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  • 1
    Electronic Resource
    Electronic Resource
    Production and appearance size of multiply charged stoichiometric and nonstoichiometric SO2 cluster ions (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1288-1289 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report the first well resolved SO2 cluster ion spectrum showing doubly charged parent and fragment ions. The critical appearance size deduced for doubly charged SO2 clusters is n2=21 and for triply charged SO2 clusters n3=49. This result is compared with theoretical predictions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456135
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  • 2
    Electronic Resource
    Electronic Resource
    Production and properties of singly and multiply charged Kr clusters (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3240-3245 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Kr clusters produced in a supersonic nozzle expansion have been studied by electron impact ionization mass spectrometry. Mass resolved spectra (with n up to 180) show two homologous series consisting of Kr+n and Kr2+n ions. The distribution of Kr+n ions shows distinct magic number effects, the observed abundance anomalies being very similar to the ones observed in Ar and Xe. This confirms the superior stability of closed-shell and -subshell icosahedral structures. Moreover, we have found evidence for the occurrence of Kr3+n and Kr4+n ions. It was possible to determine appearance sizes of these multiply charged cluster ions (yielding n2=69, n3=156, and n4=264), and to study the electron energy dependence of singly and doubly charged cluster ions (yielding a linear threshold law). These results are discussed in view of various theoretical considerations and previous results where available.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456898
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  • 3
    Electronic Resource
    Electronic Resource
    Critical appearance size of doubly charged Xe clusters revisited (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4091-4094 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: In previous experiments on doubly charged Xe clusters, no Xe2+n cluster ions were observed for n less than 53 atoms and no Xe3+n for n less than 114 atoms. From recent computer simulations it was inferred that Xe2+51 ions have lifetimes ∼100 ps while Xe2+55 ions have lifetimes ∼10 μs in agreement with these previous experimental results. Using a high performance mass spectrometer we have repeated these experiments. In contrast to these earlier findings, we are here able to observe doubly charged Xe cluster ions with sizes down to n2=47 (at lifetimes of ∼400 μs). The critical appearance size for triply charged Xe clusters is n3=108. In accordance with a recently suggested sequential ionization mechanism for the production of stable doubly charged van der Waals cluster ions, the appearance energy of Xe2+n was found to lie well below the appearance energy of Xe2+ from Xe.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455766
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamics and kinetics of the metastable decay series: Ar3+*→Ar2+*→Ar+ (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 295-301 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Metastable decay of Ar+@B|3 produced by electron impact ionization of a supersonic Ar cluster beam has been investigated qualitatively and quantitatively with a double focusing sector field mass spectrometer. We present direct experimental proof that the observed metastable decay of Ar+*3 into Ar+ in the microsecond time regime proceeds predominantly via a sequential decay series Ar+@B|3→k3,2Ar+*2→ k2,1Ar+ involving the evaporation of a single monomer in each of these successive decays. The metastable decay rates deduced are very different, i.e., k3,2 =45 s−1 and k2,1 =680 s−1 at an ion acceleration voltage of 3 kV. Moreover, the metastable decay rates of Ar+@B|3 exhibit a strong dependence on time elapsed since electron impact production of the Ar+3, and on ion production parameters (i.e., size and internal excitation energy of the neutral precursor). For instance photodissociation (with visible laser light) of the neutral cluster beam leads to a dramatic increase of the observed metastable reaction rules yielding values of up to 100 000 3−1 in the μs time regime.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.455469
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  • 5
    Electronic Resource
    Electronic Resource
    Production and properties of singly, doubly, and triply charged N2 clusters (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4289-4293 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Clusters of N2 molecules formed in a supersonic nozzle expansion have been studied by electron impact ionization mass spectrometry. Mass resolved spectra (with n up to 190) show three homologous series, i.e., consisting of (N2)+n, (N2)nN+, and [(N2)n N]2+ ions. The distribution of (N2)+n ions shows distinct magic number effects. Moreover, there is evidence for the existence of (N2)2+n and (N2)3+n ions. The critical appearance sizes of observed multiply charged cluster ions are (N2)2+99, (N2)99N2+, and (N2)3+215. These results are compared with theoretical predictions. Moreover, a study of the electron energy dependence of singly and doubly charged N2 cluster ions close to threshold (appearance energies) gives new insight into the ionization mechanism.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453787
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  • 6
    Electronic Resource
    Electronic Resource
    Absolute partial and total cross-section functions for the electron impact ionization of C60 and C70 (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 105 (1996), S. 1880-1896 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron impact ionization of C60 and C70 was studied using a molecular/electron beam ion source in combination with a two sector field mass spectrometer operated in the ion beam deflection mode. Relative partial ionization cross sections for the production of singly and multiply charged parent ions (up to charge state z=4) and fragment ions (down to C+44 in the case of C60 and down to C2+50 in the case of C70) were determined from threshold up to 1000 eV electron energy. Absolute partial and total ionization cross sections are obtained using a novel approach for the absolute calibration involving an intercomparison of the cation with the anion yield. The results obtained reveal not only an anomalous large parent ion cross section as compared to other ionization channels [e.g., σ(C+60/C60) is more than a factor of 30 larger than σ(C+58/C60)] but also anomalies for the production of multiply charged parent and fragment ions. For instance, the maximum cross section for the formation of C2+60 amounts to 30% of the maximum C+60 cross section and that of C2+70 to about 50% of C+70. Moreover, for all fragment ions, the formation of the doubly charged fragment ions has a larger cross section than that of the respective singly charged fragment ion. These peculiar features of the kinetics of electron impact ionization of C60 and C70 are related to the specific electronic and geometric structures of these fullerenes. The present absolute cross-section data for the summed up partial cross sections are in good agreement with a recent semiclassical calculation from our laboratory. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.472059
