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  • 1
    ISSN: 1434-6079
    Keywords: 36.40 ; 07.75
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Clusters of Ar, Kr, Xe, N2, O2, CO2, SO2 and NH3 formed by supersonic nozzle expansion have been studied by electron impact ionization mass spectrometry (up to 15000 amu). Besides mass spectra of singly charged ions showing the characteristic anomalous distributions, we have in particular investigated the properties of multiply charged cluster ions. Critical appearance sizes of doubly and triply charged cluster ions, n2 and n3 respectively, found in the present study confirm recent theoretical predictions about n3/n2 and their dependence on the properties of the cluster constituents. The appearance energies of multiply charged cluster ions determined are shifted way below the appearance energies of the respective monomer ions. These huge red shifts together with the observed linear threshold laws and large maximum ionization efficiencies indicate that multiply charged cluster ions are produced by sequential single ionization events of one incoming electron at different cluster sites. Furthermore, we have also obtained for the first time clear evidence that (for electron energies above the appearance energy of doubly charged ions) an appreciable amount of singly charged (also fragment) ions is produced via Coulomb explosion of unstable doubly charged ions in the ion source.
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  • 2
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electron attachment and electron impact ionization of SF6 clusters have been investigated quantitatively in a molecular beam/electron ion source/mass spectrometer system as a function of electron energy E (0≤E≤180 eV) and as a function of cluster size.
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  • 3
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Stoichiometric and non-stoichiometric, positive and negative oxygen cluster ions (n up to 70) have been produced in a crossed neutral beam/electron beam ion source. The abundance and stability of the ions formed have been analyzed with a double focussing sector field mass spectrometer in a series of experiments. Positive and negative ion mass spectra observed exhibit distinct abundance anomalies, however, at different cluster sizes. Abundance maxima and minima correlate with correspondingly small and large metastable fractions of (O2) n + and (O2) n − ions, respectively. (O2) n + ions may also lose up top=(n−1) monomers by collision induced dissociation with monotonously decreasing probability with increasingp. Metastable fractions determined for (O2) n − ions produced with appr. zero eV electrons are in general larger than those for ions produced with appr. 7 eV electrons. (O2) n − ions are also observed to decay via autodetachment, with lifetimes increasing with increasing cluster size. Finally, here we were able to prove that an apparent loss of the monomer fragment O (and higher homologues) observed in the metastable time regime is due to ordinary metastable monomer evaporation in the acceleration region. Moreover, we will also present here some new data and interpretation concerning the electron attachment cross section function for O2 clusters.
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  • 4
    ISSN: 1434-6079
    Keywords: 33.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have observed strong photodissociation (using visible laser light) of neutral van der Waals clusters (Ar, N2, O2, CO2, SO2, NH3) produced by supersonic expansion and detected by electron ionization/mass spectrometer. Several tests were performed, all of them supporting this surprising discovery. We suggest that Raman induced photodissociation (RIP) is responsible for this phenomenon. This first observation of Raman induced photodissociation provides a new technique for the study of neutral van der Waals clusters.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 26 (1993), S. 210-212 
    ISSN: 1434-6079
    Keywords: 36.40 +d ; 35.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mixed ionized clusters have been produced in a supersonic nozzle beam experiment by attachment of stagnant cations (i.e. NO+ and Xe+) to neutral van der Waals clusters (i.e.Ar n ) within a Nier type ion source. This new ionization technique leads to less fragmentation than electron impact ionization and the measured cluster distributions exhibit icosahedral shell and subshell closures which have not been detected in the case of electron impact of Ar n -clusters ionization so far. Additionally, the obtained appearance energies and metastable fractions give insight into the production mechanism and the stability of the resulting ions.
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  • 6
    ISSN: 1434-6079
    Keywords: PACS: 36.40.Qv Stability and fragmentation of clusters – 81.05.Tp Fullerenes and related materials; diamonds, graphite
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: 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 C2 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.
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  • 7
    ISSN: 1434-6079
    Keywords: PACS: 36.40.-c Atomic and molecular clusters – 34.80.Lx Electron–ion recombination and electron attachment
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract. The formation of both positively and negatively charged ions after interaction of electrons with different cluster beams is investigated, by the use of highly monochomatized electron beams. In the case of the electron attachment to neutral NO clusters, the formation of the monomer ion NO- could be observed for the first time. The only explanation for the creation of such an ion is an intracluster reaction. In the case of carbon monoxide clusters, the appearance energies were determined with high accuracy. From these data, we derived the binding energy of the cluster dimer. Our results are in good agreement with photoionization studies.
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  • 8
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The formation of fragment ions from C60 due to electron impact ionization leading to a bimodal fragmentation pattern with a minimum around the cluster size of 30 is investigated with help of mass spectrometric techniques. Based on a detailed analysis of the energetics and kinetics of the singly- and multiply-charged fragment ions by two-sector field mass spectrometry (MIKE-scans) we can conclude that on the one hand some of the dissociation reactions proceed via evaporation of an intact C6 + or C4 + unit (and not via the sequential loss of smaller molecular carbon units). On the other hand, measured appearance energies and the direct observation of sequential C2-loss reactions confirm that the sequential loss of neutral C2 units is the dominant production mechanism for Cn z+ fragment ions with sizes 40 〈 n 〈 60.
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  • 9
    ISSN: 1572-9540
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Highly-charged fullerene ions C 60 z+ and C 70 z+ with charge states up to z=7 have been produced in an electron impact ion source of a two sector field mass spectrometer by using ion source operating conditions similar to those used in EBIT sources. The stability of these ions was investigated quantitatively in the two field free regions of the mass spectrometer. It was found that besides C2 evaporation the dominant fission process for ions with charges larger than +2 is the loss of a charged C 2 + unit via a super-asymmetric charge separation reaction C 60 z+ → C 58 (z−1)+ +C 2 + and C 70 z+ → C 68 (z−1)+ +C 2 + , respectively. The most important finding from these studies is that this super-asymmetric dissociation reaction proceeds via a three stage reaction sequence involving an electron transfer reaction at the second stage between a receding C2 unit and the remaining highly-charged fullerene cage.
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  • 10
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract N2 cluster ions are produced by electron impact ionization of a supersonic N2 cluster beam and analyzed with a double focussing sector field mass spectrometer. It is found that metastable N2 cluster ions lose more than one N2 molecule in the μs time regime and decay predominantly via sequential series (N2) n + *→(N2) n−1 + *→...→N 2 + , evaporating a single monomer in each of these successive decay steps. The metastable decay rates determined in detail for cluster sizes 2≤n≤6 andn=20 lie between 1 and 106s−1. These rates(i) depend strongly on the time elapsed after ion formation and on the respective parent cluster ion size, and(ii) exhibit a quasiperiodic pattern in magnitude.
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