P. Scheier

Université Paris-Sud 11, Orsay, Île-de-France, France

Are you P. Scheier?

Claim your profile

Publications (421)1021.69 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: The self-assembly of salt nanocrystals from chemical reactions inside liquid helium is reported for the first time. Reaction is initiated by an electron impacting a helium nanodroplet containing sodium atoms and SF6 molecules, leading to preferential production of energetically favorable structures based on the unit cell of crystalline NaF. These favorable structures are observed as magic number ions (anomalously intense peaks) in mass spectra and are seen in both cationic and anionic channels in mass spectra, for example, (NaF)nNa+ and (NaF)nF−. In the case of anions the self-assembly is not directly initiated by electrons: the dominant process involves resonant electron-induced production of metastable electronically excited He− anions, which then initiate anionic chemistry by electron transfer.
    Angewandte Chemie 11/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: The self-assembly of salt nanocrystals from chemical reactions inside liquid helium is reported for the first time. Reaction is initiated by an electron impacting a helium nanodroplet containing sodium atoms and SF6 molecules, leading to preferential production of energetically favorable structures based on the unit cell of crystalline NaF. These favorable structures are observed as magic number ions (anomalously intense peaks) in mass spectra and are seen in both cationic and anionic channels in mass spectra, for example, (NaF)nNa+ and (NaF)nF−. In the case of anions the self-assembly is not directly initiated by electrons: the dominant process involves resonant electron-induced production of metastable electronically excited He− anions, which then initiate anionic chemistry by electron transfer.
    Angewandte Chemie International Edition 11/2014; · 11.34 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The formation of dianions in helium nanodroplets is reported for the first time. The fullerene cluster dianions (C60)n2− and (C70)n2− were observed by mass spectrometry for n≥5 when helium droplets containing the appropriate fullerene were subjected to electron impact at approximately 22 eV. A new mechanism for dianion formation is described, which involves a two-electron transfer from the metastable He− ion. As well as the prospect of studying other dianions at low temperature using helium nanodroplets, this work opens up the possibility of a wider investigation of the chemistry of He−, a new electron-donating reagent.
    Angewandte Chemie 10/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Electron ionization of the DNA nucleobase, adenine, and the tRNA nucleobase, hypoxanthine, was investigated near the threshold region (~5-20 eV) using a high-resolution hemispherical electron monochromator and a quadrupole mass spectrometer. Ion efficiency curves of the threshold regions and the corresponding appearance energies (AEs) are presented for the parent cations and the five most abundant fragment cations of each molecule. The experimental ionization energies (IEs) for adenine and hypoxanthine were determined to be 8.70 ± 0.3 eV and 8.88 ± 0.5 eV, respectively. Quantum chemical calculations (B3LYP/6 311+G(2d,p)) yielded a vertical IE of 8.08 eV and an adiabatic IE of 8.07 eV for adenine and a vertical IE of 8.51 eV and an adiabatic IE of 8.36 eV for hypoxanthine, and the lowest energy optimized structures of the fragment cations and their respective neutrals were calculated. The enthalpies of the possible reactions from the adenine and hypoxanthine cations were also determined computationally, which assisted in determining the most likely electron ionization pathways leading to the major fragment cations. Our results suggest that the imidazole ring is more stable than the pyrimidine ring in several of the fragmentation reactions from both adenine and hypoxanthine. This electron ionization study contributes to understanding the biological effects of electrons on nucleobases and contributes to the database of electronic properties of biomolecules, which is necessary for modeling damage of DNA in living cells that is induced by ionizing radiation.
    Physical Chemistry Chemical Physics 10/2014; · 4.20 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: A cavity-hollow cathode, consisting of two specifically formed disks of Ti with an additional cavity intended for enhancement of the pendulum effect of the electrons, was in-vestigated as a low-cost sputtering source. A discharge in Ar gas was produced inside the hol-low cathode. Measurements using Langmuir probes yielded evidence for the formation of a space charge double layer in front of the cathode. The sputtered atoms form negatively charged clusters, which bombard the film substrate. Titanium thin films were produced on highly oriented pyrolytic graphite. Film morphology and elemental composition were investi-gated by scanning tunnel microscopy (STM) and X-ray photoelectron spectroscopy (XPS).
    37th EPS Conference on Plasma Physics; 09/2014
  • [Show abstract] [Hide abstract]
    ABSTRACT: Niederenergetische Elektronen (NEEs) mit Energien unter 2 eV zersetzen 4-Nitroimidazol (4NI) sehr effizient über dissoziative Elektronenanlagerung (DEA). Diese Reaktionen umfassen einfache Bindungsbrüche, aber auch komplexere Prozesse wie mehrfache Bindungsbrüche und die Bildung neuer Moleküle. Alle diese Reaktionen zeigen sich als scharfe Strukturen im detektierten Anionensignal und werden als Feshbach-Resonanzen gedeutet, die effiziente Wegbereiter für DEA sind. Die außergewöhnlich vielfältigen chemischen Reaktionen von 4NI werden bei Methylierung von 4NI an der N1-Position komplett blockiert. Diese bemerkenswerten Resultate haben auch Auswirkung auf die Entwicklung von Radiosensibilisatoren für die Strahlungstherapie von Tumoren auf Basis von Nitroimidazol.
