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  • 1
    Electronic Resource
    Electronic Resource
    Photoionization spectroscopy of small mercury clusters in the energy range from vacuum ultraviolet to soft x ray (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 680-689 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the single and double photoionization efficiency of Hgn mass selected clusters as a function of photon energy between 30 and 110 eV for masses ranging from n=1 to 36 for the singly ionized and from n=5 to 70 for the doubly ionized clusters, using the light beam issued from a wiggler at the BESSY synchrotron. The results show in all cases a spectrum similar to the 5d→εf shape resonance previously observed in the isolated atom. In contrast, the expected 5p→6p transition allowed by hybridization of the 6s and 6p orbitals is not observed. We also compared the mass spectra of singly and doubly charged mercury clusters ionized by electron impact (30–90 eV) to those of clusters ionized by synchrotron radiation (30–70 eV). We found that the ratio Hg2+n/Hg+n was higher for photoionization at low energy and for electron impact ionization at high energy. Finally, we estimated the critical stability size of the triply charged clusters. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469180
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  • 2
    Electronic Resource
    Electronic Resource
    Electronic properties and geometric structures of Li4H and Li9H from optical absorption spectra (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 2727-2736 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Optical absorption spectra of Li4H and Li9H clusters have been recorded by depletion spectroscopy in the visible range. From comparison with ab initio calculations, geometries of both clusters are identified. The hydrogen atom assumes a peripheral position bridging two and three Li atoms in the planar and three-dimensional structures of Li4H and Li9H, respectively. Na4F and Na9F clusters are also theoretically studied and it is shown how the strong electronegativity of the F atom leads to different geometries than in lithium hydrids. Finally, the metallic character of these clusters is discussed and in both cases, the hydrogen or fluorine atom localizes one valence electron. However, the optical absorption spectra are much broader than in pure Lin and Nan clusters due to the lower symmetry. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468649
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  • 3
    Electronic Resource
    Electronic Resource
    Study of bimetallic Pd–Pt clusters in both free and supported phases (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 8574-8585 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We study PdPt bimetallic clusters in both free and supported phases. These clusters have been produced with a laser vaporization source. Free clusters directly produced by the source are studied by time of flight mass spectrometry and photofragmentation technique. We observed a sequential evaporation of Pd atoms in the mixed clusters consistent with a palladium segregation process. This tendency has been also observed on supported particles from which the structure and the composition are determined by high resolution transmission electron microscopy and energy dispersive x-ray analysis. A main result is that each particle has the composition of the massic rod vaporized in the source. The supported particles are well crystallized and exhibit truncated octahedron shapes. Experimental observations are well explained using a modified tight binding model. Indeed, within this model, we found that the equilibrium shape is strongly related to the variation of the cohesive energy with atomic coordination number. Also, some preliminary results on the specific reactivity of these bimetallic clusters are presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468847
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  • 4
    Electronic Resource
    Electronic Resource
    Photolysis experiments on SiC mixed clusters: From silicon carbide clusters to silicon-doped fullerenes (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 6927-6938 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Silicon carbon binary clusters are generated in a laser vaporization source from SixC1−x mixed targets (x=0 to 50%). We have first analyzed stoichiometric (SiC)n (n≤40) clusters grown from a silicon carbide target (x=50%). Both high fluence photoionization of (SiC)n neutral clusters and photofragmentation of size-selected (SiC)n+ natural positive ions show that silicon-doped fullerenes emerge as stable photoproducts through the laser induced annealing of these clusters. They are detected as stable species as soon as a sufficient amount of silicon is eliminated through unimolecular processes involving the sequential losses of Si2C and Si3C neutral molecules in the earliest evaporation steps. This result is in favor of an efficient substitution of silicon atoms (about 12) into stable "cagelike" carbon networks. We will also show that an efficient doping of carbon fullerenes with silicon atoms can be obtained in carbon-rich mixed clusters directly grown as positive ions from nonstoichiometric targets (x〈25%). Mass abundance spectroscopy gives a clear signature of cagelike structures where silicon atoms are substituted for carbon ones. The results on the favored stability of even-numbered C2n−qSiq+ clusters with q=0, 1, 2 are presented here in the size range: 2n=32–80. More largely doped species (q≥3) cannot be evidenced in abundance mass spectroscopy because of unavoidable mass coincidences. A careful analysis of the photofragmentation behavior of selected sizes relative to the laser fluence nevertheless succeeds in indicating the contribution to the photofragmentation spectra of largely doped heterofullerenes C2n−qSiq+ (q=7 at least) that mainly dissociate by the loss of small even-numbered mixed molecules such as Si2,Si3C,... . Both approaches are consistent with the surprising capability of substituting a large number of silicon atoms into fullerenes without destabilizing their cage structure too much. In this respect, a value close to 12 seems to be an upper limit. