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  • Springer  (259)
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  • 101
    Electronic Resource
    Electronic Resource
    The role of Ga-droplet formation in nanometer-scale GaAs cluster synthesis from organometallic precursors (1993)
    Springer
    The European physical journal 26 (1993), S. 219-221 
    Details
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recently we demonstrated the formation of crystalline nanometer scale GaAs clusters from organometallic precursors using an aerosol process derived from organometallic vapor phase epitaxy (OMVPE) [P. C. Sercelet al., Appl Phys. Lett.61, 696 (1992)]. Here, we explore the influence of precracking the Ga precursor (trimethyl-gallium), forming nanometer scale Ga droplets, prior to introduction of AsH3 to the reaction. We find the GaAs clusters so formed have an entirely different morphology than do those formed when the reactants are pre-mixed prior to reaction. This data supports our earlier contention that homogeneous nucleation is the dominant reaction mechanism for the formation of the clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01425670
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  • 102
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    The optical extinction of ligand-stabilized Au13- and Au55-clusters: The vanishing of the Mie-resonance (1993)
    Springer
    The European physical journal 26 (1993), S. 1-3 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 33.20K
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present optical extinction spectra of ligand-stabilized Au-clusters AuN with sizes of N=13 and N=55. They are compared to larger, embedded clusters up to N=5·103 (diameter 5nm). The Mie resonance due to excitation of the dipole plasmon polariton vanishes with decreasing cluster size. For N〉55, this effect has recently been interpreted as caused by smearing out of the interband transition edge of Au.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01425599
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  • 103
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    Quantum mechanical study of the structure and stability of molecular van der Waals' clusters I: hydrates of SO2 (1993)
    Springer
    The European physical journal 26 (1993), S. 326-328 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20.Gm ; 31.20.D ; 82.40.We
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The structure and stability of the mixed clusters SO2(H2O)n, n ranging from 1 to 4, have been examined using semi-empirical quantum mechanical Hartree Fock methods with the improved PM3 parameter set as implemented in MOPAC [1]. Limited molecular dynamics studies together with investigation of the potential surface reveal potential barriers of 1 kcal/mol or less between many of the stable structures for a cluster of a given size. For n=1,2 the results are compared with those ofab initio calculations using a double zeta basis at the MP4 level.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01425705
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  • 104
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    Energy exchanges following very low energy electron attachment to neat CS2 and CS2-containing clusters (1993)
    Springer
    The European physical journal 27 (1993), S. 365-369 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.70.+e
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied electron transfer from state-selected Rydberg atoms to (CS2) N and CS2(Ar) N clusters and compared the results to Rydberg electron transfer to isolated CS2 molecules. At large Rydberg principal quantum numbers (n〉20), the influence of the positive ionic core becomes negligible and we are able to directly investigate the competition between electronic autodetachment of the anions and intracluster energy exchanges between the anions and their environment. We show that argon atoms are unable to achieve efficient internal energy exchanges in heterogeneous clusters as compared to the high efficiency of CS2 molecules in homogeneous clusters.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437470
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  • 105
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    Exchange effects on electronic states in jellium clusters (1993)
    Springer
    The European physical journal 28 (1993), S. 73-80 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 71.70.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Hartree-Fock calculations are done for finite number of valence electrons (8, 20, 40, and 58) in a positively charged uniform background (jellium) with the density of bulk sodium. Differences and similarities with the results of Kohn-Sham local-density calculations are discussed. State-dependence and suppression of the wave functions are the two important effects coming from the nonlocality of the Hartree-Fock potential. These two effects, however, cancel in the density profile of electrons. The Kohn-Sham calculations consequently produce similar density profiles as in the Hartree-Fock calculations. The dipole polarizability is also calculated for 8-mers. The calculated value is still smaller than the measured one and is not an improvement of the insufficient Kohn-Sham result.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437457
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  • 106
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    Binary metal alloy clusters (1986)
    Springer
    The European physical journal 3 (1986), S. 223-231 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 82.65 ; 81.20.6
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01384811
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  • 107
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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 
    Details
    ISSN: 1434-6079
    Keywords: 33.65 ; 33.80E ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01384823
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  • 108
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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
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437200
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  • 109
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    Photoionization studies of transition metal clusters: Ionization potentials of ScnO (n=5−36) (1994)
    Springer
    The European physical journal 31 (1994), S. 199-203 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 22.80.E
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The photoionization efficiency (PIE) spectra and ionization potentials are reported for scandium cluster monoxides (Sc n O,n=5−36). As found for other transition metal clusters, strong dependence of ionization potential on cluster size is found for small clusters, with the ionization potentials of larger clusters decreasing relatively smoothly with increasing size. The IPs are 0.6–0.8 eV lower than that predicted by conducting spherical droplet model.
