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  • Electronic Resource  (14)
  • 1985-1989  (12)
  • 1970-1974  (2)
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  • Electronic Resource  (14)
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  • 1
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1288-1289 
    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
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  • 2
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 91 (1989), S. 3240-3245 
    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
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  • 3
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 4091-4094 
    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
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  • 4
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 89 (1988), S. 295-301 
    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
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  • 5
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 4289-4293 
    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
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  • 6
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 6884-6888 
    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
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  • 7
    Electronic Resource
    Electronic Resource
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 83 (1985), S. 2942-2946 
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Electron attachment to CO2 clusters formed by nozzle expansion was investigated in a crossed molecular-beam–electron-impact–mass spectrometer system. In addition to cluster ions previously observed at 3–4 eV electron energy we observe presently cluster ions produced at around zero electron energy. Some of these ions are likely produced by a less dissociative production mechanism allowing the probing of cluster beams with better reliability than previously.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of neurology 198 (1970), S. 256-279 
    ISSN: 1432-1459
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Description / Table of Contents: Zusammenfassung Unter den bisher erschienenen Mitteilungen über cerebrale Anfälle als besonderes Symptom der Multiplen Sklerose (MS) werden 70 Kasuistiken ausgewertet, bei denen der Zusammenhang gesichert erschien. 19 eigene Beobachtungen aus einer Zahl von insgesamt mehr als 4000 Patienten mit MS werden dieser Gruppe gegenübergestellt. Es ergibt sich, daß nach dem klinischen Anfallstyp in 40% primär generalisierte, gewöhnlich tonisch-klonisch ablaufende Iktus vorkommen. Unter den übrigen Anfallstypen (60%), die durch Herderscheinungen eingeleitet werden oder herdförmig bleiben, überwiegen die mit rein motorischen Erscheinungen. In diesen Fällen kann ein Herd in oder nahe der Präzentralregion vermutet werden. Sie machen einen Anteil von 25% am Gesamtmaterial aus. Die Zuordnung der epileptogenen Herde zu den verschiedenen Hirnabschnitten an Hand des vorliegenden MS-Materials spiegelt in der Häufigkeitsverteilung weitgehend die bekannte Disposition der Rindenareale zur Ausbildung epileptogener Foci wider. Die Gesamthäufigkeit cerebraler Anfälle bei der MS liegt nach den Mitteilungen der Literatur zwischen 1 und 6%. Berechnungen am eigenen Krankengut der Würzburger wie der Göttinger Neurologischen Universitätskliniken nach kritischer Sichtung und Ausscheidung aller nicht gesicherten oder wahrscheinlich zu machenden Fälle ergaben jedoch nur 0,5–0,6%. Beide Umstände zeigen, daß sich die MS wohl nicht im Sinne einer spezifischen epileptogenen Noxe auswirkt. Die Frage nach der Lage der epileptogenen Läsionen in Beziehung zu corticalen Strukturen wird diskutiert. Abschließend wird kurz auf die EEG-Befunde eingegangen.
    Notes: Summary From the communications hitherto reported on cerebral attacks as a particular feature of multiple sclerosis (MS) 70 case histories with an apparently proven relationship were evaluated. The observations in 19 own cases from a total number of 4000 patients with MS are compared to this group. It was found that according to the clinical type of seizure primarily generalized usually tonic-clonic attacks occurred in 40%. Among the other types of seizures (60%) which begin with focal symptoms or remain localized, those with strictly motor symptoms prevail. A focus within or near the precentral region may be presumed to exist in these cases. They comprise 25% of the entire group. The association of the epileptogenic foci with the various brain areas as illustrated by the present cases of MS and the frequency distribution reflect to a large measure the well known predisposition of cortical areas to form epileptogenic foci. The total incidence of cerebral attacks in MS varies between 1 and 6% according to the literature. Computations based on the patients of our own seen at the neurological departments of the universities of Würzburg and Göttingen yielded 0.5 to 0.6% only after all cases were critically reviewed and rejected if not or only partially fufilling our criteria. Both of these observations demonstrate that MS might not act in terms of a specific epileptogenic noxa. The localization of epileptogenic lesions in relation to cortical structures is discussed. In conclusion, EEG findings are briefly mentioned.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Journal of thermal analysis and calorimetry 4 (1972), S. 479-482 
    ISSN: 1572-8943
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract A simple method is described for use with the differential scanning calorimeter for baseline interpolation in continual processes over a wide temperature interval. For the process of water desorption from the synthetic zeolite LiA with the coveragegq=1.5, the measured heat of desorption wasQ=11.2±0.5 kcal/mole.
    Type of Medium: Electronic Resource
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  • 10
    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.
    Type of Medium: Electronic Resource
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