    Angewandte Chemie 09/2014;
  • [Show abstract] [Hide abstract]
    ABSTRACT: Low-energy electrons (LEEs) at energies of less than 2 eV effectively decompose 4-nitroimidazole (4NI) by dissociative electron attachment (DEA). The reactions include simple bond cleavages but also complex reactions involving multiple bond cleavages and formation of new molecules. Both simple and complex reactions are associated with pronounced sharp features in the anionic yields, which are interpreted as vibrational Feshbach resonances acting as effective doorways for DEA. The remarkably rich chemistry of 4NI is completely blocked in 1-methyl-4-nitroimidazole (Me4NI), that is, upon methylation of 4NI at the N1 site. These remarkable results have also implications for the development of nitroimidazole based radiosensitizers in tumor radiation therapy.
    Angewandte Chemie International Edition 09/2014; · 11.34 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The mechanism of ionization of helium droplets has been investigated in numerous reports but one observation has not found a satisfactory explanation: How are He+ ions formed and ejected from undoped droplets at electron energies below the ionization threshold of the free atom? Does this path exist at all? A measurement of the ion yields of He+ and He2+ as a function of electron energy, electron emission current, and droplet size reveals that metastable He*- anions play a crucial role in the formation of free He+ at subthreshold energies. The proposed model is testable.
    Physical Chemistry Chemical Physics 09/2014; · 4.20 Impact Factor
  • International Journal of Mass Spectrometry 08/2014; · 2.23 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Helium droplets provide the possibility to study phenomena at the very low temperatures at which quantum mechanical effects are more pronounced and fewer quantum states have significant occupation probabilities. Understanding the migration of either positive or negative charges in liquid helium is essential to comprehend charge-induced processes in molecular systems embedded in helium droplets. Here, we report the resonant formation of excited metastable atomic and molecular helium anions in superfluid helium droplets upon electron impact. Although the molecular anion is heliophobic and migrates toward the surface of the helium droplet, the excited metastable atomic helium anion is bound within the helium droplet and exhibits high mobility. The atomic anion is shown to be responsible for the formation of molecular dopant anions upon charge transfer and thus, we clarify the nature of the previously unidentified fast exotic negative charge carrier found in bulk liquid helium.
    Journal of Physical Chemistry Letters 07/2014; 5(14):2444-2449. · 6.69 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Dissociative electron attachment to PtBr2 in the gas phase was studied in the low electron energy range from zero up to 10 eV with an energy resolution of 150 meV. The experiments were carried out using a hemispherical electron monochromator coupled with a quadrupole mass spectrometer and pulse counting acquisition system. The only anion observed was Br−. This ion is formed at three resonance electron energies: 0.4 eV, 1.2 eV and 7 eV. By the measurements of the Br− formation at different sample temperatures (in the 360–460 K range) the 0.4 eV resonance was associated with the electron capture by HBr generated in the apparatus at elevated temperatures. In addition, the thermodynamic thresholds for dissociative electron attachment reactions for platinum(II) bromide were calculated and compared with the experimental results.
    International Journal of Mass Spectrometry 05/2014; 365-366:152-156. · 2.23 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Electron attachment to CO2 embedded in superfluid He droplets leads to ionic complexes of the form (CO2)n(-) and (CO2)nO(-) and, at much lower intensities, He containing ions of the form Hem(CO2)nO(-). At low energies (< 5 eV), predominantly the non-decomposed complexes (CO2)n(-) are formed via two resonance contributions, similar to electron attachment to pristine CO2 clusters. The significantly different shapes and relative resonance positions, however, indicate particular quenching and mediation processes in CO2@He. A series of further resonances in the energy range up to 67 eV can be assigned to electronic excitation of He and capture of the inelastically scattered electron generating (CO2)n(-) and two additional processes where an intermediately formed He* leads to the non-stoichiometric anions (CO2)nO(-).
    The Journal of Physical Chemistry A 05/2014; · 2.77 Impact Factor