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    URL: http://dx.doi.org/10.1007/BF01437836
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  • 110
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    Odd-even staggering in simple models of metal clusters (1994)
    Springer
    The European physical journal 31 (1994), S. 259-267 
    Details
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The odd-even staggering of free-electron metal clusters is studied using several simple models: Noninter-acting electrons in a rectangular box, triaxial harmonic oscillator, and Hückel model. Finite temperature effects are studied using the Monte Carlo method. All the models show qualitatively similar odd-even staggering. In the ground state the HOMO-LUMO gap is larger than the neighbouring energy gaps. The reduction of the odd-even staggering due to exchange and correlation is studied using the local-spin-density approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01445004
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  • 111
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    Molecular dynamics study of A18B lennard-jones clusters (1994)
    Springer
    The European physical journal 31 (1994), S. 299-301 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.20.J
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Low temperature structures, melting and evaporation temperatures of A18B clusters with Lennard-Jones interactions have been studied using Molecular Dynamics simulations for different values of the parameters representing (a) the size ratio between A and B atoms, and (b) the ratio between the strengths of the A - B and A - A interactions.
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    URL: http://dx.doi.org/10.1007/BF01445011
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  • 112
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    Static, statistical, and dynamical properties of small sodium clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 232-235 
    Details
    ISSN: 1434-6079
    Keywords: 31.20.D ; 31.30 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This paper reports results obtained in the study of small alkali metal clusters (2≤n≤34). Properties of interest include static descriptions of the Potential Energy Surfaces (PES) using a Distance-Dependent Tight Binding hamiltonian (DDTB) and new results obtained with the same hamiltonian through a Monte-Carlo Growth Method (MCGM) which is shown to give an efficient way to sample the PES, but may also be helpful to estimate the statistical occurrences of the various isomers (catching areas). The probability for generating a given configuration is proportional to a Boltzmann distribution factor and hence a temperature dependence is introduced in the study of the PES. In section 2, the temperature dependence of the optical response for small clusters (on the example of Na4) is simulated throughab initio calculations of the electronic structure coupled with Monte-Carlo dynamics on the absorbing system in the ground state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429154
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  • 113
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    Compound clusters of heavy post-transition elements (1988)
    Springer
    The European physical journal 10 (1988), S. 329-335 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80.D ; 81.20.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    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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    URL: http://dx.doi.org/10.1007/BF01384868
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  • 114
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    Abundance of Na cluster ions ejected from a liquid metal ion source (1989)
    Springer
    The European physical journal 11 (1989), S. 87-91 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 79.70 ; 35.20.X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    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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    URL: http://dx.doi.org/10.1007/BF01436588
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  • 115
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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)
    Springer
    The European physical journal 13 (1989), S. 355-361 
    Details
    ISSN: 1434-6079
    Keywords: 31.20 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    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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    URL: http://dx.doi.org/10.1007/BF01398902
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  • 116
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    Size-dependent thermodynamic properties of silver aggregates. Simulation of the photographic development process (1989)
    Springer
    The European physical journal 12 (1989), S. 31-35 
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    ISSN: 1434-6079
    Keywords: 82.50 ; 36.40 ; 35.20.V
    Source: Springer Online Journal Archives 1860-2000
    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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    URL: http://dx.doi.org/10.1007/BF01426900
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  • 117
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    Intermolecular vibronic spectroscopy of small Van Der Waals clusters: phenol- and aniline-(argon)2 complexes (1990)
    Springer
    The European physical journal 17 (1990), S. 153-155 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We report the clear observation and assignment of the symmetric stretching and bending van der Waals modes in two three-bodyC 2v complexes, phenol- and aniline-(Ar)2, using resonant two-photon ionization.
