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  • Articles  (108)
  • 36.40  (108)
  • Springer  (108)
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  • Physics  (108)
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  • Springer  (108)
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  • Physics  (108)
  • 1
    Electronic Resource
    Electronic Resource
    Stability and structure of singly-charged argon clusters Ar n + ,n=3–27. A Monte-Carlo simulation (1989)
    Springer
    The European physical journal 11 (1989), S. 239-248 
    Details
    ISSN: 1434-6079
    Keywords: 31.20.T ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Monte-Carlo calculations have been performed for positively charged argon clusters in the temperature range between 10 K and 40 K using two different models (one with a dimer ion core, the other one with a trimer ion). The argon-argon interaction potential stems from empirical data, the ion-neutral atoms potential is determined by ab initio MRD-CI calculations. Special stability is found for clusters sizesn=13, 19, 23 and 25/26 atoms using the ‘trimeric core model’ and for those withn=14,n=17,n=20 using the ‘dimeric core model’. The geometrical structure of the clusters is given and the construction principles are discussed in light of the interactions among neutral argon atoms and the ion-neutral atoms interaction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01438010
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  • 2
    Electronic Resource
    Electronic Resource
    Stability of relaxed Lennard-Jones models made of 500 to 6000 atoms (1989)
    Springer
    The European physical journal 12 (1989), S. 85-87 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 61.55
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present a study of the stability of clusters models made of a numberN of atoms in the range 500 to 6000 atoms, freely interacting through the Lennard-Jones potential. The potential energy per atom, calculated for relaxed models, shows that stable models belong to an icosahedral sequence whenN〈1600 and to a decahedral sequence beyond. A coexistence size range of both structures is discussed in connection with experimental results on argon clusters in free jet expansions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426911
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  • 3
    Electronic Resource
    Electronic Resource
    Dynamic and quantum size effects in molecular clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 167-171 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 64.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The evolution of thermodynamic, dynamic and quantum size effects in clusters is expected to contribute towards the merging between microscopic and macroscopic points of view in molecular, surface and bulk phenomena.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426930
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  • 4
    Electronic Resource
    Electronic Resource
    Metal-insulator transitions in microclusters? Mixed sodium/sodium chloride aggregates (1989)
    Springer
    The European physical journal 12 (1989), S. 241-244 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80.E ; 34.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photoionization measurements on cluster beams obtained by coexpanding sodium and sodium chloride vapors allow inferences regarding the thermodynamic stability of a number of mixed metal/salt aggregates. We discuss the possibility of observing composition dependent metal/insulator transitions among clusters with a fixed number of monomer units.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426947
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  • 5
    Electronic Resource
    Electronic Resource
    Chemisorption and chemical reactions on size selected clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 551-554 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.50 ; L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Low energy ion beam techniques have been used to perform a detailed study of the reactions of Al 25 + and Si 25 + with a range of simple molecules (D2, CH4, O2, C2H4, CO and N2). The reactions were studied over a center of mass collision energy range from 0.2eV up to 7eV. Activation barriers for chemisorption onto the clusters were deduced from the experimental results. The activation barriers for chemisorption on Al 25 + and Si 25 + are generally similar and show a qualitative correlation with the electronic properties of the reactant molecule. However, the products of the chemical reactions of Al 25 + and Si 25 + which result from cluster fragmentation are quite different. Si 25 + shows a tendency to undergo fission as observed in a number of recent studies of the dissociation of the bare clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01427016
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  • 6
    Electronic Resource
    Electronic Resource
    Structure of Ag, Fe and Ge microclusters (1989)
    Springer
    The European physical journal 12 (1989), S. 103-105 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 78.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The structures of Ag, Fe and Ge microclusters were determined using EXAFS. The measurements were performed over a wide range of clusters sizes. The clusters were prepared using the gas aggregation technique and isolated in solid argon at 4.2 K. The measurements were performed at the National Synchrotron Light Source (NSLS) at beam line X-18B. A strong contraction of the interatomic distances was observed for Ag dimers and multimers. Silver clusters larger than 12 A mean diameter show a small contraction of thenn distance and a structure consistent with an fcc lattice. By contrast clusters smaller than 12 A show the presence of a small expansion and a strong reduction or absence ofnnn in the EXAFS signal. This points towards a different crystallographic structure for Ag microclusters with diameter less than 12 A. In iron clusters we observe a gradual reduction of thenn distance as the cluster size decreases. The interatomic distance for iron dimers was determined to be 1.94 A, in good agreement with earlier measurements. The iron microclusters show a bcc structure down to a mean diameter of 9 A. Iron clusters with 9 A mean diameter show a structure inconsistent with a bcc lattice. The new structure is consistent with an fcc or hcp lattice. The measurements on Ge clusters show the presence of only nearest neighbors. There was clear evidence of temporal annealing as determined by variations in the near edge structure of the K-absorption edge. Absorption edge measurements were also performed for free Ge clusters travelling perpendicular to the direction of the synchrotron radiation beam. The measurements performed on the free clusters were consistent with those obtained for matrix isolated clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426915
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  • 7
    Electronic Resource
    Electronic Resource
    Ionization dynamics of van-der-Waals clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 253-261 
    Details
    ISSN: 1434-6079
    Keywords: 33.65 ; 33.80E ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The ionization process of homogeneous and heterogeneous van-der-Waals clusters has been investigated using various ionization methods (electron bombardment, charge exchange, photoionization methods), and different analyzing techniques. Direct and indirect ionization processes can be distinguished in the experiments from the shape of the ionization curve which depends on the type of cluster. These features appear differently in homogeneous and heterogeneous systems: Homogeneous systems exhibit characteristic ionization efficiency curves where the direct ionization path appears as a sudden increase in the ionization efficiency while the indirect transition gives rise to a long drawn out tail extending to the true ionization threshold. In heterogeneous clusters the indirect ionization path proceeds via excited states of the component with the larger ionization potential and subsequent energy transfer to the other component. These transitions are shifted and broadened depending on the type of internal interaction. Conclusions are drawn concerning the geometry and the interaction potential inside the cluster. The resolution of the TEPICO (Threshold Electron Photo Ion Coincidence) experiments makes it possible to determine the kinetic energy release of the fragments. It is shown that the results are related to the stabilities of the cluster ions involved in the fragmentation chain. Results are presented for pure rare gas clusters (Ar n , Kr n , Xe n ) and for mixed systems (Ar n O2m , Ar n Xe, Kr n Xe, (CH4) n Ne).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426950
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  • 8
    Electronic Resource
    Electronic Resource
    Observation and investigation of metastable decay series of (N2) n + cluster ions (1989)
    Springer
    The European physical journal 12 (1989), S. 285-287 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract N2 cluster ions are produced by electron impact ionization of a supersonic N2 cluster beam and analyzed with a double focussing sector field mass spectrometer. It is found that metastable N2 cluster ions lose more than one N2 molecule in the μs time regime and decay predominantly via sequential series (N2) n + *→(N2) n−1 + *→...→N 2 + , evaporating a single monomer in each of these successive decay steps. The metastable decay rates determined in detail for cluster sizes 2≤n≤6 andn=20 lie between 1 and 106s−1. These rates(i) depend strongly on the time elapsed after ion formation and on the respective parent cluster ion size, and(ii) exhibit a quasiperiodic pattern in magnitude.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426957
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  • 9
    Electronic Resource
    Electronic Resource
    Electron bombardment fragmentation of size selected molecular clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 293-295 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.40 ; 34.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract (CO2) n , (NO) n and (NH3) n clusters are generated in a supersonic molecular beam and size selected by scattering from an He beam. By measurements of angular dependent mass spectra, TOF distributions and the angular dependence of the scattered signal quantitative information on the fragmentation probability by electron impact is derived. The van der Waals systems (CO2) n and (NO) n appear only at masses which are simply multiples of the monomer mass. The preferred cluster ion is the monomer ion for all investigated cluster sizes withn=2 to 4. The fragment pattern for the quasi-hydrogen bonded (NH3) n -cluster shows, beside a large number of fragment masses, a preference for protonated ions. The results are explained in terms of simple models based on the structural change from the neutral to the ionized configuration and the fragmentation pattern of the monomer followed by ionmolecule reactions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426960
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  • 10
    Electronic Resource
    Electronic Resource
    Kinetic energy release of clusters after multiphoton ionisation with time of flight and electrostatic analyser techniques (1989)
    Springer
    The European physical journal 12 (1989), S. 297-301 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 32.80.K
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A new technique is presented which allows direct observation of initial kinetic energies in multiphoton ionisation-fragmentation processes of molecules and clusters and provides an unambiguous determination of metastable decay channels. Results are presented for the unimolecular loss of a monomer from clusters (C6H6) 8 + to (C6H6) 12 + and for the reaction C6H 6 + →C4H 4 + +C2H2. We also observe a significant amount of probably collision induced fragmentation processes (C6H6) n + →(C6H6) n−x + + (C6H6) x withx much larger than 1.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426961
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  • 11
    Electronic Resource
    Electronic Resource
    Electronic structure of metal clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 319-326 
    Details
    ISSN: 1434-6079
    Keywords: 79.60 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photoemission spectra of valence electrons in metal clusters, together with threshold ionization potential measurements, provide a coherent picture of the development of the electronic structure from the isolated atom to the large metallic cluster. An insulator-metal transition occurs at an intermediate cluster size, which serves to define the boundary between small and large clusters. Although the outer electrons may be delocalized over the entire cluster, a small cluster remains insulating until the density of states near the Fermi level exceeds 1/kT. In large clusters, with increasing cluster size, the band structure approaches that of the bulk metal. However, the bands remain significantly narrowed even in a 1000-atom cluster, giving an indication of the importance of long-range order. The core-electron binding-energy shifts of supported metal clusters depend on changes in the band structure in the initial state, as well as on various final-state effects, including changes in core hole screening and the coulomb energy of the final-state charge. For cluster supported on amorphous carbon, this macroscopic coulomb shift is often dominant, as evidenced by the parallel shifts of the core-electron binding energy and the Fermi edge. Auger data confirm that final-state effects dominate in cluster of Sn and some other metals. Surface atom core-level shifts provide a valuable guide to the contributions of initial-state changes in band structure to cluster core-electron binding energy shifts, especially for Au and Pt. The available data indicate that the shift observed in supported, metallic clusters arise largely from the charge left on the cluster by photoemission. As the metal-insulator transition is approached from above, metallic screening is suppressed and the shift is determined by the local environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426965