  • International Journal of Mass Spectrometry 05/2014; · 2.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: We present a detailed experimental investigation of anion production in electron collisions with ethylene, C2H4. The investigated energy range is between 0 and 90 eV where anions are formed by two processes, in the low energy regime by dissociative electron attachment (DEA) and at higher energy by dipolar dissociation (DD). These electron induced processes are studied in two different experimental apparatus using two different mass spectrometry techniques. One is a time of flight spectrometer operating with velocity slice imaging technique and the other is a two sector field mass spectrometer. The former allows efficient collection of ions compared to standard mass spectrometers, while the latter provides high mass resolution. Eight fragment anions formed via DEA in the electron energy range between 5 and 17 eV have been detected; two fragments have not reported as DEA products in any previous studies. DD in C2H4 leads to the formation of the same anions as found in the case of DEA. Quantum chemical calculations have been carried out to determine the thermochemical thresholds of anion formation.
    International Journal of Mass Spectrometry 05/2014; · 2.23 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Dissociative electron attachment (DEA) to chlorotrimethylsilane (Me3SiCl) and chlorodimethylphenylsilane (PhMe2SiCl) was studied to reveal a possible enhancing effect of the aromatic side group on the Si-Cl bond dissociation. Calculations point to a relevant interaction between the lowest unoccupied π* orbital of the phenyl ring and the σ*(Si-Cl) orbital and a consequent lowering of the lowest-energy electron attachment channel. It was previously reported that such a situation can lead to a significant enhancement of DEA. However, the lowest energy DEA channel in the investigated chlorosilanes lies below the thermodynamic limit for dissociation of the Si-Cl bond in the radical anion and thus cannot contribute to the Cl− yield. In consequence, release of chloride ions is in fact the dominant fragmentation channel but the Cl− yield is not noticeably enhanced in PhMe2SiCl. In contrast to the DEA results, comparative experiments on the reductive coupling in THF of Me3SiCl, PhMe2SiCl, and benzyldimethylchlorosilane (BzMe2SiCl) under identical conditions reveal a significant enhancement of the reactivity by aromatic side groups. As this finding does not correlate with the DEA results, an alternative explanation for the different reactivity of Me3SiCl and PhMe2SiCl in solution is suggested based on their vertical electron attachment energies and considering the impact of these quantities on the equilibrium between solvated electrons and neutral reactants on one side and the solvated radical anion on the other.
    International Journal of Mass Spectrometry 05/2014; 365-366:169-176. · 2.23 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Helium nanodroplets are doped with carbon dioxide and ionized by electrons. Doubly charged cluster ions are, for the first time, identified based on their characteristic patterns of isotopologues. Thanks to the high mass resolution, large dynamic range, and a novel method to eliminate contributions from singly charged ions from the mass spectra, we are able to observe doubly charged cluster ions that are smaller than the ones reported in the past. The likely mechanism by which doubly charged ions are formed in doped helium droplets is discussed.Dedicated to Tilmann Märk, a long-time friend and colleague, on the occasion of his 70th birthday.
    International Journal of Mass Spectrometry 05/2014; · 2.23 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: In spite of extensive investigations of ethylene adsorbed on graphite, bundles of nanotubes, and crystals of fullerenes, little is known about the existence of commensurate phases; they have escaped detection in almost all previous work. Here we present a combined experimental and theoretical study of ethylene adsorbed on free C60 and its aggregates. The ion yield of (C60)m(C2H4)n+ measured by mass spectrometry reveals a propensity to form a structurally ordered phase on monomers, dimers and trimers of C60 in which all sterically accessible hollow sites over carbon rings are occupied. Presumably the enhancement of the corrugation by the curvature of the fullerene surface favors this phase which is akin to a hypothetical 1 × 1 phase on graphite. Experimental data also reveal the number of molecules in groove sites of the C60 dimer through tetramer. The identity of the sites, adsorption energies and orientations of the adsorbed molecules are determined by molecular dynamics calculations based on quantum chemical potentials, as well as density functional theory. The decrease in orientational order with increasing temperature is also explored in the simulations whereas in the experiment it is impossible to vary the temperature.
    Carbon 04/2014; 69:206-220. · 6.16 Impact Factor
  • Chemical Physics Letters 01/2014; · 1.99 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The formation of monocarbon cluster ions has been investigated by electron ionization mass spectrometry of cold helium nanodroplets doped with nitrogen/methane mixtures. Ion yields for two groups of clusters, CHmN2+ or CHmN4+, were determined for mixtures with different molecular ratios of CH4. The possible geometrical structures of these clusters were analyzed using electronic structure computations. Little correlation between the ion yields and the associated binding energies has been observed indicating that in most cases kinetic control is more important than thermodynamic control for forming the clusters.
    The Journal of Chemical Physics 12/2013; 140(3). · 3.12 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Figure optionsDownload full-size imageDownload high-quality image (226 K)Download as PowerPoint slide
    International Journal of Mass Spectrometry 11/2013; 354-355:271-274. · 2.23 Impact Factor