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    URL: http://dx.doi.org/10.1007/BF01437671
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  • 118
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    Stability of alkali-atom clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 199-203 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    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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    URL: http://dx.doi.org/10.1007/BF01426937
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  • 119
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    Jellium-model calculation for monomer and dimer decays of some potassium clusters (1989)
    Springer
    The European physical journal 12 (1989), S. 205-208 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    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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    URL: http://dx.doi.org/10.1007/BF01426938
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  • 120
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    Role of fragmentation processes in the liquid metal ion source production of aggregates (1989)
    Springer
    The European physical journal 12 (1989), S. 221-224 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 79.00
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    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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    URL: http://dx.doi.org/10.1007/BF01426942
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  • 121
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    Enrichment of Zintl cluster ions (1989)
    Springer
    The European physical journal 12 (1989), S. 235-236 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80.G
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    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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    URL: http://dx.doi.org/10.1007/BF01426945
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  • 122
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    Neutral mass-selected lead cluster beams (1991)
    Springer
    The European physical journal 19 (1991), S. 199-201 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Neutral lead cluster beams with ultra-narrow size distribution were produced by neutralization of mass-selected lead cluster ions, Pb n + withn≤12, in sodium vapor under near-resonant conditions. Absolute charge exchange cross sections were measured as a function of cluster size and are on the order of 40 Å2 forn≥4. Possible fragmentation of the clusters associated with charge transfer was examined by translational spectroscopy. No indication of fragmentation was found.
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    URL: http://dx.doi.org/10.1007/BF01448291
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  • 123
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    Core-hole photoionization study of polysilane compounds (1992)
    Springer
    The European physical journal 23 (1992), S. 159-164 
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    ISSN: 1434-6079
    Keywords: 33.10 ; 33.20.N ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present the results obtained with a new experimental set-up designed for the study of free semi-conductor clusters. This set-up is aimed to study the mass distribution of particles and the evolution of electronic properties as a function of the size, using the technique of core hole photoionization. The cluster production is based on the technique of radio-frequency discharge decomposition of a gas. We study the gaseous particles (Si n H x , 0〈x〈2n+2) generated by pure silane (SiH4) discharges at low pressures (〈10 millitorr) under continuous RF (Radio-Frequency) excitation conditions. We have studied the neutral species present in the post discharge zone and the positive ions present in the discharge. We identify the neutral species as polysilane compounds. We have also compared the ionization spectra obtained near Si-2p edge for the particles containing few silicon atoms with the spectra of SiH4 and Si2H6 molecules. For these molecules, the experimental observations are in agreement with theoretical calculations.
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    URL: http://dx.doi.org/10.1007/BF01436739
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  • 124
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    Thermionic emission from giant fullerenes (1991)
    Springer
    The European physical journal 19 (1991), S. 409-412 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Large even-numbered carbon clusters in the size range from 100 to 600 atoms (giant fullerenes) were generated by laser vaporization and directly injected as positive ions via a supersonic beam into the magnetic trap of an ion cyclotron resonance apparatus. Intense laser excitation of the magnetically levitated fullerenes at 4.0 eV was found to result in production of multiply charged fragments in the trap. Details of the time scale and size dependence of this process suggest it is due to thermionic emission from the superheated gas phase clusters.
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    URL: http://dx.doi.org/10.1007/BF01448340
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  • 125
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    Electronic transitions in C60 and its ions (1991)
    Springer
    The European physical journal 19 (1991), S. 435-438 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electronic spectrum of C60 is calculated using quantum mechanical methods. The first allowed transition in C60 is calculated at an energy of 3.5 eV and with an oscillator strength of 0.09. Several transitions are found at higher energies with comparatively strong oscillator strengths, the strongest one being at 5.78 eV (λ=214 nm). The calculated energy level diagram of C60 is also used to predict wavelengths for transitions in C 60 + and C 60 − . A comparison is made with some recently observed diffuse interstellar bands at 1180 nm and 1320 nm, which have been speculated to originate from C 60 + .
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    URL: http://dx.doi.org/10.1007/BF01448346
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  • 126
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    Experimental study of the dissociation of 100–600 keV hydrogen cluster ions in an argon gas target (1986)
    Springer
    The European physical journal 2 (1986), S. 87-90 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.90
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied the break-up of accelerated hydrogen cluster ions passing through an argon gas target. The absolute dissociation cross section has been measured for a wide variety of H n + (odd masses only) cluster ions, withn between 5 and 23 and with projectile velocities ranging from 1.5 to 5 × 108 cm/s. We discuss the dissociation processes and the dependence of their cross-sections upon the cluster mass and velocity.
