutes. Additionally, mass spectra of isotope-labeled compounds were also obtained. A number of fragment ions, previously wrongly interpreted or not interpreted, have been rationalized. For example, formation of an abundant fragment at m/z 208 originating from the protonated amoxicillin molecule (ion [Amox + H](+)) was previously rationalized as a result of breaking of two bonds of the β-lactam ring. We found that this fragment ion had to be formed by the loss of ammonia and breaking of three bonds of the bicyclic system. The discussion presented enables a better understanding of the MS decompositions of amoxicillin and ampicillin as well as their degradation products. MS decomposition is used for the determinations of these compounds, when the so-called multiple-reaction monitoring is applied during liquid chromatography (LC)/ESI-MS analysis. Thus, better understanding of MS decompositions of the above compounds seems to be important. Copyright © 2014 John Wiley & Sons, Ltd.

  3. Gas-phase dissociation study of erythrinian alkaloids by electrospray ionization mass spectrometry and computational methods.

    PubMed

    Guaratini, T; Feitosa, L G P; Silva, D B; Lopes, N P; Lopes, J L C; Vessecchi, R

    2017-09-01

    Alkaloids from plants of the genus Erythrina display important biological activities, including anxiolytic action. Characterization of these alkaloids by mass spectrometry (MS) has contributed to the construction of a spectral library, has improved understanding of their structures and has supported the proposal of fragmentation mechanisms in light of density functional calculations. In this study, we have used low-resolution and high-resolution MS(n) analyses to investigate the fragmentation patterns of erythrinian alkaloids; we have employed the B3LYP/6-31+G(d,p) model to obtain their reactive sites. To suggest the fragmentation mechanism of these alkaloids, we have studied their protonation sites by density functional calculation, and we have obtained their molecular electrostatic potential map and their gas-phase basicity values. These analyses have indicated the most basic sites on the basis of the proton affinities of the nitrogen and oxygen atoms. The protonated molecules were generated by two major fragmentations, namely, neutral loss of CH3 OH followed by elimination of H2 O. High-resolution analysis confirmed elimination of NH3 by comparison with the losses of H2 and •CH3 . NH3 was eliminated from compounds that did not bear a substituent on ring C. The benzylic carbocation initiated the dissociation mechanism, and the first reaction involved charge transfer from a lone pair of electrons in the oxygen atoms. The second reaction consisted of ring contraction with loss of a CO molecule. The presence of hydroxy and epoxy groups could change the intensity or the occurrence of the fragmentation pathways. Given that erythrinian alkaloids are applied in therapeutics and are promising leads for the development of new drugs, the present results could aid identification of several analogues of these alkaloids in biological samples and advance pharmacokinetic studies of new plant derivatives based on MS(n) and MS/MS analyses. Copyright © 2017 John Wiley & Sons

  4. Channel-specific photoelectron angular distribution in laboratory and molecular frames for dissociative ionization of methanol in intense ultraviolet laser fields

    NASA Astrophysics Data System (ADS)

    Fukahori, Shinichi; Nakano, Motoyoshi; Yamanouchi, Kaoru; Itakura, Ryuji

    2017-03-01

    We investigate dissociative ionization of CH3OH in an intense laser field (398 nm, 76 fs, 8.9 × 1012 W/cm2) by photoelectron-photoion coincidence momentum imaging. It is revealed from the analysis of the channel-specific photoelectron angular distributions that CH3OH is decomposed into CH2OH+ + H after the four-photon ionization to the vibrationally highly excited states of the electronic ground state of CH3OH+ and into CH3+ + OH after the five-photon ionization to the second electronically excited state of CH3OH+, and that these two channels are also opened after CH3OH+, prepared by the four-photon ionization, is photoexcited further into the electronically excited states.

  5. Differentiation and Distributions of DNA/Cisplatin Crosslinks by Liquid Chromatography-Electrospray Ionization-Infrared Multiphoton Dissociation Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Xu, Zhe; Brodbelt, Jennifer S.

    2014-01-01

    Liquid chromatography-electrospray ionization-infrared multiphoton dissociation (IRMPD) mass spectrometry was developed to investigate the distributions of intrastrand crosslinks formed between cisplatin and two oligodeoxynucleotides (ODNs), d(A1T2G3G4G5T6A7C8C9C10A11T12) (G3-D) and its analog d(A1T2G3G4G5T6T7C8C9C10A11T12) (G3-H), which have been reported to adopt different secondary structures in solution. Based on the formation of site-specific fragment ions upon IRMPD, two isobaric crosslink products were differentiated for each ODN. The preferential formation of G3G4 and G4G5 crosslinks was determined as a function of reaction conditions, including incubation temperature and presence of metal ions. G3-D consistently exhibited a greater preference for formation of the G4G5 crosslink compared with the G3-H ODN. The ratio of G3G4:G4G5 crosslinks increased for both G3-D and G3-H at higher incubation temperatures or when metal salts were added. Comparison of the IRMPD fragmentation patterns of the unmodified ODNs and the intramolecular platinated crosslinks indicated that backbone cleavage was significantly suppressed near the crosslink.

  6. Differentiation and Distributions of DNA/Cisplatin Crosslinks by Liquid Chromatography-Electrospray Ionization-Infrared Multiphoton Dissociation Mass Spectrometry

    PubMed Central

    Xu, Zhe; Brodbelt, Jennifer S.

    2013-01-01

    Liquid chromatography-electrospray ionization-infrared multiphoton dissociation (IRMPD) mass spectrometry was developed to investigate the distributions of intrastrand crosslinks formed between cisplatin and two oligodeoxynucleotides (ODNs), d(A1T2G3G4G5T6A7C8C9C10A11T12) (G3-D) and its analog d(A1T2G3G4G5T6T7C8C9C10A11T12) (G3-H), that have been reported to adopt different secondary structures in solution. Based on the formation of site-specific fragment ions upon IRMPD, two isobaric crosslink products were differentiated for each ODN. The preferential formation of G3G4 and G4G5 crosslinks was determined as a function of reaction conditions, including incubation temperature and presence of metal ions. G3-D consistently exhibited a greater preference for formation of the G4G5 crosslink compared to the G3-H ODN. The ratio of G3G4:G4G5 crosslinks increased for both G3-D and G3-H at higher incubation temperatures or when metal salts were added. Comparison of the IRMPD fragmentation patterns of the unmodified ODNs and the intramolecular platinated crosslinks indicated that backbone cleavage was significantly suppressed near the crosslink. PMID:24135806

  7. Identification of isomers and control of ionization and dissociation processes using dual-mass-spectrometer scheme and genetic algorithm optimization

    NASA Astrophysics Data System (ADS)

    Chen, Zhou; Tong, Qiu-Nan; Zhang, Cong-Cong; Hu, Zhan

    2015-04-01

    Identification of acetone and its two isomers, and the control of their ionization and dissociation processes are performed using a dual-mass-spectrometer scheme. The scheme employs two sets of time of flight mass spectrometers to simultaneously acquire the mass spectra of two different molecules under the irradiation of identically shaped femtosecond laser pulses. The optimal laser pulses are found using closed-loop learning method based on a genetic algorithm. Compared with the mass spectra of the two isomers that are obtained with the transform limited pulse, those obtained under the irradiation of the optimal laser pulse show large differences and the various reaction pathways of the two molecules are selectively controlled. The experimental results demonstrate that the scheme is quite effective and useful in studies of two molecules having common mass peaks, which makes a traditional single mass spectrometer unfeasible. Project supported by the National Basic Research Program of China (Grant No. 2013CB922200) and the National Natural Science Foundation of China (Grant No. 11374124).

  8. Applications of a matrix-assisted laser desorption/ionization orthogonal time-of-flight mass spectrometer. l. Metastable decay and collision-induced dissociation for sequencing peptides.

    PubMed

    Ackloo, Suzanne; Loboda, Alexandre

    2005-01-01

    The use of a high-performance orthogonal time-of-flight (o-TOF) mass spectrometer for sequence analysis is described. The mass spectrometer is equipped with a matrix-assisted laser desorption/ionization (MALDI) source that operates at elevated pressure, 0.01-1 Torr. Ion fragmentation is controlled by varying the pressure of the buffer gas, the laser energy, the voltage difference between the MALDI target and the adjacent sampling cone, and between the cone and the quadrupole ion guide. The peptides were analyzed under optimal ionization conditions to obtain their molecular mass, and under conditions that promote ion dissociation via metastable decomposition or collision-induced dissociation (CID). The fragmentation spectra were used to obtain sequence information. Ion dissociation was promoted via three configurations of the ionization parameters. All methods yielded sequencing-grade b- and y-type ions. Two binary mixtures of peptides were used to demonstrate that: (1) external calibration provides a standard deviation (sigma) of 4 ppm with a mode of 9 ppm; and (2) that peptides with molecular masses that differ by a factor of two may be independently fragmented by appropriately choosing the CID energy and the low-mass cut-off. Analyses of tryptic digests employed liquid chromatography (LC), deposition of the eluant on a target, and finally MALDI-TOF mass spectrometry. The mass fingerprint and the (partial) sequence of the tryptic peptides were matched to their precursor protein via database searches.

  9. Absolute total and partial dissociative cross sections of pyrimidine at electron and proton intermediate impact velocities

    SciTech Connect

    Wolff, Wania Luna, Hugo; Sigaud, Lucas; Montenegro, Eduardo C.; Tavares, Andre C.

    2014-02-14

    Absolute total non-dissociative and partial dissociative cross sections of pyrimidine were measured for electron impact energies ranging from 70 to 400 eV and for proton impact energies from 125 up to 2500 keV. MOs ionization induced by coulomb interaction were studied by measuring both ionization and partial dissociative cross sections through time of flight mass spectrometry and by obtaining the branching ratios for fragment formation via a model calculation based on the Born approximation. The partial yields and the absolute cross sections measured as a function of the energy combined with the model calculation proved to be a useful tool to determine the vacancy population of the valence MOs from which several sets of fragment ions are produced. It was also a key point to distinguish the dissociation regimes induced by both particles. A comparison with previous experimental results is also presented.

  10. Electrospray ionization collision-induced dissociation mass spectrometry: a tool to characterize synthetic polyaminocarboxylate ferric chelates used as fertilizers.

    PubMed

    Orera, Irene; Orduna, Jesús; Abadía, Javier; Alvarez-Fernández, Ana

    2010-01-01

    Fertilizers based on synthetic polyaminocarboxylate ferric chelates have been known since the 1950s to be successful in supplying Fe to plants. In commercial Fe(III)-chelate fertilizers, a significant part of the water-soluble Fe-fraction consists of still uncharacterized Fe byproducts, whose agronomical value is unknown. Although collision-induced dissociation (CID) tandem mass spectrometry (MS/MS) is a valuable tool for the identification of such compounds, no fragmentation data have been reported for most Fe(III)-chelate fertilizers. The aim of this study was to characterize the CID-MS(2) fragmentation patterns of the major synthetic Fe(III)-chelates used as Fe-fertilizers, and subsequently use this technique for the characterization of commercial fertilizers. Quadrupole-time-of-flight (QTOF) and spherical ion trap mass analyzers equipped with an electrospray ionization (ESI) source were used. ESI-CID-MS(2) spectra obtained were richer when using the QTOF device. Specific differences were found among Fe(III)-chelate fragmentation patterns, even in the case of positional isomers. The analysis of a commercial Fe(III)-chelate fertilizer by high-performance liquid chromatography (HPLC) coupled to ESI-MS(QTOF) revealed two previously unknown, Fe-containing compounds, that were successfully identified by a comprehensive comparison of the ESI-CID-MS(2)(QTOF) spectra with those of pure chelates. This shows that HPLC/ESI-CID-MS(2)(QTOF), along with the Fe(III)-chelate fragmentation patterns, could be a highly valuable tool to directly characterize the water-soluble Fe fraction in Fe(III)-chelate fertilizers. This could be of great importance in issues related to crop Fe-fertilization, both from an agricultural and an environmental point of view.

  11. Cluster ions of diquat and paraquat in electrospray ionization mass spectra and their collision-induced dissociation spectra.

    PubMed

    Milman, Boris L

    2003-01-01

    Cluster ions such as [Cat+X+nM](+) (n = 0-4); [Cat-H+nM](+) (n = 1-3); and [2(Cat-H)+X+nM](+) (n = 0-2), where Cat, X, and M are the dication, anion, and neutral salt (CatX(2)), respectively, are observed in electrospray ionization (ESI) mass spectrometry of relatively concentrated solutions of diquat and paraquat. Collision-induced dissociation (CID) reactions of the clusters were observed by tandem mass spectrometry (MS/MS), including deprotonation to form [Cat-H](+), one-electron reduction of the dication to form Cat(+.), demethylation of the paraquat cation to form [Cat-CH(3)](+), and loss of neutral salt to produce smaller clusters. The difference in acidity and reduction power between diquat and paraquat, evaluated by thermodynamical estimates, can rationalize the different fractional yields of even-electron ([Cat-H](+) and its clusters) and odd-electron (mostly Cat(+)) ions in ESI mass spectra of these pesticides. The [Cat+n. Solv](2+) doubly charged cluster ions, where n

  12. Structural characterization of saturated branched chain fatty acid methyl esters by collisional dissociation of molecular ions generated by electron ionization.

    PubMed

    Ran-Ressler, Rinat R; Lawrence, Peter; Brenna, J Thomas

    2012-01-01

    Saturated branched chain fatty acids (BCFA) are present as complex mixtures in numerous biological samples. The traditional method for structure elucidation, electron ionization (EI) mass spectrometry, sometimes does not unambiguously enable assignment of branching in isomeric BCFA. Zirrolli and Murphy (Zirrolli , J. A. , and R. A. Murphy. 1993. Low-energy tandem mass spectrometry of the molecular ion derived from fatty acid methyl esters: a novel method for analysis of branched-chain fatty acids. J. Am. Soc. Mass Spectrom. 4: 223-229.) showed that the molecular ions of four BCFA methyl ester (BCFAME) yield highly characteristic fragments upon collisional dissociation using a triple quadrupole instrument. Here, we confirm and extend these results by analysis using a tabletop 3-D ion trap for activated molecular ion EI-MS/MS to 30 BCFAME. iso-BCFAME produces a prominent ion (30-100% of base peak) for [M-43] (M-C₃H₇), corresponding to the terminal isopropyl moiety in the original iso-BCFAME. Anteiso-FAME yield prominent ions (20-100% of base peak) corresponding to losses on both side of the methyl branch, [M-29] and [M-57], and tend to produce more prominent m/z 115 peaks corresponding to a cyclization product around the ester. Dimethyl and tetramethyl FAME, with branches separated by at least one methylene group, yield fragment on both sides of the sites of methyl branches that are more than 6 C away from the carboxyl carbon. EI-MS/MS yields uniquely specific ions that enable highly confident structural identification and quantification of BCFAME.

  13. Electron impact excitation of atomic oxygen - Revised cross sections. [in thermosphere and auroral substorms

    NASA Technical Reports Server (NTRS)

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

    1985-01-01

    Revised cross-section values for the excitation of three O I resonance transitions at 1304, 1027, and 989 A, by electron impact on atomic oxygen are presented from threshold to 300 eV. These results are smaller than the excitation cross sections used in some airglow models by a factor of about 2.8. The revised values are in good agreement with recent quantum-scattering calculations. The downward revision is required by new laboratory studies in which the direct and dissociative cross sections for 1304 A excitation were normalized with small probable error to the O and O2 ionization cross sections. The results also reflect new advances in VUV optical calibration techniques. A number of outstanding airglow problems are simplified by these revisions.

  14. Formation and Dissociation of the Interstrand i-Motif by the Sequences d(XnC4Ym) Monitored with Electrospray Ionization Mass Spectrometry

    NASA Astrophysics Data System (ADS)

    Cao, Yanwei; Qin, Yujiao; Bruist, Michael; Gao, Shang; Wang, Bing; Wang, Huixin; Guo, Xinhua

    2015-06-01

    Formation and dissociation of the interstrand i-motifs by DNA with the sequence d(XnC4Ym) (X and Y represent thymine, adenine, or guanine, and n, m range from 0 to 2) are studied with electrospray ionization mass spectrometry (ESI-MS), circular dichroism (CD), and UV spectrophotometry. The ion complexes detected in the gas phase and the melting temperatures (Tm) obtained in solution show that a non-C base residue located at 5' end favors formation of the four-stranded structures, with T > A > G for imparting stability. Comparatively, no rule is found when a non-C base is located at the 3' end. Detection of penta- and hexa-stranded ions indicates the formation of i-motifs with more than four strands. In addition, the i-motifs seen in our mass spectra are accompanied by single-, double-, and triple-stranded ions, and the trimeric ions were always less abundant during annealing and heat-induced dissociation process of the DNA strands in solution (pH = 4.5). This provides a direct evidence of a strand-by-strand formation and dissociation pathway of the interstrand i-motif and formation of the triple strands is the rate-limiting step. In contrast, the trimeric ions are abundant when the tetramolecular ions are subjected to collision-induced dissociation (CID) in the gas phase, suggesting different dissociation behaviors of the interstrand i-motif in the gas phase and in solution. Furthermore, hysteretic UV absorption melting and cooling curves reveal an irreversible dissociation and association kinetic process of the interstrand i-motif in solution.

  15. Gas-phase synthesis of singly and multiply charged polyoxovanadate anions employing electrospray ionization and collision induced dissociation.

    PubMed

    Al Hasan, Naila M; Johnson, Grant E; Laskin, Julia

    2013-09-01

    Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including VxOy(n-) and VxOyCl(n-) ions (x = 1-14, y = 2-36, n = 1-3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V14O36Cl(L)5 (L = Et4N(+), tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged VxOyCl(n-) and VxOyCl(L)((n-1)-) clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/Δm = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller VxOyCl((1-2)-) and VxOy ((1-2)-) anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged VxOyCl and VxOy species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively complex CID spectra. These results are consistent with the formation of more stable structures of VxOyCl and VxOy anions through low-energy CID. Furthermore, our results demonstrate that solution-phase synthesis of one precursor cluster anion combined with gas-phase CID is an efficient approach for the top

  16. Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation

    NASA Astrophysics Data System (ADS)

    Al Hasan, Naila M.; Johnson, Grant E.; Laskin, Julia

    2013-09-01

    Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including VxOy n- and VxOyCln- ions (x = 1-14, y = 2-36, n = 1-3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V14O36Cl(L)5 (L = Et4N+, tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged VxOyCln- and VxOyCl(L)(n-1)- clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/Δm = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller VxOyCl(1-2)- and VxOy (1-2)- anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged VxOyCl and VxOy species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively complex CID spectra. These results are consistent with the formation of more stable structures of VxOyCl and VxOy anions through low-energy CID. Furthermore, our results demonstrate that solution-phase synthesis of one precursor cluster anion combined with gas-phase CID is an efficient approach for the top-down synthesis of a

  17. Imaging multiphoton ionization and dissociation of rotationally warm CO via the B+Σ1 and E1Π electronic states

    NASA Astrophysics Data System (ADS)

    Sun, Z.-F.; Scheidsbach, R. J. A.; Suits, A. G.; Parker, D. H.