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  • 12
    Electronic Resource
    Electronic Resource
    The relationship of Au55(PPh3)12Cl6 to colloidal gold (1989)
    Springer
    The European physical journal 12 (1989), S. 533-536 
    Details
    ISSN: 1434-6079
    Keywords: 33.20.K ; 35.20.G ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electronic (UV-visible) spectrum of the molecular cluster Au55(PPh3)12Cl6 shows features corresponding to the 520 nm plasma resonance and the shorter-wavelength interband transition of colloidal gold. These absorptions differ qualitatively from the simpler one-electron transitions of lower-nuclearity cluster molecules. Differential scanning calorimetry has been used to measure the enthalpy of decomposition of Au55(PPh3)12Cl6. The Au-Au bonding appears to be substantially stronger than in bulk gold.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01427012
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  • 13
    Electronic Resource
    Electronic Resource
    Reactivity of free clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 537-541 
    Details
    ISSN: 1434-6079
    Keywords: 82.30 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recent studies of the reactions of free or isolated transition metal clusters with simple molecules will be reviewed. Cluster chemical reactions are carried out in a laser-vaporization cluster source coupled to a continuous-flow reactor. Reactions can be categorized as chemisorptive (or surface) reactions, and bulk reactions. Chemisorptive reactions can be characterized asfacile, in which most cluster sizes of a given metal are equally reactive towards a particular reagent, oractivated, in which strong dependence of reactivity on cluster size is found. Under the normal operating conditions of the cluster reactor, a reaction may be kinetically controlled or at equilibrium. Following chemisorption, adsorbate decomposition and product desorption may occur. Specific reactions to be discussed include the reactions of iron clusters with ammonia and with water and the reactions of nickel clusters with ammonia.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01427013
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  • 14
    Electronic Resource
    Electronic Resource
    Reaction of Aln clusters with oxygen and ammonia (1989)
    Springer
    The European physical journal 12 (1989), S. 571-573 
    Details
    ISSN: 1434-6079
    Keywords: 82.30 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Aluminum clusters were generated by a laser vaporization method. Ionization potential of Al2 was found to be lower than that of Al. In the reaction with oxygen at high concentration, the mixed cluster Al9O7 survives predominantly as a stable cluster. Ammonia was found to be adsorbed weakly on the Aln surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01427020
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  • 15
    Electronic Resource
    Electronic Resource
    Influence of the precursors on the properties of alumina supported rhodium particles (1989)
    Springer
    The European physical journal 12 (1989), S. 579-582 
    Details
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The effect of chlorine on the properties of Rh particles supported on alumina was studied using the hydroconversion of alkanes as a molecular probe. Chloride ions on the alumina have little influence on the Rh particles. Chlorine adsorbed on the Rh particles decreases the chemisorption capacity and increases the metal-support interaction, which results in modifications of their catalytic properties. Depending on the alkane processed, specific activity can be depressed up to four orders of magnitude.
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    URL: http://dx.doi.org/10.1007/BF01427022
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  • 16
    Electronic Resource
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    Influence of dispersion on the energies of adsorption: H2, CO, propylene and propyne on supported Pd or Pt (1989)
    Springer
    The European physical journal 12 (1989), S. 583-586 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 82.65.Jv ; 82.60.Cx
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The aim of this work is to contribute to an explanation of thelowering of the specific activity of Pd/Al2O3 catalysts, towards hydrogenation of acetylenic molecules,as the dispersion increases. For this purpose, the interaction energy between these catalysts and H2, CO, propylene and propyne was directly measured by adsorption microcalorimetry at 323 K. In the case of propyne, the enthalpy of adsorption was found to be more than 50% higher for the catalysts with 97% dispersion than for the one with 26% dispersion, for coverages ranging from 0.2 to 0.7.This high enthalpy of adsorption (up to 290 kJ.mol−1) is attributed to a different proportion of edges and crystalline planes in the smallest Pd crystallites and is indeed consistent with a “blocking”chemisorption or with a hindered desorption of the products of a catalytic hydrogenation, i.e. with a lowering of the specific activity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01427023
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  • 17
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    First-principle calculations ofK-edge X-ray absorption spectra for small iron and nickel clusters (1989)
    Springer
    The European physical journal 13 (1989), S. 153-159 
    Details
    ISSN: 1434-6079
    Keywords: 31.20 ; 36.40 ; 78.70.D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this study we present theoretical X-ray absorption near-edge spectra (XANES) evaluated for Fe2, Ni2, and Ni3 using a modified multiple-scattered wave procedure. The calculations were performed for different internuclear distances of the dimers and by varying the geometry from linear to equilateral triangular for Ni3. The calculated absorption spectra for both Fe2 and Ni2 predict a broad resonant structure at the threshold and weak 1s transitions to unoccupied valence orbitals −5→0 eV giving a shoulder at the threshold. The resonance structure at the threshold of Ni3 appeared to be sensitive to the geometry of the clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01398585
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  • 18
    Electronic Resource
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    The smoke ion source: a device for the generation of cluster ions via inert gas condensation (1989)
    Springer
    The European physical journal 12 (1989), S. 3-6 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the development of an ion source for generating intense, continuous beams of both positive and negative cluster ions. This device is the result of the marriage of the inert gas condensation method with techniques for injecting electrons directly into expanding jets. In the preliminary studies described here, we have observed cluster ion size distributions ranging fromn=1−400 for Pb n + and Pb n − , and fromn=12−5700 for Li n − .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426893
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  • 19
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    Structural fluctuation and atom-permutation in transition-metal clusters (1989)
    Springer
    The European physical journal 14 (1989), S. 247-261 
    Details
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The atomic structure and thermodynamic properties of transition-metal clusters containingN atoms are investigated forN=6 and 7 using the method of molecular dynamics, where Gupta's potential taking into account many-body interaction is employed. The caloric curve (total energy — temperature curve) and the structural fluctuations are studied. The “fluctuating state” is found forN=6 in the region of the temperature near below the melting point, where clusters undergo structural transition from one isomer to others without making any topological change. The fluctuating state differs from the coexistence state in that the former involves no atomic diffusion, and goes to a structural phase transition of the bulk whenN is increased. On the other hand, the motion of atom-permutation is found in the low-temperature region of the liquid state, being induced by the cooperative motion of two atoms. It is discussed that such a motion easily occurs along the surface and may be considered to be one of the characteristics of small clusters. The fluctuating state is discussed in relation to the structural fluctuation of gold clusters observed experimentally.
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    URL: http://dx.doi.org/10.1007/BF01437325
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  • 20
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    Investigation of the stabilities of neutral and ionic lead and lead-antimony clusters under single and multiphoton ionization conditions (1989)
    Springer
    The European physical journal 14 (1989), S. 353-360 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The fluence dependence of lead cluster ion distributions at 222 nm and 308 nm reveal markedly different behavior. Results obtained at 308 nm display a simple uniform increase in intensity with higher laser fluence with little change in relative intensities. At 222 nm, however, a significant transformation is found from a markedly different low fluence distribution to a high fluence pattern, which is essentially indistinguishable from that observed at 308 nm. It is concluded that mass spectra obtained at 308 nm, regardless of fluence, or at 222 nm and high fluence contain appreciable contributions from fragmentation. Hence, under these conditions the mass spectra are found to be dominated by cluster ion stabilities. Magic numbers observed at both high and low fluence correspond well to those obtained using electron-impact ionization, and in many instances parallel the magic numbers characteristic of rare-gas clusters. This suggests the stabilities of both neutral and monovalent cationic lead clusters are largely determined by close-packing considerations, and are not appreciably influenced by electronic structure. Similar preferences for close-packed structures are also found for mixed lead-antimony clusters containing one or two antimony atoms that are ionized using high fluence 308 nm excitation.
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    URL: http://dx.doi.org/10.1007/BF01429285
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  • 21
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    Coulomb explosion of charged jellium clusters (1989)
    Springer
    The European physical journal 11 (1989), S. 323-326 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The Density Functional Formalism is used to calculate the minimum number of atoms (N c ) a multiply charged jellium-like spherical cluster must contain to be stable against coulomb explosion into two smaller fragments. In the case of alkaline clusters, which are systems for which the jellium model can be applied, we findN c equal to 31 and 23 for the explosion of Na N 2+ and Cs N 2+ respectively, in good agreement with the experimental value ofN c = 18 for Cs N 2+ . Calculated critical numbers for triply and tetracharged Cs clusters are 108 and 323 respectively. In addition the model predicts that the most favourable fragmentation channel is the ejection of a singly charged monomer.
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    URL: http://dx.doi.org/10.1007/BF01438506
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  • 22
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    Enrichment and segregation in alkali heteroclusters (1989)
    Springer
    The European physical journal 12 (1989), S. 237-239 
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    ISSN: 1434-6079
    Keywords: 31.20 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A spherical average pseudopotential method (SAPS) is used to investigate some properties of compound alkali clusters. The effect that the substitution of a Sodium atom by a Lithium atom in a Na n cluster has on the stabilities and geometries is studied forn≤21. We have found that substitution is always energetically possible. On the other hand equiatomic Na n Cs n clusters are considered in the size rangen≤16. We find a strong segregation effect of the Cesium atoms towards the cluster surface. This agrees with what happens in liquid Na x Cs1−x alloys.
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    URL: http://dx.doi.org/10.1007/BF01426946
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  • 23
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    Sodium halide clusters: evidence for direct electronic fragmentation (1989)
    Springer
    The European physical journal 12 (1989), S. 249-251 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80 ; 33.80
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Sodium halide clusters are generated by inert gas condensation and probed by electron and photon induced dissociation. The dependence of fragmentation on electron energy and initial cluster temperature indicates a direct electronic fragmentation process without an intermediate state of vibrationally hot clusters.
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    URL: http://dx.doi.org/10.1007/BF01426949
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  • 24
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    Intra-cluster ion-molecule reactions and photodissociation of molecular clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 269-271 
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    ISSN: 1434-6079
    Keywords: 33.80.E ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Intra-cluster ion-molecule reactions in benzene clusters and benzene-water binary clusters were observed in Resonance-Enhanced Multi-Photon Ionization (REMPI) Time-of-Flight (TOF) mass spectra. Condensation reactions of the excited dimer unit or higher cluster unit are found to occur within clusters.
