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  • 1
    Electronic Resource
    Electronic Resource
    Multiply charged cluster ions of Ar, Kr, Xe, N2, O2, CO2, SO2 and NH3: Production mechanism, appearance size and appearance energy (1989)
    Springer
    The European physical journal 12 (1989), S. 279-281 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426955
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  • 2
    Electronic Resource
    Electronic Resource
    Observation and investigation of metastable decay series of (N2) n + cluster ions (1989)
    Springer
    The European physical journal 12 (1989), S. 285-287 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426957
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  • 3
    Electronic Resource
    Electronic Resource
    Interactions of electrons with SF6: ionization and attachment (1989)
    Springer
    The European physical journal 12 (1989), S. 303-305 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426962
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  • 4
    Electronic Resource
    Electronic Resource
    Production and stability of oxygen cluster cations and anions, revisited (1991)
    Springer
    The European physical journal 20 (1991), S. 201-203 
    Details
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01543973
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  • 5
    Electronic Resource
    Electronic Resource
    Metastable decay of Ar n + involving single monomer evaporation and the loss of peculiar numbers of monomers (1991)
    Springer
    The European physical journal 20 (1991), S. 157-159 
    Details
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Production and stability of Ar n +* ions (withn up to 420) formed by electron impact ionization of a supersonic Ar cluster beam were investigated with a double focussing sector field mass spectrometer. The present study confirms previous magic number determinations up to the 4th icosahedral shell. A systematic study of metastable dissociations (monomer evaporation, magic number evaporation) for singly charged cluster ions as a function of cluster size, internal excitation energy and time elapsed since ion formation gives new insight into the ionization process and subsequent reactions of the ions formed. At a well-defined threshold energy ofca. 28 eV, the magic number loss mechanism occurs simultaneously with the well known single monomer evaporation process which proceeds at all energies. 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/10.1007/BF01543962
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  • 6
    Electronic Resource
    Electronic Resource
    Metastable decay of rare gas cluster ions: mechanism and kinetics (1989)
    Springer
    The European physical journal 12 (1989), S. 263-267 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Metastable decay of cluster ions has been discovered only recently. It was noted that one has to take this metastable decay into account when using mass spectrometry to probe neutral clusters, because ion abundance anomalies in mass spectra of rare gas and molecular clusters are caused by delayed metastable evaporation of monomers following ion production. Moreover, it was found that(i) the individual metastable reaction rates k depend strongly on cluster size and cluster ion production pathways and that(ii) there exists experimental evidence (k=k(t)) and a theoretical prediction that a given mass selected cluster ion generated by electron impact ionization of a nozzle expansion beam will comprise a range of metastable decay rates. In addition, it was discovered that metastable Ar cluster ions which lose two monomers in the μs time regime decay via sequential decay series Ar n + *→Ar n−1 + *→Ar n−2 + * with cluster sizes 7≤n≤10 andn=3 (similar results were obtained recently in case of N2 cluster ions). Conversely, the dominant metastable decay channel of Ar 4 + * into Ar 2 + was found to proceed predominantly via a single step fissioning process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426951
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  • 7
    Electronic Resource
    Electronic Resource
    Investigations on processes induced by single- and multiple-scattering of electrons in clusters involving excimer-induced fragmentation and a new metastable fragmentation channel observed for ArnO+* cluster ions (1993)
    Springer
    The European physical journal 26 (1993), S. 335-337 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 33.40.Hp ; 32.30.Bv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new metastable decay reaction of ArnO+ cluster ions produced by the electron impact ionization of argonoxygen clusters has been discovered, leading to the evaporation of more than two monomers in the metastable time regime. It is estimated that an energy of approx. 1 eV has to be released from the intramolecular to intermolecular modes prior to this metastable decay. In contrast to previously observed excimer-induced fragmentation of pure argon cluster ions, it has been concluded that the localized metastable state of an ionic rather than a neutral species is involved in the fragmentation. A reaction mechanism involving an electronic transition from the a2Π ArO+* (O(3P)-Ar+(2P)) excited state to the X4Σ− ArO+ (O+(4S)-Ar(1S)) ground state of the ArO+ complex ion within the cluster and subsequent release of considerable amount of vibrational energy to cluster modes is suggested to account for the observed fragmentation. Based on these measurements, a lifetime of approx. 2 µsis proposed for the excited state a2Π ArO+*.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01425708
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  • 8
    Electronic Resource
    Electronic Resource
    Electron attachment to SO2 clusters (1987)
    Springer
    The European physical journal 6 (1987), S. 351-362 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electron attachment to SO2 clusters formed by nozzle expansion was investigated (n up to 8) in a molecular-beam electron-ionization mass-spectrometer system. Electron ionization of SO2 clusters was also studied (n up to 18) showing no pronounced structure in the mass spectra and no strong dependence on electron energy, the dominant positive ion being the (SO2) n + series. Also present but less abundant are the fragment ion series (SO2) n SO+, (SO2) n S+ and (SO2) n O+ with decreasing intensities in that order. The dominant negative ion is (SO2) n − . The homologous series (SO2) n O− and (SO2) n SO− are less abundant, the series (SO2) n S− has not been observed at all (except SO2·S− produced in the background gas via secondary processes). The negative ion mass spectra show a strong dependence on electron energy due to a rich resonance like structure of the attachment cross sections involved. These attachment cross sections have been determined (up to 40 eV) and they show significant differences for the different homologous series. The most striking feature is that for instance (SO2) n SO− ions do not show any signal at the first main resonance of SO− from SO2. Likewise (SO2) n O− ions only show a strongly diminished signal at the first main resonance of O− from SO2. This is in contrast to results in O2, CO2 and N2O. Conversely, (SO2) n − ions show — besides peaks at the position of the first and second O− resonance — additional resonances below and above these peaks. In addition, (SO2) 5 − and larger ones show a zero energy peak consisting of stoichiometric SO2 cluster ions similar to observations in O2, CO2 and H2O. The attachment cross section of S− from SO2 has been found to show an additional previously undetected peak at ∼1 eV. Moreover, the present study revealed the existence of a S n − (n up to 8) series being produced with nearly zero energy electrons via volume and surface processes in and around the ion source.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437062
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