    2017-07-01

    Pathways for formation of C+ and O+ ions when applying (2 + 1) resonance enhanced multiphoton ionization (REMPI) of CO via the B1Σ+ and E1Π electronic states are characterized with the velocity map imaging technique. By employing an unskimmed pulsed valve, it was possible to obtain sharp images for a wide range of initial CO J-states. Most of the atomic ion production pathways could be assigned as one- or two-photon dissociation of a series of vibrational levels of the CO+ X2Σ+ and A2Π states. Large enhancements in dissociation of particular CO+ vibrational states in these progressions could be accurately assigned to accidental resonances of the REMPI laser with CO+ X2Σ+ -B2Σ+ transitions.

  18. Extraction Behaviors of Heavy Rare Earths with Organophosphoric Extractants: The Contribution of Extractant Dimer Dissociation, Acid Ionization, and Complexation. A Quantum Chemistry Study.

    PubMed

    Jing, Yu; Chen, Ji; Chen, Li; Su, Wenrou; Liu, Yu; Li, Deqian

    2017-03-30

    Heavy rare earths (HREs), namely Ho(3+), Er(3+), Tm(3+), Yb(3+) and Lu(3+), are rarer and more exceptional than light rare earths, due to the stronger extraction capacity for 100 000 extractions. Therefore, their incomplete stripping and high acidity of stripping become problems for HRE separation by organophosphoric extractants. However, the theories of extractant structure-performance relationship and molecular design method of novel HRE extractants are still not perfect. Beyond the coordination chemistry of the HRE-extracted complex, the extractant dimer dissociation, acid ionization, and complexation behaviors can be crucial to HRE extraction and reactivity of ionic species for understanding and further improving the extraction performance. To address the above issues, three primary fundamental processes, including extractant dimer dissociation, acid ionization, and HRE complexation, were identified and investigated systematically. The intrinsic extraction performances of HRE cations with four acidic organophosphoric extractants (P507, P204, P227 and Cyanex 272) were studied by using relativistic energy-consistent 4f core pseudopotentials, combined with density functional theory and a solvation model. Four acidic organophosphoric extractants have been qualified quantitatively from microscopic structures to chemical properties. It has been found that the Gibbs free energy changes of the overall extraction process (sequence: P204 > P227 > P507 > Cyanex 272) and their differences as a function of HREs (sequence: Ho/Er > Er/Tm > Tm/Yb > Yb/Lu) are in good agreement with the experimental maximum extraction capacities and separation factors. These results could provide an important approach to evaluate HRE extractants by the comprehensive consideration of dimer dissociation, acid ionization, and complexation processes. This paper also demonstrates the importance of the P-O bond, the P-C bond, isomer substituent, and solvation effects on the structure

  19. Ultrafast dynamics of strong-field dissociative ionization ofCH2Br2 probed by femtosecond soft x-ray transient absorptionspectroscopy

    SciTech Connect

    Loh, Zhi-Heng; Leone, Stephen R.

    2008-01-15

    Femtosecond time-resolved soft x-ray transient absorption spectroscopy based on a high-order harmonic generation source is used to investigate the dissociative ionization of CH{sub 2}Br{sub 2} induced by 800 nm strong-field irradiation. At moderate peak intensities (2.0 x 10{sup 14} W/cm{sup 2}), strong-field ionization is accompanied by ultrafast C-Br bond dissociation, producing both neutral Br ({sup 2}P{sub 3/2}) and Br* ({sup 2}P{sub 1/2}) atoms together with the CH{sub 2}Br{sup +} fragment ion. The measured rise times for Br and Br* are 130 {+-} 22 fs and 74 {+-} 10 fs, respectively. The atomic bromine quantum state distribution shows that the Br/Br* population ratio is 8.1 {+-} 3.8 and that the Br {sup 2}P{sub 3/2} state is not aligned. The observed product distribution and the timescales of the photofragment appearances suggest that multiple field-dressed potential energy surfaces are involved in the dissociative ionization process. In addition, the transient absorption spectrum of CH{sub 2}Br{sub 2}{sup +} suggests that the alignment of the molecule relative to the polarization axis of the strong-field ionizing pulse determines the electronic symmetry of the resulting ion; alignment of the Br-Br, H-H, and C{sub 2} axis of the molecule along the polarization axis results in the production of the ion {tilde X}({sup 2}B{sub 2}), {tilde B}({sup 2}B{sub 1}) and {tilde C}({sup 2}A{sub 1}) states, respectively. At higher peak intensities (6.2 x 10{sup 14} W/cm{sup 2}), CH{sub 2}Br{sub 2}{sup +} undergoes sequential ionization to form the metastable CH{sub 2}Br{sub 2}{sup 2+} dication. These results demonstrate the potential of core-level probing with high-order harmonic transient absorption spectroscopy for studying ultrafast molecular dynamics.

  20. The cage fragmentation of doubly ionized norbornane: A Born-Oppenheimer molecular dynamics study

    NASA Astrophysics Data System (ADS)

    Knippenberg, S.; Hajgató, B.

    2013-10-01

    Results are reported of Born-Oppenheimer molecular dynamics calculations performed on the singlet dication of norbornane, starting from the neutral ground state geometry. Intramolecular rearrangements and charge dissociation processes, which probably take place in the innermost valence ionization spectrum, are discussed and an analysis by means of natural bond orders and Wiberg bond indices has been performed. The outcome of these simulations and the observed cage fragmentation might explain a tremendous rise of electron-impact (e, 2e) ionization cross sections of norbornane at electron binding energies around the double-ionization threshold.

  1. A perspective on MALDI alternatives-total solvent-free analysis and electron transfer dissociation of highly charged ions by laserspray ionization.

    PubMed

    Trimpin, Sarah

    2010-05-01

    Progress in research is hindered by analytical limitations, especially in biological areas in which sensitivity and dynamic range are critical to success. Inherent difficulties of characterization associated with complexity arising from heterogeneity of various materials including topologies (isomeric composition) and insolubility also limit progress. For this reason, we are developing methods for total solvent-free analysis by mass spectrometry consisting of solvent-free ionization followed by solvent-free gas-phase separation. We also recently constructed a novel matrix-assisted laser desorption ionization (MALDI) source that provides a simple, practical and sensitive way of producing highly charged ions by laserspray ionization (LSI) or singly charged ions commonly observed with MALDI by choice of matrix or matrix preparation. This is the first ionization source with such freedom-an extremely powerful analytical 'switch'. Multiply charged LSI ions allow molecules exceeding the mass-to-charge range of the instrument to be observed and permit for the first time electron transfer dissociation fragment ion analysis.

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

    NASA Astrophysics Data System (ADS)

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

    2003-10-01

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

  3. Electron impact cross sections for surrogates of DNA sugar phosphate backbone

    NASA Astrophysics Data System (ADS)

    Bhowmik, Pooja; Joshipura, K. N.; Pandya, Siddharth

    2012-11-01

    Ionization and elastic cross sections by electron impact on H3PO4 and OP(OCH3)3 which are substitutes for the components of DNA phosphate group. We have employed the Complex Scattering Potential-ionization contribution (CSP-ic) formalism to calculate the cross sections in the energy range from ionization threshold to 2000 eV.

  4. Gas-Phase Synthesis of Singly and Multiply Charged Polyoxovanadate Anions Employing Electrospray Ionization and Collision Induced Dissociation

    SciTech Connect

    Al Hasan, Naila M.; Johnson, Grant E.; Laskin, Julia

    2013-07-02

    Electrospray ionization mass spectrometry (ESI-MS) combined with in-source fragmentation and tandem mass spectrometry (MS/MS) experiments were used to generate a wide range of singly and multiply charged vanadium oxide cluster anions including VxOy n– and VxOyCln– ions (x = 1–14, y = 2–36, n = 1–3), protonated clusters, and ligand-bound polyoxovanadate anions. The cluster anions were produced by electrospraying a solution of tetradecavanadate, V14O36Cl(L)5 (L = Et4N+, tetraethylammonium), in acetonitrile. Under mild source conditions, ESI-MS generates a distribution of doubly and triply charged VxOyCln– and VxOyCl(L)(n–1)– clusters predominantly containing 14 vanadium atoms as well as their protonated analogs. Accurate mass measurement using a high-resolution LTQ/Orbitrap mass spectrometer (m/Δm = 60,000 at m/z 410) enabled unambiguous assignment of the elemental composition of the majority of peaks in the ESI-MS spectrum. In addition, high-sensitivity mass spectrometry allowed the charge state of the cluster ions to be assigned based on the separation of the major from the much less abundant minor isotope of vanadium. In-source fragmentation resulted in facile formation of smaller VxOyCl(1–2)– and VxOy (1–2)– anions. Collision-induced dissociation (CID) experiments enabled systematic study of the gas-phase fragmentation pathways of the cluster anions originating from solution and from in-source CID. Surprisingly simple fragmentation patterns were obtained for all singly and doubly charged VxOyCl and VxOy species generated through multiple MS/MS experiments. In contrast, cluster anions originating directly from solution produced comparatively

  5. Comparison of vibration dissociation coupling and radiative heat transfer models for AOTV/AFE flowfields

    NASA Technical Reports Server (NTRS)

    Carlson, Leland A.; Bobskill, Glenn J.; Greendyke, Robert B.

    1988-01-01

    A series of detailed studies comparing various vibration dissociation coupling models, reaction systems and rates, and radiative heating models has been conducted for the nonequilibrium stagnation region of an AFE/AOTV vehicle. Atomic and molecular nonequilibrium radiation correction factors have been developed and applied to various absorption coefficient step models, and a modified vibration dissociation coupling model has been shown to yield good vibration/electronic temperature and concentration profiles. While results indicate sensitivity to the choice of vibration dissociation coupling model and to the nitrogen electron impact ionization rate, by proper combinations accurate flowfield and radiative heating results can be obtained. These results indicate that nonequilibrium effects significantly affect the flowfield and the radiative heat transfer. However, additional work is needed in ionization chemistry and absorption coefficient modeling.

  6. Dissociative recombination and the decay of a molecular ultracold plasma

    NASA Astrophysics Data System (ADS)

    Rennick, C. J.; Saquet, N.; Morrison, J. P.; Ortega-Arroyo, J.; Godin, P.; Fu, L.; Schulz-Weiling, M.; Grant, E. R.

    2011-07-01

    Double-resonant photoexcitation of nitric oxide in a molecular beam creates a dense ensemble of 51f(2) Rydberg states, which evolves to form a plasma of free electrons trapped in the potential well of an NO+ spacecharge. The plasma travels at the velocity of the molecular beam, and, on passing through a grounded grid, yields an electron time-of-flight signal that gauges the plasma size and quantity of trapped electrons. This plasma expands at a rate that fits with an electron temperature as low as 5 K. Dissociative recombination of NO+ ions with electrons provides the primary dissipation mechanism for the plasma. We have identified three dissociation pathways, and quantified their relative contributions to the measured rate: Two-body dissociative recombination competes with direct three-body recombination to neutral dissociation products, and with a process in which three-body recombination and electron-impact ionization form an equilibrium population of high-Rydberg states that decays by predissociation. Using available collision-theory rate constants for three-body recombination and ionization, together with quantum mechanical estimates of predissociation rates, we predict that the relaxation of the plasma to a high-Rydberg equilibrium outpaces direct three-body dissociative recombination, and, among second-order processes, the rate of two-body electron-cation dissociative recombination substantially exceeds the rate at which the high-Rydberg equilibrium dissociatively relaxes. The rate constant for dissociative recombination extracted from these data conforms with predictions drawn from theory for isolated electron-ion collisions. Methods based on the dissipation of molecular ultracold plasmas may provide a means for estimating rates of dissociative recombination for a variety of complex molecules.

  7. Electron impact induced fragmentation of N₂H⁺ and N₂D⁺.

    PubMed

    El Ghazaly, M O A; Mitchell, J B A; Jureta, J J; Defrance, P

    2014-10-30

    Electron impact dissociation of protonated and deuterated nitrogen ions has been studied using a crossed beams apparatus. Absolute cross sections for dissociation channels producing N(+) and NH(+), respectively, are presented. The observations of subthreshold signals in these measurements indicate the presence of ro-vibrationally and possibly electronically excited states in the parent ions. Comparisons with other measurements are given.

  8. Chemical ionization by [NO]+ and subsequent collision-induced dissociation for the selective on-line detection of monoterpenes and linalool.

    PubMed

    Rimetz-Planchon, Juliette; Dhooghe, Frederik; Schoon, Niels; Vanhaecke, Frank; Amelynck, Crist

    2011-03-15

    Existing on-line Chemical Ionization Mass Spectrometry (CIMS) techniques for quantification of atmospheric trace gases, such as Biogenic Volatile Organic Compounds (BVOCs), suffer from difficulty in discriminating between isomeric (and more generally isobaric) compounds. Selective detection of these compounds, however, is important because they can affect atmospheric chemistry in different ways, depending on their chemical structure. In this work, Flowing Afterglow Tandem Mass Spectrometry (FATMS) was used to investigate the feasibility of the selective detection of a series of monoterpenes, an oxygenated monoterpene (linalool) and a sesquiterpene (β-caryophyllene). Ions at m/z 137 from [H(3)O](+) chemical ionization of α-pinene, linalool and β-caryophyllene have been subjected to Collision-Induced Dissociation (CID) with Ar in the collision cell of a tandem mass spectrometer at center-of-mass energies ranging between 0 and 8 eV. Similar fragmentation patterns were obtained, demonstrating that this method is not suited for the selective detection of these compounds. However, CID of the ions at m/z 136 produced via [NO](+) chemical ionization of a series of monoterpenes has revealed promising results. Some tracer-product ions for individual compounds or groups of compounds were found, which can be considered as a step forward towards selective on-line monitoring of BVOCs with CIMS techniques.

  9. Comparison of laser-induced dissociation and high-energy collision-induced dissociation using matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) for peptide and protein identification.

    PubMed

    Macht, Marcus; Asperger, Arndt; Deininger, Sören-Oliver

    2004-01-01

    The fragmentation of peptides under laser-induced dissociation (LID) as well as high-energy collision-induced dissociation (CID) conditions has been investigated. The effect of the different fragmentation mechanisms on the formation of specific fragment ion types and the usability of the resulting spectra, e.g. for high-throughput protein identification, has been evaluated. Also, basic investigations on the influence of the matrix, as well as laser fluence, on the fragment ion formation and the consequences in the spectral appearance are discussed. The preconditions for obtaining 'pure' CID spectra on matrix-assisted laser desorption/ionization tandem time-of-flight (MALDI-TOF/TOF) instruments are evaluated and discussed as well as the differences between LID and CID in the resulting fragment ion types. While containing a wealth of information due to additional fragment ions in comparison with LID, CID spectra are significantly more complex than LID spectra and, due to different fragmentation patterns, the CID spectra are of limited use for protein identification, even under optimized parameter settings, due to significantly lower scores for the individual spectra. Conditions for optimal results regarding protein identification using MALDI-TOF/TOF instruments have been evaluated. For database searches using tandem mass spectrometric data, the use of LID as fragmentation technique in combination with parameter settings supporting the use of internal fragment ions turned out to yield the optimal results.

  10. Linkage analysis of chromophore-labeled disaccharides and linear oligosaccharides by negative ion fast atom bombardment ionization and collisional-induced dissociation with B/E scanning.

    PubMed

    Li, D T; Her, G R

    1993-06-01

    Negative ion fast atom bombardment ionization in combination with collisional-induced dissociation mass spectrometry differentiates the linkage position(s) of chromophore-labeled di- and oligosaccharides. The formation of glycosylamines rather than the more popular reductive amination has been used to label the reducing end of sugars with ultraviolet or fluorescence tags. Two types of fragment ions were detected, one with the charge carried on the chromophore end and the other with the charge carried on the nonreducing terminus. These ions are essential to the determination of interglycosidic linkage and they are produced from the ring cleavage of the reducing end monosaccharide. Additionally, the anomeric configuration of the 1-4-linked residue could be assigned according to the relative abundance of the fragment ions.

  11. Effects of molecular rotation after ionization and prior to fragmentation on observed recoil-frame photoelectron angular distributions in the dissociative photoionization of nonlinear molecules

    NASA Astrophysics Data System (ADS)

    López-Domínguez, Jesús A.; Lucchese, Robert R.

    2016-03-01

    Experimental angle-resolved photoelectron-photoion coincidence experiments measure photoelectron angular distributions (PADs) in dissociative photoionization (DPI) in the reference frame provided by the momenta of the emitted heavy fragments. By extension of the nomenclature used with DPI of diatomic molecules, we refer to such a PAD as a recoil-frame PAD (RFPAD). When the dissociation is fast compared to molecular rotational and bending motions, the emission directions of the heavy fragments can be used to determine the orientation of the bonds that are broken in the DPI at the time of the ionization, which is known as the axial-recoil approximation (ARA). When the ARA is valid, the RFPADs correspond to molecular-frame photoelectron angular distributions (MFPADs) when the momenta of a sufficient number of the heavy fragments are determined. When only two fragments are formed, the experiment cannot measure the orientation of the fragments about the recoil axes so that the resulting measured PAD is an azimuthally averaged RFPAD (AA-RFPAD). In this study we consider how the breakdown of the ARA due to rotation will modify the observed RFPADs for DPI processes in nonlinear molecules for ionization by light of arbitrary polarization. This model is applied to the core C 1 s DPI of CH4, with the results compared to experimental measurements and previous theoretical calculations done within the ARA. The published results indicate that there is a breakdown in the ARA for two-fragment events where the heavy-fragment kinetic energy release was less than 9 eV. Including the breakdown of the ARA due to rotation in our calculations gives very good agreement with the experimental AA-RFPAD, leading to an estimate of upper bounds on the predissociative lifetimes as a function of the kinetic energy release of the intermediate ion states formed in the DPI process.