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    URL: http://dx.doi.org/10.1007/BF01426952
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  • 25
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    Metastable decay of rare gas cluster ions: mechanism and kinetics (1989)
    Springer
    The European physical journal 12 (1989), S. 263-267 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Metastable decay of cluster ions has been discovered only recently. It was noted that one has to take this metastable decay into account when using mass spectrometry to probe neutral clusters, because ion abundance anomalies in mass spectra of rare gas and molecular clusters are caused by delayed metastable evaporation of monomers following ion production. Moreover, it was found that(i) the individual metastable reaction rates k depend strongly on cluster size and cluster ion production pathways and that(ii) there exists experimental evidence (k=k(t)) and a theoretical prediction that a given mass selected cluster ion generated by electron impact ionization of a nozzle expansion beam will comprise a range of metastable decay rates. In addition, it was discovered that metastable Ar cluster ions which lose two monomers in the μs time regime decay via sequential decay series Ar n + *→Ar n−1 + *→Ar n−2 + * with cluster sizes 7≤n≤10 andn=3 (similar results were obtained recently in case of N2 cluster ions). Conversely, the dominant metastable decay channel of Ar 4 + * into Ar 2 + was found to proceed predominantly via a single step fissioning process.
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    Multiply charged cluster ions of Ar, Kr, Xe, N2, O2, CO2, SO2 and NH3: Production mechanism, appearance size and appearance energy (1989)
    Springer
    The European physical journal 12 (1989), S. 279-281 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 07.75
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    Notes: Abstract Clusters of Ar, Kr, Xe, N2, O2, CO2, SO2 and NH3 formed by supersonic nozzle expansion have been studied by electron impact ionization mass spectrometry (up to 15000 amu). Besides mass spectra of singly charged ions showing the characteristic anomalous distributions, we have in particular investigated the properties of multiply charged cluster ions. Critical appearance sizes of doubly and triply charged cluster ions, n2 and n3 respectively, found in the present study confirm recent theoretical predictions about n3/n2 and their dependence on the properties of the cluster constituents. The appearance energies of multiply charged cluster ions determined are shifted way below the appearance energies of the respective monomer ions. These huge red shifts together with the observed linear threshold laws and large maximum ionization efficiencies indicate that multiply charged cluster ions are produced by sequential single ionization events of one incoming electron at different cluster sites. Furthermore, we have also obtained for the first time clear evidence that (for electron energies above the appearance energy of doubly charged ions) an appreciable amount of singly charged (also fragment) ions is produced via Coulomb explosion of unstable doubly charged ions in the ion source.
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    A mechanism of electron attachment to small clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 291-292 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.50.H ; 34.80.D
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    Topics: Physics
    Notes: Abstract Van der Waals clusters of various molecules were collisionally ionized by high-Rydberg rare gas atoms and slow electrons. Negative cluster ions thus produced were detected by mass spectroscopy. The ionization mechanism were investigated by measurements of the size- and the energy-dependences of the electron attachment cross sections.
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    Interactions of electrons with SF6: ionization and attachment (1989)
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    The European physical journal 12 (1989), S. 303-305 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80.G
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    Notes: Abstract Electron attachment and electron impact ionization of SF6 clusters have been investigated quantitatively in a molecular beam/electron ion source/mass spectrometer system as a function of electron energy E (0≤E≤180 eV) and as a function of cluster size.
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    Dynamics of transition-metal clusters (1989)
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    The European physical journal 12 (1989), S. 189-191 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 64.60
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    Notes: Abstract The atomic structure and thermodynamic properties of transition-metal 6- and 7-atom clusters are investigated using the molecular dynamics method, where Gupta's potential taking into account many-body interaction is employed. The caloric and the structural fluctuations are studied. The “fluctuating state” is found forN=6 in the region of the temperature near and below the melting point, where clusters undergo structural transition from one isomer to others without making any topological change. The fluctuating state differs from the “coexistence state” found in Ar clusters [1] i.e. the former involves no liquid state. In the liquid state the motion of atom-permutation occurs besides the breathing motion. On the other hand, the fluctuating state is not found forN=7 but only the motion of atom-permutation in the liquid state. The coexistence state is found in both cases of 6- and 7-atom clusters. We also discuss a possibility of larger clusters displaying the fluctuating state.
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    Theoretical study of the stability of X N n (n=−1, 0, +1, +2; X=Ag, Cu;N≤25) clusters as a function of size using a non-local density functional formalism (1989)
    Springer
    The European physical journal 12 (1989), S. 209-211 
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    Keywords: 36.40 ; 31.20
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    Notes: Abstract The spherical jellium model and self-consistent Weighted Density Approximation (WDA) to density functional theory have been used to study the stability of X N n (n=−1, 0, +1, +2; X=Ag, Cu;N≤25) clusters. The calculated magic numbers coincide with the observed ones. The first (IP1) and second (IP2) ionization potentials of Ag N and Cu N as a function of size show the typical oscillations induced by the electronic shell-filling effect. IP1 of Cu N is about 0.5 eV higher than IP1 of Ag N in the range studied (N≤25). For both Cu N and Ag N , IP1 appears to converge well towards the respective experimental values of the work function. The use of WDA allows us to obtain bound negative clusters of small size or with a nearly empty external shell, which is not possible using the Local Density Approximation (LDA) [1, 2]. However the electron affinity of X N clusters obtained as the difference of energies of the neutral and the negatively charged clusters, becomes negative forN=2, 3 and 8 (very close to zero forN=8), revealing that WDA needs further refinements.
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    Cluster cations ejected from liquid metal ion source: alkali metals (Li, Na) and group IV elements (Si, Ge, Sn, Pb) (1989)
    Springer
    The European physical journal 12 (1989), S. 225-227 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 79.70 ; 35.20.X
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    Notes: Abstract Cluster abundance of Li n + (n≤19), Na n + (n≤25), Si n z+ (n≤8 forz=1, 3≤n≤7 forz=2), Ge n z+ (n≤11 forz=1, 3≤n≤9 forz=2,n=4 forz=3), Sn n z+ (n≤7 forz=1, 3≤n≤9 forz=2,n=4 forz=3) and Pb n z+ (n≤6 forz=1, 5≤n≤7 forz=2) ejected from a liquid metal ion source has been investigated by mass spectrometry. The abundance spectra of alkali metal clusters showed distinct maxima and steps atn=3, 7, 9, 13 and 19 for Li, and atn=3, 5, 11, 13 and 19 for Na. Mass spectra of Si, Ge and Sn clusters were very similar each other, showing intensity drops aftern=4 and 6 (and alson=10 for Ge) for singly charged clusters. The magic numbers observed are discussed in terms of stability of charged clusters.
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    NMR of metal-core bonded31P in polynuclear metal cluster compounds (1989)
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    The European physical journal 12 (1989), S. 451-452 
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    Keywords: 76.60 ; 36.40
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    Notes: Abstract In this paper we present measurements of nuclear relaxation times of31P in the polynuclear cluster compounds Au55(PPh3)12Cl6 and Ru55(P(t-Bu)3)12Cl20. Above 15 K the data can be described as a Korringa process, while below 15 K the relaxation time appears to be thermally activated.
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    Cluster-model study of the interaction of halogen atoms with Ag clusters (1989)
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    The European physical journal 12 (1989), S. 543-546 
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    Keywords: 31.20 ; 36.40
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    Notes: Abstract Analysis of ab initio wave functions shows that the interaction between halogen atoms (F, Cl, and Br) and Ag clusters is ionic, and that the halogen ionicity is essentially −1. The interaction and the bonding arise, almost entirely, from the Coulomb attraction between the charged halogen and the metal and from polarization of the two subunits. Large shifts in equilibrium bond distances and vibrational energies are caused by an external electric field. These changes arise from a dominant Stark effect.
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    Reactions of small carbon cluster ions with HCN: a structural probe (1989)
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    The European physical journal 12 (1989), S. 567-570 
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    Keywords: 36.40 ; 82.30
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    Notes: Abstract The results of a detailed study of the primary and secondary reactions of carbon cluster ions, C n + (3≤n≤20), with HCN are presented and discussed. The experiments were performed in a Fourier transform (ICR) mass spectrometer, using direct laser vaporization of graphite to form the carbon cluster ions. Evidence for two structural forms of then=7, 8 and 9 cluster ions is obtained from their differing reactivity with HCN. The C 7 + ion is anomalous in its behavior in many respects, which is interpreted by an isomerization mechanism. The HCN reactions offer a contrast to the reactions with nonpolar neutrals studied previously. All HCN reactions produced ions of the type CnX+ (primary product) or CnXY+ (secondary product) where X, Y=H, CN or HCN. Fragmentation of the original carbon cluster was not observed, while radiative association is an important reaction channel. Low-energy collision-induced dissociation studies of the product ions support the mechanism of insertion into the H-CN bond and formation of covalent bonds at the carbene site for the primary reactions. In most secondary reactions however, the HCN associates weakly with the ion, rather than binding covalently.
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    Internal temperatures of neutral sodium clusters: a “PIE-thermometer” (1989)
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    The European physical journal 13 (1989), S. 171-178 
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    Keywords: 35.20.V ; 35.20.W ; 36.40
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    Topics: Physics
    Notes: Abstract Distinct temperature effects could be observed in the threshold regions of photoionisation efficiency (PIE) measurements of sodium clusters. Simulations of the PIE thresholds at various temperatures were carried out with a simple, semiclassical model. Fitting the simulations to the experimental data allows to correct ionisation potential assignments for thermal effects and estimate internal temperatures of polyatomic sodium clusters.
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    Photoionisation studies of homogeneous argon and krypton clusters using TPEPICO (1989)
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    The European physical journal 14 (1989), S. 339-351 
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    Keywords: 36.40 ; 35.20.V ; 33.80.E
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    Notes: Abstract The photoionisation threshold region of homogeneous Argon and Krypton clusters Ar n and Kr n forn up to 24 formed in a free jet expansion has been studied in detail, using the threshold photoelectron photoion coincidence (TPEPICO) time of flight technique. Measurements performed at a variety of different expansion conditions (nozzle temperature and stagnation pressure) demonstrate that fragmentation of larger clusters contributes substantially to the shape of the TPEPICO spectra even for the smallest clusters and at all photon energies higher than about 200 meV to 400 meV above the ionisation threshold. The determination of ionisation potentials for these cluster ions is discussed and careful estimates are given and compared with recent theoretical values.
