H. Drexel

University of Innsbruck, Innsbruck, Tyrol, Austria

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Publications (17)24.2 Total impact

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    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 01/2010; 31(13).
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    ABSTRACT: Electron emission for impact of singly and multiply charged fullerene ions Cnq+ (15 ≤ n ≤ 60; 1 ≤ q ≤ 5) on atomically clean polycrystalline gold has been studied at impact energies far from below threshold up to 250 eV/amu by measuring the number statistics of emitted electrons, from which accurate absolute total electron yields have been determined. In contrast to impact of atomic ions the fullerene charge q apparently has no influence on the total electron yield, i.e. no potential emission takes place. There is also no clear threshold for the electron emission which becomes measurable already around 10 eV/amu, above which it rises faster than linear with the ion impact velocity. Isotachic Cnq+ ions cause electron yields in direct proportion to their size n, with 250 eV/amu C60q+ producing on average more than 25 electrons. These results are tentatively explained by assuming that either the fullerene ions are completey shattered at the gold surface and individual carbon atoms produce kinetic emission, or electrons originate from thermionic emission of projectiles and their fragments heated up in the surface collision.
    Physica Scripta 12/2006; 1997(T73):318. · 1.03 Impact Factor
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    ABSTRACT: We demonstrate that the phase between the carrier and the pulse envelope of a few-cycle laser pulse can be retrieved from non phase stable laser systems, provided that such laser pulses are about 5fs long and the repetition rate is in the order of 1kHz. Our approach is based on online determination of the phase using f-2f interferometry. By a comparison of the self referencing interferometric signal with the photoelectron current emitted into a 7 degree solid angle parallel to the laser polarization, we obtain the absolute value of the carrier envelope phase. This is provided that a Coulomb correction for electron energies below 10eV can be correctly taken into account.
    Applied Physics B 02/2004; 78(5):583-587. · 1.78 Impact Factor
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    ABSTRACT: Electron attachment to tetrachloroethene (C2Cl4) has been studied in the energy range from ∼0 eV up to 9.5 eV, using a trochoidal electron monochromator with an energy resolution of about 70 meV. Production yields for the parent anion and various fragment anions are compared with previously published data in order to clarify some existent discrepancies. In particular, an inconsistency concerning the Cl−/C2Cl4 peak is investigated, and additional transitions leading to anion formation are presented. Moreover, a newly discovered mechanism for the production of a spurious anion signal at zero electron energy is presented. This mechanism appears when metastable anions that have been formed initially upon attachment undergo autodetachment in regions where electrostatic fields are present. Zero-energy peaks generated that way represent dangerous pitfalls and have to be taken into account, at least in electron attachment studies that are based on in-line instruments. © 2003 American Institute of Physics.
    The Journal of Chemical Physics 04/2003; 118(16):7394-7400. · 3.12 Impact Factor
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    ABSTRACT: Low energy electron attachment to the potent greenhouse gas SF5CF3 is studied at high energy resolution by means of mass spectrometric detection of the product anions. A large dissociative electron attachment (DA) cross-section forming SF5−+CF3 is observed within a very narrow energy range close to zero eV. In addition, comparatively weak resonances are observed near 1 eV yielding the fragment ions CF3− and F−. Some implications for the atmospheric lifetime of SF5CF3 and hence its global warming potential (GWP) are considered.
    Chemical Physics Letters 01/2002; 351(1):71-78. · 2.15 Impact Factor
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    ABSTRACT: Electron monochromators which are operated within an axial magnetic (guiding) field are especially suitable for the production of monochromatic electrons at low energies. Although in principle the technology of such devices has an appreciable historic background, we have discovered experimentally important new features, which cannot be understood using the previously published theories of operation. An in-depth study of the electron trajectories in a crossed electric and magnetic field using Simion1 showed a number of possible pitfalls, which have to be avoided in construction and operation. From our simulations we derived a novel design and operational method, which is currently under evaluation. We have already demonstrated that using this novel design an electron energy resolution of about 50 meV is realistic.
    Journal of Mass Spectrometry 03/2001; 36(2):151-8. · 3.21 Impact Factor
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    ABSTRACT: On the basis of a number of different experiments employing various principles, we have demonstrated that the energy resolution of the trochoidal electron monochromator used in our laboratory the past 5 yr is not independent from the electron energy used, that is, the very high nominal-energy-resolution close-to-zero electron energy in the range of several meV deteriorates quickly with increasing electron energy reaching values of up to 100 meV at ∼1-eV electron energy. Carrying out extensive electron trajectory calculations with the Simion program, we were able to show that our variant of a trochoidal monochromator does not only operate on the trochoidal dispersion principle but also involves a retarding field component right after the dispersion region in achieving this high-energy-resolution close-to-zero energy. This retarding field is, however, weakened at higher electron energies (caused by the influence of the electron-acceleration field) leading to the decrease in energy resolution with increasing electron energy. On the basis of further simulations, we have designed and constructed a new monochromator avoiding this and other deficiencies. This new monochromator currently has an energy resolution of ∼45 meV independent of the electron energy. Further improvements are under consideration.
    International Journal of Mass Spectrometry 02/2001; · 2.14 Impact Factor
  • International Journal of Mass Spectrometry - INT J MASS SPECTROM. 01/2001; 205:209-226.
