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  • 1
    Electronic Resource
    Electronic Resource
    Magic metastable decay of singly charged argon clusters (1991)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 94 (1991), S. 810-811 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.460302
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  • 2
    Electronic Resource
    Electronic Resource
    Appearance and ionization energies of Cz+60-2m and Cz+70-2m ions (with z and m up to 4) produced by electron impact ionization of C60 and C70, respectively (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 8674-8679 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.468062
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  • 3
    Electronic Resource
    Electronic Resource
    Autoscavenging of electrons in mixed van der Waals clusters: a new approach to the spectroscopy of cluster anions (1992)
    s.l. : American Chemical Society
    The @journal of physical chemistry 〈Washington, DC〉 96 (1992), S. 1528-1530 
    Details
    Source: ACS Legacy Archives
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/j100183a006
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  • 4
    Electronic Resource
    Electronic Resource
    Near-threshold electron emission from impact of slow van der Waals clusters and fullerene ions on clean gold (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 8254-8261 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.465651
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  • 5
    Electronic Resource
    Electronic Resource
    Metastable fragmentation of (C4H10)nC4H+7 cluster ions induced by delayed isomerization reactions of C4H+7 (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 5213-5219 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.462729
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  • 6
    Electronic Resource
    Electronic Resource
    Formation of the superhalogen ion SF−7 via electron attachment to SF6 clusters (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 9241-9242 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.462236
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  • 7
    Electronic Resource
    Electronic Resource
    On the unimolecular fragmentation of C60+ fullerene ions: The comparison of measured and calculated breakdown patterns (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 98 (1993), S. 9624-9634 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.464393
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  • 8
    Electronic Resource
    Electronic Resource
    Size and temporal dependence of the metastable decay probabilities of ionized rare gas clusters (1992)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 96 (1992), S. 3624-3627 
    Details
    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
    URL: http://dx.doi.org/10.1063/1.461915
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  • 9
    Electronic Resource
    Electronic Resource
    Study of clusters by mass spectrometry (1991)
    New York, NY : Wiley-Blackwell
    Rapid Communications in Mass Spectrometry 5 (1991), S. 51-57 
    Details
    ISSN: 0951-4198
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Physics
    Notes: A review of mass spectrometric methods used to study different kinds of clusters is presented. These methods have proved to be indispensable in the cluster field owing to their great flexibility, sensitivity and wide dynamic range. This reviews presents new mass spectrometric methods and techniques such as quadrupole analysers and RF lenses, different ion-trap geometries, time-of-flight (TOF) methods including the reflectron geometry). A variety of ionization methods, both for the production of positive and negative ions, with different amounts of released excess energy, are discussed in detail. Special attention is given to different degree of post-ionization fragmentaqtion and metastability of ions produced by the respective ionization methods. The ability to follow the metastable decay processes in rather different time-windows is also one of the salient features of the mass spectrometric methods reviewed here, involving both classical and new geometries. Detection of very large cluster ions by conventional methods is not always effective, and alternative methods like post-acceleration and using a conversion dynode in front of the multiplier will be included here. Moreover, mass spectrometric methods offer the possibility of producing beams of mass-selected cluster ions necessary for the study of a whole line of process like optical spectrometry, photodetachment, photofragmentation, photoionization, electron beam ionization, and charge-exchange processes. Examples of these processes are also discussed in this review.
    Additional Material: 6 Ill.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1002/rcm.1290050115
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  • 10
    Electronic Resource
    Electronic Resource
    Absolute partial and total electron impact ionization cross sections for C3H8 from threshold up to 950 eV (1993)
    Springer
    The European physical journal 25 (1993), S. 217-226 
    Details
    ISSN: 1434-6079
    Keywords: 34.80.Gs ; 35.20.Wg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electron impact ionization of propane (C3H8) was studied using the ion beam deflection technique and a double focussing mass spectrometer in conjunction with a recently developed correction procedure that accounts for discrimination due to the initial kinetic energy of fragment ions. The relative corrected partial ionization cross sections for the production of C3H 8 + , C3H 7 + , C3H 6 + , C3H 5 + , C3H 4 + , C3H 3 + , C3H 2 + , C3H+, C 3 + ; C2H 5 + , C2H 4 + , C2H 3 + , C2H 2 + , C2H+, C 2 + ; CH 3 + , CH 2 + , CH+, C+; C3H 5 2+ , C3H 4 2+ , C3H 3 2+ and C3H 2 2+ were determined from threshold up to 950 eV. Absolute partial ionization cross sections were obtained by charge weighted summing of all the observed partial ionization cross sections and by normalizing to a recent accurate determination of the total ionization cross section at 100 eV by Djuric et al. 1991. The absolute total ionization cross section curve obtained is in excellent agreement in shape and magnitude with the low energy data (〈200 eV) of Djuric et al. 1991 and the high energy data points of Schram et al. 1966.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426883
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