P. Scheier

University of Innsbruck, Innsbruck, Tyrol, Austria

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Publications (461)1049.22 Total impact

  • [Show abstract] [Hide abstract] ABSTRACT: We show, both experimentally and theoretically, that the adsorption of CO2 is sensitive to charge on a capturing model carbonaceous surface. In the experiment we doped superfluid helium droplets with C60 and CO2 and exposed them to ionising free electrons. Both positively and negatively charged C60(CO2)n(+/-) cluster ion distributions are observed using a high-resolution mass spectrometer and they show remarkable and reproducible anomalies in intensities that are strongly dependent on the charge. The highest adsorption capacity is seen with C60(+). Complementary density functional theory calculations and molecular dynamics simulations provided insight into the nature of the interaction of charged C60 with CO2 as well as trends in the packing of C60(+) and C60(-). The quadrupole moment of CO2 itself was found to be decisive in determining the charge dependence of the observed adsorption features. Our findings are expected to be applied for the adsorption of CO2 on charged surfaces in general.
    No preview · Article · Dec 2015 · Physical Chemistry Chemical Physics
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    Martina Harnisch · Paul Scheier · Zdenek Herman
    [Show abstract] [Hide abstract] ABSTRACT: Interaction of NH3+ (ND3+) and NH+ with a hydrocarbon-covered tungsten surface kept at room temperature or heated to 150 and 300 °C showed a series of reactions between the projectile ion and hydrocarbons adsorbed on the tungsten surface. Collisions with NH3+ showed formation of NH4+, HCNH+, and CH2NH2+, with NH4+ strongly prevailing at low incident energies of the projectile ion. Analogously, collisions with ND3+ showed formation of ND3H+, HCND+, and CH2ND2+ with dominant contributions of ND3H+ at low incident energies. No formation of HCN+ (DCN+) could be positively identified. In reactions with NH+, formation of HCN+ was clearly observed; the dependence of the normalized yield of HCN+ on incident energy indicated a threshold at about 40 eV which might be due to an activation energy or an endothermicity of the surface reaction of about 2.4–3.2 eV.
    Full-text · Article · Oct 2015
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    [Show abstract] [Hide abstract] ABSTRACT: Electron addition to cobalt tricarbonyl nitrosyl (Co(CO3NO) and its clusters has been explored in helium nanodroplets. Anions were formed by adding electrons with controlled energies, and reaction products were identified by mass spectrometry. Dissociative electron attachment (DEA) to the Co(CO)3NO monomer gave reaction products similar to those reported in earlier gas phase experiments. However, loss of NO was more prevalent than loss of CO, in marked contrast to the gas phase. Since the Co–N bond is significantly stronger than the Co–C bond, this preference for NO loss must be driven by selective reaction dynamics at low temperature. For [Co(CO)3NO]N clusters, the DEA chemistry is similar to that of the monomer, but the anion yields as a function of electron energy show large differences, with the relatively sharp resonances of the monomer being replaced by broad profiles peaking at much higher electron energies. A third experiment involved DEA of Co(CO)3NO on a C60 molecule in an attempt to simulate the effect of a surface. Once again, broad ion yield curves are seen, but CO loss now becomes the most probable reaction channel. The implication of these findings for understanding focused electron beam induced deposition of cobalt is described.
    Preview · Article · Sep 2015 · The Journal of Physical Chemistry C
  • No preview · Article · Sep 2015 · Journal of Physics Conference Series
  • No preview · Article · Sep 2015 · Journal of Physics Conference Series
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    Full-text · Article · Sep 2015 · Journal of Physics Conference Series
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    [Show abstract] [Hide abstract] ABSTRACT: Helium nanodroplets provide an enviroment that allow studies of chemical reactions at ultracold temperatures. We use these droplets as a matrix to study the formation of water upon electron bombardment of oxyhydrogen clusters
    Preview · Article · Sep 2015 · Journal of Physics Conference Series
  • [Show abstract] [Hide abstract] ABSTRACT: Low energy electrons (0 - 8 eV) effectively decompose 4-nitroimidazole (4NI) and the two methylated isomers 1-methyl-5-nitroimidazole and 1-methyl-4-nitroimidazole via dissociative electron attachment (DEA). The involved unimolecular decompositions range from simple bond cleavages (loss of H•, formation of NO2-) to complex reactions possibly leading to a complete degradation of the target molecule (formation of CN-, etc.). At energies below 2 eV the entire rich chemistry induced by DEA is completely quenched by methylation as already demonstrated in a previous Communication (K. Tanzer, L. Feketeová, B. Puschnigg, P. Scheier, E. Illenberger, and S. Denifl, Angew. Chem. Int. E. 53 (2014) 12240). The observation that in 4NI neutral radicals and radical anions are formed via DEA at high efficiency already at threshold (0 eV) may have significant implications for the development of nitroimidazole based radiosensitisers in tumour radiation therapy.