  12. Electron impact excitation of Hg/+/

    NASA Technical Reports Server (NTRS)

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

    1974-01-01

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

  13. Thermal dissociation atmospheric chemical ionization ion trap mass spectrometry with a miniature source for selective trace detection of dimethoate in fruit juices.

    PubMed

    Ouyang, Yongzhong; Zhang, Xinglei; Han, Jing; Guo, Xiali; Zhu, Zhiqiang; Chen, Huanwen; Luo, Liping

    2013-01-21

    A miniature thermal dissociation atmospheric chemical ionization (TDCI) source, coupled with LTQ-MS, has been developed for rapid trace detection of pesticide residues such as dimethoate in highly viscous fruit juice samples. Instead of toxic organic solvents and the high electric field used in the conventional ionizations, an ionic liquid, a "green solvent", was employed to directly generate reagent ions in the TDCI process, followed by the proton or charge transfer with the analytes prior to the LTQ instrument for mass analysis. Trace amounts of dimethoate in fresh orange juices have been quantitatively detected, without any sample pretreatment or aid of high-pressure gas. A low limit of detection (LOD = 8.76 × 10(-11) g mL(-1)), acceptable relative standard deviation (RSD = 3.1-10.0%), and reasonable recoveries (91.2-102.8%) were achieved with this method for direct detection of dimethoate in highly viscous orange juice samples. The average analysis time for each single sample was less than 30 seconds. These experimental results showed that the miniature TDCI developed here is a powerful tool for the fast trace detection of pesticide residues in complex viscous fruit juices, with the advantage of high sensitivity, high speed, and high-throughput, ease of operation, and so on. Because of no chemical contamination and high voltage damage to the analytes and the environment, the technique has promising applications for online quality monitoring in the area of food safety.

  14. Improved accuracy of low affinity protein-ligand equilibrium dissociation constants directly determined by electrospray ionization mass spectrometry.

    PubMed

    Jaquillard, Lucie; Saab, Fabienne; Schoentgen, Françoise; Cadene, Martine

    2012-05-01

    There is continued interest in the determination by ESI-MS of equilibrium dissociation constants (K(D)) that accurately reflect the affinity of a protein-ligand complex in solution. Issues in the measurement of K(D) are compounded in the case of low affinity complexes. Here we present a K(D) measurement method and corresponding mathematical model dealing with both gas-phase dissociation (GPD) and aggregation. To this end, a rational mathematical correction of GPD (f(sat)) is combined with the development of an experimental protocol to deal with gas-phase aggregation. A guide to apply the method to noncovalent protein-ligand systems according to their kinetic behavior is provided. The approach is validated by comparing the K(D) values determined by this method with in-solution K(D) literature values. The influence of the type of molecular interactions and instrumental setup on f(sat) is examined as a first step towards a fine dissection of factors affecting GPD. The method can be reliably applied to a wide array of low affinity systems without the need for a reference ligand or protein.

  15. Electron impact excitation studies of unstable atomic species

    NASA Astrophysics Data System (ADS)

    Abdellatif, Ady Kamel

    The polarization of Balmer-alpha radiation excited in collisions of electrons with atomic hydrogen is presented for an electron energy range from threshold to 1000 eV. Measurements are in good agreement with calculations carried out using either convergent-close-coupling or R-matrix with pseudo-states approaches. Cascade is demonstrated to have a significant effect. Balmer-alpha excitation function data are also presented. A previous measurement of the polarization of Balmer-alpha following dissociative excitation of H2 by electrons is confirmed and extended. The electron impact excitation spectrum of atomic and molecular nitrogen in the VUV range (800 A--1800 A) is presented. The excitation functions of the 1135 A and the 1200 A transitions are obtained. About 5% of nitrogen molecules are dissociated using a microwave discharge source and a mixture of 95% helium and 5% nitrogen gases. Other lines proved to have too small an emission cross section for the electron impact excitation process on atomic nitrogen. Thus the 1243 A, 1494 A, 1745 A N lines and the 1085 A N+ line could not be studied using the small dissociation fractions obtained in the present work. Electron impact excitation of fluorine and sulfur atoms is presented. The spectrum of Sulfur Hexafluoride (SF6) in the VUV range from 800 A--1700 A is recorded. A 70% dissociation fraction was obtained using the microwave discharge unit with SF6 and He targets. The absolute emission cross section for the 807 A fluorine transition is found to be 2.21 +/- 1.20 x 10-19 cm 2 at 200 eV electron energy. As for sulfur, the absolute emission cross section for the 1474 A transition is 2.46 +/- 1.38 x 10-19 cm2 at 95 eV and for the 1667 A transition is 1.87 +/- 1.31 x 10-19 cm 2 at 85 eV.

  16. Low Energy Electron Impact Excitation of Water

    NASA Astrophysics Data System (ADS)

    Ralphs, Kevin; Serna, Gabriela; Hargreaves, Leigh R.; Khakoo, Murtadha A.; Winstead, Carl; McKoy, B. Vincent

    2011-10-01

    We present normalized absolute differential and integral cross-section measurements for the low energy electron impact excitation of the lowest dissociative 3B1, 1B1,3A1 and 1A1 states of H2O. The DCS were taken at incident energies of 9 eV, 10 eV, 12 eV, 15 eV and 20 eV and scattering angles of 15° to 130° and normalized to the elastic electron scattering measurements of. The DCS were obtained after a sophisticated unfolding of the electron energy loss spectrum of water using photoabsorption data in the literature as investigated by Thorn et al.. Our measurements extend those of to near-threshold energies. We find both important agreements and differences between our DCS and those of. Comparison to our theory (multi-channel Schwinger) and that of earlier work will also be presented. Funded by an NSF grant # RUI-PHY 0968874.

  17. Collision-induced dissociation of the A + 2 isotope ion facilitates glucosinolates structure elucidation by electrospray ionization-tandem mass spectrometry with a linear quadrupole ion trap.

    PubMed

    Cataldi, Tommaso R I; Lelario, Filomena; Orlando, Donatella; Bufo, Sabino A

    2010-07-01

    An approach is presented that can be of general applicability for structural elucidation of naturally occurring glucosinolates (GLSs) in crude plant extracts based on the fragmentation of isotopic A and A + 2 peaks. The most important fragmentation pathways were studied by tandem mass spectrometry (MS(n), n = 2, 3) using a linear quadrupole ion trap (LTQ) upon GLSs separation by optimized reversed-phase liquid chromatography (RPLC) and electrospray ionization (ESI) in negative ion mode. As the LTQ MS analyzer ensures high sensitivity and linearity, the fragmentation behavior under collision induced dissociation (CID) of the isotopic peaks A and A + 2 as precursor ions was carefully examined. All GLSs (R-C(7)H(11)O(9)NS(2)(-)) share a common structure with at least two sulfur atoms and significant isotopic abundance of (34)S. Thus, dissociation of the +2 Da isotopomeric ions results in several fragment ion doublets containing a combination of (32)S and (34)S. Accordingly, their relative abundances allow one to speed up the structural recognition of GLSs with great confidence, as it produces more structurally informative ions than conventional tandem MS performed on A ions. This approach has been validated on known GLSs bearing two, three, four, and six sulfur atoms by comparing expected and measured isotopic peak abundance ratios (I(A)/I(A)(+2)). Both group- and compound-specific fragments were observed; the predominant pathway of fragmentation of GLSs gives rise to species having the following m/z values, [M - SO(3) - H](-), [M - 196 - H](-), [M - 178 - H](-), and [M - 162 - H](-) after H rearrangement from the R- side chain. The present strategy was successfully applied to extracts of rocket salad leaves (Eruca sativa L.), which was sufficient for the chemical identification of a not already known 6-methylsulfonyl-3-oxohexyl-GLS, a long-chain-length aliphatic glucosinolate, which contains three sulfurs and exhibits a deprotonated molecular ion at m/z 494.1.

  18. Molecular frame photoemission in dissociative ionization of H2 and D2 induced by high harmonic generation femtosecond XUV pulses

    NASA Astrophysics Data System (ADS)

    Billaud, P.; Géléoc, M.; Picard, Y. J.; Veyrinas, K.; Hergott, J. F.; Marggi Poullain, S.; Breger, P.; Ruchon, T.; Roulliay, M.; Delmotte, F.; Lepetit, F.; Huetz, A.; Carré, B.; Dowek, D.

    2012-10-01

    We report the first results of molecular frame photoelectron emission for dissociative photoionization (DPI) of H2 and D2 molecules induced by a spectrally filtered single high harmonic of a few femtosecond duration, using coincident electron-ion velocity vector correlation techniques. For the studied photon energies around 32 eV, where the resonant excitation of the Q1 and Q2 doubly excited states occurs, autoionization and nuclear dynamics are coupled on a few femtosecond timescale, giving rise to quantum interferences. Molecular frame photoelectron angular distributions (MFPADs), traced as a function of the kinetic energy release of the atomic fragments, provide the most sensitive observables for such complex dynamics. These results compare well with recent spectrally resolved experiments using synchrotron radiation which are also reported. As a novel XUV light source running at multi-kHz repetition rate and synchronized with laser pulses, high-order harmonic generation (HHG) opens new possibilities for extending these investigations to time-resolved studies at the femtosecond scale.

  19. Surface ionization mass spectrometry of drugs in the thermal and hyperthermal energy range -- a comparative study

    NASA Astrophysics Data System (ADS)

    Dagan, Shai; Amirav, Aviv; Fujü, Toshihiro

    1995-12-01

    Thermal and hyperthermal surface ionization (SI) mass spectra of nicotine, caffeine and lidocaine were obtained using a rhenium oxide surface. Thermal surface ionization was studied on an oxidized surface positioned inside an electron impact ion source, while hyperthermal surface ionization (HSI) was obtained upon seeding the compounds into a hydrogen or helium supersonic molecular beam that scattered from the rhenium oxide surface. Both HSI and SI provide rich, informative and complementary mass spectral information. The results indicate that SI follows thermal dissociation processes on the surface prior to the desorption of the ion, while in HSI no thermal equilibrium is established and the ionization process is impulsive, followed by mostly unimolecular ion dissociation. HSI mass spectra are similar to electron impact mass spectra in the fragment ion masses, but the observed relative intensities are different. HSI is a softer ionization method compared to SI, and enables the degree of ion fragmentation to be tuned so that it can be minimized to a low level at low molecular kinetic energy. In SI, limited control over the degree of fragmentation is possible through the surface temperature. The analytical mass spectrometric applications of SI and HSI are briefly mentioned.

  20. Electron-impact detachment from B-

    NASA Astrophysics Data System (ADS)

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

    1998-10-01

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

  1. Electron impact excitation of molecular hydrogen

    DOE PAGES

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

    2017-02-06

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

  2. Electron-impact excitation of molecular hydrogen

    NASA Astrophysics Data System (ADS)

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

    2017-02-01

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

  3. Dissociation Rates of Diatomic Molecules

    DTIC Science & Technology

    1992-12-01

    relatively simple design that we have used extensively in earlier research; its characteristics were recently described in detail. 10 This source is by...the dominant dissociation background when observing electron- impact dissociation products. This background constitutes the single greatest impediment...a3aF) + o(3P) at 11.385 eV. Photoexcitation studies indeed find that O(1S) and CO(a) are the dominant photodissociation products. 32,33 If the energy

  4. Electron impact cross sections applicable to molecular lasers

    NASA Astrophysics Data System (ADS)

    Wong, S. F.

    1981-08-01

    In the program on excited molecules we have completed the experiments on dissociative attachment from vibrationally excited HCl and HF. In this work we observed an unusually large cross section (10 to the -14th power sq cm.) for Cl-/HCl (v=2) and proposed a new mechanism for dissociative attachment by electron impact. These results have been published in Journal of Chemical Physics, 1981. In the program on electronic excitation of noble-gas atoms we have established the experimental methods for studies up to the threshold region. The first results have been obtained for the n=2 states of He, within 4 eV of threshold. In the 2 3S and 2 3P cross sections we observed anomalous angular dependences attributable to a new 2P resonance.

  5. Cross-sections for the formation of negative ions by electron impact on silane

    NASA Technical Reports Server (NTRS)

    Srivastava, S. K.; Krishnakumar, E.; De A. E Souza, A. C.

    1991-01-01

    Cross-sections and appearance potentials for the production of various negative ion species by electron impact on SiH4 have been measured. They are compared with two previous measurements which widely differ with each other. Hess' law has been applied to predict the various possible channels of dissociation.

  6. Structural characterization of flavonol di-O-glycosides from Farsetia aegyptia by electrospray ionization and collision-induced dissociation mass spectrometry.

    PubMed

    Shahat, Abdelaaty A; Cuyckens, Filip; Wang, Wu; Abdel-Shafeek, Khaled A; Husseiny, Husseiny A; Apers, Sandra; Van Miert, Sabine; Pieters, Luc; Vlietinck, Arnold J; Claeys, Magda

    2005-01-01

    This study reports the application of mass spectrometric methods to characterize unknown flavonoids of the herb Farsetia aegyptia Turra (Crucifereae). High-performance liquid chromatography was performed in combination with UV-photodiode array detection (LC/UV-DAD) and electrospray ionization mass spectrometry (LC/ESI-MS) in both positive and negative ion modes. Collision-induced dissociation (CID) mass spectral data were obtained off-line by nanospray (nano-ESI) analysis, which provided a wealth of information and led to the structural proposal of the flavonol di-O-glycosides present in the herb extract. In addition to the mass spectral data, we also report NMR data for the major compound which allowed the completion of its structural elucidation. The Farsetia aegyptia Turra herb extract was found to contain three flavonol di-O-glycosides containing a monosaccharidic residue linked to the 3-O position and a disaccharidic residue linked to the 7-O position; the major compound was characterized as the new flavonoid, isorhamnetin 3-O-alpha-L-arabinoside 7-O-[beta-D-glucosyl-1 --> 2]-alpha(L)rhamnoside. Different types of CID spectra, i.e., low-energy [M+H]+, [M+Na]+ and [M--H]- spectra as well as high-energy [M+Na]+ spectra, were evaluated with respect to their utility to locate the O-linked saccharidic residues in flavonol di-O-glycosides and to determine the sequence in the disaccharidic part. In agreement with previously published data, the 3-O-glycosyl residue was more readily lost from the protonated molecule than the 7-O-glycosyl residue. The opposite behavior was noted for the fragmentation of the deprotonated and sodiated molecules. Radical ions were observed in the high-energy [M+Na]+ CID spectra which provided supporting information on the glycosylation positions. (c) 2005 John Wiley & Sons, Ltd.

  7. Electron Impact Ionization Cross Sections of Gold, Chromium and Iron

    DTIC Science & Technology

    1976-01-01

    experiment, the atom beam was collected on a gold-coated quartz crystal which served as a 203transducer to a Kronos film thickness monitor. By... Kronos Inc., 1647-7 W. Sepul- veda Blvd., Torrance, Calif. 90501 21. V.W. Hughes, H.L. Scbultz (ed.), Methods of Experimental Physics, Vol. 4A

  8. Ionization Properties of Molecules Commonly Used for Plasma Processing of Semi-Conductors

    NASA Technical Reports Server (NTRS)

    Srivastava, S. K.

    2000-01-01

    Two types of processes are involved in plasma processing of semi-conductors. They are: plasma etching or cleaning and plasma deposition of the semi-conducting materials. For plasma etching of semi-conductors mostly halogen containing gases are used as additives to gases such as O2 and N2. For plasma deposition gases such as C2H2, SiH4, Si2H6 have been tested in the past. For an optimal performance of a reactor it is important to model the plasma. In this modeling effort electron impact excitation and ionization cross sections play a central role. For ionization balance calculations values of ionization cross sections are needed. Ion molecule reactions determine the ultimate composition of the plasma. Recently it has been discovered that the by products of many of these plasmas are per fluro hydrocarbons (PFCs) which are highly infrared absorbing species and have long life times in the atmosphere. They cause global warming. A lot of research is being pursued at the present time to find alternative molecules which do not produce global warming gases as the and product of the plasma processing reactor. There is also interest in the ionization and dissociative ionization properties of these molecules from the point view of the plasma abatement of the pollutant gases at the exhaust of the semi-conductor processing reactors. At the conference ionization and dissociative ionization properties of some of these molecules will be presented.

  9. Ionization Properties of Molecules Commonly Used for Plasma Processing of Semi-Conductors

    NASA Technical Reports Server (NTRS)

    Srivastava, S. K.

    2000-01-01

    Two types of processes are involved in plasma processing of semi-conductors. They are: plasma etching or cleaning and plasma deposition of the semi-conducting materials. For plasma etching of semi-conductors mostly halogen containing gases are used as additives to gases such as O2 and N2. For plasma deposition gases such as C2H2, SiH4, Si2H6 have been tested in the past. For an optimal performance of a reactor it is important to model the plasma. In this modeling effort electron impact excitation and ionization cross sections play a central role. For ionization balance calculations values of ionization cross sections are needed. Ion molecule reactions determine the ultimate composition of the plasma. Recently it has been discovered that the by products of many of these plasmas are per fluro hydrocarbons (PFCs) which are highly infrared absorbing species and have long life times in the atmosphere. They cause global warming. A lot of research is being pursued at the present time to find alternative molecules which do not produce global warming gases as the and product of the plasma processing reactor. There is also interest in the ionization and dissociative ionization properties of these molecules from the point view of the plasma abatement of the pollutant gases at the exhaust of the semi-conductor processing reactors. At the conference ionization and dissociative ionization properties of some of these molecules will be presented.

  10. The nature of collision-induced dissociation processes of doubly protonated peptides: comparative study for the future use of matrix-assisted laser desorption/ionization on a hybrid quadrupole time-of-flight mass spectrometer in proteomics.