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    ABSTRACT: On the basis of a number of different experiments employing various principles, we have demonstrated that the energy resolution of the trochoidal electron monochromator used in our laboratory the past 5 yr is not independent from the electron energy used, that is, the very high nominal-energy-resolution close-to-zero electron energy in the range of several meV deteriorates quickly with increasing electron energy reaching values of up to 100 meV at ∼1-eV electron energy. Carrying out extensive electron trajectory calculations with the Simion program, we were able to show that our variant of a trochoidal monochromator does not only operate on the trochoidal dispersion principle but also involves a retarding field component right after the dispersion region in achieving this high-energy-resolution close-to-zero energy. This retarding field is, however, weakened at higher electron energies (caused by the influence of the electron-acceleration field) leading to the decrease in energy resolution with increasing electron energy. On the basis of further simulations, we have designed and constructed a new monochromator avoiding this and other deficiencies. This new monochromator currently has an energy resolution of ∼45 meV independent of the electron energy. Further improvements are under consideration.
    International Journal of Mass Spectrometry - INT J MASS SPECTROM. 01/2001; 205(1):209-226.
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    ABSTRACT: Using two different crossed-beams high-resolution electron attachment instruments (employing either a trochoidal electron monochromator or a hemispherical electron monochromator) we have determined the cross section curve for H [iopmath latex="$^-$"] - [/iopmath] production from H2 via the 4 eV resonance at two different temperatures. These relative partial cross sections have been calibrated by comparing present values for the 14 eV resonance with absolute total cross sections determined previously. Taking into account the experimental energy distribution and the rotational excitation and its influence on the cross section shape we obtain very good agreement with theoretical predictions in terms of both the shape and magnitude of this resonance peak.
    Journal of Physics B Atomic Molecular and Optical Physics 01/2001; · 2.03 Impact Factor
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    ABSTRACT: Dissociative electron attachment (DA) to ClOCl is studied in a high resolution crossed beam experiment. Two complementary ion pairs, Cl−/ClO− and O−/Cl2−, are observed. The Cl−/ClO− pair arises from a simple Cl–OCl bond cleavage with the electron sitting on either of the two fragments. The O−/Cl2− pair is formed by a concerted reaction with the expulsion of O− (or O) and formation of Cl2 (or Cl2−). Ab initio calculations indicate that in low energy electron attachment an electronically excited state of the precursor anion () is involved.
    Chemical Physics Letters 01/2001; · 2.15 Impact Factor
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    ABSTRACT: The production of O- and O2- by dissociative electron attachment to ozone has been studied between about 0 and 10 eV with a high resolution crossed beam apparatus recently developed in the Innsbruck laboratory. A previously unobserved sharp structure is observed in the formation of O- ions at zero incident energy. This large additional cross section peak has important consequences for the role of ozone in anion formation processes in the terrestrial ionosphere. .
    01/2000;
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    ABSTRACT: Spontaneous (metastable) and surface-induced decay reactions for multiply charged fullerene ions, investigated recently in Innsbruck, are reviewed. Results discussed include the mechanisms and energetics of C 2 evaporation and charge separation reactions, the secondary electron emission upon impact on gold surfaces, and surface-induced reactions of singly and multiply charged fullerene ions.
    The European Physical Journal D 11/1999; 9(1):91-94. · 1.51 Impact Factor
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    ABSTRACT: We have studied negative ion formation following low-energy electron impact (0-10 eV) to OClO including a time-of-flight analysis of the ions. The dominant feature is formation of a transient negative ion (OClO-*) by resonant electron capture in the vicinity of 0.7 eV which decomposes into Cl-, O-, ClO- and O2-. The total dissociative attachment (DA) cross section at the resonance maximum (0.7 eV) is near 10-15 cm2 with ClO-+O the dominant channel. Although the DA reaction O2+Cl- is exothermic by nearly 4 eV the Cl- ion appears with a mean kinetic energy of only 0.4±0.1 eV indicating effective vibrational excitation of neutral O2. Also observed at higher target gas pressures is the parent anion ClO2- which arises from an effective charge transfer process involving a metastable complex formed in the collision between the dominant DA product ClO- and the sample molecule OClO. Possible implications of these results for the heterogeneous chemistry of OClO on polar stratospheric cloud particles are considered.
    Journal of Physics B Atomic Molecular and Optical Physics 07/1999; 32(14):3615. · 2.03 Impact Factor
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    ABSTRACT: We have measured absolute total electron emission yields for impact of carbon cluster ions Ciq+ on atomically clean gold, as a function of cluster size (up to i=60), charge (up to q=5), and kinetic energy (up to 165 keV). Besides a linear dependence on cluster size and occurrence of electron emission well below the classical kinetic emission threshold, we find no dependence on the fullerene charge, and thus a suppression of potential electron emission. This is in contrast to the interaction of multicharged atomic ions with surfaces. We present molecular-dynamics calculations which provide evidence of fast quenching of the primary excitation energy via fragmentation of the projectiles.
    Physical Review A 01/1997; 56(4). · 3.04 Impact Factor
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    ABSTRACT: Distinction between multiply charged fullerene ions C60q+ and their fragments with equal charge-to-mass ratio in a mixed cluster ion beam has been achieved by measuring the number statistics for the electron emission induced by impact of the respective ions on a clean metal surface. The new method is described with a practical example for a mixed beam of C604+ and C15+. In addition, we show that this principle — that is, different electron emission characteristics for fullerene ions with different charges and masses but the same charge-to-mass ratio — can be utilized in any common ion mass spectrometer to distinguish various fullerene ions and their coinciding fragments by a judicious choice of the detector multiplier voltage.
    International Journal of Mass Spectrometry and Ion Processes 01/1997; 163(3):9-14.
  • Phys. Rev. A. 56:3007.