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    Abundance of Na cluster ions ejected from a liquid metal ion source (1989)
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    The European physical journal 11 (1989), S. 87-91 
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    Keywords: 36.40 ; 79.70 ; 35.20.X
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    Notes: Abstract Sodium cluster ions Na+ n withn ranging up to 25 have been observed from a liquid sodium ion source by using a magnetic mass analyzer. Ion intensity as a function of cluster size showed distinct steps and local maxima atn=3, 5, 11, 13 and 19 (magic numbers), and a pronounced odd-even alternation. The features in the ion abundance curve are attributed to the relative stability of cluster ions. The observed magic numbers are only partially explained by the electronic shell model, indicating need to include a consideration of atomic structure in a cluster.
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    Core-valence correlation potentials based on density functional theory. Applications to valence-electron-only calculations on Na and K diatomics (1989)
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    The European physical journal 13 (1989), S. 355-361 
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    Keywords: 31.20 ; 36.40
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    Notes: Abstract The core-valence correlation potential has been derived for Na and K employing atomic calculations which make use of the density functional formula worked out by Lee, Yang and Parr based on Colle-Salvetti approach. The numerical potential is fitted with a small number of Gaussians leading to a very simple expression for an one-electron corevalence correlation operatorŴ cv . The core-valence correlation corrections can be computed by applyingŴ cv on a quite general class of wavefunctions. Applications of theŴ cv operator within the framework of valence-electron-only calculations using effective Hamiltonians are presented for Na and K atoms, for Na2, K2, NaK and their cations. Almost all the corrections calculated for the physical properties due to the core-valence correlation lead to results which are in good agreement with those obtained from much more sophisticated treatments and experimental data.
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    Size-dependent thermodynamic properties of silver aggregates. Simulation of the photographic development process (1989)
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    The European physical journal 12 (1989), S. 31-35 
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    ISSN: 1434-6079
    Keywords: 82.50 ; 36.40 ; 35.20.V
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    Topics: Physics
    Notes: Abstract Pulse radiolysis and time-resolved optical spectroscopy were used to observe the earliest steps of silver aggregation in the presence of an electron donor whose electrochemical potential is close to those of usual photographic developers. A critical size has to be reached by the silver aggregate before it is thermodynamically able to accept electrons from the donor, then to grow by an autocatalytic process with alternate adsorption of Ag+ ions and electron scavenging. From a computer simulation the critical aggregation numbern c is found to be 4 and hence the electrochemical potential of the critical aggregate is ≈−0.4 V/NHE. The size-dependence of the electrochemical potential in an aqueous solution is discussed and compared with that of the ionization potential in the gas phase. A tentative extrapolation of the present interpretation to the mechanism of the photographic development is proposed.
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    Stability of alkali-atom clusters (1989)
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    The European physical journal 12 (1989), S. 199-203 
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    Keywords: 36.40
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    Notes: Abstract A detailed study of the stability of alkali-atom clusters is presented and discussed. Free clusters are produced in an unseeded adiabatic expansion and ionized by a pulsed laser beam. A tandem time-of-flight system provides a size selection of ionized species and mass spectrometry of fragments. We have investigated for sodium and potassium clusters containing up to fifty atoms: the metastable decay following ionization, the photo-induced dissociation, the collisional induced dissociation and the collisional charge exchange. Experimental evidence is shown for dissociative process involving evaporation of monomers and dimers. This is explained by the statistical unimolecular theory and by the energetics of the systems.
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    Jellium-model calculation for monomer and dimer decays of some potassium clusters (1989)
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    The European physical journal 12 (1989), S. 205-208 
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    Keywords: 36.40 ; 31.20
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    Notes: Abstract We have studied several decay processes of potassium clusters and found that a dimer-decay mechanism can explain the observed lowest abundance of K10 in the K n mass spectra. Total-energy curves for decay processes are calculated using a jellium-background model for positive-ion cores and the local-spin-density-functional approximation for valence electrons. The energy-barrier height for a dimer decay of K10 from the energy-minimum point is found to be 0.18 eV, which is a reasonable magnitude for the decay to take place thermally in the experiment. The monomer decay of K9 and the dimer decay of K11, which are expected to be the most favorable decays of K9 and K11, are found to have high barriers. Monomer and dimer decays of K8 are also studied and the monomer decay is found to be more favorable, in accord with the high-nozzle-temperature mass spectrum.
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    Role of fragmentation processes in the liquid metal ion source production of aggregates (1989)
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    The European physical journal 12 (1989), S. 221-224 
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    Keywords: 36.40 ; 79.00
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    Notes: Abstract We analyse the role of the fragmentation processes in the liquid metal ion source technique from a theoretical and an experimental point of view. We show that the “double peak” structure of the energy distribution of Sn 7 + ions is due to the fact that there are two kinds of ions. On the one hand, ions which are directly emitted from the tip; on the other hand, ions produced by fragmentation at some distance (100–1000 Å) from the tip. We show that the existence of a peak for the second kind of ions strongly depends on the electric field mapping. We also deduce from the energy separation of the two peaks a life-time of the mother particles. The value obtained is compared to an evaluation made with the RRKM theory. The charge and mass of the mother particles are also discussed.
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    Enrichment of Zintl cluster ions (1989)
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    The European physical journal 12 (1989), S. 235-236 
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    Keywords: 36.40 ; 34.80.G
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    Notes: Abstract Compound cluster ions of heavy post-transition atoms (In, Pb, As, Sb, Bi) are enriched by electron induced dissociation if they are analogous to the Zintl polyanions Pb 5 2− and Pb 9 4− with respect to the atom and valence electron number.
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    Triangle contraction in six-membered-ring silicon clusters (1989)
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    The European physical journal 14 (1989), S. 237-245 
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    Keywords: 36.40 ; 31.20
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    Notes: Abstract We propose the “triangle contraction” as an important reconstruction mechanism of six-membered-ring silicon clusters on the basis of the force and virial analysis for Si6, Si10, Si14, Si18, Si22, and Si26 clusters. Forces acting on atoms have been calculated using the local-density-functional scheme with linear-combination-of-atomic-orbitals-Xα method. Calculated forces show that most of the (111)-surface equilateral triangles have tendency to contract, indicating the generality of the triangle-contraction mechanism.
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    Equilibrium intermetallic particles in the gas phase — A Knudsen cell mass spectrometric study (1989)
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    The European physical journal 12 (1989), S. 11-13 
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    Keywords: 07.75 ; 36.40 ; 34.80.G
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    Notes: Abstract Using the Knudsen cell effusion technique it is possible to generate a molecular beam containing intermetallic molecules. Mass spectrometric studies were carried out with the systems: cesium/antimony, cesium/antimony/bismuth, cesium/antimony/indium, cesium/antimony/tin and cesium/antimony/bismuth/tin. In all these systems intermetallic particles with extraordinary stoichiometries could be detected. A brief discussion of the appearance energies and the bonding principle of these molecules or clusters are given.
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    A group theoretical paradigm for describing the skeletal molecular orbitals of cluster compounds. Part 3 (1989)
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    The European physical journal 12 (1989), S. 53-59 
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    Keywords: 31.20N ; 36.40
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    Notes: Abstract The group theoretical consequences of the Tensor Surface Harmonic Theory have been developed for [ML2] n , [ML4] n and [ML5] n clusters where either thexz andyz orx 2−y 2 andxy components toL d π andL d δ do not contribute equally to the bonding. The closed shell requirements for such clusters are defined and the orbital symmetry constraints pertaining to the interconversion of conformers of these clusters are described.
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    Quantum mechanics and the structure of noble-gas clusters (1989)
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    The European physical journal 12 (1989), S. 65-68 
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    Keywords: 36.40
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    Notes: Abstract The importance of quantum mechanics for the thermal behaviour of Argon clusters with special respect to phase transitions is investigated applying a Path-Integral Monte-Carlo (PIMC) method. Results for the small-angle neutron scattering function (SANS) for various cluster sizes and temperatures are presented.
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    Energy barriers and structural transitions of small Al clusters (1989)
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    The European physical journal 12 (1989), S. 73-75 
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    Keywords: 36.40 ; 31.20
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    Notes: Abstract Energy barriers between low-lying configurational states were calculated for several small Al clusters. Calculations were carried out considering a model potential comprising two- and three-body interactions. Parameters used in this potential energy function were evaluated from fits to high level ab initio calculations for Al clusters. Energy barriers separating low-lying configurations were found to be in varying heights. Results indicate that isomeric transformations between several low-lying high-symmetry forms of small Al clusters are quite likely and may take place at relatively low temperatures.
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    Hydrogen bonded clusters of alcohol molecules in inert solvents: a chain statistics approach (1989)
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    The European physical journal 11 (1989), S. 249-255 
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    Keywords: 36.40 ; 61.20
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    Notes: Abstract A theory is proposed for modeling the autoassociation of alcohol molecules either in the neat liquid or in inert (non-complexing) solvents. This autoassociation by hydrogen bonds takes the form of clusters which can be predominantly open or cyclized chains, depending on the concentration. Chain conformation statistics are used for calculating the dipole moment of each type of chain. Cyclization equilibrium theory is employed for obtaining formulae for the fraction of all types of clusters. The total Kirkwood angular correlation factorg is calculated in function of the concentration. For this only two parameters are used; the first one is a common equilibrium constant for H bond dissociation; the second one is closely linked to the stiffness of the chains. A numerical illustration is presented for the case of normal hexanol in various aliphatic solvents, for which several dielectric data exist in the literature.
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    Electron diffraction studies of pulsed cluster beams (1989)
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    The European physical journal 12 (1989), S. 7-9 
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    Keywords: 36.40 ; 47.55.E ; 61.14.F
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    Notes: Abstract A pulsed nozzle source has been installed in the electron diffraction unit at the University of Michigan. The pulsed mode of operation is found to offer several important advantages in the investigation of clusters generated in nozzle flow. These advantages, including the feasibility of operating without a skimmer, are discussed. Design features and characteristic results are briefly outlined.