Publication Stats

4k Citations
1,021.69 Total Impact Points

Institutions

  • 2014
    • Université Paris-Sud 11
      Orsay, Île-de-France, France
  • 1986–2014
    • University of Innsbruck
      • • Institute for Ion Physics and Applied Physics
      • • Institut für Experimentalphysik
      Innsbruck, Tyrol, Austria
  • 2006–2012
    • University of Nebraska at Lincoln
      • Department of Physics and Astronomy
      Lincoln, Nebraska, United States
  • 2011
    • University of Notre Dame
      • Department of Physics
      Indiana, PA, United States
    • University of New Hampshire
      • Department of Physics
      Durham, NH, United States
  • 2008
    • New University of Lisbon
      • Faculty of Sciences and Technology
      Lisboa, Lisbon, Portugal
  • 2001–2008
    • Claude Bernard University Lyon 1
      • • Institut de physique nucléaire de Lyon (IPNL)
      • • Laboratoire de spectrométrie ionique et moléculaire (LASIM)
      Villeurbanne, Rhône-Alpes, France
  • 2001–2007
    • Freie Universität Berlin
      • Division of Physical and Theoretical Chemistry
      Berlin, Land Berlin, Germany
  • 2000–2007
    • University of Hawaiʻi at Mānoa
      • Department of Physics and Astronomy
      Honolulu, HI, United States
  • 2005
    • Maria Skłodowska-Curie Institute of Oncology
      Cracovia, Lesser Poland Voivodeship, Poland
  • 2004
    • University of Greifswald
      • Institute of Physics
      Greifswald, Mecklenburg-Vorpommern, Germany
  • 2000–2001
    • Justus-Liebig-Universität Gießen
      • Institut für Atom- und Molekülphysik
      Gießen, Hesse, Germany
  • 1999
    • Comenius University in Bratislava
      • Department of Experimental Physics
      Presburg, Bratislavský, Slovakia