    PubMed

    Cramer, R; Corless, S

    2001-01-01

    Comparative MS/MS studies of singly and doubly charged electrospray ionization (ESI) and matrix-assisted laser desorption/ionization (MALDI) precursor peptide ions are described. The spectra from these experiments have been evaluated with particular emphasis on the data quality for subsequent data processing and protein/amino acid sequence identification. It is shown that, once peptide ions are formed by ESI or MALDI, their charge state, as well as the collision energy, is the main parameter determining the quality of collision-induced dissociation (CID) MS/MS fragmentation spectra of a given peptide. CID-MS/MS spectra of singly charged peptides obtained on a hybrid quadrupole orthogonal time-of-flight mass spectrometer resemble very closely spectra obtained by matrix-assisted laser desorption/ionization post-source decay time-of-flight mass spectrometry (MALDI-PSD-TOFMS). On the other hand, comparison of CID-MS/MS spectra of either singly or doubly charged ion species shows no dependence on whether ions have been formed by ESI or MALDI. This observation confirms that, at the time of precursor ion selection, further mass analysis is effectively decoupled from the desorption/ionization event. Since MALDI ions are predominantly formed as singly charged species and ESI ions as doubly charged, the associated difference in the spectral quality of MS/MS spectra as described here imposes direct consequences on data processing, database searching using ion fragmentation data, and de novo sequencing when ionization techniques are changed.

  11. Electron-impact study of the S2 molecule using the R-matrix method

    NASA Astrophysics Data System (ADS)

    Rajvanshi, Jasmeet Singh; Baluja, K. L.

    2011-10-01

    The present study deals with the calculation of elastic [integrated and differential cross section (DCS)], momentum-transfer, excitation, and ionization cross sections for electron impact on S2 molecules using the R-matrix method. The target states are represented by including correlations via a configuration-interaction technique. We used a double zeta plus polarization Gaussian basis set contracted as (12,8,1)/(6,4,1) for S atoms. The results of the static exchange, correlated one-state, and 20-state close-coupling approximations are presented. We have detected a stable anionic bound state 2Πg of S2- having the configuration 1σg2⋯5σg2 1σu2⋯4σu2 1πu4 1πg4 2πu4 2πg3. The vertical electron affinity value is 1.42 eV, which is comparable with the experimental value of 1.67±0.015 eV. We detected two shape resonances, both of 2Πu symmetry in the excitation cross sections of the 1Δg and 1Σg+ excited states. The dissociative nature of these resonances is explored by performing scattering calculations in which the S-S bond is stretched. These resonances support dissociative attachment, yielding S and S-. We have also predicted six resonances of various symmetries (2Au, 2B1g,4Au, 4B1g) in the X3Σg- → B3Σu- transition. We have calculated the DCS, in a correlated one-state model, by using the polydcs program of Sanna and Gianturco. The data from the momentum-transfer cross section, generated from DCS, are used to compute effective collision frequencies over a wide electron temperature range (200-30 000 K). The ionization cross sections are calculated in the binary-encounter Bethe model in which Hartree-Fock molecular orbitals at a self-consistent level are used to calculate kinetic and binding energies of the occupied molecular orbitals. We have included up to g-partial wave (l=4) in the scattering calculations. For this molecule we have used a Born-closure top-up procedure to account for the higher partial waves for the convergence of the cross

  12. Characterization of Neutral Radicals from a Dissociative Electron Attachment Process

    NASA Astrophysics Data System (ADS)

    Li, Zhou; Milosavljević, Aleksandar R.; Carmichael, Ian; Ptasinska, Sylwia

    2017-08-01

    Despite decades of gas-phase studies on dissociative electron attachment (DEA) to various molecules, as yet there has been no direct detection and characterization of the neutral radical species produced by this process. In this study, we performed stepwise electron spectroscopy to directly measure and characterize the neutrals produced upon zero-electron-energy DEA to the model molecule, carbon tetrachloride (CCl4 ). We observed the direct yield of the trichloromethyl radical (CCl3. ) formed by DEA to CCl4 and measured the appearance energies of all the other neutral species. By combining these experimental findings with high-level quantum chemical calculations, we performed a complete analysis of both the DEA to CCl4 and the subsequent electron-impact ionization of CCl3. . This work paves the way toward a complete experimental characterization of DEA processes, which will lead to a better understanding of the low-energy electron-induced formation of radical species.

  13. Dissociative photoionization of β-pinene: an experimental and theoretical study.

    PubMed

    Sheng, Liusi; Cao, Maoqi; Chen, Jun; Fang, Wenzhen; Li, Yuquan; Ge, Shaolin; Shan, Xiaobin; Liu, Fuyi; Zhao, Yujie; Zhenya Wang, Zhenya Wang

    2014-01-01

    We investigated the photoionization and dissociation photoionization of the β-pinene molecular using time-of-flight mass spectrometry with a tunable vacuum ultraviolet source in the region from 8.00eV to 15.50eV. The experimental ionization energy (IE) value is 8.60eV using electron impact as the ionization source which is not in good agreement with theoretical value (8.41 eV) with a G3MP2 method. We obtained the accurate IE of β-pinene (8.45 ± 0.03eV) derived from the efficiency spectrum which is in good agreement with the theoretical value (8.38eV) of the CBS-QB3 method. We elucidated the dissociation pathways of primary fragment ions from the β-pinene cation on the basis of experimental observations in combination with theoretical calculations. Most of the dissociation pathways occur via a rearrangement reaction prior to dissociation. We also determined the structures of the transition states and intermediates for those isomerization processes.

  14. Dissociative Disorders

    MedlinePlus

    ... last minutes, hours, or rarely, months or years. Dissociative identity disorder. Formerly known as multiple personality disorder, this disorder ... each identity is with the others. People with dissociative identity disorder typically also have dissociative amnesia and often have ...

  15. Structure and end-group analysis of complex hexanediol-neopentylglycol-adipic acid copolyesters by matrix-assisted laser desorption/ionization collision-induced dissociation tandem mass spectrometry.

    PubMed

    Weidner, Steffen M; Falkenhagen, Jana; Knop, Karin; Thünemann, Andreas

    2009-09-01

    Sequences and end groups of complex copolyesters were determined by fragmentation analysis by means of matrix-assisted laser desorption/ionization collision-induced dissociation tandem mass spectrometry (MALDI CID MS/MS). The complexity of the crude copolyester mixture was reduced by a chromatographic separation followed by a MALDI time-of-flight (TOF) investigation of fractions. Due to overlapping compositional and end-group information a clear assignment of end groups was very difficult. However, the fragmentation of suitable precursor ions resulted in typical fragment ion patterns and, therefore, enabled a fast and unambiguous determination of the end groups and composition of this important class of polymers.

  16. Dissociative attachment of electrons to N2O

    NASA Technical Reports Server (NTRS)

    Krishnakumar, E.; Srivastava, S. K.

    1990-01-01

    Cross sections for the production of O(-) from N2O by the process of dissociative electron attachment have been measured for electron-impact energies ranging from 0 to 50 eV. Three new O(-) peaks are observed. The present data above 5-eV electron-impact energy differ considerably from the previous measurements.

  17. The EUV spectrum of H2O by electron impact

    NASA Technical Reports Server (NTRS)

    Ajello, J. M.

    1984-01-01

    The vacuum ultraviolet (VUV) spectrum of H2O produced by electron impact at 200 eV is presented. A total of 25 spectral features are identified at a resolution of 0.5 nm over the wavelength range from 40 to 280 nm. Absolute emission cross-sections were obtained for each of the features. The differences of the features are all attributed to the various excited states of the dissociation products, H, O and O(+). The Lyman-alpha feature is the brightest for electron-induced fluorescence of H2O from the UV to the near-IR, and had a cross-section of 6.3 (+ or - 1.0 x 10 to the -18th) sq cm at 200 eV. The Lyman-alpha feature contributed 74 percent of the total measured emission cross-section in the EUV.

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

    NASA Astrophysics Data System (ADS)

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

    2017-03-01

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

  19. Dissociative Disorders

    MedlinePlus

    ... of continuity between thoughts, memories, surroundings, actions and identity. People with dissociative disorders escape reality in ways ... at bay. Symptoms — ranging from amnesia to alternate identities — depend in part on the type of dissociative ...

  20. Electron Impact Induced VUV Emission from Argon

    NASA Astrophysics Data System (ADS)

    Young, J. A.; Malone, C. P.; Johnson, P. V.

    2011-10-01

    Emission intensity and spectra are important tools for diagnosing plasma properties such as electron temperature and neutral density. In order to properly interpret emissions from low-density plasmas, accurate cross sections are needed, particularly low energy electron-impact cross sections. Of interest are the cross sections for Argon, a common species used in industrial and lighting applications. In this paper, we present recent measurements of electron-impact induced VUV emissions from Ar using a magnetically collimated monoenergetic beam of electrons and a 0.2m spectrometer. Specifically, we present emission excitation functions for both Ar I(1048 Å) and Ar I(1066 Å) emissions. Similarities and differences between current results and previously published emission results will be discussed. Also discussed will be the relation to recent electron energy loss results.

  1. Calculated ionization rates, ion densities, and airglow emission rates due to precipitating electrons in the nightside ionosphere of Mars

    NASA Technical Reports Server (NTRS)

    Haider, S. A.; Kim, J.; Nagy, A. F.; Keller, C. N.; Verigin, M. I.; Gringauz, K. I.; Shutte, N. M.; Szego, K.; Kiraly, P.

    1992-01-01

    The calculations presented in this paper clearly establish that the electron fluxes measured by the HARP instrument, carried on board Phobos 2, could cause significant electron impact ionization and excitation in the nightside atmosphere of Mars, if these electrons actually do precipitate. The calculated peak electron densities were found to be about a factor of 2 larger than the mean observed nightside densities, indicating that if a significant fraction of the measured electrons actually precipitate, they could be the dominant mechanism responsible for maintaining the nightside ionosphere. The calculated zenith column emission rates of the O I 5577-A and 6300-A and CO Cameron band emissions, due to electron impact and dissociative recombination mechanisms, were found to be significant.

  2. Calculated ionization rates, ion densities, and airglow emission rates due to precipitating electrons in the nightside ionosphere of Mars

    NASA Technical Reports Server (NTRS)

    Haider, S. A.; Kim, J.; Nagy, A. F.; Keller, C. N.; Verigin, M. I.; Gringauz, K. I.; Shutte, N. M.; Szego, K.; Kiraly, P.

    1992-01-01

    The calculations presented in this paper clearly establish that the electron fluxes measured by the HARP instrument, carried on board Phobos 2, could cause significant electron impact ionization and excitation in the nightside atmosphere of Mars, if these electrons actually do precipitate. The calculated peak electron densities were found to be about a factor of 2 larger than the mean observed nightside densities, indicating that if a significant fraction of the measured electrons actually precipitate, they could be the dominant mechanism responsible for maintaining the nightside ionosphere. The calculated zenith column emission rates of the O I 5577-A and 6300-A and CO Cameron band emissions, due to electron impact and dissociative recombination mechanisms, were found to be significant.

  3. Core excitation of Li by electron impact

    SciTech Connect

    Tiwary, S.N.

    1985-07-01

    Cross sections for the excitation of a core electron, which leads to autoionization, in lithium (Li) atomic system by electron impact have been calculated with use of the single-configuration Hartree-Fock wave function within the asymptotic Green's-function approximation (AGFA) in the low-bombarding-energy region. Comparison is made with available results. Our investigation demonstrates that the AGFA supports the R-matrix as well as the distorted-wave Born-approximation behavior.

  4. Generation of a pair of photons through the three-body dissociation of a multiply excited water molecule around the double ionization potential

    NASA Astrophysics Data System (ADS)

    Odagiri, Takeshi; Nakano, Motoyoshi; Tanabe, Takehiko; Kumagai, Yoshiaki; Suzuki, Isao H.; Kouchi, Noriyuki

    2009-11-01

    The cross sections for the generation of a photon-pair from excited fragments in photoexcitation of H2O have been measured as a function of incident photon energy. The multiply excited states of H2O have been observed even above the adiabatic double ionization potential.

  5. Electron impact excitation of SO2 - Differential, integral, and momentum transfer cross sections

    NASA Technical Reports Server (NTRS)

    Vuskovic, L.; Trajmar, S.

    1982-01-01

    Electron impact excitation of the electronic states of SO2 was investigated. Differential, integral, and inelastic momentum transfer cross sections were obtained by normalizing the relative measurements to the elastic cross sections. The cross sections are given for seven spectral ranges of the energy-loss spectra extending from the lowest electronic state to near the first ionization limit. Most of the regions represent the overlap of several electronic transitions. No measurements for these cross sections have been reported previously.

  6. High efficiency noble gas electron impact ion source for isotope separation

    SciTech Connect

    Appelhans, A. D.; Olson, J. E.; Dahl, D. A.; Ward, M. B.

    2016-07-01

    An electron impact ion source has been designed for generation of noble gas ions in a compact isotope separator. The source utilizes a circular filament that surrounds an ionization chamber, enabling multiple passes of electrons through the ionization chamber. This report presents ion optical design and the results of efficiency and sensitivity measurements performed in an ion source test chamber and in the compact isotope separator. The cylindrical design produced xenon ions at an efficiency of 0.37% with a sensitivity of ~24 µA /Pa at 300 µA of electron current.

  7. Dissociative Electron Attachment to chloroacetylene

    NASA Astrophysics Data System (ADS)

    Ngassam, V.; Orel, A. E.

    2007-06-01

    The production of two fragments with σ symmetry from electron-impact dissociation of C2H2, which has only a low lying &*circ; resonance at equilibrium geometry, has been explained by the existence of interactions with &*circ; resonances at bent geometries. We are investigating the presence of such multidimensional effects in the dissociative attachment of chloroacetylene (C2HCl). We have performed electron scattering calculations using the Complex Kohn variational method to determine the resonance energies and widths of the chloroacetylene resonances as a function of both the Cl--C2H bond distance as well as the variation with C-C stretch and bend. We will discuss our results and our prediction of the dissociation dynamics in comparison to the findings for for C2H2. This work was supported by the U.S. DOE Office of Basic Energy Sciences, Division of Chemical Sciences and the National Science Foundation, PHY-05-55401.

  8. Comparison between Source-induced Dissociation and Collision-induced Dissociation of Ampicillin, Chloramphenicol, Ciprofloxacin, and Oxytetracycline via Mass Spectrometry.

    PubMed

    Lee, Seung Ha; Choi, Dal Woong

    2013-06-01

    Mass spectrometry (MS) is a very powerful instrument that can be used to analyze a wide range of materials such as proteins, peptides, DNA, drugs, and polymers. The process typically involves either chemical or electron (impact) ionization of the analyte. The resulting charged species or fragment is subsequently identified by the detector. Usually, single mass uses source-induced dissociation (SID), whereas mass/mass uses collision-induced dissociation (CID) to analyze the chemical fragmentations Each technique has its own advantages and disadvantages. While CID is most effective for the analysis of pure substances, multiple- step MS is a powerful technique to get structural data. Analysis of veterinary drugs ampicillin, chloramphenicol, ciprofloxacin, and oxytetracycline serves to highlight the slight differences between SID and CID. For example, minor differences were observed between ciprofloxacin and oxytetracycline via SID or CID. However, distinct fragmentation patterns were observed for ampicllin depending on the analysis method. Both SID and CID showed similar fragmentation spectra but different signal intensities for chloramphenicol. There are several factors that can influence the fragmentation spectra, such as the collision energy, major precursor ion, electrospray mode (positive or negative), and sample homogeneity. Therefore, one must select a fragmentation method on an empirical and case-by-case basis.

  9. On the role of electron impact in an atmospheric-pressure microwave discharge in liquid n-heptane

    NASA Astrophysics Data System (ADS)

    Lebedev, Yu. A.; Tatarinov, A. V.; Epstein, I. L.

    2017-04-01

    The role of electron impact in the dissociation of n-heptane in an atmospheric-pressure microwave discharge in liquid n-heptane was investigated using a self-consistent two-dimensional model. The model includes the Navier-Stokes equations for a two-phase subsonic flow of incompressible liquid and compressible gas, the heat conduction equation, Maxwell's equations for the microwave field, the Boltzmann equation for plasma electrons, and the balance equations for the electron density and weight fraction of n-heptane in the gaseous and liquid phases. It is shown that the effect of electron impact is negligible at times longer than 10-3 s.

  10. Ionizing Collisions of Electrons with Radical Species OH, H2 O2 and HO2; Theoretical Calculations

    NASA Astrophysics Data System (ADS)

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

    2016-05-01

    In this paper we present our calculated total ionization cross sections (TICS) of electron impact on radical targets OH, H2 O2 and HO2 at energies from threshold to 2000 eV. Reactive species such as these pose difficulties in measurements of electron scattering cross sections. No measured data have been reported in this regard except an isolated TICS measurement on OH radical, and hence the present work on the title radicals hold significance. These radical species are present in an environment in which water molecules undergo dissociation (neutral or ionic) in interactions with photons or electrons. The embedding environments could be quite diverse, ranging from our atmosphere to membranes of living cells. Ionization of OH, H2 O2 or HO2 can give rise to further chemistry in the relevant bulk medium. Therefore, it is appropriate and meaningful to examine electron impact ionization of these radicals in comparison with that of water molecules, for which accurate da are available. For the OH target single-centre scattering calculations are performed by starting with a 4-term complex potential, that describes simultaneous elastic plus inelastic scattering. TICS are obtained from the total inelastic cross sections in the complex scattering potential - ionization contribution formalism , a well established method. For H2 O2 and HO2 targets, we employ the additivity rule with overlap or screening corrections. Detailed results will be presented in the Conference.

  11. Dissociative disorders.

    PubMed

    Kihlstrom, John F

    2005-01-01

    The dissociative disorders, including "psychogenic" or "functional" amnesia, fugue, dissociative identity disorder (DID, also known as multiple personality disorder), and depersonalization disorder, were once classified, along with conversion disorder, as forms of hysteria. The 1970s witnessed an "epidemic" of dissociative disorder, particularly DID, which may have reflected enthusiasm for the diagnosis more than its actual prevalence. Traditionally, the dissociative disorders have been attributed to trauma and other psychological stress, but the existing evidence favoring this hypothesis is plagued by poor methodology. Prospective studies of traumatized individuals reveal no convincing cases of amnesia not attributable to brain insult, injury, or disease. Treatment generally involves recovering and working through ostensibly repressed or dissociated memories of trauma; at present, there are few quantitative or controlled outcome studies. Experimental studies are few in number and have focused largely on state-dependent and implicit memory. Depersonalization disorder may be in line for the next "epidemic" of dissociation.