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    Sodium clusters in zeolites (1989)
    Springer
    The European physical journal 12 (1989), S. 37-40 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.30 ; 33.20.E
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    Topics: Physics
    Notes: Abstract The method of loading sodium clusters in zeolites, consisting of the controlled thermal decomposition of physisorbed sodium azide, is discussed. The influence of the azide loading, the azide decomposition rate and the sintering process on the amount of ionic and metallic sodium clusters in zeolite Y was followed by ESR. The method is compared to other metal deposition techniques.
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    Theoretical studies on carbon and silicon clusters: comparison of the structures and stabilities of neutral and ionic forms (1989)
    Springer
    The European physical journal 12 (1989), S. 61-64 
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    ISSN: 1434-6079
    Keywords: 31.20 ; 36.40
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    Topics: Physics
    Notes: Abstract Optimized molecular geometries and electronic structures are determined for neutral, positively charged, and negatively charged carbon and silicon clusters containing up to ten atoms. The effects of polarization functions and electron correlation are included in these claculations. Carbon clusters have linear or monocyclic ground state geometries whereas silicon clusters containing five or more atoms have three-dimensional ground state structures. Neutral C4, C6 and C8 all have linear and monocyclic isomers of comparable stability whereas the ionic forms appear to be generally more stable as linear geometrical arrangements. In the case of neutral and positively charged carbon clusters, the odd-numbered clusters are significantly more stable than the adjacent even-numbered clusters whereas the opposite order of stability occurs for the negative ions. This is due to the large values of the electron affinities of the linear forms of even-numbered clusters such as C4 and C6. The relative stabilities of silicon clusters does not change with the charge state of the clusters.
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    Binding energy of large icosahedral and cuboctahedral Lennard-Jones clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 69-71 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.55
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    Notes: Abstract It is widely believed that the lowest energy configurations for small rare gas clusters have icosahedral symmetry. This contrasts with the bulk crystal structures which have cuboctahedral fcc symmetry. It is of interest to understand the transition between this finite and bulk behavior. To model this transition in rare gas clusters we have undertaken optimization studies within the Lennard-Jones pair potential model. Using a combination of Monte Carlo and Partan Search optimization methods, the lowest energy relaxed structures of Lennard-Jones clusters having icosahedral and cuboctahedral symmetry were found. Studies were performed for complete shell clusters ranging in size from one shell having 13 atoms to 14 shells having 10,179 atoms. It was found that the icosahedral structures are lower in energy than the cuboctahedral structures for cluster sizes having 13 shells or fewer. Additional studies were performed using the more accurate Aziz-Chen [HFD-C] pair potential parameterized for argon. The conclusions appear to be relatively insensitive to the form of the potential.
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    Description of metallic and covalent clusters with icosahedral symmetry: the polytope model (1989)
    Springer
    The European physical journal 12 (1989), S. 89-92 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.55
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    Notes: Abstract Compact and tetravalent clusters with icosahedral local or global symmetries are generated by mapping from ideal structures in curved space onto a tangent euclidean 3D space. The observed elastic energy of the clusters can thus be interpreted as an intrinsic curvature associated to a frustrated local order. It is then proposed a kind of classification of the very rich family of possible clusters using a limited set of parameters.
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    Neutralization and matrix deposition experiments on mass-selected silver atoms and clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 15-18 
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    ISSN: 1434-6079
    Keywords: 33.20.N ; 36.40
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    Notes: Abstract A new apparatus for depositing intense beams of neutral, mass selected metal clusters in rare gas matrices or on a solid surface has been constructed. Metal cluster cations, produced by Ar+ sputtering, may be energy analyzed and then mass selected in a quadrupole mass filter. The clusters are neutralized by low energy electrons and then co-deposited with a rare gas on a 4 K sapphire window. Matrix samples were interrogated in situ by UV-optical absorption spectroscopy. Good quality neutral Ag spectra were obtained following a 30 min. Kr deposition of a ca. 2.5 nA cm−2 beam of Ag+. Line strength measurements imply matrices containing about 1013 atoms cm−2, corresponding to a neutralization efficiency of about 50%. Preliminary experiments on Ag 2 + yielded only Ag spectra, but with a lesser yield, perhaps indicative of incomplete fragmentation.
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    Structural transition in SF6 clusters (1989)
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    The European physical journal 12 (1989), S. 93-96 
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    ISSN: 1434-6079
    Keywords: 61.14 ; 36.40
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    Notes: Abstract SF6 clusters are produced during the free jet expansion of a Ne-SF6 mixture and studied by electron diffraction methods. Present experiments have been performed at constant nozzle diameter, stagnation pressure and stagnation temperature, adjustable parameters being the SF6 mole fraction X and the nozzle-to-skimmer distancex s /d. It is possible to warm up SF6 clusters by increasing either X, and thus the cluster size, orx s /d, which makes them collide with background molecules downstream of the Mach disk. In both cases, cold clusters made of several hundreds of molecules experience a structural transition, similar to that observed in bulk material, from the triclinic to the bcc plastic structure. A molecular dynamics simulation accounts correctly for intermediate stages of the transition which are visible in experimental patterns. Contrary to bulk results, cluster results show that the structural transition occurs over some temperature range.
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    General properties of the electronic structure of alkali metal clusters and Ia-IIa mixed clusters (1989)
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    The European physical journal 12 (1989), S. 307-314 
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    ISSN: 1434-6079
    Keywords: 31.20.D ; 31.30 ; 36.40
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    Topics: Physics
    Notes: Abstract The results of the systematic ab-initio CI investigation of neutral and charged Li n , Na n , BeLi k and MgNa k clusters are summarized and analyzed. The general characteristic features of the electronic structure are pointed out:a) The participation of the atomic orbitals, which are empty in Ia and IIa metal atoms, allows for a higher valency of these atoms in clusters.b) Jahn-Teller and pseudo-Jahn-Teller effects strongly influence the electronic and geometric structure of clusters.c) Deformations of cluster geometry can lead to biradicaloid structures with higher spin multiplicity in their ground states.d) The peculiarities of the electronic structures of clusters can be deduced from the presence of many “surface” atoms. The theoretical results agree with experimental data presently available and they are useful for interpretation of the experimental findings.
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    Electronic correlation and effective interactions in small alkali clusters (1989)
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    The European physical journal 12 (1989), S. 341-346 
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    Keywords: 31.20.D ; 36.40
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    Notes: Abstract The crucial importance of correlation effects versus delocalization, and their nature in small Alkali clusters is analysed from an ab-initio point of view through a detailed investigation of the Li2 dimer. The role of the external correlation (provided by extended basis sets and large Configuration Interaction calculations) is shown to lower the energy of ionic configurations and to increase their weight in the electronic wavefunction, increasing simultaneously the importance of delocalization versus internal correlation within thes-band. Effective interactions are determined from accurate diabatic calculations on dimers and transfered to clusters via an effective hamiltonian spanned bys orthogonal orbitals. Although not including explicitely thep-band, this model provides results in good agreement with abinitio calculations on Lithium clusters.
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    Compared electronic structure of negative ions M p C n − : I. Normal elements in Hückel theory (1989)
    Springer
    The European physical journal 12 (1989), S. 381-386 
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    ISSN: 1434-6079
    Keywords: 31.20.N ; 36.40 ; 79.20.N
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    Notes: Abstract Negative cluster ions M p C n − (M normal element,n〈10,p=1−4) produced by various experimental techniques from carbides show in their emission intensities a very strong even-odd effect according to the parity of the carbon atom numbern. This is in particular the case when M=N, F, Cl (p=1), M=H, Al, Si, S (p=1, 2) or M=B (p=1−4). The largest intensities of M p C n − ions always take place for evenn except in the cases of NC n − , B2C n − and Al2C n − , for which the maxima of emission occur for oddn. This oscillating behaviour corresponds to alternations in the stability of the clusters which are mainly due to the fact that, in Pitzer and Clementi model (linear chains in thesp hybridization within the framework of Hückel theory), the HOMO (highest occupied molecular orbital) of the clusters lies in a double degenerateπ level band: a cluster with a complete HOMO is always more stable than a cluster with a nearly empty HOMO. This result involves that the total number ofπ electrons is the main factor governing the parity of the stability alternations. Accordingly, since the knowledge of theπ electron number requires the determination of theσ electron number too, these alternations enable us to infer a very likely electronic structure of the ions.
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    Size dependence of the paramagnetic susceptibility of Mg and Zn clusters (1989)
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    The European physical journal 12 (1989), S. 401-403 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.35.Ex
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    Notes: Abstract The paramagnetic susceptibility of small divalent clusters (Mg and Zn) trapped in Xe and Adamantane matrices has been studied with EPR spectroscopy. This study represents an observation of the transition between the atomic behaviour and the extended solid. The signal of clusters 〉15 Å as a function of temperatures shows that their susceptibility has a Curie-low behaviour. These results are contrary to the quantum size effects models of Kubo [1] and Mühlschlegel [2].
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    Vacuum-UV photoemission-photoion coincidence spectroscopy of neutral metal atom clusters (1989)
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    The European physical journal 12 (1989), S. 431-434 
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    ISSN: 1434-6079
    Keywords: 35.20.V ; 36.20 ; 36.40
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    Notes: Abstract A newly developed photoion-photoelectron Vacuum-UV coincidence spectrometer has been coupled to a supersonic metal atom cluster beam source and has been used to investigate the electronic structure of isolated mercury clusters in the size range from 1 to 110 at several selected discrete excitation energies between 11.3 and 7.1 eV. Excitation of the van der Waals cluster Hg10 at the center of the strongD 3/2-autoionization line at 10.7 eV yields a photoelectron kinetic energy distribution between 0 and 2.5 eV indicating the population of Hg10 ionic states, which are also accessible by threshold ionization.
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    Electronic shell structure in Cs-O clusters (1989)
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    The European physical journal 12 (1989), S. 443-444 
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    Keywords: 07.75 ; 36.40
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    Notes: Abstract Unusually high ionization energies have been observed for Cs-O clusters having certain sizes and composition, namely for Cs2n+zOn with z=8, 18, 34, 58 and 92. The anomalies are well-defined for clusters containing from 1 to 7 oxygen atoms. The indicated values of z are identical to the number of electrons in closed shells of angular momentum.
