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  • 1
    Electronic Resource
    Electronic Resource
    Dynamics of unimolecular dissociation of sodium cluster ions (1989)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 90 (1989), S. 1492-1498 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigate the unimolecular dissociation dynamics of energy-rich sodium cluster ions, Na+n (5≤n≤40) by measuring the time evolution of their sequential monomer or dimer evaporative cooling. The experimental technique, tandem time-of-flight mass spectroscopy, measures the relative rate of competing dissociation channels from metastable ion clusters selected during an initial sampling time interval immediately following the creation of the ion cluster ensemble. Pulsed laser UV photoionization converts the distribution of neutral clusters emerging from a free-jet expansion to the distribution of ion clusters from which the initial selection takes place. For the smaller clusters, 3≤n≤14, we compare the measured dissociation rates with those calculated from a modified version of the RRK theory of unimolecular dissociation. In applying the theory we use monomer and dimer binding energies determined from theoretical calculation. For larger clusters, 15≤n≤40, the binding energies are not known, and we invert the calculation, using measured dissociation fractions, to determine the binding energies of the cluster ions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.456675
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  • 2
    Electronic Resource
    Electronic Resource
    Cohesive energies of K+n 5〈n〈200 from photoevaporation experiments (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 93 (1990), S. 7449-7456 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Evaporative cooling of internal energy rich potassium cluster ions K+n (5〈n〈200) is investigated within two well defined but quite different time windows. One of the time windows starts 1 μs after the photoexcitation of the cluster ions isolates one step in the evaporative cooling cascade. The experimental technique insures the complete determination of the dissociation channels. Tandem time-of-flight mass spectroscopy measures the relative rate of competing dissociation channels from ion fragmentation patterns. The corresponding neutral fragments are unambiguously determined after the reionization. Values for the dissociation energies of K+n (up to n=25) have been deduced from the unimolecular dissociation rates using statistical methods. These values are compared to Hückel calculations. The second time window starting just after the reexcitation of mass selected K+n is used to follow the steps of the photoinduced sequential evaporation from "hot'' clusters. The photofragmentation patterns for several photon energies give the atomization energies of ionized clusters up to n=200. Their evolution vs 1/R is compared to the droplet model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.459418
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  • 3
    Electronic Resource
    Electronic Resource
    Photothermodissociation of selenium clusters (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 10197-10203 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The dissociation of selenium cluster ions containing from 7 up to 30 atoms has been studied using unimolecular decay of photothermoexcited clusters. Clusters containing more than 14 atoms evaporate Se6, Se7, and Se8 species, whereas smaller clusters with 7–10 atoms dissociate manly by Se2 loss. When the size increases, Se6 becomes the predominant channel showing a dissociation which evolves toward the bulk behavior. The changes in the observed channels correlate to changes in the dissociation energies which are deduced from the measured fractional dissociation rates and from the entropy contribution. Together with the previous study of tellurium clusters, this work provides comparative behavior of dissociation energies of group VI clusters and their convergence toward bulk properties. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481661
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  • 4
    Electronic Resource
    Electronic Resource
    Optical excitation in small ionized sodium clusters: closed-shell and open-shell systems
    Amsterdam : Elsevier
    Chemical Physics Letters 189 (1992), S. 28-34 
    Details
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0009-2614(92)85148-4
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  • 5
    Electronic Resource
    Electronic Resource
    Collective excitation in closed-shell potassium cluster ions
    Amsterdam : Elsevier
    Chemical Physics Letters 164 (1989), S. 433-437 
    Details
    ISSN: 0009-2614
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
    URL: http://linkinghub.elsevier.com/retrieve/pii/0009-2614(89)85233-9
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  • 6
    Electronic Resource
    Electronic Resource
    Coulombic fission and evaporation of antimony cluster ions (1995)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 102 (1995), S. 763-769 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The preferential dissociation channels of singly and doubly charged antimony clusters have been determined from the unimolecular dissociation of energy rich cluster ions, using an ion stopping technique. It is found that singly charged Sb+n clusters with 5≤n≤80 dissociate by loss of neutral molecules. Neutral dimer loss is observed for n=5, 6, 7 whereas for n≥8, Sb+n loses Sb4. The fragmentation of doubly charged Sb++n has been investigated above the critical size n++c=24 from which doubly charged clusters are detectable in mass spectra. On the time scale of the experiment, which is 1 μs≤t≤100 μs with respect to photoionization, the delayed Coulombic fission into two singly charged clusters competes with the evaporation of Sb4. It is shown that for the smaller Sb++n clusters with 26≤n≤36 the fission to two singly charged clusters is of relatively asymmetrical character, leading to the detachment of five and seven atom cationic fragments. In larger clusters n≥40 the fission is of more symmetrical character and the difference in the fission products is less than 30%. Such a behavior totally deviates from the drop model predictions. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.469189