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478598
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  • 5
    Electronic Resource
    Electronic Resource
    Static dipole polarizability of small mixed sodium–lithium clusters (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 5568-5577 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We have measured the static dipole polarizability of Nay−xLix clusters (with y=2, 3, 4, and 8) by molecular beam deflection technique. For a given size, the polarizability of pure lithium clusters is smaller than the polarizability of pure sodium clusters. For mixed clusters, a smooth decrease in the polarizability is observed as the proportion of lithium atoms increases. For the NaLi molecule, both experimental permanent dipole and average polarizability have been obtained. Experimental results are compared to results of density functional theory and configuration interaction single and double (CISD) ab initio calculations. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478455
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  • 6
    Electronic Resource
    Electronic Resource
    Unimolecular dissociation of trivalent metal cluster ions: The size evolution of metallic bonding (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 757-771 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474374
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  • 7
    Electronic Resource
    Electronic Resource
    Dissociation pathways and binding energies of (LiH)nLi+ and (LiH)nLi+3 clusters (1996)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 104 (1996), S. 110-119 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The metastable decomposition of hydrogenated lithium cluster ions (LiH)nLi+m(m=0, 1 and 3; n≤15) is studied by using a reflectron mass spectrometer. These clusters are found to decompose by evaporation of a LiH or a Li2H2 molecule. The binding energy of these clusters are determined, using a statistical model which has been adapted to mixed clusters. Comparison with other mixed clusters suggests that (LiH)nLi+ clusters form compact cubic structure similar to pieces of a crystal lattice. For (LiH)nLi+3 clusters, the dissociation channels are more surprising, and the localization of the two excess electrons is discussed, as well as the possible existence of an energy barrier for the dissociation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.470880
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  • 8
    Electronic Resource
    Electronic Resource
    Direct measurement of the electric polarizability of isolated C60 molecules (1999)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 110 (1999), S. 9771-9772 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We present the first direct measurement of the electric polarizability of isolated C60 molecules by molecular beam deflection technique. We have obtained a value of 76.5±8.0 Å3 which is consistent with most of the recent calculations and slightly lower than the value of the polarizability of C60 measured in fullerite crystals. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.478944
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  • 9
    Electronic Resource
    Electronic Resource
    Metal-insulator segregation in lithium rich LinHm〈sup ARRANGE="STAGGER"〉 + clusters (1997)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 107 (1997), S. 2664-2672 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The metallicity of lithium rich LinHm〈sup ARRANGE="STAGGER"〉 + cluster ions [1≤m≤6, n≤22, and (n–m)〉3] is studied by measuring unimolecular dissociation rates. These clusters are found to decompose by evaporation of a Li atom or a Li2 molecule. The evaporative rates of mixed clusters display features characteristic of metallic clusters. This confirms and extends to a larger size range the previous results obtained by photoionization and absorption cross-section measurements. The simulation of the evaporative rates, with a statistical Rice–Ramsperger–Kassel (RRK) model which has been adapted to mixed clusters, confirms that there is a clear separation between a metallic Lin–m〈sup ARRANGE="STAGGER"〉 + part and an insulating (LiH)m part. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.474628
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  • 10
    Electronic Resource
    Electronic Resource
    A cylindrical reflectron time-of-flight mass spectrometer (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2312-2318 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: 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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148141
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