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    Physical properties of high-nuclearity metal cluster compounds (1989)
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    The European physical journal 12 (1989), S. 445-450 
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    Keywords: 36.40 ; 75.20
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    Notes: Abstract Metal cluster compounds are composed of large macromolecules, which consist of a metal core (cluster) containing a certain number (n=6–560) of metal atoms, to which core a shell of ligands is coordinated. They provide excellent model systems for an assembly of identical metal clusters, embedded in a dielectric matrix. We discuss a number of physical properties of these materials.
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    Magnetic properties and EPR spectroscopy of molecular metal clusters (1989)
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    The European physical journal 12 (1989), S. 453-455 
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    ISSN: 1434-6079
    Keywords: 33.30 ; 36.40
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    Notes: Abstract The magnetic properties of molecular metal cluster compounds resemble those of small metal particles in the metametallic size regime. Even-electron metal carbonyl clusters with 10 or more metal atoms are paramagnetic, because their frontier orbital separations of less than 1 eV lead to high-spin electronic configurations. The rhodium cluster [Rh17S2(CO)32]3− gives EPR below 200 K withg=2.04, the first example of this type of paramagnetism in an even-electron carbonyl cluster of this 4d metal. Its spectral parameters are compared with those of osmium carbonyl clusters and some significant differences highlighted. Attempts have also been made to generate radical cations from lower-nuclearity, diamagnetic molecular clusters such as Rh6(CO)16 by chemical oxidation in sulphuric acid. An EPR active species (g=2.09) believed to be [Rh6(CO)16]+ has been obtained.
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    Optical properties of systems containing Au55-clusters (1989)
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    The European physical journal 12 (1989), S. 515-520 
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    Keywords: 33.20.K ; 36.40 ; 42.20 ; 78.40 ; 82.70
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    Topics: Physics
    Notes: Abstract Gold cluster compounds were investigated which contain clusters of 55 gold atoms in each unit. The ligands stabilize these clusters and, hence, many-cluster systems can be prepared which mainly show the properties of the single dressed cluster. Experimental results of optical and electron-microscopical investigations are presented and shortly discussed in view of the question whether the clusters are molecular or solid-state like.
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    Electronic structure of spheroidal metal containing carbon shells: study of the LaC60 and C60 clusters and their ions within the local density approximation (1989)
    Springer
    The European physical journal 12 (1989), S. 387-390 
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    Keywords: 31.20.N ; 36.40
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    Notes: Abstract Ionization thresholds and electron affinities have been calculated within the Local Density Approximation (LDA) for the neutral, positively and negatively charged clusters of LaC60 and C60. The evaluated energies are found to be in good agreement with available experimental data. More accurate measurements are however necessary to verify the suggested spheroidal cage structure for these molecules.
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    Bonding in nickel cluster carbonyls (1989)
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    The European physical journal 12 (1989), S. 395-397 
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    Keywords: 36.40 ; 31.20.R
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    Notes: Abstract Semiempirical (INDO) and ab initio valence only calculations of the electronic structure of Ni n and Ni n (CO) m clusters support the idea that the bonding with the CO ligands destabilizes the 4s-like MOs of the Ni n fragment thus eliminating their contribution to the metal-metal bonding in the carbonylated form. This process is accompanied by a complete quenching of the magnetic moment of the bare cluster.
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    Electron distribution of small Ni particles and Ce ions in X and Y zeolites related to their catalytic properties (1989)
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    The European physical journal 12 (1989), S. 425-429 
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    Keywords: 79.60 ; 36.40
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    Notes: Abstract Catalytic behaviour of nickel particles smaller than 1.3 nm, encaged in X and Y zeolites, in the presence of Ce3+, is related to their electronic properties. In general the rates of reaction are lower than those of a standard catalyst made of 2.5 nm nickel particles on SiO2; this is attributed to the strong localization of the Ni 3d states due to the size effect. However a high rate, more than twice the standard, is found for Ni in X zeolite, in relation with a Ni 3d 10 configuration. On the other hand the fragmentation of butane is deeper with Ni in Y support than in X support and this corresponds to a high density of Nid states at the Fermi level.
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    Fluorescence of rare gas clusters excited with synchrotron radiation (1989)
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    The European physical journal 12 (1989), S. 435-437 
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    Keywords: 36.40 ; 33.20 ; 78.40
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    Notes: Abstract A cluster beam experiment for fluorescence measurements on rare gas clusters has been built up. First results on the evolution of energy levels of neutral krypton clusters with a cluster size between 200–8500 atoms/cluster are reported. The well known bulk excitons of solid krypton do not merge into the first atomic lines and appear only in clusters larger than 300 atoms/cluster. Smaller clusters absorb only at energies which fit well with surface excitons of the solid.
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    Optical absorption of small metallic particles (1989)
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    The European physical journal 12 (1989), S. 469-470 
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    Keywords: 36.40 ; 78.00
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    Notes: Abstract In an extremely small metallic particle in which electron energies take discrete values, a light is absorbed by the surface plasmon which is not decayed by the surface scattering. The usually used relation between polarizability of a particle and electrical susceptibility does not hold.
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    Absorption spectroscopy of size-selected trimers and pentamers transition metal clusters isolated in rare gas solids: preliminary steps (1989)
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    The European physical journal 12 (1989), S. 481-484 
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    Keywords: 36.40 ; 33.20
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    Notes: Abstract Size-selected positive ionic silver trimers and pentamers and nickel trimers have been codeposited, at low kinetic energy, with rare gas (Kr) onto a cold transparent surface. They have been neutralized onto the surface by electrons of few eV, with an efficiency of 80±20%. The optical absorption spectra of the resulting matrix-isolated neutral species have been recorded, with good sensitivity, in the UV-visible range. The evaporation of clusters, detected on the atom signal after deposition of Ni trimers of 20 eV, neutralized by electrons of 5 eV, is shown to be roughly 20%. This indicates that Ni3 clusters are present in the matrix but their number is actually too low to be optically detected.
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    Many-cluster-systems: models of inhomogeneous matter (1989)
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    The European physical journal 12 (1989), S. 505-514 
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    Keywords: 36.40 ; 42.20 ; 78.00 ; 81.20 ; 81.40 ; 82.70
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    Notes: Abstract First, some general remarks concerning macroscopic “cluster matter” are given. In the second part, three recent, mainly optically and electron-microscopically performed investigations are discussed which deal with special properties of noble metal cluster systems forming the building units of this kind of matter:(1) dressed Au-55 clusters,(2) electromagnetic coupling effects among coagulated clusters,(3) the transition towards compact inhomogeneous matter caused by coalescence of clusters.
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    Geometries and stabilities of Si8 clusters (1989)
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    The European physical journal 13 (1989), S. 301-306 
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    Keywords: 36.40
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    Notes: Abstract The relative stabilities of eight-atom Si clusters were calculated with the semiempirical MO method SINDO1. With the aid of the group theoretical concept of kernels and epikernels, stationary points ofD 2d, C 2v andC s symmetry on the potential energy surface near the unstable cube were found. Apart from these stationary points which adopt epikernel symmetries, aD 4d stationary point not derivable from group theory is possible in configuration space. The cubic array with eight equivalent atoms can be classified as a diradical.
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    Fragmentation spectroscopy of heterogeneous clusters (1988)
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    The European physical journal 10 (1988), S. 319-327 
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    Keywords: 33.65 ; 33.80.E ; 36.40
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    Topics: Physics
    Notes: Abstract Photoionisation experiments were performed with heterogeneous Ar-Xe-clusters produced by supersonic expansion of argon gas with small quantities of xenon added to it. A threshold-electron photoionisation (TEPICO) technique was used to obtain time of flight cluster mass spectra. These mass spectra show particularly strong intensities for Ar12Xe+ and Ar18Xe+ which are attributed to the extraordinary stabilities of these cluster ions. Maxima in the ionic size distribution around Ar7Xe+ are related to a particular abundance ofneutral Ar12Xe which is fragmented after ionization. These stabilities are explained in terms of geometries consisting of a central Xe atom or ion surrounded by shells of Ar atoms. Filled shells exhibit particular strong bonding because these exhibit the largest number of atom-atom bonds. This conclusion is supported by simple theoretical calculations. The ionization process is discussed in terms of two direct and one indirect ionization channels the latter one proceeding via an intermediate electronic excitation of the Ar component in the neutral cluster.
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    A molecular beam study of a van der Waals complex; vibration-inversion transitions in NH3-Ar (1988)
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    The European physical journal 10 (1988), S. 291-293 
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    Keywords: 36.40 ; 33.20.E ; 33.80.G
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    Notes: Abstract Three ν2 vibration-inversion transitions of NH3-Ar have been found with linewidths smaller than 2 MHz, yielding a minimum predissociation lifetime of 80 ns. While one of these lines was previously identified as a low frequency inversion doublet transition, the other two lines belong to the high frequency component of the ν2 vibration-inversion doublet.
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    Electronic and atomic structure of Na, Mg, Al and Pb clusters (1988)
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    The European physical journal 11 (1988), S. 163-174 
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    Keywords: 36.40 ; 31.20
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    Notes: Abstract Density functional theory is used to study the electronic and atomic structure of small clusters of Na, Mg, Al and Pb. We study the quantityE N−1–E N , which has relevance to the processes of cluster growth and evaporation (E N is the total energy of the cluster withN atoms). By comparing the results of the jellium model with those of a more realistic model (although still simple) we are able to appreciate “structural” effects beyond the “electronic-shell effects” which form the essence of the predictions of the jellium model. The calculations predict formation of atomic shells and appreciable reconstruction as the cluster grows.
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    Exciton absorption and intramolecular Penning ionisation in small molecular clusters I: (N2O)n and C6H5CN·(N2O)n (1988)
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    The European physical journal 11 (1988), S. 153-162 
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    Keywords: 36.40
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    Notes: Abstract Photoionisation efficiency (PIE)-spectra are measured for small (N2O)n-clusters,n=2...8, using synchrotron radiation from the electron storage ring BESSY at Berlin. Ionisation thresholds are reported. Resonances in the wavelength-range 97...100 nm forn〉2 are attributed to exciton absorption with N2O-Rydberg levels, series I and II parentage. This interpretation is supported by measurements of the PIE of mixed benzonitrile · (N2O)n clusters where benzonitrile serves as a monitor for photon absorption in N2O at energies above the ionisation limit of benzonitrile.
