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  • 1
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 8459-8466 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The electronic and geometric properties of gas-phase exohedral C60NaN−, C70NaN−, and C60AuN− cluster anions are investigated. Time-of-flight mass spectrometry and photoelectron spectroscopy (PES) reveal complex-specific arrangements of the sodium and the gold atoms on the fullerene cage. The electron affinity of C60AuN clearly shows even–odd alternation with the number of Au atoms, which suggests a "dry" structure where Au atoms aggregate as a cluster on the C60. In contrast, C60NaN and C70NaN show a "wet" structure having the Na atoms packed into stable trimers on the surface. For C60NaN (N=0 to 4), PES experiments at a high photodetachment energy (5.81 eV) allow us to deduce the net charge transferred from the sodium atoms to the lowest unoccupied molecular orbital of the fullerene. For larger C60NaN, moreover, a metallic transition is shown to occur at N∼13, and analysis of the adiabatic electron affinity variations allows the identification of the first magic sizes corresponding to electronic shell closure in the sodium layer. © 2001 American Institute of Physics.
    Materialart: Digitale Medien
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  • 2
    Digitale Medien
    Digitale Medien
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 757-771 
    ISSN: 1089-7690
    Quelle: AIP Digital Archive
    Thema: Physik , Chemie und Pharmazie
    Notizen: The unimolecular decomposition of size selected cluster cations of trivalent metals (Aln+, Gan+, and Inn+), induced by high fluence laser ionization, has been investigated in the n=7 to n=85, 55, and 75 size ranges, respectively. This method is applied for the first time to photoexcited trivalent clusters generated in an evaporative ensemble and the experimental data cover a size range that was not explored in previous pioneering experiments on their dynamics. Small clusters dissociate through the loss of a neutral or a charged atom whereas clusters larger than a well defined critical size merely dissociate through the first channel. In the framework of the RRK statistical theory, the measured evaporation rates provide some information about the size evolution of the cluster dissociation energies and their ionization potentials in the low size range. The competition between the ion and the atom evaporation is found to be consistent with the size evolution of the ionization potentials independently measured by direct photoionization. The agreement between theory and experiment is discussed in relation to cluster structure, especially in the case of gallium. © 1997 American Institute of Physics.
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  • 3
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2312-2318 
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A new reflectron time-of-flight mass spectrometer with a cylindrical electrostatic mirror instead of the usual plane reflector is described. When it is mounted at right angles to the direction of an incoming molecular beam, this system automatically compensates for the transverse drift of the ions in the spectrometer due to their initial velocity parallel to the molecular beam direction. As a consequence, ions of any mass can be collected onto the detector, whatever their initial transverse velocity is. The mass range accessible in a single scan with our cylindrical reflectron is thus strongly increased as compared to the case of a usual plane reflectron. This article presents the general design of our cylindrical reflectron. A detailed description of the apparatus is given and its performances are illustrated on selected examples. Cluster mass spectra extending over a very wide size range are presented. A mass resolution of about 4000 is achieved in mass spectra of laser photoionized aluminum clusters. Moreover, the cylindrical geometry of the reflector gives rise to focusing properties onto the detector, which could be interesting in view of collection efficiency improvement. © 1997 American Institute of Physics.
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  • 4
    Digitale Medien
    Digitale Medien
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 84 (1998), S. 4532-4536 
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The second order nonlinear response from 4 nm diam gold clusters embedded in an alumina matrix deposited on a pure silica substrate has been recorded as a function of the wavelength of the fundamental incident beam. The spectrum exhibits a narrow resonance band peaked at 520 nm as a result of the coupling of the second harmonic field with the surface plasmon of the particles. The nonlinear second harmonic response of gold clusters is found to be blueshifted compared to the bulk, due to the finite size effects on the cluster optical properties, as already observed with the linear response. Furthermore, this nonlinear response appears to be well described with a simple free electron model where the valence electrons only participate through the screening of the ionic cores, owing to the weakness of the interband transition contribution. © 1998 American Institute of Physics.
    Materialart: Digitale Medien
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  • 5
    Digitale Medien
    Digitale Medien
    Springer
    The European physical journal 9 (1999), S. 585-589 
    ISSN: 1434-6079
    Schlagwort(e): PACS: 36.40.-c Atomic and molecular clusters – 36.20.Ng Vibrational and rotational structure, infrared and Raman spectra – 63.20.Pw Localized modes
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract. Absorption and low-frequency Raman scattering experiments have been performed on thin films consisting of small silver clusters embedded in a porous alumina matrix. When the Raman excitation wavelength is close to the maximum (≈420 nm) of the Mie band (dipolar surface plasmon resonance) the Raman spectra exhibit a strong band located around 10 cm-1, the maximum of which depends on the mean cluster diameter 〈D〉 in the sample according to the approximate law ωvib∝〈D〉-1. The Raman band corresponds to the excitation of the quadrupolar vibration mode of the clusters. Moreover, the maximum of the Raman band shifts towards lower frequencies when the excitation light is shifted to the red. This feature, as well as the rather large Mie-band width, is thought to reflect the ellipsoidal shape distribution of part of the embedded clusters.
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  • 6
    ISSN: 1434-6079
    Schlagwort(e): PACS. 36.40.-c Atomic and molecular clusters[:AND:] 71.45.-d Collective effects - 71.45.Gm Exchange, correlation, dielectric and magnetic functions, plasmons
    Quelle: Springer Online Journal Archives 1860-2000
    Thema: Physik
    Notizen: Abstract: The optical response of free and matrix-embedded gold metal clusters AuN is investigated in the framework of the time-dependent local-density-approximation (TDLDA). The characteristics of the surface plasmon resonance are carefully analyzed as a function of the model parameters and the particle radius. The strong influence of the frequency-dependence of the 5d core-electron dielectric function in the vicinity of the interband threshold is emphasized. The size evolution of the Mie-frequency in free gold clusters exhibits a noticeable blue-shift trend as the particle size decreases, much stronger than in silver clusters. The width and shape of the resonance, essentially ruled by the decay via the interband transitions, are found closely correlated to the imaginary component of the core-electron dielectric function. In presence of a surrounding matrix the blue-shift trend is largely rubbed out. Agreement with recent experimental results on size-selected gold clusters embedded in an alumina matrix may be achieved by taking into account the porosity effects at the metal/matrix interface. The comparison with the predictions of classical models is also provided.
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