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    Multiphoton ionization and photodissociation of (NO)mArn clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 220-222 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80 ; 35.20
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    Topics: Physics
    Notes: Abstract Picosecond multiphoton ionization of (NO)mArn clusters produced in a supersonic expansion of NO/Ar gas mixtures has been studied using time-of-flight mass spectrometry. Two-photon ionization with 266 nm photons show that dilute gas mixtures (1% NO/Ar) yield clusters limited to m≤7, but with as many as 37 argon atoms. Magic numbers are observed for NO+Ar12, NO+Ar18, (NO) 2 + Ar17, NO+Ar22, and (NO) 2 + Ar21 and are understood in terms of solvation of the NO+ and (NO) 2 + by argon in icosahedral arrangements. Four-photon ionization with 532 nm light produces dissociation of the clusters to yield only NO+Arn with n up to 54. This distribution exhibits an additional magic number at n=54, consistent with the completion of a second solvation sphere about the NO+. The known wavelength dependence for photodissociation of (NO) 2 + and (NO) 3 + and comparison of MPI spectra obtained with 266, 355, and 532 nm light indicate that the dissociation is occurring in the cluster ions.
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    Interplay between collective and single electron excitations in large metal clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 267-269 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 73.20 ; 78.65 ; 82.65
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    Topics: Physics
    Notes: Abstract Collective and single electron excitations of large metal clusters supported on transparent substrates are investigated. The applied experimental techniques include extinction spectroscopy and laser induced dissociation accompanied by the ejection of individual atoms. The optical spectra depend on the electromagnetic far field and reflectcollective electron excitations of the conduction electrons, i.e. surface plasmons. Dissociation, however, is correlated to repulsivesingle electron energy levels. The characteristics of these localized excitations indicate a strong influence of collective excitations. In particular, it is found that nonlocal optical effects are important. In this picture surface plasmons catalytically enhance the number of single electron excitations and therefore of the metal atoms ejected as a result of the absorption of visible light. Results will be presented, which illustrate this interplay between collective and single electron excitations.
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    Surface melting in Ni55 (1993)
    Springer
    The European physical journal 26 (1993), S. 304-306 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract The phenomenon of surface melting in a Ni55 cluster is predicted from results of molecular dynamics simulations.
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    Peculiarities of structures and meltinglike transition in gold clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 316-318 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Notes: Abstract Structural and dynamical properties of gold clusters are derived from a Gupta-type potential using numerical simulations and are compared to features of nickel clusters derived from the same potential. The major implication of the comparison is that the properties of clusters mimicked by this many-body potential depend, in general, on the values of its parameters.
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    Structural models for intermediate-sized Si clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 346-348 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20.Sy
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    Notes: Abstract We have investigated two generic structural models for Si clusters in the size range 20–33 atoms. The first model consists of stacks of puckered six-fold rings, with capping atoms on the two ends. The second model comprises compact structures with as many bulk-like four-fold coordinated atoms as possible. We have found the cohesive energy of the ring structures to be nearly constant as a function of cluster size, while that of the compact structures decreases dramatically with increasing size as more four-fold coordinated atoms are incorporated into the structures. We compare our results with recent experiments which suggest a crossover in stability between two cluster types in the size range studied here.
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    Photoelectron spectroscopy of (CO2)n(H2O) m − clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 367-369 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80
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    Notes: Abstract Photoelectron spectra of (CO2)nH2O− (2≤n≤8) and (CO2)n(H2O) 2 − (1≤n≤2) were measured at the photon energy of 3.49 eV. The spectra show unresolved broad features, which are approximated by Gaussians. The vertical detachment energies (VDEs) were determined as a function of the cluster size. For (CO2)nH2O−, the VDE-n plots exhibit a sharp discontinuity between n=3 and 4; the VDE value is ≈3.5 eV at n=3, while it drops down abruptly to 2.59 eV at n=4. This discontinuity in VDE is ascribed to "core switching" at n=4; a C2O 4 − dimer anion forms the core of (CO2)nH2O− for n≤3, while a monomer CO 2 − is the core for n≥4. The (CO2)2(H2O) 2 − ion has a VDE of 2.33 eV, indicating the presence of a CO 2 − monomer core in the binary clusters containing two H2O molecules.