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    IR predissociation of halogenated methane van der Waals complexes (1988)
    Springer
    The European physical journal 11 (1988), S. 175-180 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80.G ; 35.20.G
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    Topics: Physics
    Notes: Abstract The infrared dissociation spectra of several halogenated methanes (CHCl2F, CH3F, CF3I and CF3Br) have been studied. Bonded and free C–F stretch excitations have been observed.H-bridges forming the bonding in CHCl2F or CH3F dimers lead to very large red-shifts in the dissociation spectrum with respect to the gas-phase absorptions. Double resonance techniques have been employed to study the homogeneity of the spectral features.
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    Compound clusters of heavy post-transition elements (1988)
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    The European physical journal 10 (1988), S. 329-335 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80.D ; 81.20.G
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    Notes: Abstract Neutral binary clusters of Pb-As, Pb-Se, Pb-Te, Bi-In and Bi-Te are generated by inert gas condensation in a double oven source and probed by electron impact. Cluster ions corresponding to the Zintl polyanions Pb 5 2− and Pb 9 4− with respect to atom and valence electron number, are strongly enriched by electron induced dissociation ((Pb2As3)+, (Bi4In)+, (Pb4As5)+, (Bi7In2)+). For the corresponding systems, no other compound cluster ions are enriched in a comparable manner. Enhanced stability is found for (Pbn−1As)+ (n=7, 10, 13) and (Bi3Te)+, which are isoelectronic with neutral ‘magic’ Pbn clusters and the very stable Bi4 molecule, respectively.
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    Stability and structure of singly-charged xenon-argon clusters [Xe1Arn−1]+,n=3–27 (1988)
    Springer
    The European physical journal 8 (1988), S. 91-101 
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    ISSN: 1434-6079
    Keywords: 31.20.T ; 36.40
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    Topics: Physics
    Notes: Abstract Monte-Carlo calculations have been performed for positively charged xenon-argon clusters in the temperature range between 10K and 40K for cluster sizes up ton=27. The argon-argon interaction potential stems from empirical data, the Xe+-Ar potential is determined by ab initio MRD-CI calculations and a semi-empirical treatment of spin-orbit effects. Special stability is found for cluster sizesn=10, 13, 19 and less pronounced forn=23 and 25 fairly independent of the temperature. The geometrical structure of the clusters are given and the construction principle is discussed in light of the interactions among neutral argon atoms and the xenon ion — argon interaction. Comparison with measured mass spectra for mixed rare-gas clusters and [Xen]+ clusters is made and shows a consistent picture for the building principle.
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    A DIM model for homogeneous noble gas ionic clusters (1988)
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    The European physical journal 8 (1988), S. 195-208 
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    ISSN: 1434-6079
    Keywords: 31.20.G ; 36.40 ; 34.20
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    Topics: Physics
    Notes: Abstract The method of diatomics-in-molecules (DIM) is applied to the calculation of the energy of the homogeneous noble-gas ionic clusters Ar n + and Xe n + forn=3, 4, ..., 22. The trimers are stable symmetric linear molecules exhibiting chemical binding, a result in agreement both with ab initio calculations and with previous DIM work. The clusters up ton=13 are best described as a trimer ion surrounded by neutrals, whereby the charge distribution changes slightly with increasingn. Both noble gases exhibit a special stability associated with the completion of the first shell of neutral atoms atn=13. Asn increases from 13 to 22, there is a greater delocalization of the positive charge, the central ion tending to become a linear tetramer, symmetric for Xe and unsymmetric for Ar. Energies of the excited electronic states are reported and the possibility of developing simpler DIM models for the clusters and for mixed noble gases is discussed.
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    A theoretical study of internal rearrangements and open channels for fission and mass exchanges in Xe n + clusters (1988)
    Springer
    The European physical journal 8 (1988), S. 289-294 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20.G ; 35.20.J
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    Topics: Physics
    Notes: Abstract In a previous work the equilibrium geometrical and electronic structures of Xe n + clusters had been established using a non-empirical model hamiltonian. The same model is used to determine the energetic barriers between the nearly degenerate isomers; the movement of the neutral atoms around the Xe 3 + or Xe 4 + ionized linear cores are quite easy (ΔE⋍0.9 kcal/mole), the changes from a Xe 3 + to a Xe 4 + core are more difficult (ΔE⋍2.0 kcal/mole). The energetically possible fissions from a vertical photoionization $$Xe_n \xrightarrow{{h v}}Xe_n^{v + } \to Xe_p^ + + Xe_{n - p} $$ forn≦19,p=1–9 and 12–14 and mass exchanges Xe p + +Xe q →Xe p+m + +Xe q−m (m=1,2,3) from relaxed Xe p + clusters are given forp+m≦9 and 12–14 andq≦19. Surprisingly the reverse reactions are shown to occur for some values ofp andq. Numerous processes lead to Xe 13 + , which is especially stable.
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    Liquid drop and optical model calculations of elastic, vibrationally inelastic and absorptive scattering of4He atoms from4He n -clusters (1988)
    Springer
    The European physical journal 8 (1988), S. 295-304 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.50
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    Notes: Abstract The scattering of He atoms from liquid He n -clusters withn=10 to 1000 at energies between 0.01 and 5.0 meV has been investigated by calculating integral cross sections for elastic scattering, absorption scattering and vibrational excitation of the liquid drop vibrations using a hard core potential, a transparent core potential, a black core and an optical model potential. The implications for planned scattering experiments are discussed.
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    Quantum mechanics and phase transitions in small noble-gas clusters (1988)
    Springer
    The European physical journal 9 (1988), S. 343-349 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract The quantum-statistical properties of Argon clusters are calculated applying a Path-Integral Monte-Carlo (PIMC) method. Results for pair correlation functions and kinetic-and configurational energy expectations for various cluster sizes and temperatures are presented. Physical phenomena such as ground-state kinetic energy and quantum admixture of different atomic configurations are studied and experiences with the method are given. In particular, the relation between metastable cluster states and phase transitions is discussed.
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    Condensation in free jets: Comparison of rare gases and metals (1987)
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    The European physical journal 4 (1987), S. 291-299 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 51.30 ; 64.90
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    Topics: Physics
    Notes: Abstract In view of the recent interest in metal cluster beams obtained from free jet expansions, the paper extends the scaling laws and similarity relations developed for rare gases to metal vapors. The enthalpy of evaporation at 0 K and the density of the solid are used to define for both metals and rare gases, a species-characteristic temperature and length,T ch andr ch. This allows to transform the scaling parameter for condensation of a given gas,π=n 0·d q·T 0 (0.25q-1.5) , into a reduced scaling parameter π* by replacingn 0,d andT 0 by their respective reduced termsn*=n·r ch 3 ,d*=d/r ch, andT*=T/T ch. As shown before for the rare gases, free jets with the same π* are similar with respect to cluster formation. Based on an analysis of existing experimental data in terms of the respective π*, onset of condensation of metals in free jets is correlated by π* too. For π*〈200 the free jets do not produce clusters, while for π*〉1,000 clusters exceeding 100 atoms/cluster are being observed.
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    Stability of multiply charged silver clusters (1987)
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    The European physical journal 4 (1987), S. 379-381 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20X ; 79.20K
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    Topics: Physics
    Notes: Abstract Using the gasaggregation technique it is possible to generate metal clusters in narrow size distributions and to vary their mean size by adjusting the cell parameters. The high intensity of this source allows to detect besides singly charged clusters also multiply charged ones. Ag n 2+ and Ag n 3+ are observed forn≧9 andn≧31, respectively; i.e. at values well below the critical sizes reported for spheres.
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    Pressure enhancement of gas-phase water oligomer populations: A RRHO MCY-B/EPEN computational study (1987)
    Springer
    The European physical journal 5 (1987), S. 181-186 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 94.10
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    Topics: Physics
    Notes: Abstract Existing theoretical data, including the recently suggested MCY-B water pair potential and EPEN data on water oligomers in conjunction with rigid-rotor and harmonic-oscillator (RRHO) partition functions, are combined to evaluate equilibrium constants of water associate, (H2O) i , formation. The equilibrium constant set obtained is employed to study water cluster populations under various temperatures and pressures. Within the model it is shown that the pressure dependence of the mole fraction of a cluster in the equilibrium steam exhibits a maximum. The maximum with increasing temperature is shifted towards higher pressure values, however, its height is increasing, too. The importance of the finding for an assessment of optimum conditions for a cluster observation as well as reliability of the RRHO MCY-B model of steam are discussed.
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    Electronic structures and stabilities of sodium clusters: jellium-sphere dimer calculation (1987)
    Springer
    The European physical journal 7 (1987), S. 289-292 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20
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    Notes: Abstract Bonding properties of sodium-cluster dimers, (X 4)2 and (X 8)2, whereX n is a jellium sphere corresponding to a cluster ofn atoms, were investigated by the linear-combination-of-jellium-orbitals method with local-spin-density-functional approximation. The stability ofn=8 clusters, observed in the experiment, is discussed in relation to the binding properties of dimers. We have found that (1) the (X 4)2 bonding has a covalent character, which makes theX 8 formation favorable, and (2)X 8 has an inert property because the force between jellium spheres in (X 8)2 is due to a weak dispersion force.
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    A model approach to far infrared absorption in strongly polar fluids: Clusters and their internal angular modes (1987)
    Springer
    The European physical journal 5 (1987), S. 367-374 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.20
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    Topics: Physics
    Notes: Abstract It is suggested that highly polar molecules tend to aggregate into microclusters of various configurations. For neat liquids at high densities such clustering might account for the strong orientational correlations which have been observed in numerical simulations. Three examples are given to illustrate the far infrared spectroscopic properties of such microclusters: the fundamental modes of libration of linear “dimer” and “trimer”, and an adiabatic rotational mode in a seven dipoles cluster. In the latter example the rotational motions are concerted so that no potential barrier exist along a complete rotational cycle; consequently the corresponding absorption should extend over the thermal free rotation spectral region. Such an absorption has been recently observed by F.I.R. spectroscopy in liquid methyl chloride.