    No preview · Article · May 2015 · The Journal of Physical Chemistry A
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    [Show abstract] [Hide abstract] ABSTRACT: Adsorption of helium on free, negatively charged fullerenes is studied in this work. Helium nanodroplets have been doped with fullerenes and ionised by electron attachment. For suitable experimental conditions, C−60 and C−70 anions are found to be complexed with a large number of helium atoms. Prominent anomalies in the ion abundances indicate the high stability of the commensurate 1×1 phase in which all hollow adsorption sites are occupied by one atom each. The adsorption energy for an additional helium atom is about 40% less than for atoms in the commensurate layer, similar to our previous findings for fullerene cations and in agreement with theoretical dissociation energies. Similarly, an anomaly in the adsorption energy occurs when 60 helium atoms are attached to C−60 or 65 to C−70. For C60, the anomaly coincides with the one observed for cationic complexes but for C70 it does not. Implications of these features are discussed in light of several theoretical studies of neutral and positively charged helium-fullerene complexes.
    Full-text · Article · May 2015 · Molecular Physics
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    [Show abstract] [Hide abstract] ABSTRACT: Nitroimidazoles are important compounds with chemotherapeutic applications as antibacterial drugs or as radiosensitizers in radiotherapy. Despite their use in biological applications, little is known about the fundamental properties of these compounds. Understanding the ionization reactions of these compounds is crucial in evaluating the radiosensitization potential and in developing new and more effective drugs. Thus, the present study investigates the decomposition of negative and positive ions of 2-nitroimidazole and 4(5)-nitroimidazole using low- and high-energy Collision-Induced Dissociation (CID) and Electron-Induced Dissociation (EID) by two different mass spectrometry techniques and is supported by quantum chemistry calculations. EID of [M+H]+ leads to more extensive fragmentation than CID and involves many radical cleavages including loss of H• leading to the formation of the radical cation, M•+. The stability (metastable decay) and the fragmentation (high-energy CID) of the radical cation M•+ have been probed in a crossed-beam experiment involving primary electron ionization of the neutral nitroimidazole. Thus, fragments in the EID spectra of [M+H]+ that come from further dissociation of radical cation M•+ has been highlighted. The loss of NO• radical from M•+ is associated with a high Kinetic Energy Release (KER) of 0.98 eV. EID of [M−H]− also leads to additional fragments compared to CID, however, with much lower cross section. Only EID of [M+H]+ leads to a slight difference in the decomposition of 2-nitroimidazole and 4(5)-nitroimidazole.
    Full-text · Article · Apr 2015 · Physical Chemistry Chemical Physics
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    [Show abstract] [Hide abstract] ABSTRACT: The effects of interactions between He(-) and clusters of fullerenes in helium nanodroplets are described. Electron transfer from He(-) to (C60)n and (C70)n clusters results in the formation of the corresponding fullerene cluster dianions. This unusual double electron transfer appears to be concerted and is most likely guided by electron correlation between the two very weakly bound outer electrons in He(-). We suggest a mechanism which involves long range electron transfer followed by the conversion of He(+)into He2 (+), where formation of the He-He bond in He2 (+) releases sufficient kinetic energy for the cation and the dianion to escape their Coulombic attraction. By analogy with the corresponding dications, the observation of a threshold size of n ≥ 5 for formation of both (C60)n (2-) and (C70)n (2-) is attributed to Coulomb explosion rather than an energetic constraint. We also find that smaller dianions can be observed if water is added as a co-dopant. Other aspects of He(-) chemistry that are explored include its role in the formation of multiply charged fullerene cluster cations and the sensitivity of cluster dianion formation on the incident electron energy.
    Preview · Article · Mar 2015 · The Journal of Chemical Physics
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    [Show abstract] [Hide abstract] ABSTRACT: The availability of high resolution mass spectrometry in the study of atomic and molecular clusters opens up challenges for the interpretation of the data. In complex systems each resolved mass peak may contain contributions from multiple species because of the isotope structure of constituent elements and because a multitude of different types of clusters with different compositions are present. A computational procedure which can help to identify a specific cluster from this complex dataset and quantify its relative abundance would be extremely helpful to many who work in this field. Here some new software designed for this purpose, known as IsotopeFit, is described.
    Full-text · Article · Feb 2015 · International Journal of Mass Spectrometry