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    In-situ STM observation of coalescence of metal particles in liquid (1993)
    Springer
    The European physical journal 26 (1993), S. 42-44 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.16.D ; 82.65.F
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    Topics: Physics
    Notes: Abstract We have madein-situ observation of electrodeposition on the graphite surface in electrolyte(0.5 mM-Bi2O3, 10 mM-HClO4) by means of Scanning Tunneling Microscopy(STM). We have observed the growth and the stripping of Bi metal particles of about 10 nm in diameter, with increase and decrease in the electrode potential, respectively. The STM images are taken in real time in a period of about 30 sec. They show that small particles grow in the initial stage, come in contact with each other, and coalesce in the contact area connecting two neighboring particles.
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    Supported Pdn (n=1−20) cluster reactivity : CO chemisorption (1993)
    Springer
    The European physical journal 26 (1993), S. 64-66 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 82.30
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    Topics: Physics
    Notes: Abstract The Pdn clusters are prepared by vapour deposition in an UHV chamber providing static secondary ion mass spectrometry (SSIMS) and thermo-programmed desorption analysis (TPD) facilities. By adjusting deposition parameters we are able to obtain isolated Pd species, dimers etc... In the present work we used as substrates thin films of γ-Alumina. We show that the reactivity and the kinetics of the CO-Pdn association depends on the cluster size.
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    An optical method for temperature measurement of silver clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 115-117 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract Generating silver clusters by means of the gas aggregation technique, we have observed that in addition to larger clusters, a substantial amount of silver dimers is always present. This allows us to determine the vibrational population in the electronic ground state and, hence, the vibrational temperature of Ag2 optically. Temperatures between 70–300 K were measured in this experiment, dependent on cell parameters, e.g. evaporation rate, argon flow rate, length of the drift tube, etc. The high volume collisional rate of 1021 cm−3s−1 at the given pressures allows us to assume that the cluster temperature does not differ considerably from that of dimer.
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    Comparison of small metal clusters: Ni, Pd, Pt, Cu, Ag, Au (1993)
    Springer
    The European physical journal 26 (1993), S. 156-158 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract Structures of small clusters of Ni, Pd, Pt, Cu, Ag, and Au with n=2−34 and n=55 atoms are calculated as functions of number of atoms and temperature by the simulated annealing Monte Carlo method using an embedded atom potential.
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    Gas-phase chemical kinetics of small metal clusters: developmen and characterization of a fast-flow reactor for neutral clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 168-170 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 82.20.Pm ; 82.30.Cf
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    Topics: Physics
    Notes: Abstract The development and characterization of a new fast-flow reactor for the study of the gas-phase chemical kinetics of small metal clusters is reported. The flow reactor has been designed to study the reactivity of well-thermalized clusters over a range of well-determined pressures in order to obtain quantitative absolute kinetic rate constants, especially in the low pressure limit. The apparatus has been characterized and proven through the study of known reactions of atoms and is capable of measuring bimolecular rate constants ranging five orders of magnitude down from gas kinetic at total pressures from 0.2 to 6 Torr. Application to the study of cluster kinetics has been demonstrated by measurements made on reactions of the copper dimer, Cu2.
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    Clustering in expanding nozzle flows (1993)
    Springer
    The European physical journal 27 (1993), S. 89-92 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.50.C
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    Topics: Physics
    Notes: Abstract A simplified model for the calculation of the maximum possible cluster size in expanding nozzle flows, assuming a coagulation growth, is presented. For this model we assume seeded beams with lean mixtures, where the ratio of carrier gas pressure to vapour pressure is much larger than one. In this case the heat of condensation is effectively absorbed by the carrier gas. To estimate the maximum possible cluster size it is assumed that every collision of condensable material contributes to the cluster growth. The cluster sizeN, which is the number of monomers or atoms per cluster, is then given by the number of cluster-cluster collisionsZ N by the relation $$N = 2^{Z_N } $$ .
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    The Hubbard model for small clusters (1986)
    Springer
    The European physical journal 3 (1986), S. 91-96 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 71.10 ; 75.10
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    Topics: Physics
    Notes: Abstract The Hubbard model with nearest neighbor hopping, and one type of orbital is applied to clusters of 4 and 5 sites. Results are reported for the ground state as a function of the number of electrons. A rather complicated dependence of the spin of the ground state on occupation number, geometry, and model parameters is found. Ground state energies are compared. The excitation spectrum is illustrated in a particular example.