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    Quantum chemical investigations of the latent image formation (1987)
    Springer
    The European physical journal 6 (1987), S. 193-198 
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    ISSN: 1434-6079
    Keywords: 31.15 ; 36.40 ; 82.65
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    Topics: Physics
    Notes: Abstract Having studied free silver clusters by quantum chemical calculations we now present a method to take into account the influence of a silver halide surface on adsorbed silver clusters. The model for the surface will be a silver halide cluster as frozen crystal section. The interactions are discussed in detail; a new bromide pseudopotential may be of special interest. Results with this method will be given in subsequent papers.
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    High resolution measurements of IR predissociation of C2H4 dimers (1987)
    Springer
    The European physical journal 6 (1987), S. 199-209 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.20E ; 33.80G
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    Topics: Physics
    Notes: Abstract The narrow lines on top of the broad homogeneous background of the (C2H4)2 predissociation spectrum are studied. The high resolution spectra are measured tuning the length of a CO2 waveguide laser by means of a PZT yielding a frequency scan of 230 MHz around the CO2 laser lines. In the absense of power broadening a minimum non-instrumental linewidth of 3.5 MHz fwhm is found, corresponding to a lower limit for the predissociation lifetime of 45 ns. From the power broadening of the strongest sharp line a transition dipole moment of 0.14 Debye has been determined. To this transition corresponds a saturation fluenceF sat=3 µJ/cm2, in strong contrast withF sat=20 mJ/cm2 for the broad background. The dependence of the ratio structure/background on the concentration of C2H4 in He, on the source temperature and on the stagnation pressure, yields insight in the origin of the co-existence of the broad background and the narrow lines. Evidence is found that the sharp lines are due to dimers with low internal energies, whereas the background originates mainly from dimers with higher internal energy. By means of a two-laser experiment it is shown that the sharp peaks are inhomogeneous. Moreover, the first laser can significantly diminish the background predissociation signal produced by the second laser without consequences for the height of the sharp peaks.
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    Quantum chemical investigations of the latent image formation (1987)
    Springer
    The European physical journal 6 (1987), S. 287-292 
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    ISSN: 1434-6079
    Keywords: 31.20 ; 36.40 ; 82.65
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    Topics: Physics
    Notes: Abstract The adsorption of Ag+ and Ag on a (100) AgBr surface is investigated. Interstitial subsurface sites and incomplete surfaces (with ledges and kinks) are also considered. Equilibrium geometries, adsorption energies and ionization potentials have been calculated. Migration of neutral Ag on the surface and crystal growth of AgBr are discussed, and a comparison with other theoretical results is given.
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    Electron attachment to SO2 clusters (1987)
    Springer
    The European physical journal 6 (1987), S. 351-362 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20
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    Topics: Physics
    Notes: Abstract Electron attachment to SO2 clusters formed by nozzle expansion was investigated (n up to 8) in a molecular-beam electron-ionization mass-spectrometer system. Electron ionization of SO2 clusters was also studied (n up to 18) showing no pronounced structure in the mass spectra and no strong dependence on electron energy, the dominant positive ion being the (SO2) n + series. Also present but less abundant are the fragment ion series (SO2) n SO+, (SO2) n S+ and (SO2) n O+ with decreasing intensities in that order. The dominant negative ion is (SO2) n − . The homologous series (SO2) n O− and (SO2) n SO− are less abundant, the series (SO2) n S− has not been observed at all (except SO2·S− produced in the background gas via secondary processes). The negative ion mass spectra show a strong dependence on electron energy due to a rich resonance like structure of the attachment cross sections involved. These attachment cross sections have been determined (up to 40 eV) and they show significant differences for the different homologous series. The most striking feature is that for instance (SO2) n SO− ions do not show any signal at the first main resonance of SO− from SO2. Likewise (SO2) n O− ions only show a strongly diminished signal at the first main resonance of O− from SO2. This is in contrast to results in O2, CO2 and N2O. Conversely, (SO2) n − ions show — besides peaks at the position of the first and second O− resonance — additional resonances below and above these peaks. In addition, (SO2) 5 − and larger ones show a zero energy peak consisting of stoichiometric SO2 cluster ions similar to observations in O2, CO2 and H2O. The attachment cross section of S− from SO2 has been found to show an additional previously undetected peak at ∼1 eV. Moreover, the present study revealed the existence of a S n − (n up to 8) series being produced with nearly zero energy electrons via volume and surface processes in and around the ion source.
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    The velocity distribution of clusters generated by inert gas condensation (1986)
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    The European physical journal 1 (1986), S. 131-134 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 07.75
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    Topics: Physics
    Notes: Abstract The velocity distribution of sodium chloride clusters produced by inert gas condensation is determined by means of a mechanical chopping technique. It is found to be the same for all cluster sizes between 1 and more than 200 molecular units per cluster, ruling out the possibility of cluster mass separation by velocity filters. This is explained by an adiabatic expansion occuring during the cluster's exit from the condensation chamber into the high vacuum of the mass spectrometer.
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    On the history of cluster beams (1986)
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    The European physical journal 3 (1986), S. 101-107 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract The methods to produce and investigate cluster beams have been developed primarily with the use of permanent gases. A summary is given of related work carried out at Marburg and Karlsruhe. The report deals with the effect of carrier gases on cluster beam production; ionization, electrical acceleration and magnetic deflection of cluster beams; the retarding potential mass spectrometry of cluster beams; cluster size measurement by atomic beam attenuation; reflection of cluster beams at solid surfaces; scattering properties of4He and3He clusters; the application of cluster beams in plasma physics, and the reduction of space charge problems by acceleration of cluster ions.
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    The formation and kinetics of Ionized Cluster Beams (1986)
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    The European physical journal 3 (1986), S. 137-142 
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    Keywords: 36.40 ; 47.55E ; 68.55.tb
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    Topics: Physics
    Notes: Abstract The formation and kinetics of large vapourized-material cluster beams (large size metal clusters) are discussed. The clusters are formed by injecting the vapour of solid state materials into a high vacuum region through a nozzle of a heated crucible. The conditions under which metal clusters form are analysed using nucleation theory. Computer simulation by combining the nucleation and flow equations has also been made. The results show that the theory can be useful in predicting qualitative dependences of metal cluster formation on operation conditions. Several experimental results are also presented, which support the finding that a large size metal cluster is formed by homogeneous nucleation and growth. The advantageous characteristics of ionized cluster beam for thin film formation are also discussed.
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    Analysis of the reactivity of small cobalt clusters (1986)
    Springer
    The European physical journal 3 (1986), S. 205-209 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20G
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    Topics: Physics
    Notes: Abstract The electronic structures of small cobalt clusters have been calculated within the local spin density approximation using the LCAO method. The calculations were done for simple geometries with the optimized number of interatomic bonds, and both for the bond length of the cobalt dimer and the bulk metal. The Fermi energy is found to be smaller for Co N clusters withN=3, 4, 5 andN〉10 than for the other ones. The variation of the Fermi energy with the cluster size correlates in a striking way with the observed H2 tendency for chemisorption as found for cobalt clusters in a supersonic beam. Furthermore, the magnetic moments are somewhat smaller for these active clusters. In addition the lowest unoccupied levels of majority spin appear close to the highest occupied levels of minority spin which is not the case for the inert clusters.
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    Binary metal alloy clusters (1986)
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    The European physical journal 3 (1986), S. 223-231 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 82.65 ; 81.20.6
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    Topics: Physics
    Notes: Abstract Binary alloy clustersA n B m (A,B: Bi, Sb, Pb, Ag, in different compositions) have been generated by simultaneous inert gas condensation of the two vapours. Under suitable condensation conditions the adsorption of single atomsA to clustersB m can be studied. The adsorption probabilities are found to vary with cluster size. The cluster reactivities depend on the number of absorbed foreign atoms. Lead and bismuth clusters are found to be highly reactive in cracking the strongly bound Sb4-tetrahedron. One single interaction channel is found for Pb n /Sb4 (symmetrical dissociation) and three interaction channels are found for Bi n /Sb4 (symmetrical and nonsymmetrical dissociation). Pb- and Bi-clusters have different onset thresholds for dissociative reactivity.
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    An improved clusterion-photoelectron coincidence technique for the investigation of the ionisation dynamics of clusters (1986)
    Springer
    The European physical journal 3 (1986), S. 323-327 
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    ISSN: 1434-6079
    Keywords: 33.65 ; 33.80E ; 36.40
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    Topics: Physics
    Notes: Abstract The introduction of photoion-photoelectron coincidence techniques has made it possible to investigate photoionisation properties of heavy clusters, which are not accessible by conventional mass spectrometry. This technique has been further developed in combination with a zero-volt electron energy analyser and greatly improved in performance. The method has been applied to the investigation of different homogeneous and heterogeneous clusters. This type of cluster experiment requires both a very high resolution and a large dynamic range in order to identify also clusters present in low abundance. As an example, a series of coincidence mass spectra of Xe clusters has been recorded at different wavelengths. Below a photon energy of 11.1 eV, the range of observable clusters shifts to higher cluster sizes with decreasing energy. Appearance potentials and the binding energy of different cluster ions were obtained. Intensity fluctuations, already observed in spectra with electron bombardment ionisation (magic numbers), have also been detected in the coincidence spectra and become most pronounced near the ionisation threshold. This indicates that these fluctuations are caused by the size-dependent stability of the ionic and not the neutral cluster. Furthermore, the threshold size does not change linearly with cluster size. The binding energy per particle seems to change drastically aroundn=13 which indicates the existence of a shell structure in the cluster ion.
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    The three-band model. A pattern for the electronic structure of M6L8L′6 cluster compounds (1986)
    Springer
    The European physical journal 3 (1986), S. 411-420 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20
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    Topics: Physics
    Notes: Abstract The electronic structure of M6L8L′6 cluster compounds (where M=Mo, Re and L, L′=S, Se, Cl, Br) has been investigated using Tight-Binding band-structure calculations and “solid-like” Extended Huckel method. In spite of the variety of structural features and physical properties of these octahedral cluster compounds (from insulators to superconductors), it has been found that a simple three-band model was convenient to describe the whole of the M6L8L′6 serie.
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