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    [Show abstract] [Hide abstract] ABSTRACT: Negative ion formation through dissociative electron attachment to the gas-phase volatile anaesthetics enflurane and isoflurane (C3H2ClF5O) and to two chlorinated ethanes, pentachloroethane (C2HCl5) and hexachloroethane (C2Cl6), have been studied in a crossed electron-molecular beam two sector field mass spectrometer experiment. Anion efficiency curves for the negatively charged fragments have been measured over an electron energy range of approximately 0–17 eV, with an energy resolution of ∼1 eV. For the chlorinated ethanes, resonance features were generally found at ∼ 0 eV and at 7.5 eV. For the volatile anaesthetics, no zero energy resonances were observed. Instead, product anions were detected mainly in the 2–3 eV and 9 eV energy regions, with the exception of Cl-, whose dominant resonance occurs at approximately 0.6 eV and 0.9 eV for isoflurane and enflurane, respectively. To aid in the interpretation of the experimental results, quantum chemical calculations providing thermochemical thresholds of anion formation are also presented.
    Full-text · Article · Feb 2015 · International Journal of Mass Spectrometry
  • Simon Penner · Thomas Möst · Paul Scheier · Antonia Kaleve
    [Show abstract] [Hide abstract] ABSTRACT: Dem Rastertunnelmikroskop kommt in der Hochschulausbildung eine immer größere Bedeutung zu, erlaubt es doch einen relativ einfachen Zugang nicht nur zur Sichtbarmachung der atomaren und elektronischen Struktur von Festkörpern, sondern auch zu verwandten, meist schwer fasslichen physikalisch-chemischen Themen und Phänomenen. Dazu gehört auch der quantenmechanische Tunneleffekt, welcher der Messmethode zugrunde liegt. Didaktisch wertvoll, erlaubt die neue Generation der eigens für den Unterricht konzipierten Rastertunnelmikroskope eine einfache Bedienung und Datenanalyse durch Studierende selbst. Im vorliegenden Manuskript werden die Möglichkeiten des Einsatzes solcher Mikroskope in der universitären Lehre kritisch beleuchtet und durch einen Ausblick auf den Schulunterricht ergänzt.The use of the Scanning Tunneling Microscope (STM) in university teaching allows for both a very easy access to the atomic and electronic structure of solids and to gain insight into various, sometimes hardly comprehensible, physico-chemical phenomena like the quantum mechanical tunneling effect. The new generation of easy-to-use STMs, specially designed for teaching purposes, allows self-operation and data-analysis by interested university students. The present manuscript critically discusses the possibilities of STM in university teaching, but also gives an outlook to the use in high-school teaching.
    No preview · Article · Jan 2015 · Chemkon
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    [Show abstract] [Hide abstract] ABSTRACT: Clusters of sulfur are grown by passing superfluid helium nanodroplets through a pickup cell filled with sulfur vapor. In some experiments the droplets are codoped with C60. The doped droplets are collided with energetic electrons and the abundance distributions of positively and negatively charged cluster ions are recorded. We report, specifically, distributions of Sm+, Sm–, and C60Sm– containing up to 41 sulfur atoms. We also observe complexes of sulfur cluster anions with helium; distributions are presented for HenSm– with n ≤ 31 and m ≤ 3. The similarity between anionic and cationic C60Sm± spectra is in striking contrast to the large differences between spectra of Sm+ and Sm–.
    Full-text · Article · Jan 2015 · The Journal of Physical Chemistry C
  • [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.
    No preview · Article · Dec 2014 · Angewandte Chemie
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    [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.
    Preview · Article · Dec 2014 · Angewandte Chemie International Edition
  • [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.
    No preview · Article · Dec 2014 · Angewandte Chemie
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    [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.
    Preview · Article · Nov 2014 · Angewandte Chemie
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    [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.
    Preview · Article · Nov 2014 · Angewandte Chemie International Edition

Publication Stats

7k Citations
1,049.22 Total Impact Points

Institutions

  • 1986-2014
    • University of Innsbruck
      • • Institute for Ion Physics and Applied Physics
      • • Institute for Experimental Physics
      Innsbruck, Tyrol, Austria
  • 2013
    • University of Birmingham
      Birmingham, England, United Kingdom
  • 2004-2008
    • Claude Bernard University Lyon 1
      • Institut de physique nucléaire de Lyon (IPNL)
      Villeurbanne, Rhône-Alpes, France
  • 2003
    • University of Hawaiʻi at Mānoa
      • Department of Physics and Astronomy
      Honolulu, Hawaii, United States
  • 2000-2001
    • Justus-Liebig-Universität Gießen
      • Institut für Atom- und Molekülphysik
      Gießen, Hesse, Germany
    • Honolulu University
      Honolulu, Hawaii, United States
  • 1996
    • Hebrew University of Jerusalem
      • Fritz Haber Center for Molecular Dynamics Research
      Yerushalayim, Jerusalem, Israel