  12. Dissociative amnesia.

    PubMed

    Staniloiu, Angelica; Markowitsch, Hans J

    2014-08-01

    Dissociative amnesia is one of the most enigmatic and controversial psychiatric disorders. In the past two decades, interest in the understanding of its pathophysiology has surged. In this report, we review new data about the epidemiology, neurobiology, and neuroimaging of dissociative amnesia and show how advances in memory research and neurobiology of dissociation inform proposed pathogenetic models of the disorder. Dissociative amnesia is characterised by functional impairment. Additionally, preliminary data suggest that affected people have an increased and possibly underestimated suicide risk. The prevalence of dissociative amnesia differs substantially across countries and populations. Symptoms and disease course also vary, indicating a possibly heterogeneous disorder. The accompanying clinical features differ across cultural groups. Most dissociative amnesias are retrograde, with memory impairments mainly involving the episodic-autobiographical memory domain. Anterograde dissociative amnesia occurring without significant retrograde memory impairments is rare. Functional neuroimaging studies of dissociative amnesia with prevailing retrograde memory impairments show changes in the network that subserves autobiographical memory. At present, no evidence-based treatments are available for dissociative amnesia and no broad framework exists for its rehabilitation. Further research is needed into its neurobiology, course, treatment options, and strategies to improve differential diagnoses. Copyright © 2014 Elsevier Ltd. All rights reserved.

  13. ELECTRON IMPACT DISSOCIATION X {sup 1}{Sigma}{sup +} {sub g} {yields} b {sup 3}{Sigma} {sub u} {sup +} AND EXCITATIONS X {sup 1}{Sigma}{sup +} {sub g} {yields} a {sup 3}{Sigma} {sub g} {sup +} AND X {sup 1}{Sigma}{sup +} {sub g} {yields} B {sup 1}{Sigma} {sub u} {sup +} OF MOLECULAR HYDROGEN IN NONTHERMAL ASTROPHYSICAL PLASMAS

    SciTech Connect

    Ki, Dae-Han; Jung, Young-Dae

    2013-02-15

    We investigate the electronic transitions X {sup 1}{Sigma}{sup +} {sub g} {yields} b {sup 3}{Sigma} {sub u} {sup +}, X {sup 1}{Sigma}{sup +} {sub g} {yields} a {sup 3}{Sigma} {sub g} {sup +}, and X {sup 1}{Sigma}{sup +} {sub g} {yields} B {sup 1}{Sigma} {sub u} {sup +} of molecular hydrogen by studying electron impacts in astrophysical Lorentzian plasmas. Useful fitting formulae for the X {sup 1}{Sigma}{sup +} {sub g} {yields} b {sup 3}{Sigma} {sub u} {sup +}, X {sup 1}{Sigma}{sup +} {sub g} {yields} a {sup 3}{Sigma} {sub g} {sup +}, and X {sup 1}{Sigma}{sup +} {sub g} {yields} B {sup 1}{Sigma} {sub u} {sup +} excitation cross sections are employed in order to obtain the electronic excitation rate coefficients of H{sub 2} as functions of the spectral index and temperature. In low-temperature regions, it is found that the excitation rate coefficients R{sub b{sup 3}{Sigma}{sub u{sup {sub +}}}}, R{sub a{sup 3}{Sigma}{sub g{sup {sub +}}}}, and R{sub B{sub {sup 1}{Sigma}{sub u{sup {sub +}}}}} of H{sub 2} in non-Maxwellian plasmas are smaller than those in Maxwellian plasmas. However, in high-temperature regions, the excitation rate coefficients of H{sub 2} in non-Maxwellian plasmas are greater than those in Maxwellian plasmas. It is also shown that the X {sup 1}{Sigma}{sup +} {sub g} {yields} b {sup 3}{Sigma} {sub u} {sup +} excitation rate coefficient is the main contributor in low-temperature regions. In contrast, it is found that the X {sup 1}{Sigma}{sup +} {sub g} {yields} B {sup 1}{Sigma} {sub u} {sup +} electronic excitation is dominant in high-temperature regions.

  14. High-energy and low-energy collision-induced dissociation of protonated flavonoids generated by MALDI and by electrospray ionization

    NASA Astrophysics Data System (ADS)

    March, Raymond E.; Li, Hongxia; Belgacem, Omar; Papanastasiou, Dimitris

    2007-04-01

    Product ion mass spectra of a series of nine protonated flavonoids have been observed by electrospray ionization combined with quadrupole/time-of-flight (ESI QTOF), and matrix-assisted laser desorption ionization combined either with quadrupole ion trap (MALDI QIT) tandem mass spectrometry or time-of-flight tandem mass spectrometry (MALDI TOF ReTOF). The compounds examined are 3,6-, 3,2'-, and 3,3'-dihydoxyflavone, apigenin (5,7,4'-trihydroxyflavone), luteolin (5,7,3',4'-tetrahydroxyflavone), apigenin-7-O-glucoside, hesperidin (5,7,3'-trihydroxy-4'-methoxyflavanone), daidzen (7,4'-dihydroxyisoflavone), and rutin (quercitin-3-O-rutinoside) where quercitin is 3,5,7,3',4'-pentahydroxyflavone; sodiated rutin was examined also. The center-of-mass energies in ESI QTOF and MALDI QIT are similar (1-4 eV) and their product ion mass spectra are virtually identical. In the MALDI TOF ReTOF instrument, center-of-mass energies range from 126-309 eV for sodiated rutin to protonated dihydroxyflavones, respectively. Due to the high center-of-mass energies available with the MALDI TOF ReTOF instrument, some useful structural information may be obtained; however, with increasing precursor mass/charge ratio, product ion mass spectra become simplified so as to be of limited structural value. Electronic excitation of the protonated (and sodiated) species examined here offers an explanation for the very simple product ion mass spectra observed particularly for glycosylated flavonoids.

  15. The SILCC project - IV. Impact of dissociating and ionizing radiation on the interstellar medium and Hα emission as a tracer of the star formation rate

    NASA Astrophysics Data System (ADS)

    Peters, Thomas; Naab, Thorsten; Walch, Stefanie; Glover, Simon C. O.; Girichidis, Philipp; Pellegrini, Eric; Klessen, Ralf S.; Wünsch, Richard; Gatto, Andrea; Baczynski, Christian

    2017-04-01

    We present three-dimensional radiation-hydrodynamical simulations of the impact of stellar winds, photoelectric heating, photodissociating and photoionizing radiation, and supernovae on the chemical composition and star formation in a stratified disc model. This is followed by a sink-based model for star clusters with populations of individual massive stars. Stellar winds and ionizing radiation regulate the star formation rate at a factor of ∼10 below the simulation with only supernova feedback due to their immediate impact on the ambient interstellar medium after star formation. Ionizing radiation (with winds and supernovae) significantly reduces the ambient densities for most supernova explosions to ρ < 10-25 g cm-3, compared to 10-23g cm-3 for the model with only winds and supernovae. Radiation from massive stars reduces the amount of molecular hydrogen and increases the neutral hydrogen mass and volume filling fraction. Only this model results in a molecular gas depletion time-scale of 2 Gyr and shows the best agreement with observations. In the radiative models, the Hα emission is dominated by radiative recombination as opposed to collisional excitation (the dominant emission in non-radiative models), which only contributes ∼1-10 per cent to the total Hα emission. Individual massive stars (M ≥ 30 M⊙) with short lifetimes are responsible for significant fluctuations in the Hα luminosities. The corresponding inferred star formation rates can underestimate the true instantaneous star formation rate by a factor of ∼10.

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

    NASA Astrophysics Data System (ADS)

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

    2004-04-01

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

  17. Asymmetry in the momentum distribution of H+p from dissociative ionization of H2 controlled by the carrier-envelope phase of a few-cycle pulse

    NASA Astrophysics Data System (ADS)

    Zeng, Shuo; Anis, Fatima; Esry, B. D.

    2010-03-01

    We present theoretical results on the interaction of H2 with an ultrashort linearly polarized laser pulse of 6 fs duration. We investigate the carrier-envelope phase effects of this ultrashort laser pulse on the asymmetry of the momentum distribution of H+p along the laser polarization direction. To do so, we model the H2 ionization by launching a coherent wavepacket on H2^+ potential curves at each field maximum, and then propagate wavepackets in time on H2^+ Born-Oppenheimer potential curves coupled by the laser. Nuclear rotation and vibration are both included in the Schrödinger equation for H2^+ . Our results will be compared to a recent experimental measurement [1]. We will also compare our results to calculations neglecting rotation and discuss the limitations of such a model.[4pt] [1] Manuel Kremer et al., Phys. Rev. Lett. 103.213003 (2009)

  18. Ionization of excited xenon atoms by electrons

    NASA Astrophysics Data System (ADS)

    Erwin, Daniel A.; Kunc, Joseph A.

    2004-08-01

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

  19. Excitation of atomic nitrogen by electron impact

    NASA Technical Reports Server (NTRS)

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

    1972-01-01

    Absolute cross sections were measured for the excitation of the N I(1134, 1164, 1168, 1200, 1243, and 1743 A) multiplets by electron impact on atomic nitrogen. The presence of vibrationally excited molecular nitrogen in the discharged gas was confirmed, and its effect on the measurements is discussed. The ratio of the oscillator strengths of the 1200 and 1134 A resonance transitions is presented, as well as the branching ratio for the N I(1311/1164 A) multiplets. Striking differences in the distribution of intensity between the spectra of atomic nitrogen and molecular nitrogen excited by energetic electrons suggest an optical method for measuring the density of atomic nitrogen in the upper atmosphere.

  20. The Middle Ultraviolet-Visible Spectrum of H2 Excited by Electron Impact

    NASA Technical Reports Server (NTRS)

    James, Geoffrey K.; Ajello, Joseph M.; Pryor, Wayne R.

    2000-01-01

    The electron-impact-induced emission spectrum of H2 has been measured in the extended wavelength region 175-530 mm at a spectral resolution of 1.7 mm (FWHM). The laboratory spectra are characterized by underlying H2 (a (sup 3) Sigma(sup +, sub g) to b (sup 3) Sigma(sup +, sub u) continuum emission. together with many strong lines assigned to the radiative decay of the gerade singlet states of H2, and to members of the H Balmer series resulting from dissociative excitation of H2.

  1. Absolute cross sections for electronic excitations of cytosine by low energy electron impact

    PubMed Central

    Bazin, M.; Michaud, M.; Sanche, L.

    2013-01-01

    The absolute cross sections (CS) for electronic excitations of cytosine by electron impact between 5 and 18 eV were measured by electron-energy loss (EEL) spectroscopy of the molecule deposited at low coverage on an inert Ar substrate. The lowest EEL features found at 3.55 and 4.02 eV are ascribed to transitions from the ground state to the two lowest triplet 1 3A′(π→π*) and 2 3A′(π→π*) valence states of the molecule. Their energy dependent CS exhibit essentially a common maximum at about 6 eV with a value of 1.84 × 10−17 cm2 for the former and 4.94 × 10−17 cm2 for the latter. In contrast, the CS for the next EEL feature at 4.65 eV, which is ascribed to the optically allowed transition to the 2 1A′(π→π*) valence state, shows only a steep rise to about 1.04 × 10−16 cm2 followed by a monotonous decrease with the incident electron energy. The higher EEL features at 5.39, 6.18, 6.83, and 7.55 eV are assigned to the excitations of the 3 3, 1A′(π→π*), 4 1A′(π→π*), 5 1A′(π→π*), and 6 1A′(π→π*) valence states, respectively. The CS for the 3 3, 1A′ and 4 1A′ states exhibit a common enhancement at about 10 eV superimposed on a more or less a steep rise, reaching respectively a maximum of 1.27 and 1.79 × 10−16 cm2, followed by a monotonous decrease. This latter enhancement and the maximum seen at about 6 eV in the lowest triplet states correspond to the core-excited electron resonances that have been found by dissociative electron attachment experiments with cytosine in the gas phase. The weak EEL feature found at 5.01 eV with a maximum CS of 3.8 × 10−18 cm2 near its excitation threshold is attributed to transitions from the ground state to the 1 3, 1A″(n→π*) states. The monotonous rise of the EEL signal above 8 eV is attributed to the ionization of the molecule. It is partitioned into four excitation energy regions at about 8.55, 9.21, 9.83, and 11.53 eV, which correspond closely to the ionization energies of

  2. Theoretical electron impact total cross sections for tetrahydrofuran (C4H8O)

    NASA Astrophysics Data System (ADS)

    Swadia, Mohit; Thakar, Yogesh; Vinodkumar, Minaxi; Limbachiya, Chetan

    2017-04-01

    We report electron impact total cross sections for tetrahydrofuran (C4H8O) from ionization threshold to 5 keV. We have employed Spherical Complex Optical Potential (SCOP) to calculate total cross sections QT, total inelastic cross sections Qinel and total elastic cross sections Qel and have used Complex Scattering Potential - ionization contribution (CSP-ic) formalisms to compute total ionization cross sections Qion and summed total excitation cross sections ∑ Qexc. We have compared our cross sections with available experimental as well as theoretical results and have found good agreement wherever available. This is the maiden attempt to report the total excitation cross sections for this target. Contribution to the Topical Issue "Low-Energy Interactions related to Atmospheric and Extreme Conditions", edited by S. Ptasinska, M. Smialek-Telega, A. Milosavljevic, B. Sivaraman.

  3. Selfconsistent vibrational and free electron kinetics for CO2 dissociation in cold plasmas

    NASA Astrophysics Data System (ADS)

    Capitelli, Mario

    2016-09-01

    The activation of CO2 by cold plasmas is receiving new theoretical interest thanks to two European groups. The Bogaerts group developed a global model for the activation of CO2 trying to reproduce the experimental values for DBD and microwave discharges. The approach of Pietanza et al was devoted to understand the dependence of electron energy distribution function (eedf) of pure CO2 on the presence of concentrations of electronically and vibrationally excited states taken as parameter. To understand the importance of the vibrational excitation in the dissociation process Pietanza et al compared an upper limit to the dissociation process from a pure vibrational mechanism (PVM) with the corresponding electron impact dissociation rate, the prevalence of the two models depending on the reduced electric field and on the choice of the electron molecule cross section database. Improvement of the Pietanza et al model is being considered by coupling the time dependent Boltzmann solver with the non equilibrium vibrational kinetics of asymmetric mode and with simplified plasma chemistry kinetics describing the ionization/recombination process and the excitation-deexcitation of a metastable level at 10.5eV. A new PVM mechanism is also considered. Preliminary results, for both discharge and post discharge conditions, emphasize the action of superelastic collisions involving both vibrationally and electronically excited states in affecting the eedf. The new results can be used to plan a road map for future developments of numerical codes for rationalizing existing experimental values, as well as, for indicating new experimental situations.

  4. Photo-ionization rate coefficients for the rare gases

    NASA Astrophysics Data System (ADS)

    Pang, Xuexia

    2005-01-01

    By introducing the converting method from electron-impact ionization cross sections to rate coefficients through using a semi-experiential formula, we try to probe a semi-experiential formula for converting the photo-ionization cross sections into photo-ionization rate coefficient. It"s found that photo-ionization rate coefficient is direct proportion to photo-ionization cross sections, the rate S is related with light resource.

  5. A simultaneous determination method for 5-fluorouracil and its metabolites in human plasma with linear range adjusted by in-source collision-induced dissociation using hydrophilic interaction liquid chromatography-electrospray ionization-tandem mass spectrometry.

    PubMed

    Ishii, Hideaki; Shimada, Miki; Yamaguchi, Hiroaki; Mano, Nariyasu

    2016-11-01

    We applied a new technique for quantitative linear range shift using in-source collision-induced dissociation (CID) to complex biological fluids to demonstrate its utility. The technique was used in a simultaneous quantitative determination method of 5-fluorouracil (5-FU), an anticancer drug for various solid tumors, and its metabolites in human plasma by liquid chromatography-electrospray ionization-tandem mass spectrometry (LC/ESI-MS/MS). To control adverse effects after administration of 5-FU, it is important to monitor the plasma concentration of 5-FU and its metabolites; however, no simultaneous determination method has yet been reported because of vastly different physical and chemical properties of compounds. We developed a new analytical method for simultaneously determining 5-FU and its metabolites in human plasma by LC/ESI-MS/MS coupled with the technique for quantitative linear range shift using in-source CID. Hydrophilic interaction liquid chromatography using a stationary phase with zwitterionic functional groups, phosphorylcholine, was suitable for separation of 5-FU from its nucleoside and interfering endogenous materials. The addition of glycerin into acetonitrile-rich eluent after LC separation improved the ESI-MS response of high polar analytes. Based on the validation results, linear range shifts by in-source CID is the reliable technique even with complex biological samples such as plasma. Copyright © 2016 John Wiley & Sons Ltd. Copyright © 2016 John Wiley & Sons, Ltd.

  6. Liquid chromatography coupled with ultraviolet absorbance detection, electrospray ionization, collision-induced dissociation and tandem mass spectrometry on a triple quadrupole for the on-line characterization of polyphenols and methylxanthines in green coffee beans.

    PubMed

    Alonso-Salces, Rosa Maria; Guillou, Claude; Berrueta, Luis A

    2009-02-01

    Liquid chromatography coupled with a photodiode array detector, electrospray ionization, collision-induced dissociation and tandem mass spectrometry (LC-DAD/ESI-CID-MS/MS) on a triple quadrupole (QqQ) has been used to detect and characterize polyphenols and methylxanthines in green coffee beans: three phenolic acids (caffeic acid, ferulic acid and dimethoxycinnamic acid), three isomeric caffeoylquinic acids (M(r) 354), three feruloylquinic acids (M(r) 368), one p-coumaroylquinic acid (M(r) 338), three dicaffeoylquinic acids (M(r) 516), three feruloyl-caffeoylquinic acids (M(r) 530), four p-coumaroyl-caffeoylquinic acids (M(r) 500), three diferuloylquinic acids (M(r) 544), six dimethoxycinnamoyl-caffeoylquinic acids (M(r) 544), three dimethoxycinnamoyl-feruloylquinic acids (M(r) 558), six cinnamoyl-amino acid conjugates, three cinnamoyl glycosides, and three methylxanthines (caffeine, theobromine and theophylline). Dimethoxycinnamic acid, three isomers of dimethoxycinnamoyl-caffeoylquinic acids and another three of dimethoxycinnamoyl-feruloylquinic acids, as well as the three cinnamoyl glycosides, had not previously been reported in coffee beans. Structures have been assigned on the basis of the complementary information obtained from UV-visible spectra, relative hydrophobicity, scan mode MS spectra, and fragmentation patterns in MS(2) spectra (both in the positive and negative ion modes) obtained using a QqQ at different collision energies. A structure diagnosis scheme is provided for the identification of different isomers of polyphenols and methylxanthines. Copyright 2009 John Wiley & Sons, Ltd.