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  • 7
    Electronic Resource
    Electronic Resource
    Kinetic energy release in electron-induced decay reactions of molecular ions: C3H8+ and C3H7+ (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 113 (2000), S. 616-620 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the kinetic energy release (KER) distributions for electron-induced dissociation of mass-selected molecular parent and fragment ions of propane. They are compared with distributions determined for spontaneous (metastable) dissociation. The average KER for induced dissociation of C3H8+ into C3H7+ is 13.2±1.2 meV, about 42% larger than for the spontaneous reaction. This large difference is attributed to the dramatically reduced time at which the induced reaction can be sampled. In contrast, the KER for dissociation of C3H7+ into C3H5+, which is characterized by a large reverse activation energy, is hardly affected by the experimental time scale. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481837
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  • 8
    Electronic Resource
    Electronic Resource
    Electron attachment and electron impact ionization of SF6 and SF6/Ar clusters (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6884-6888 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron attachment and electron impact ionization of SF6 and SF6/Ar clusters have been investigated in a molecular beam/electron impact ion source/mass spectrometer system. Positive ion mass spectra of neat SF6 clusters contain [(SF6)n⋅SFx]+ fragment ion series with 0≤x≤5 and in addition [(SF6)nS2F5]+ ions which have to be formed via international ion molecule reactions. Positive ion mass spectra of mixed SF6/Ar clusters include ion series of nonstoichiometric fragment ions (SF5⋅Arn)+, (SF6⋅SF5⋅Arn)+, [(SF6)2⋅SF5⋅Arn]+, and, in addition, stoichiometric ions comprised of (SF6⋅Arn)+ and [(SF6)2Arn]+. These stoichiometric ions are only present with n≥3. Electron attachment to neat SF6 clusters gives rise only to stoichiometric (SF6)−n ions, whereas attachment to mixed SF6/Ar clusters yields ion series consisting of (ArnSF6)−, [Arn(SF6)2]−, and [Arn⋅(SF6)3]−. This indicates that the dissociative channel into SF−5 present in the monomer is efficiently quenched in case of clusters. The negative ion mass spectra show in contrast to the positive ion mass spectra a strong dependence on electron energy due to a strong resonance of the attachment cross sections near zero electron energy.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454385
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  • 9
    Electronic Resource
    Electronic Resource
    Electron attachment to oxygen clusters studied with high energy resolution (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 111 (1999), S. 3548-3558 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Highly monochromatized electrons (with energy distributions of less than 30 meV FWHM) are used in a crossed beam experiments to investigate electron attachment to oxygen clusters (O2)n at electron energies from approximately zero eV up to several eV. At energies close to zero the attachment cross section for the reaction (O2)n+e→(O2)m− (for m=1, 2, and 3) rises strongly with decreasing electron energy compatible with s-wave electron capture to (O2)n. Peaks in the oxygen attachment cross sections present at higher energies ((approximate)80 meV, 193 meV, 302 meV) can be ascribed to vibrational levels of the anion populated by attachment of an electron to a single oxygen molecule within the target cluster via a direct Franck–Condon transition from the ground vibrational state v=0 to a vibrational excited state v′=7,8,9,... of the anion produced. The vibrational structures observed here for the first time can be quantitatively accounted for by model calculations using a microscopic model to examine the attachment of an electron to an oxygen molecule inside a cluster. This involves (i) molecular dynamics simulations to calculate the structure of neutral clusters prior to the attachment process and (ii) calculation of the solvation energy of an oxygen anion in the cluster from the electrostatic polarization of the molecules of the cluster. The occurrence of this polarization energy at the surface of larger clusters explains the appearance of an s-wave capturing cross section at 0 eV and the slightly smaller spacings (compared to the monomer case) between the peaks at finite energy, as observed experimentally. The relative transition probabilities from the ground state of the neutral oxygen molecule to the different vibrational levels of the anion are obtained by calculating the corresponding Franck–Condon factors thereby resulting in a reasonable theoretical fit to the observed yields of negatively charged oxygen molecules and clusters. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.479637
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  • 10
    Electronic Resource
    Electronic Resource
    Dissociative electron attachment cross section to CHCl3 using a high resolution crossed beams technique (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 8955-8962 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Using a crossed electron-molecule beam ion source in combination with a quadrupole mass spectrometer we have studied the electron energy dependence of the dissociative attachment process CHCl3+e→Cl− at electron energies from about 0 to 2 eV and in a target gas temperature range of about 300–430 K. The energy resolution and working conditions of this newly constructed crossed beams machine have been characterized using CCl4 as a test and calbrant gas. Utilizing the improved energy resolution of the present experimental setup (which allows measurements with FWHM energy spreads down to below 5 meV) it was possible to determine the accurate shape and magnitude of the cross section function in the low-energy range. This leads to the conclusion that between an electron energy of about 20 and 130 meV the reaction proceeds via deBroglie s-wave capture, whereas at higher energy (above about 0.4 eV) autodetachment plays a significant role. Moreover, the present measurements allow us to clarify previously reported differences in the absolute cross section, the number of peaks and in the energy position of these peaks. Finally, by analyzing the measured strong temperature dependence of the cross section close to zero electron energy the activation barrier for this dissociative attachment was determined to be 110±20 meV in good agreement with thermochemical data from swarm experiments performed under thermal equilibrium. Taking into account the present results it is also possible to discuss the mechanism for the existence of the second peak. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.475187
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