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    Spectroscopy of Na3 (1986)
    Springer
    The European physical journal 3 (1986), S. 131-136 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract The excitation spectrum of Na3 was systematically investigated from 700 to 330 nm. Four excited states were observed. One of them exhibits fractional quantization of the vibronic pseudorotation which constitutes the first direct verification of the adiabatic sign-change theorem. Photofragmentation is studied by depletion spectroscopy and the 420 nm system is found to be completely predissociated. The structure of the ground state and the ionization potential are also measured.
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    Ionized cluster beam technique for thin film deposition (1986)
    Springer
    The European physical journal 3 (1986), S. 271-278 
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    ISSN: 1434-6079
    Keywords: 81.15J ; 68.55 ; 36.40
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    Topics: Physics
    Notes: Abstract The ionized cluster beam (ICB) technique can be classified as an ion-assisted technique for film formation, and it has the feature of transferring low energy and equivalently high current beams. The clusters can be created by condensation of supersaturated vapour atoms produced by an adiabatic expansion process. These clusters are large size macro-aggregates of 100–2,000 atoms formed by pure expansion of vapourized solid state materials. The clusters are first partially ionized by an electron impact, then the kinetic energy can be added to the ionized clusters. The ICB has unique capabilities of film deposition due to cluster properties and its low energy ion beam transport in a range from thermal energy to a few hundred eV, with the ability to use the effective influence from the ions without space charge problems. This allows high quality deposition and epitaxy of materials at low temperature onto a wide variety of substrates and even permits the formation of thin film materials not previously possible.
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    Formation of water and ammonia cluster anions by electron transfer from laser excited Rydberg atoms (1992)
    Springer
    The European physical journal 24 (1992), S. 297-306 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 82.30.f ; 82.60.L
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    Topics: Physics
    Notes: Abstract Using a laser excited Rydberg atomic beam as a very low energy (10-270 meV) electron source, we have investigated the experimental conditions for observation of water (from dimer to 40-mer) and ammonia cluster anions. From simple model calculations, estimates of the small water cluster adiabatic electron affinities have been determined as well as the orders of magnitude of autodetachment lifetimes and attached electron critical energies.
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    Molecular dynamics study of orientational order and rotational melting in clusters of TeF6 (1994)
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    The European physical journal 31 (1994), S. 117-123 
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    Keywords: 36.40 ; 64.60.Qb ; 82.20.Wt
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    Topics: Physics
    Notes: Abstract Molecular dynamics simulations of the behavior of molecules in crystalline clusters of TeF6 were carried out on systems of 100, 150, 250, and 350 molecules. Several diagnostic functions were applied to investigate whether rotational melting occurred before translational melting. These functions included the coefficient of rotational diffusionD θ(T), the “orientational Lindemann index” δθ(T), the “orientational angular distribution function”Q(θ,T), and the “orientational pair-correlation function”g θ(r, T). All indicators implied that rotational melting occurred before translational melting, that it began with the outermost molecules, and that its onset for smaller clusters was at lower temperatures than for larger clusters. Results also showed that the rotational transition coincided with the transition from a lower symmetry phase (monoclinic) to cubic, a phenomenon that had been noted by others to occur with some regularity for systems of globular molecules.
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    Photoelectron spectroscopy of sodium chloride anions with two excess electrons (1993)
    Springer
    The European physical journal 26 (1993), S. 184-186 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract Photoelectron spectroscopy measurements of (NaCl)nNa− (n=1–13, except n=10) are reported. The observed electron energy spectra fall into three distinct types, reflecting different correlations between the two excess electrons and ions. Depending on the host clusters' structures, the experimental evidence indicates that the two excess electrons in these sodium chloride clusters could be spin paired, forming a bipolaron or a Na− anion. The two excess electrons could also be spin parallel, forming a double F-center state.