  7. Rapid determination of oxidized methionine residues in recombinant human basic fibroblast growth factor by ultra-performance liquid chromatography and electrospray ionization quadrupole time-of-flight mass spectrometry with in-source collision-induced dissociation.

    PubMed

    Ohkubo, Tsutomu; Inagaki, Shinsuke; Min, Jun Zhe; Kamiya, Daiki; Toyo'oka, Toshimasa

    2009-07-01

    The primary structure of the deteriorated recombinant human basic fibroblast growth factor (rhbFGF) was determined by ultra-performance liquid chromatography and electrospray ionization quadrupole time-of-flight mass spectrometry (UPLC/ESI-QTOF-MS) with in-source collision-induced dissociation (CID). The rhbFGFs before and after treatment with hydrogen peroxide (H(2)O(2)) were separated using an ACQUITY UPLC BEH300 C18 column (1.7 microm, 150 mm x 2.1 mm i.d.) with a gradient elution of a mixture of water/acetonitrile containing 0.1% formic acid. The separated proteins were then detected by a SYNAPT High Definition Mass Spectrometry system (SYNAPT-MS). Two methionine (Met) residues in the rhbFGF structure were oxidized to Met-sulfoxide (Met-O) in 0.03% H(2)O(2) at pH 2.0. As the result, three peaks, except for the peak of rhbFGF, appeared on the chromatogram. The three proteins corresponding to each peak were estimated as the denatured rhbFGFs including the Met-O residue(s) with TOF-MS. Furthermore, the position of the Met-O residue(s) was efficiently identified by UPLC/ESI-QTOF-MS using the in-source CID technique. The proposed method seems to be very useful for the structural elucidation of proteins, because the oxidized Met residues in rhbFGF were easily and rapidly identified.

  8. Dynamics of cluster dissociation

    SciTech Connect

    Keesee, R.G.; Castleman, A.W. Jr.

    1986-01-01

    The dynamics of dissociation of clusters induced by multiphoton ionization (MPI) is examined by time-of-flight mass spectrometry with the aid of a reflecting electric field. The systems discussed include ammonia, methanol, xenon, and p-xylene(Ar)/sub n/ clusters. Ammonia and methanol clusters undergo rapid intracluster reactions to yield protonated clusters. Much of the excess energy which leads to dissociation in ammonia, methanol, and xenon clusters results from the energy differences in the ground states of the neutral and ionic systems. On the other hand, in the case of p-xylene(Ar)/sub n/ the energetic differences are much smaller, so that the excess absorbed photon energy may be an important contribution. 10 refs., 3 figs.

  9. Dynamics of cluster dissociation

    SciTech Connect

    Keesee, R.G.; Castleman A.W. Jr.

    1987-09-25

    The dynamics of dissociation of clusters induced by multiphoton ionization (MPI) is examined by time-of-flight mass spectrometry with the aid of a reflecting electric field. The systems discussed include ammonia, methanol, xenon, and p-xylene(Ar)/sub n/ clusters. Ammonia and methanol clusters undergo rapid intracluster reactions to yield protonated clusters. Much of the excess energy which leads to dissociation in ammonia, methanol, and xenon clusters results from the energy differences in the ground states of the neutral and ionic systems. On the other hand, in the case of p-xylene(Ar)/sub n/ the energetic differences are much smaller, so that the excess absorbed photon energy may be an important contribution.

  10. Electron-impact excitation of Ne4+

    NASA Astrophysics Data System (ADS)

    Griffin, D. C.; Badnell, N. R.

    2000-10-01

    We present the results of extensive close-coupling calculations of electron-impact excitation of the C-like ion, Ne4+. We first compare effective collision strengths determined from a 20-level Breit-Pauli R-matrix calculation with those obtained from a 20-level intermediate-coupling frame transformation (ICFT) R-matrix calculation. The ICFT method was also employed to perform two much larger calculations; we compare the effective collision strengths determined from these calculations with each other and with those obtained from the 20-level calculations in order to assess the effects of increasing both the size of the configuration-interaction expansion of the target and the size of the close-coupling expansion. Our final calculation, with 130 terms and 261 levels in the configuration-interaction expansion of the target and 66 terms and 138 levels in the close-coupling expansion, provides improved data for excitation between the levels of the 2s22p2, 2s2p3 and 2p4 configurations and the first close-coupling results for excitation to the levels of the 2s22p3ℓ configurations in Ne4+.

  11. Electron Impact Exciation of Fe IX

    NASA Astrophysics Data System (ADS)

    Tayal, Swaraj; Zatsarinny, Oleg

    2015-05-01

    Transition probabilities and electron impact excitation collision strengths and rates for astrophysically important extreme ultraviolet lines of Fe IX are calculated. The 322 fine-structure levels of the 3s2 3p6 , 3s2 3p5 3 d , 3 s 3p6 3 d , 3s2 3p5 4 s , and 3s2 3p4 3d2 configurations are included in our calculations. The collision strengths have been calculated using the B-spline Breit-Pauli R-matrix method for all fine-structure transitions among the 322 levels. The mass, Darwin, and spin-orbit relativistic effects are included in the Breit-Pauli Hamiltonian in the scattering calculation. The one-body and two-body relativistic operators are included in the multi-configuration Hartree-Fock calculations of transition probabilities. Several sets of non-orthogonal spectroscopic and correlation radial orbitals are used to obtain accurate description of Fe IX levels and to represent the scattering functions. The calculated excitation energies are in very good agreement with experiment and represents an improvement over the previous calculations. The present collision strengths show reasonable agreement with the previously available R-matrix and distorted-wave calculations. This research is supported by NASA grant from the Solar and Heliophysics Program.

  12. Electron impact exctation of Al X

    NASA Astrophysics Data System (ADS)

    Aggarwal, Kanti; Keenan, Francis

    2013-05-01

    Emission lines of Al ions, including Al X, are important for the modeling and diagnostics of lasing, fusion and astrophysical plasmas, for which atomic data are required for a variety of parameters, such as energy levels, radiative rates (A- values), and excitation rates or equivalently the effective collision strengths (Υ), which are obtained from the electron impact collision strengths (Ω). Experimentally, energy levels are available for Al X on the NIST website, but there is paucity for accurate collisional atomic data. Therefore, here we report a complete set of results (namely energy levels, radiative rates, and effective collision strengths) for all transitions among the lowest 98 levels of Al X. These levels belong to the (1s2) 2s2, 2s2p, 2p2, 2s3 l, 2p3 l, 2s4 l, and 2p4 l configurations. Finally, we also report the A- values for four types of transitions, namely electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2), because these are also required for plasma modeling. For our calculations of wavefunctions, we have adopted the fully relativistic GRASP code, and for the calculations of Ω, the Dirac atomic R-matrix code (DARC) of PH Norrington and IP Grant. Additionally, parallel ca

  13. Electron Impact Excitation Of Ti XIX

    NASA Astrophysics Data System (ADS)

    Aggarwal, Kanti M.; Keenan, F. P.

    2012-05-01

    Emission lines of Ti XIX are important for the modeling and diagnostics of lasing, fusion and astrophysical plasmas, for which atomic data are required for a variety of parameters, such as energy levels, radiative rates (A- values), and excitation rates or equivalently the effective collision strengths (Υ), which are obtained from the electron impact collision strengths (Ω). Experimentally, energy levels are available for Ti XIX on the NIST website, but there is paucity for accurate collisional atomic data. Therefore, here we report a complete set of results (namely energy levels, radiative rates, and effective collision strengths) for all transitions among the lowest 98 levels of Ti XIX. These levels belong to the (1s2) 2s2, 2s2p, 2p2, 2s3l, 2p3l, 2s4l, and 2p4l configurations. Finally, we also report the A- values for four types of transitions, namely electric dipole (E1), electric quadrupole (E2), magnetic dipole (M1), and magnetic quadrupole (M2), because these are also required for plasma modeling. For our calculations of wavefunctions, we have adopted the fully relativistic GRASP code, and for the calculations of Ω, the Dirac atomic R-matrix code (DARC) of PH Norrington and IP Grant. Additionally, parallel calculations have also been performed with the Flexible Atomic Code (FAC) of Gu, so that all atomic parameters can be rigorously assessed for accuracy.

  14. Electron-Impact Excitation Cross Sections for Modeling Non-Equilibrium Gas

    NASA Technical Reports Server (NTRS)

    Huo, Winifred M.; Liu, Yen; Panesi, Marco; Munafo, Alessandro; Wray, Alan; Carbon, Duane F.

    2015-01-01

    In order to provide a database for modeling hypersonic entry in a partially ionized gas under non-equilibrium, the electron-impact excitation cross sections of atoms have been calculated using perturbation theory. The energy levels covered in the calculation are retrieved from the level list in the HyperRad code. The downstream flow-field is determined by solving a set of continuity equations for each component. The individual structure of each energy level is included. These equations are then complemented by the Euler system of equations. Finally, the radiation field is modeled by solving the radiative transfer equation.

  15. Delayed extraction time-of-flight mass spectrometer with electron impact for PAH studies

    NASA Astrophysics Data System (ADS)

    Najeeb, P. K.; Kadhane, U.

    2017-03-01

    A time-of-flight (ToF) mass spectrometer with a pulsed electron beam as well as pulsed extraction of the recoil ions, with variable delay is reported. The effectiveness of this technique is highlighted by studying the statistical decay of mono-cations over microsecond time scales. Various details of the design and operation are discussed in the context of electron impact ionization and fragmentation of naphthalene (C10H8). The temporal behavior of acetylene (C2H2) and diacetylene (C4H2) loss is observed and compared with the associated Arrhenius decay constant, internal energy and plasmon excitation energy.

  16. Electron-impact vibrational excitation of cyclopropane

    SciTech Connect

    Čurík, R. Čársky, P.; Allan, M.

    2015-04-14

    We report a very detailed test of the ab initio discrete momentum representation (DMR) method of calculating vibrational excitation of polyatomic molecules by electron impact, by comparison of its results with an extensive set of experimental data, covering the entire range of scattering angles from 10{sup ∘} to 180{sup ∘} and electron energies from 0.4 to 20 eV. The DMR calculations were carried out by solving the two-channel Lippmann-Schwinger equation in the momentum space, and the interaction between the scattered electron and the target molecule was described by exact static-exchange potential corrected by a density functional theory (DFT) correlation-polarization interaction that models target’s response to the field of incoming electron. The theory is found to quantitatively reproduce the measured spectra for all normal modes, even at the difficult conditions of extreme angles and at low energies, and thus provides full understanding of the excitation mechanism. It is shown that the overlap of individual vibrational bands caused by limited experimental resolution and rotational excitation must be properly taken into account for correct comparison of experiment and theory. By doing so, an apparent discrepancy between published experimental data could be reconciled. A substantial cross section is found for excitation of the non-symmetric HCH twisting mode ν{sub 4} of A{sub 1}{sup ″} symmetry by the 5.5 eV A{sub 2}{sup ′} resonance, surprisingly because the currently accepted selection rules predict this process to be forbidden. The DMR theory shows that the excitation is caused by an incoming electron in an f-wave of A{sub 2}{sup ′} symmetry which causes excitation of the non-symmetric HCH twisting mode ν{sub 4} of the A{sub 1}{sup ″} symmetry and departs in p- and f-waves of A{sub 2}{sup ″} symmetry.

  17. Solar cycle dependence of the helium focusing cone from SOHO/UVCS observations. Electron impact rates and associated pickup ions

    NASA Astrophysics Data System (ADS)

    Lallement, R.; Raymond, J. C.; Bertaux, J.-L.; Quémerais, E.; Ko, Y.-K.; Uzzo, M.; McMullin, D.; Rucinski, D.

    2004-11-01

    The Ultraviolet Coronograph on board SOHO (UVCS) has observed the 58.4 nm glow of the interplanetary He focusing cone at regular intervals since 1996. The intensity decrease with time already observed during the first two years (Michels et al. \\cite{michels}) has dramatically amplified during the solar activity increase. Intensities seem to reach a plateau in 2001. Using a model of the cone emission which takes into account both photoionization and electron impact ionization of neutral helium we show that the photoionization increase alone cannot explain the observed intensity drop. Data can be fitted if at minimum activity the electron impact ionization rate is the solar cycle average rate predicted by Rucinski & Fahr (\\cite{1989A&A...224..290R}), and if this rate is increased by a factor of about 3.5 between 1996 and 2001. Assuming the Rucinski and Fahr radial dependence, such high electron impact rates create averaged He+ pickup ion (PUI) fluxes which may reach 50% of the fluxes of ions born after photoionization, or 35% of PUI total fluxes, as far as 1 AU from the Sun. In slow and dense solar wind enhancements, in particular in the presence of strong suprathermal tails, PUIs from electron impact could be the dominant species. This could explain a fraction of the observed correlation between He+ and H+ pickups and anticorrelation of He+ fluxes with solar wind velocity.

  18. A vacuum ultraviolet laser pulsed field ionization-photoion study of methane (CH4): determination of the appearance energy of methylium from methane with unprecedented precision and the resulting impact on the bond dissociation energies of CH4 and CH4().

    PubMed

    Chang, Yih-Chung; Xiong, Bo; Bross, David H; Ruscic, Branko; Ng, C Y

    2017-04-05

    We report on the successful implementation of a high-resolution vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) detection method for the study of unimolecular dissociation of quantum-state- or energy-selected molecular ions. As a test case, we have determined the 0 K appearance energy (AE0) for the formation of methylium, CH3(+), from methane, CH4, as AE0(CH3(+)/CH4) = 14.32271 ± 0.00013 eV. This value has a significantly smaller error limit, but is otherwise consistent with previous laboratory and/or synchrotron-based studies of this dissociative photoionization onset. Furthermore, the sum of the VUV laser PFI-PI spectra obtained for the parent CH4(+) ion and the fragment CH3(+) ions of methane is found to agree with the earlier VUV pulsed field ionization-photoelectron (VUV-PFI-PE) spectrum of methane, providing unambiguous validation of the previous interpretation that the sharp VUV-PFI-PE step observed at the AE0(CH3(+)/CH4) threshold ensues because of higher PFI detection efficiency for fragment CH3(+) than for parent CH4(+). This, in turn, is a consequence of the underlying high-n Rydberg dissociation mechanism for the dissociative photoionization of CH4, which was proposed in previous synchrotron-based VUV-PFI-PE and VUV-PFI-PEPICO studies of CH4. The present highly accurate 0 K dissociative ionization threshold for CH4 can be utilized to derive accurate values for the bond dissociation energies of methane and methane cation. For methane, the straightforward application of sequential thermochemistry via the positive ion cycle leads to some ambiguity because of two competing VUV-PFI-PE literature values for the ionization energy of methyl radical. The ambiguity is successfully resolved by applying the Active Thermochemical Tables (ATcT) approach, resulting in D0(H-CH3) = 432.463 ± 0.027 kJ mol(-1) and D0(H-CH3(+)) = 164.701 ± 0.038 kJ mol(-1).

  19. A vacuum ultraviolet laser pulsed field ionization-photoion study of methane (CH4): Determination of the appearance energy of methylium from methane with unprecedented precision and the resulting impact on the bond dissociation energies of CH4 and CH4+

    DOE PAGES

    Chang, Yih -Chung; Xiong, Bo; Bross, David H.; ...

    2017-03-27

    Here, we report on the successful implementation of a high-resolution vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) detection method for the study of unimolecular dissociation of quantum-state- or energy-selected molecular ions. As a test case, we have determined the 0 K appearance energy (AE0) for the formation of methylium, CH3+, from methane, CH4, as AE0 (CH3+/CH4) = 14.32271 ± 0.00013 eV. This value has a significantly smaller error limit, but is otherwise consistent with previous laboratory and/or synchrotron-based studies of this dissociative photoionization onset. Furthermore, the sum of the VUV laser PFI-PI spectra obtained for the parent CH4+ ionmore » and the fragment CH3+ ions of methane is found to agree with the earlier VUV pulsed field ionization-photoelectron (VUV-PFI-PE) spectrum of methane, providing unambiguous validation of the previous interpretation that the sharp VUV-PFI-PE step observed at the AE0 (CH3+/CH4) threshold ensues because of higher PFI detection efficiency for fragment CH3+ than for parent CH4+. This, in turn, is a consequence of the underlying high-n Rydberg dissociation mechanism for the dissociative photoionization of CH4, which was proposed in previous synchrotron-based VUV-PFI-PE and VUV-PFI-PEPICO studies of CH4. The present highly accurate 0 K dissociative ionization threshold for CH4 can be utilized to derive accurate values for the bond dissociation energies of methane and methane cation. For methane, the straightforward application of sequential thermochemistry via the positive ion cycle leads to some ambiguity because of two competing VUV-PFI-PE literature values for the ionization energy of methyl radical. The ambiguity is successfully resolved by applying the Active Thermochemical Tables (ATcT) approach, resulting in D0 (H-CH3) = 432.463 ± 0.027 kJ/mol and D0(H-CH3+) = 164.701 ± 0.038 kJ/mol.« less

  20. Dissociative Electron Attachment

    NASA Astrophysics Data System (ADS)

    Arreola, Esmeralda; Esmeralda Arreola Collaboration; Leigh Hargreaves Collaboration

    Since the pioneering work of Boudiaffa et al., it has been understood that electrons, even with energies near or below the ionization threshold, are capable of initiating strand-breaks in human DNA. This discovery raised important questions for cancer treatments, since sub-ionizing electrons are known to be the most copiously produced secondary product of radiation therapy. But even to date these factors are largely excluded from dosimetry calculations. This lack of inclusion is, at least in part, certainly due to the dearth of fundamental data describing low-energy electron interactions with nucleotide molecules that form the basis of DNA. Understanding of how such slow electrons are able to damage DNA remains incomplete, but the strongly peaked nature of Boudiaffa et al.'s data gives strong hints at resonantly driven collision processes. DNA damage is therefore most likely driven by ``dissociative electron attachment'' (DEA). DEA is a rather complicated process to model due to the coupling of electronic and nuclear degrees of freedom in the molecule. At the California State University Fullerton, we are currently commissioning a new spectrometer to study dissociation channels, reaction rates and orientation effects in DEA collisions between slow electrons and nucleotide molecules. At the meeting we will present design parameters and commissioning data for this new apparatus.