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  • 7
    Electronic Resource
    Electronic Resource
    Dissociation pathways and binding energies of lithium clusters from evaporation experiments (1994)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 101 (1994), S. 6992-7002 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The unimolecular dissociation of energy rich lithium cluster ions shows that Li+n dissociate by sequential atom or dimer loss. The binding energies of Li+n (n=4–42) generated in an evaporative ensemble are determined from unimolecular decay, within a well defined time window, and energy constraint. They present a sawtooth behavior vs cluster size less pronounced that it should be from a simple metal model. Odd–even alternation is superimposed on the sawtooth behavior, with odd sized cluster ions being more stable. Cohesive energies per atom of Li+n are deduced from these dissociation energies up to n=40 and from extended photo-induced measurements up to n=95. Cohesive energies per atom of neutral clusters Lin are derived by combining these ionic cohesive energies with the literature ionization potentials. The linearity of the neutral cluster cohesive energy vs the cluster surface to volume ratio permits a volume and a surface energy to be deduced. These values are compared to the bulk values.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.468326
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  • 8
    Electronic Resource
    Electronic Resource
    Thermodynamical properties of ionized lithium oxide clusters, Li2n+pO+n (1993)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 99 (1993), S. 6848-6855 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Lithium oxide clusters Li2n+pOn+ are generated by combining reactive nucleation in a gas aggregation source and photoionization. Unimolecular dissociation of mass selected cluster ions provides evidence that the excess of metal atoms evaporates first leading to the most stable species Li+(Li2O)n, which then evaporate Li2O molecules. The evaporation rate behavior as a function of cluster size demonstrates that Li+(Li2O)n can be prepared with different temperatures. It is discussed how metal evaporation from metal-rich oxide clusters leads to oxygen saturated clusters with a lower temperature. An estimate of the dissociation energies of Li+(Li2O)n are given for small sizes n≤10 from photoevaporation experiment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.465829
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  • 9
    Electronic Resource
    Electronic Resource
    Physical and chemical probes of metallic clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 1-7 
    Details
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Two different approaches for studying the electronic structure of clusters are presented. The physical probe uses the photoexcitation of size selected alkali-atom clusters. Giant resonances govern the absorption cross-section. It is due to the collective excitation of delocalized valence electrons. The behavior of the resonance up to large sizes, 900-atom clusters for potassium and 1500-atom clusters for lithium puts into evidence the failure of the jellium model for lithium. The chemical approach makes use of the nucleation process in the presence of oxygen. From the analysis of mass spectra of oxidized products, informations are gained on the valence of metallic atom in the cluster oxide. The method is applied to europium and thulium clusters. A comparison is done with the simple case of alkali clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429095
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  • 10
    Electronic Resource
    Electronic Resource
    Charge transfer between alkali cluster ions and atoms in the 1 to 10 keV collisional energy range (2000)
    Springer
    The European physical journal 12 (2000), S. 185-192 
    Details
    ISSN: 1434-6079
    Keywords: PACS. 36.40.-c Atomic and molecular clusters - 36.40.Jn Reactivity of clusters - 36.40.Cg Electronic and magnetic properties of clusters - 34.70.+e Charge transfer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract: The cross-sections for collisional charge transfer between singly charged free clusters M n + (M = Li, Na; n=1...50) and atomic targets A (cesium, potassium) have been measured as a function of collisional relative velocity in laboratory energy range 1–10 keV. For each cluster size, the experimental values of the charge transfer cross-section are fitted with an universal parametric curve with two independent parameters and vm, the maximum cross-section and the corresponding velocity. For small size clusters ( ), the characteristic parameters show strong variations with the number of atoms in the cluster. Abrupt dips observed for n=10 and n=22 are attributed to electronic properties. Charge transfer patterns observed for various collisional systems present similarities, which appear more sensitive to cluster quantum size effects than to collision energy defects. In their whole, the and vm parameters show differences in both their size evolution and their absolute values discussed in term of projectile and target electronic structures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s100530070056
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