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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 9241-9242 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron attachment to SF6 and SF6 clusters has been investigated in a molecular beam/electron impact ion source/mass spectrometer system. In accordance with recent theoretical predictions we were able to produce the superhalogen ion SF7− by electron attachment to SF6 clusters. SF7− has not been previously observed; its relative attachment cross section curve shows features more similar to that of F2− from SF6 than that of F− from SF6.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 810-811 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Singly charged argon cluster ions produed by electron impact ionization of a neutral argon cluster beam are found to decay in the metastable time regime by a new mechanism leading to the ejection of "magic'' numbers of neutral argon atoms. The measured dependence of this new decay process on (i) the electron energy, (ii) cluster size and cluster properties, and (iii) the time since ion formation gives insight into the unique mechanism and the nature of this process. At a well-defined threshold energy of ca. 27 eV, the magic number loss mechanism occurs simultaneously with the well-known single monomer evaporation process which proceeds at all energies. Importantly, the new mechanism is the first known example of cluster ion metastability showing an exponential dependence on time, providing further evidence that the precursor parent cluster ion is produced in a specific energy state.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3624-3627 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The temporal dependence of the metastable fractions have been measured for monomer evaporation from Ar+20, Ar+50, Ar+100, Kr+20, Kr+50, and Kr+100 ions produced by electron impact ionization of the respective neutral cluster beams. Size and temporal dependence are found to be in reasonable agreement with the predictions of the evaporative ensemble model. Small variations from the model predictions observed (in particular for the evaporation channel involving the cluster with the magic number 20) may be rationalized within this model by adjusting the appropriate parameters.
    Type of Medium: Electronic Resource
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 5213-5219 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The metastable fragmentation of the cluster ions (C4H10)nC4H+q (q=7 to 10) produced by the electron impact ionization of a neutral n-butane cluster beam has been studied with a double focusing sector field mass spectrometer. For q〉7, the usual statistical single-monomer evaporation is the only observable metastable fragmentation channel. Surprisingly, the (C4H10)nC4H+7 cluster ions were found to exhibit a more complex metastable decay pattern, involving not only the single-monomer evaporation, but also two additional fragmentation channels leading to evaporation of 2 to 4 and 4 to 7 (C4H10) monomers, respectively. After studying the dependence of the parent and the fragment ion currents on the electron energy, we concluded that the C4H+7 ionic chromophore of the (C4H10)nC4H+7 cluster ion is produced after internal H− transfer between n-C4H10 and some primary fragment ion (e.g., C2H+5, C2H+3, C3H+3, CH+3, C3H+4 ) of n-butane within the cluster. A mechanism based on the energy storage in metastable isomers of the C4H+7 chromophore ion is suggested to explain the unusual metastable fragmentation pattern of (C4H10)nC4H+7 cluster ions.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8254-8261 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Atomically clean polycrystalline gold has been bombarded by slow cluster ions (N2)+n (n≤120), Ne+n (n≤100), and Cq+60,70 (q=1–4) at kinetic energies from the apparent electron emission thresholds up to 6 kV times the cluster charge (qe). The resulting electron yields have been derived from the corresponding electron emission statistics. Grossly different electron yields were found for different cluster species of about equal masses and velocities, which is attributed to different partitions of the initial cluster kinetic energy among (a) inelastic binary collision processes involving cluster constituents and surface atoms, and (b) intramolecular vibrational excitation in the cluster ions (where possible). We found emission threshold velocities of ∼1×104 m/s, which is a lower velocity than where emission was observed in most other studies previously conducted. For (N2)+n cluster ions, clear evidence for a nonlinear behavior (i.e., increasing electron emission per cluster constituent with increasing cluster size) has been found.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8674-8679 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron impact ionization of C60 and C70 has been studied as a function of electron energy in the threshold region using a crossed molecular beam/electron beam double focusing sector field mass spectrometer system. Appearance energies have been determined (using a special threshold extrapolating procedure) for Cz+60-2m and Cz+70-2m ions with z ranging from 1 to 4 and m from 0 to 4, respectively. Whereas the different charge states of the parent ions of C60 and C70 have the same appearance energies within the experimental error bars, the fragment ions of C70 show slightly higher values than their C60 counterparts due to an increased kinetic shift. The presently deduced ionization energies for the C60 parent ions are in excellent agreement with previously reported reliable data for Cz+60 ions (previous data are available only up to z is 3). In contrast, these experimental values disagree strongly with a theoretical calculation by Yannouleas and Landman predicting an approximately linear dependence of the ionization energy on the charge state z, i.e., the experimental values deviate strongly from linearity with increasing charge.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 1528-1530 
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9624-9634 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The stability of singly charged C60+ fullerene ions, produced by electron impact ionization of C60, has been studied as a function of the electron energy and the time elapsed from ionization in a Nier-type ion source/double-focusing, sector-field mass spectrometer system. A huge kinetic shift of more than 34 eV (dependent on the observation time) was observed for the dissociation process C60+→C58++C2. The ionization efficiency curves for C58+, C56+, and C54+ fragment ions have been recorded with an energy resolution of approximately 0.5 eV. This allowed us to construct a time-resolved breakdown graph of the decaying C60+ fullerene ion. Two different methods, i.e., the finite heat bath model of Klots and the Rice–Ramsperger–Kassel–Marcus (RRKM) expression, have been used to calculate the decay rates and the breakdown graph of the C60+ ion, and the results of the calculation have been compared with the experimentally obtained breakdown graph. The best fit leads to a dissociation energy (C58+−C2) of 7.1±0.4 eV. This value is somewhat larger than the dissociation energies predicted earlier from the kinetic energy release distributions, and possible reasons for this difference are discussed in this paper. Using a quasithermochemical cycle the dissociation energy (C58−C2) of the neutral C60 molecule has been estimated to be 7.64±0.4 eV.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 24 (1992), S. 289-296 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 35.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Stoichiometric and non-stoichiometric negatively charged CO2 cluster ions have been produced in a crossed neutral cluster/electron beam ion source. The abundance and stability of these ions have been studied with a double focussing sector field mass spectrometer. The observed abundance anomalies (“magic numbers”) in the mass spectra of (CO2) n − and (CO2) n O− ions correlate with corresponding small and large metastable fractions of these ions (for loss of one CO2 unit). Variation of the measured metastable fractions as a function ofn are related to corresponding changes in the monomer binding energies. In addition, we have observed for the first time (CO2) n O 2 − ions (i.e. at electron energies above 8 eV with an energy resonance at about 14 eV) and we discuss possible production mechanisms for these ions. Relative electron attachment cross sections have been determined in the energy regime O〈E≦20 eV for (CO2) n − , (CO2) n O− and (CO2) n O 2 − withn=1 to 20. The shape of the cross section function for (CO2) n O− is strongly dependent on the cluster sizen.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 29 (1994), S. 31-37 
    ISSN: 1434-6079
    Keywords: 34.80.Dp ; 34.10.+x ; 34.80.−i
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Extending a recently developed semiclassical approach, we report the development of a formula which allows the satisfactory description and prediction of absolute electron impact ionization cross sections for K, L, and M inner-shell ionization in the energy range from threshold up to 109 eV for all elements. The present formulation also allows to derive and extend a previously noted scaling law for K-shell ionization. The present results are compared with previous theoretical and experimental determinations where available.
    Type of Medium: Electronic Resource
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