  1. Dissociative recombination of HCl+

    NASA Astrophysics Data System (ADS)

    Larson, Åsa; Fonseca dos Santos, Samantha; E. Orel, Ann

    2017-08-01

    The dissociative recombination of HCl+, including both the direct and indirect mechanisms, is studied. For the direct process, the relevant electronic states are calculated ab initio by combining electron scattering calculations to obtain resonance positions and autoionization widths with multi-reference configuration interaction calculations of the ion and Rydberg states. The cross section for the direct dissociation along electronic resonant states is computed by solution of the time-dependent Schrödinger equation. For the indirect process, an upper bound value for the cross section is obtained using a vibrational frame transformation of the elements of the scattering matrix at energies just above the ionization threshold. Vibrational excitations of the ionic core from the ground vibrational state, v = 0 , to the first three excited vibrational states, v = 1 , v = 2 , and v = 3 , are considered. Autoionization is neglected and the effect of the spin-orbit splitting of the ionic potential energy upon the indirect dissociative recombination cross section is considered. The calculated cross sections are compared to measurements.

  2. Fluid hydrogen at high density - Pressure ionization

    NASA Technical Reports Server (NTRS)

    Saumon, Didier; Chabrier, Gilles

    1992-01-01

    The Helmholtz-free-energy model for nonideal mixtures of hydrogen atoms and molecules by Saumon and Chabrier (1991) is extended to describe dissociation and ionization in similar mixtures in chemical equilibrium. A free-energy model is given that describes partial ionization in the pressure and temperature ionization region. The plasma-phase transition predicted by the model is described for hydrogen mixtures including such components as H2, H, H(+), and e(-). The plasma-phase transition has a critical point at Tc = 15,300 K and Pc = 0.614 Mbar, and thermodynamic instability is noted in the pressure-ionization regime. The pressure dissociation and ionization of fluid hydrogen are described well with the model yielding information on the nature of the plasma-phase transition. The model is shown to be valuable for studying dissociation and ionization in astrophysical objects and in high-pressure studies where pressure and temperature effects are significant.

  3. Electron ionization of acetylene.

    PubMed

    King, Simon J; Price, Stephen D

    2007-11-07

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

  4. High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formation of cobalt carbide (CoC) and its cation (CoC+).

    PubMed

    Lau, Kai-Chung; Pan, Yi; Lam, Chow-Shing; Huang, Huang; Chang, Yih-Chung; Luo, Zhihong; Shi, Xiaoyu; Ng, C Y

    2013-03-07

    The ionization energy (IE) of CoC and the 0 K bond dissociation energies (D0) and the heats of formation at 0 K (ΔH°f0) and 298 K (ΔH°f298) for CoC and CoC(+) are predicted by the wavefunction based coupled-cluster theory with single, double, triple and quadruple excitations (CCSDTQ) and complete basis set (CBS) approach. The CCSDTQ∕CBS calculations presented here involve the approximation to the CBS limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy, high-order correlation, core-valence (CV) electronic, spin-orbit coupling, and scalar relativistic effect corrections. The present calculations provide the correct symmetry, (1)Σ(+), for the ground state of CoC(+). The CCSDTQ∕CBS IE(CoC) = 7.740 eV is found in good agreement with the experimental IE value of 7.73467 ± 0.00007 eV, determined in a two-color laser photoion and pulsed field ionization-photoelectron study. This work together with the previous experimental and theoretical investigations support the conclusion that the CCSDTQ∕CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC, CoC, and NiC. Among the single-reference based coupled-cluster methods and multi-reference configuration interaction (MRCI) approach, the CCSDTQ and MRCI methods give the best predictions to the harmonic frequencies ωe (ωe (+)) = 956 (992) and 976 (1004) cm(-1) and the bond lengths re (re (+)) = 1.560 (1.528) and 1.550 (1.522) Å, respectively, for CoC (CoC(+)) in comparison with the experimental values. The CCSDTQ∕CBS calculations give the prediction of D0(Co(+)-C) - D0(Co-C) = 0.175 eV, which is also consistent with the experimental determination of 0.14630 ± 0.00014 eV. The theoretical results show that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of Co

  5. High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formation of cobalt carbide (CoC) and its cation (CoC+)

    NASA Astrophysics Data System (ADS)

    Lau, Kai-Chung; Pan, Yi; Lam, Chow-Shing; Huang, Huang; Chang, Yih-Chung; Luo, Zhihong; Shi, Xiaoyu; Ng, C. Y.

    2013-03-01

    The ionization energy (IE) of CoC and the 0 K bond dissociation energies (D0) and the heats of formation at 0 K (ΔH°f0) and 298 K (ΔH°f298) for CoC and CoC+ are predicted by the wavefunction based coupled-cluster theory with single, double, triple and quadruple excitations (CCSDTQ) and complete basis set (CBS) approach. The CCSDTQ/CBS calculations presented here involve the approximation to the CBS limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy, high-order correlation, core-valence (CV) electronic, spin-orbit coupling, and scalar relativistic effect corrections. The present calculations provide the correct symmetry, 1Σ+, for the ground state of CoC+. The CCSDTQ/CBS IE(CoC) = 7.740 eV is found in good agreement with the experimental IE value of 7.73467 ± 0.00007 eV, determined in a two-color laser photoion and pulsed field ionization-photoelectron study. This work together with the previous experimental and theoretical investigations support the conclusion that the CCSDTQ/CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC, CoC, and NiC. Among the single-reference based coupled-cluster methods and multi-reference configuration interaction (MRCI) approach, the CCSDTQ and MRCI methods give the best predictions to the harmonic frequencies ωe (ωe+) = 956 (992) and 976 (1004) cm-1 and the bond lengths re (re+) = 1.560 (1.528) and 1.550 (1.522) Å, respectively, for CoC (CoC+) in comparison with the experimental values. The CCSDTQ/CBS calculations give the prediction of D0(Co+-C) - D0(Co-C) = 0.175 eV, which is also consistent with the experimental determination of 0.14630 ± 0.00014 eV. The theoretical results show that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of CoC/CoC+. For the experimental D0 and ΔHof0

  6. Scapholunate Dissociation.

    PubMed

    Ramponi, Denise; McSwigan, Tara

    2016-01-01

    Wrist injuries are a common complaint in the emergency setting. Any disruption of the anatomy of the carpal bones can impair hand function, leading to pain, weakness, and complications. One of the most common forms of carpal bone instability is scapholunate dissociation. This injury can lead to significant morbidity including avascular necrosis, impaired healing, limited function, and arthritis. These diagnostic findings may be subtle, thus identifying high-risk mechanisms of injury, and clinical manifestations will assist the emergency practitioner with early diagnosis and treatment of this high-risk injury.

  7. Structural identification of triacylglycerol isomers using electron impact excitation of ions from organics (EIEIO).

    PubMed

    Baba, Takashi; Campbell, J Larry; Le Blanc, J C Yves; Baker, Paul R S

    2016-11-01

    Electron-induced dissociation or electron impact excitation of ions from organics (EIEIO) was applied to triacylglycerols (TAGs) for in-depth molecular structure analysis using MS. In EIEIO, energetic electrons (∼10 eV) fragmented TAG ions to allow for regioisomeric assignment of identified acyl groups at the sn-2 or sn-1/3 positions of the glycerol backbone. In addition, carbon-carbon double bond locations within the acyl chains could also be assigned by EIEIO. Beyond the analysis of lipid standards, this technique was applied to edible oils and natural lipid extracts to demonstrate the power of this method to provide in-depth structural elucidation of TAG molecular species. Copyright © 2016 by the American Society for Biochemistry and Molecular Biology, Inc.

  8. Integral cross sections for electron impact excitation of vibrational and electronic states in phenol

    SciTech Connect

    Neves, R. F. C.; Jones, D. B.; Lopes, M. C. A.; Blanco, F.; García, G.; Ratnavelu, K.; Brunger, M. J.

    2015-05-21

    We report on measurements of integral cross sections (ICSs) for electron impact excitation of a series of composite vibrational modes and electronic-states in phenol, where the energy range of those experiments was 15–250 eV. There are currently no other results against which we can directly compare those measured data. We also report results from our independent atom model with screened additivity rule correction computations, namely, for the inelastic ICS (all discrete electronic states and neutral dissociation) and the total ionisation ICS. In addition, for the relevant dipole-allowed excited electronic states, we also report f-scaled Born-level and energy-corrected and f-scaled Born-level (BEf-scaled) ICS. Where possible, our measured and calculated ICSs are compared against one another with the general level of accord between them being satisfactory to within the measurement uncertainties.

  9. Metastable Oxygen Production by Electron-Impact of Oxygen

    NASA Astrophysics Data System (ADS)

    Hein, J. D.; Malone, C. P.; Kanik, I.; Johnson, P. V.

    2013-12-01

    Electron-impact excitation processes involving atomic and molecular oxygen are important in atmospheric interactions. The production of long-lived metastable O(1S) and O(1D) through electron impact of atomic O and molecular O2 play a significant role in the dynamics of oxygen-containing atmospheres (Earth, Europa, Io). Emissions from metastable O (1S → 1D) produce the well-recognized green light from terrestrial aurora. Electron-impact excitation to 1S and 1D are sensitive channels for determining energy partitioning and dynamics from space weather. Electron-impact excitation cross sections determined through fundamental experimental studies are necessary for modeling of natural phenomena and observation data. The detection of metastable states in laboratory experiments requires a novel approach, since typical detection techniques (e.g., fluorescence by radiative de-excitation) cannot be performed due to the long-lived nature of the excited species. In this work, metastable O is incident on a cryogenically cooled rare gas matrix, where excimer production and subsequent rapid radiative de-excitation provides measurable signal that is directly related to the originating electron-impact excitation process.

  10. Electron impact action spectroscopy of mass/charge selected macromolecular ions: Inner-shell excitation of ubiquitin protein

    SciTech Connect

    Rankovic, Milos Lj.; Giuliani, Alexandre; Milosavljevic, Aleksandar R.

    2016-02-11

    In this study, we have performed inner-shell electron impact action spectroscopy of mass and charge selected macromolecular ions. For this purpose, we have coupled a focusing electron gun with a linear quadrupole ion trap mass spectrometer. This experiment represents a proof of principle that an energy-tunable electron beam can be used in combination with radio frequency traps as an activation method in tandem mass spectrometry (MS2) and allows performing action spectroscopy. Electron impact MS2 spectra of multiply protonated ubiquitin protein ion have been recorded at incident electron energies around the carbon 1s excitation. Both MS2 and single ionization energy dependence spectra are compared with literature data obtained using the soft X-ray activation conditions.

  11. Electron impact action spectroscopy of mass/charge selected macromolecular ions: Inner-shell excitation of ubiquitin protein

    DOE PAGES

    Rankovic, Milos Lj.; Giuliani, Alexandre; Milosavljevic, Aleksandar R.

    2016-02-11

    In this study, we have performed inner-shell electron impact action spectroscopy of mass and charge selected macromolecular ions. For this purpose, we have coupled a focusing electron gun with a linear quadrupole ion trap mass spectrometer. This experiment represents a proof of principle that an energy-tunable electron beam can be used in combination with radio frequency traps as an activation method in tandem mass spectrometry (MS2) and allows performing action spectroscopy. Electron impact MS2 spectra of multiply protonated ubiquitin protein ion have been recorded at incident electron energies around the carbon 1s excitation. Both MS2 and single ionization energy dependencemore » spectra are compared with literature data obtained using the soft X-ray activation conditions.« less

  12. Ionization of Interstellar Hydrogen Beyond the Termination Shock

    NASA Astrophysics Data System (ADS)

    Gruntman, Mike

    2016-11-01

    Models of solar wind interaction with the surrounding interstellar medium usually disregard ionization of interstellar hydrogen atoms beyond the solar wind termination shock. If and when included, the effects of ionization in the heliospheric interface region are often obscured by complexities of the interaction. This work assesses the importance of interstellar hydrogen ionization in the heliosheath. Photoionization could be accounted for in a straightforward way. In contrast, electron impact ionization is largely unknown because of poorly understood energy transfer to electrons at the termination shock and beyond. We first estimate the effect of photoionization and then use it as a yardstick to assess the role of electron impact ionization. The physical estimates show that ionization of interstellar hydrogen may lead to significant mass loading in the inner heliosheath which would slow down plasma flowing toward the heliotail and deplete populations of nonthermal protons, with the corresponding effect on heliospheric fluxes of energetic neutral atoms.

  13. High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formation of nickel carbide (NiC) and its cation (NiC+).

    PubMed

    Lau, Kai-Chung; Chang, Yih Chung; Shi, Xiaoyu; Ng, C Y

    2010-09-21

    The ionization energy (IE) of NiC and the 0 K bond dissociation energies (D(0)) and heats of formation at 0 K (ΔH(o)(f0)) and 298 K (ΔH(o)(f298)) for NiC and NiC(+) are predicted by the wavefunction based CCSDTQ(Full)/CBS approach and the multireference configuration interaction (MRCI) method with Davidson correction (MRCI+Q). The CCSDTQ(Full)/CBS calculations presented here involve the approximation to the complete basis set (CBS) limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy (ZPVE), high-order correlation, core-valence electronic (CV), spin-orbit coupling (SO), and scalar relativistic effect (SR) corrections. The present calculations provide the correct symmetry predictions for the ground states of NiC and NiC(+) to be (1)∑(+) and (2)∑(+), respectively. The CCSDTQ(Full)/CBS IE(NiC)=8.356 eV is found to compare favorably with the experimental IE value of 8.372 05±0.000 06 eV. The predicted IE(NiC) value at the MRCI+Q/cc-pwCV5Z level, including the ZPVE, SO, and SR effects is 8.00 eV, which is 0.37 eV lower than the experimental value. This work together with the previous experimental and theoretical investigations supports the conclusion that the CCSDTQ(Full)/CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC and NiC. Furthermore, the CCSDTQ(Full)/CBS calculations give the prediction of D(0)(Ni-C)-D(0)(Ni(+)-C)=0.688 eV, which is also consistent with the experimental determination of 0.732 21±0.000 06 eV, whereas the MRCI+Q calculations (with relativistic and CV effects) predict a significantly lower value of 0.39 eV for D(0)(Ni-C)-D(0)(Ni(+)-C). The analysis of the correction terms shows that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of NiC/NiC(+). For the experimental D(0) and ΔH(o)(f0) values of

  14. High-level ab initio predictions for the ionization energy, bond dissociation energies, and heats of formation of nickel carbide (NiC) and its cation (NiC+)

    NASA Astrophysics Data System (ADS)

    Lau, Kai-Chung; Chang, Yih Chung; Shi, Xiaoyu; Ng, C. Y.

    2010-09-01

    The ionization energy (IE) of NiC and the 0 K bond dissociation energies (D0) and heats of formation at 0 K (ΔHof0) and 298 K (ΔHof298) for NiC and NiC+ are predicted by the wavefunction based CCSDTQ(Full)/CBS approach and the multireference configuration interaction (MRCI) method with Davidson correction (MRCI+Q). The CCSDTQ(Full)/CBS calculations presented here involve the approximation to the complete basis set (CBS) limit at the coupled cluster level up to full quadruple excitations along with the zero-point vibrational energy (ZPVE), high-order correlation, core-valence electronic (CV), spin-orbit coupling (SO), and scalar relativistic effect (SR) corrections. The present calculations provide the correct symmetry predictions for the ground states of NiC and NiC+ to be ∑1+ and ∑2+, respectively. The CCSDTQ(Full)/CBS IE(NiC)=8.356 eV is found to compare favorably with the experimental IE value of 8.372 05±0.000 06 eV. The predicted IE(NiC) value at the MRCI+Q/cc-pwCV5Z level, including the ZPVE, SO, and SR effects is 8.00 eV, which is 0.37 eV lower than the experimental value. This work together with the previous experimental and theoretical investigations supports the conclusion that the CCSDTQ(Full)/CBS method is capable of providing reliable IE predictions for 3d-transition metal carbides, such as FeC and NiC. Furthermore, the CCSDTQ(Full)/CBS calculations give the prediction of D0(NiC)-D0(Ni+C)=0.688 eV, which is also consistent with the experimental determination of 0.732 21±0.000 06 eV, whereas the MRCI+Q calculations (with relativistic and CV effects) predict a significantly lower value of 0.39 eV for D0(NiC)-D0(Ni+C). The analysis of the correction terms shows that the CV and valence-valence electronic correlations beyond CCSD(T) wavefunction and the relativistic effect make significant contributions to the calculated thermochemical properties of NiC/NiC+. For the experimental D0 and ΔHof0 values of NiC/NiC+, which are not known

  15. Electron-impact-induced allowed transitions between triplet states of H{sub 2}

    SciTech Connect

    Laricchiuta, A.; Celiberto, R.; Janev, R.K.

    2004-02-01

    Electron-impact-induced excitation and dissociation processes between the excited triplet states a {sup 3}{sigma}{sub g}{sup +}{yields}d {sup 3}{pi}{sub u}, c {sup 3}{pi}{sub u}{yields}h {sup 3}{sigma}{sub g}{sup +}, and c {sup 3}{pi}{sub u}{yields}g {sup 3}{sigma}{sub g}{sup +} of molecular hydrogen are studied by using the impact-parameter method. The cross sections for {nu}{sub i}-{nu}{sub f} resolved vibronic transitions between states have been calculated in the energy range from threshold to 100 eV; their maxima being located in the region of 5-10 eV. A special treatment was required for the transition to the h {sup 3}{sigma}{sub g}{sup +} state, whose adiabatic potential-energy curve possesses a barrier at the internuclear distance of about 5a{sub 0}, sustaining three quasi-bound vibrational states with widths of 5.3x10{sup -12}, 1.5x10{sup -3}, and 42.0 cm{sup -1}, respectively. The quasistationary character of these vibrational states is taken into account when calculating the c {sup 3}{pi}{sub u}{yields}h {sup 3}{sigma}{sub g}{sup +} excitation and dissociation cross sections.

  16. Brightness measurement of an electron impact gas ion source for proton beam writing applications

    SciTech Connect

    Liu, N.; Santhana Raman, P.; Xu, X.; Pang, R.; Kan, J. A. van; Khursheed, A.

    2016-02-15

    We are developing a high brightness nano-aperture electron impact gas ion source, which can create ion beams from a miniature ionization chamber with relatively small virtual source sizes, typically around 100 nm. A prototype source of this kind was designed and successively micro-fabricated using integrated circuit technology. Experiments to measure source brightness were performed inside a field emission scanning electron microscope. The total output current was measured to be between 200 and 300 pA. The highest estimated reduced brightness was found to be comparable to the injecting focused electron beam reduced brightness. This translates into an ion reduced brightness that is significantly better than that of conventional radio frequency ion sources, currently used in single-ended MeV accelerators.

  17. Brightness measurement of an electron impact gas ion source for proton beam writing applications.

    PubMed

    Liu, N; Xu, X; Pang, R; Raman, P Santhana; Khursheed, A; van Kan, J A

    2016-02-01

    We are developing a high brightness nano-aperture electron impact gas ion source, which can create ion beams from a miniature ionization chamber with relatively small virtual source sizes, typically around 100 nm. A prototype source of this kind was designed and successively micro-fabricated using integrated circuit technology. Experiments to measure source brightness were performed inside a field emission scanning electron microscope. The total output current was measured to be between 200 and 300 pA. The highest estimated reduced brightness was found to be comparable to the injecting focused electron beam reduced brightness. This translates into an ion reduced brightness that is significantly better than that of conventional radio frequency ion sources, currently used in single-ended MeV accelerators.

  18. Kinetic energy distribution of OH+ from water fragmentation by electron impact

    NASA Astrophysics Data System (ADS)

    Ferreira, Natalia; Sigaud, L.; Montenegro, E. C.

    2017-07-01

    The release of the highly reactive radical OH+ from the fragmentation of water by electron impact is made mostly through the OH++H0 channel. This channel ejects suprathermal OH+ ions with a kinetic energy distribution whose details are unexplored so far due to the difficulty in experimentally characterizing ions ejected with very low kinetic energy without another charged partner. These ions are studied here using the delayed extraction time-of-flight technique (DETOF). The structures and substructures in the kinetic energy distribution of OH+ associated with both single and double ionization are identified qualitatively and quantitatively. A comparison with the kinetic energy distribution of the complementary channel OH0+H+ , also originating from vacancies in the 1 b2 orbital, shows marked differences between the two, mainly regarding the relative role between the fragmentation involving the H2O+ ground state or via transitions to repulsive states.

  19. Low-energy electron impact cross-sections and rate constants of NH_2

    NASA Astrophysics Data System (ADS)

    Bharadvaja, Anand; Kaur, Savinder; Baluja, K. L.

    2017-08-01

    This systematic study reports various electron impact cross-sections, rate constants and transport properties of NH_2 radical in the low-energy limit. The collision study is based on R-matrix formalism and involves the use of various scattering models employing different active spaces. Both electron excited inelastic cross-sections and resonances are found influenced by correlation and polarization effects. The non-relativistic molecular bremsstrahlung radiation cross-section for soft photons, binary encounter Bethe model-based ionization cross-sections and a few molecular properties of the target radical are also reported. The present calculations are found to be in agreement with the available results. This theoretical study provides a pathway to understand collision dynamics and generates data required in various fields of applied physics.

  20. Characterization of Nitrogen-Containing Species in Coal and Petroleum-Derived Products by Ammonia Chemical Ionization-High Resolution Mass Spectrometry

    SciTech Connect

    Veloski, Garret A.; Lynn, Ronald J.; Sprecher, Richard F.

    1997-01-01

    A coal-derived light distillate and a petroleum-derived residuum have been studied by high resolution mass spectrometry using both low-pressure ammonia chemical ionization and low-voltage electron impact ionization. A mass calibration mixture for use with ammonia chemical ionization has been developed. Selective ionization of the basic nitrogen-containing compounds by ammonia chemical ionization and compound type characterization of the resulting quasi-molecular species has been demonstrated. Several homologous series of nitrogen-containing compounds were identified in a basic extract by electron impact ionization and compared with quasimolecular analogs identified by ammonia chemical ionization.

  1. Dissociative recombination in planetary ionospheres

    NASA Technical Reports Server (NTRS)

    Fox, J. L.

    1993-01-01

    Ionization in planetary atmospheres can be produced by solar photoionization, photoelectron impact ionization, and, in auroral regions, by impact of precipitating particles. This ionization is lost mainly in dissociative recombination (DR) of molecular ions. Although atomic ions cannot undergo DR, they can be transformed locally through ion-molecule reactions into molecular ions, or they may be transported vertically or horizontally to regions of the atmosphere where such transformations are possible. Because DR reactions tend to be very exothermic, they can be an important source of kinetically or internally excited fragments. In interplanetary thermospheres, the neutral densities decrease exponentially with altitude. Below the homopause (or turbopause), the atmosphere is assumed to be throughly mixed by convection and/or turbulence. Above the homopause, diffusion is the major transport mechanism, and each species is distributed according to its mass, with the logarithmic derivative of the density with repect to altitude given approximately by -1/H, where H = kT/mg is the scale height. In this expression, T is the neutral temperature, g is the local acceleratiion of gravity, and m is the mass of the species. Thus lighter species become relatively more abundant, and heavier species less abundant, as the altitude increases. This variation of the neutral composition can lead to changes in the ion composition; furthermore, as the neutral densities decrease, dissociative recombination becomes more important relative to ion-neutral reactions as a loss mechanism for molecular ions.

  2. Charged-Particle Impact Ionization of Atoms

    SciTech Connect

    Bartschat, Klaus; Guan Xiaoxu

    2008-08-08

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

  3. Background reduction by a getter pump around the ionization volume of a Lamb-shift polarimeter and possible improvements of polarized ion sources

    SciTech Connect

    Engels, R.; Emmerich, R.; Grigoryev, K.; Paetz gen Schieck, H.; Ley, J.; Mikirtychyants, M.; Rathmann, F.; Sarkadi, J.; Seyfarth, H.; Tenckhoff, G.; Vasilyev, A.

    2005-05-15

    The Koeln-Juelich Lamb-shift polarimeter is used to measure the nuclear polarization of the hydrogen or deuterium beam produced with the atomic-beam source for the polarized target at the ANKE spectrometer at COSY-Juelich. The precision of the earlier results had been dominated by the recombination of atoms in the ionizer. Protons or deuterons from the dissociative ionization of unpolarized recombined H{sub 2} or D{sub 2} molecules had strongly contributed to the extracted ion beam. To suppress this effect, in the new ionizer a nonevaporable getter pump of about 2000 l/s H{sub 2} or D{sub 2} pumping speed surrounds the ionization volume. It reduces the extracted current of unpolarized ions, produced from the recombined molecular gas, by a factor of about 20 compared with the earlier value, which reduces the error of the polarization measurements to about 0.5%. Now the H{sub 2} or D{sub 2} molecules in the ionization volume predominantly are those which are contained in the incoming beam from the atomic beam source. This allows the measurement of the fraction of unpolarized molecules in the polarized atomic H-vector or D-vector beam. The improvement achieved is a valuable step toward the measurement of the nuclear polarization of a gas sample, extracted from the storage cell of the polarized internal gas target for the spectrometer ANKE in the COSY-Juelich storage ring with the Lamb-shift polarimeter. Furthermore, the results show that the polarization of proton or deuteron beams would be increased by the installation of such a pump around the ionization volume of atomic-beam ion sources with an electron-impact ionizer. For ECR ionizers the recombined H{sub 2} or D{sub 2} molecules would be absorbed, whereas the noble gases, used as buffer, are not pumped by the getter material.

  4. Dissociation and serenity induction.

    PubMed

    Zoellner, Lori A; Sacks, Matthew B; Foa, Edna B

    2007-09-01

    Dissociation is a common experience during or immediately after a traumatic event; yet, most of the current knowledge regarding dissociation is retrospective in nature. The aim of the present study investigated a non-pharmacological method of dissociative induction with a clinical sample. Participants with PTSD and non-trauma exposed participants were randomly assigned to receive either a dissociative induction, or a serenity induction, based on modified Velten mood induction procedures. Participants receiving the dissociative induction reported higher state-dissociation than those receiving the serenity induction. The PTSD group reported greater state dissociation than the non-trauma exposed group, regardless of induction. State dissociation was related to trait dissociation, PTSD severity, and depression. The present results provide an initial demonstration of the viability for inducing state dissociation in the laboratory with a PTSD sample.

  5. ION PAIR DISSOCIATION: Spectroscopy and Dynamics

    NASA Astrophysics Data System (ADS)

    Suits, Arthur G.; Hepburn, John W.

    2006-05-01

    Ion pair dissociation processes may be studied using coherent vacuum ultraviolet laser sources in a manner entirely analogous to photoelectron spectroscopy, albeit with the anion playing the role of a heavy electron. If the excitation energy is above the dissociation energy and the kinetic energy of the fragment is measured using ion imaging, this approach is termed ion pair imaging spectroscopy (IPIS) and is related to conventional photoelectron spectroscopy. If the excitation energy is just below the dissociation energy and pulsed-field dissociation is employed, this approach is analogous to mass analyzed threshold ionization (MATI) spectroscopy and is termed threshold ion pair production spectroscopy (TIPPS). These approaches provide a novel means of investigating ion thermochemistry and spectroscopy and superexcited state decay dynamics at high resolution.

  6. Dissociative phenomenology of dissociative identity disorder.

    PubMed

    Dell, Paul F

    2002-01-01

    The goal of this study was to investigate the dissociative phenomenology of dissociative identity disorder (DID). The Multidimensional Inventory of Dissociation (MID) was administered to 34 patients with DID, 23 patients with dissociative disorder not otherwise specified (DDNOS), 52 patients with mixed psychiatric disorders, and 58 normal individuals. DID patients obtained significantly higher scores than the other three groups on 27 dissociation-related variables. DDNOS patients had significantly higher scores than normals and mixed psychiatric patients on 17 and 15 dissociation-related variables, respectively. The findings of the present study are virtually identical to a large body of replicated findings about the dissociative phenomenology of DID. This broad range of dissociation-related phenomena, which routinely occurs in individuals with DID, is largely absent from the DSM-IV-TR account of DID. Factor analysis of the 11 dimensions of dissociation that are measured by the MID extracted only one factor that accounted for 85% of the variance. It was concluded that dissociation is a unifactorial taxon or natural type that has different aspects or epiphenomena (i.e., amnesia, depersonalization, voices, trance, etc.).

  7. Light-induced potentials ignite dissociation of N22+

    NASA Astrophysics Data System (ADS)

    Coffee, Ryan N.; Fang, Li; Gibson, George N.

    2006-04-01

    Direct ionization to dissociative potential curves is the dominant explanation for intense-field dissociative ionization of N2 . In this article we contradict this notion by showing that the dissociation of N22+ adiabatically follows the avoided crossing formed by the ∣XΠu3,n⟩ and ∣DΠg3,n-1⟩ dressed curves. Dissociation along this light-induced molecular potential implies that one photon is absorbed and adds to the kinetic release of the fragments. We compare the fragmentation energies for three different laser wavelengths and find that nitrogen shows photon absorption whereas iodine does not. From this we conclude that one must account for the absorbed photon when interpreting the time-of-flight spectra for molecules with appreciable nuclear motion during the laser pulse. In nitrogen, doing so allows us to identify enhanced ionization of the dication at 2.2Å independent of laser wavelength.

  8. Theory of dissociative electron attachment: Biomolecules and clusters

    NASA Astrophysics Data System (ADS)

    Fabrikant, Ilya I.

    2015-01-01

    Very broad σ∗ resonances, which are responsible for threshold structures and dissociative attachment in electron collisions with hydrogen halides, are also important in electron-impact bond-breaking in nucleobases and amino acids. We investigate this mechanism in more detail by carrying out model calculations of the N-H bond breaking in the uracil molecule. Although the σ∗ resonance is extremely broad at the equilibrium nuclear geometry, it is stabilized fast when the N-H bond is stretched, and this produces a substantial dissociative attachment cross section. In addition, very pronounced vibrational Feshbach resonances are seen below vibrational excitation thresholds. To incorporate the effect of a cluster environment in the dissociative electron attachment process, we develop further the multiple scattering theory for this process and calculate the dissociative attachment cross section for the CF3Cl molecule embedded in the (H2O)6 cluster.

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

    NASA Astrophysics Data System (ADS)

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

    2016-12-01

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

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

    NASA Astrophysics Data System (ADS)

    Chowdhury, Madhusree Roy; Tribedi, Lokesh C.

    2017-08-01

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

  11. Semiclassical calculations of electron impact Stark widths and shifts of singly ionized atom lines revisited

    NASA Astrophysics Data System (ADS)

    Blagojević, Branimir; Konjević, Nikola

    2017-09-01

    The Stark broadening parameters for spectral lines of singly charged Mg II, Al II, Si II, Zn II, Sn II, Hg II, and Pb II ions, calculated in numerically improved semiclassical formalism of Griem are reported and compared with the original results of Griem for Mg, Al and Si ions and the semiclassical calculations in a version of Dimitrijević and Sahal-Bréchot for Mg ions. Detailed comparison with the experimental data is carried out, also.

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

    DTIC Science & Technology

    1990-01-25

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

  13. Characterization of ice-nucleating bacteria using on-line electron impact ionization aerosol mass spectrometry.

    PubMed

    Wolf, R; Slowik, J G; Schaupp, C; Amato, P; Saathoff, H; Möhler, O; Prévôt, A S H; Baltensperger, U

    2015-04-01

    The mass spectral signatures of airborne bacteria were measured and analyzed in cloud simulation experiments at the AIDA (Aerosol Interaction and Dynamics in the Atmosphere) facility. Suspensions of cultured cells in pure water were sprayed into the aerosol and cloud chambers forming an aerosol which consisted of intact cells, cell fragments and residual particles from the agar medium in which the bacteria were cultured. The aerosol particles were analyzed with a high-resolution time-of-flight aerosol mass spectrometer equipped with a newly developed PM2.5 aerodynamic lens. Positive matrix factorization (PMF) using the multilinear engine (ME-2) source apportionment was applied to deconvolve the bacteria and agar mass spectral signatures. The bacteria mass fraction contributed between 75 and 95% depending on the aerosol generation, with the remaining mass attributed to agar. We present mass spectra of Pseudomonas syringae and Pseudomonas fluorescens bacteria typical for ice-nucleation active bacteria in the atmosphere to facilitate the distinction of airborne bacteria from other constituents in ambient aerosol, e.g. by PMF/ME-2 source apportionment analyses. Nitrogen-containing ions were the most salient feature of the bacteria mass spectra, and a combination of C4 H8 N(+) (m/z 70) and C5 H12 N(+) (m/z 86) may be used as marker ions.

  14. Electron-driven excitations and dissociation of molecules

    SciTech Connect

    Miller, Greg; Orel, Ann E.

    2015-02-13

    This program studied how energy is interchanged in electron and photon collisions with molecules leading to ex-citation and dissociation. Modern ab initio techniques, both for the photoionization and electron scattering, and the subsequent nuclear dynamics studies, are used to accurately treat these problems. This work addresses vibrational ex-citation and dissociative attachment following electron impact, and the dynamics following inner shell photoionzation. These problems are ones for which a full multi-dimensional treatment of the nuclear dynamics is essential and where non-adiabatic effects are expected to be important.

  15. Electron impact spectroscopy. [for atom and molecule quantum state investigation

    NASA Technical Reports Server (NTRS)

    Trajmar, S.

    1980-01-01

    The concepts of electron impact spectroscopy are discussed, comparing the electron spectroscopy techniques with those of the optical spectroscopy. The main advantage of the electron spectroscopy is to be found in the elimination of optical selection rules in excitation processes and the ability to scan the spectrum from the infrared to the X-ray region. The range of the method is indicated through a review of several examples, including electron impact excitation of Ba and rotational excitation of H2. The sensitivity of the method is demonstrated by vibrational excitation spectrum of N2. It is shown that the application of the method to the inner-shell excitation allows to obtain information about molecular species which are not commonly available, while spectroscopy of negative ions yields information about their energy and symmetry properties. However, the techniques are still under development and more data are expected to become available in the coming years.

  16. Electron impact excitation of autoionising states of krypton

    NASA Technical Reports Server (NTRS)

    Srivastava, S. K.; Trajmar, S.

    1978-01-01

    Energy-loss spectra of krypton in the region between 21 and 29 eV have been obtained at electron impact energies of 30, 60 and 100 eV. For each energy, the angular distribution of intensities has been measured at 5, 10 and 15 deg scattering angles. Assignments of spectral features found in this region are suggested and a comparison is made with previous measurements.

  17. Experimental techniques for cross-section measurements. [for electron impacts

    NASA Technical Reports Server (NTRS)

    Trajmar, S.; Register, D. F.

    1984-01-01

    Attention is given to electron collision phenomena which can be studied under single-collision conditions at low and intermediate electron impact energies, ranging from threshold to a few hundred eV, using gas phase molecular targets. Several of the experimental methods discussed were first developed and applied to atoms, but are equally applicable to molecules with minor modifications in the interpretation of the data, due to the greater complexity of molecular systems.

  18. Resonant vibrational excitation of adsorbed molecules by electron impact

    NASA Astrophysics Data System (ADS)

    Djamo, V.; Teillet-Billy, D.; Gauyacq, J. P.

    1993-11-01

    The vibrational excitation of N2 molecules adsorbed on a silver surface by low energy electron impact is studied within the newly developed coupled angular mode method. The process involves the formation of a transient negative molecular ion. The results account well for the observations of Demuth and co-workers. They also reveal that most of the vibrational excitation corresponds to electrons scattered into the metal and thus unobservable in a scattering experiment.

  19. Measurement of electron-impact excitation in boronlike carbon

    NASA Technical Reports Server (NTRS)

    Lafyatis, G. P.; Kohl, J. L.

    1987-01-01

    The cross section for the electron-impact excitation of C(+) (2s2 2p 2P0)-(2s2p2 2D) is measured in a colliding-beams apparatus for several collision energies near the threshold for the process. A cross section of (1.1 + or - 0.3) x 10 to the -16th sq cm at threshold is found. Reasonable agreement is found with close-coupling calculations.

  20. Experimental apparatus for measurements of electron impact excitation

    NASA Technical Reports Server (NTRS)

    Lafyatis, G. P.; Kohl, J. L.; Gardner, L. D.

    1987-01-01

    An ion beam apparatus for the absolute measurement of collision cross sections in singly and multiply charged ions is described. An inclined electron and ion beams arrangement is used. Emitted photons from the decay of collision produced excited states are collected by a mirror and imaged onto a photomultiplier. Absolute measurements of the electron impact excitation of the 2s-2p transition in C(3+) were used to demonstrate the reliability of the apparatus.