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    The dynamics of phase changes in molecular clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 101-104 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.14.F ; 64.60.Q ; 82.20.M
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    Topics: Physics
    Notes: Abstract The significant advantages offered by systems of molecular clusters in the study of homogeneous nucleation are discussed. Determinations of nucleation rates in clusters can be followed experimentally in supersonic jets or computationally in molecular dynamics simulations. Extraordinarily high rates may be encountered, both in freezing and in solid-state transitions. From such information can be inferred the interfacial free energies, σsl and σSS, mechanisms of solid-state transitions. and an explanation of why certain crystalline phases not found in bulk systems can be seen in large molecular clusters.
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    Scattering of a potassium atom beam from potassium promoted catalyst surfaces via electronically excited clusters (1995)
    Springer
    The European physical journal 34 (1995), S. 199-212 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.25 ; 82.65
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    Topics: Physics
    Notes: Abstract Surface scattering of potassium atom beams is observed from surfaces of a potassium promoted catalyst, which is known to emit Rydberg K* species and clusters K n * . The surfaces studied are cut flat from pellets of an industrial catalyst, the promoted iron oxide catalyst for styrene production. The scattering is studied in the temperature range 500–1000 K in an UHV apparatus with a K atom beam at 45° towards the normal, with surface ionization and ion detection over an angular range of −90° to +90° with respect to the surface normal. Bilobular scattering patterns are observed, which are mainly back-scattering at low temperatures, below 750 K. A large signal due to ions emitted in the backwards direction is also found with a voltage on the sample. This back-scattering indicates that the scatterers are heavy clusters outside the surface. The ion formation in the backwards direction is proposed to be due to collisions with electronically excited clusters K n * of the type recently observed by field ionization detection (Kotarba et al. 1994). The bilobular scattering transforms into asymmetric patterns with a larger forward (specular) lobe at higher temperatures, above 800 K. Only a small fraction of the beam molecules is scattered off the surface. The scattering is well described by inelastic surface scattering theory. This shows that the actual scattering surface is rather flat, which is proposed to be due to an antibonding Rydberg type interaction, of long range (hundreds of Å), between the impinging excited K atom and the surface. The temperature dependence of the neutral scattering gives a barrier of 0.96 eV, close to what is generally found for Rydberg species emission from such surfaces. At larger K surface densities, the contributions to the peaks from the beam flux is shown to agree with this picture involving collisions with excited clusters outside the surface.
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    Triaxial shapes of sodium clusters (1995)
    Springer
    The European physical journal 34 (1995), S. 125-134 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20.Wg ; 71.45.Nt
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    Topics: Physics
    Notes: Abstract A modified Nilsson-Clemenger model is combined with Strutinsky's shell correction method. For spherical clusters, the model potential is fitted to the single-particle spectra obtained from selfconsistent Kohn-Sham calculations. The deformation energy surfaces of sodium clusters with sizes of up toN=270 atoms are calculated for a combination of triaxial, quadrupole and hexadecapole deformations. The ground state shapes and energies are determined by simultaneous minimization with respect to the three shape parameters. A significant fraction of the clusters is predicted to be triaxial. The deviations from the axial shape do not generate any systematic odd-even staggering of the binding energies.
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    Ultrafast fragmentation and ionisation dynamics of ammonia clusters (1996)
    Springer
    The European physical journal 36 (1996), S. 349-364 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.30. + h
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    Notes: Abstract The formation of protonated and unprotonated ammonia cluster ions is studied by femtosecond two colour two photon pump-probe techniques applied to (NH3) n and (ND3) n clusters withn up to 8. The fourth harmonic (∼ 200 nm, 6.2 eV, 160 fs) of a Ti: Sapphire laser pulse is used to excite the clusters in a state corresponding to theà state of NH3 while the third harmonic (267 nm, 4.65 eV) is used for the subsequent ionisation step. Employing a combination of the optical Bloch equations for the excitation process and rate equations for the cluster dynamics we calibrate the zero time delay and carefully analyse the time dependence of the pump-probe signal. Several distinct intermediate steps in the time evolution can be distinguished, having characteristic time constants ranging from 40 fs to over 100 ps. They are discussed in a consistent scheme for the excitation, ionisation and protonation dynamics, accounting also for characteristic differences observed between deuterated and undeuterated species. A particularly remarkable time dependence of the homogeneous (NH3) 2 + cluster ion signal is interpreted as a fingerprint of internally protonated neutral precursors of the type NH3NH2NH4.
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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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    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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    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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    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
    Source: Springer Online Journal Archives 1860-2000
    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)
    Springer
    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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    Triangle contraction in six-membered-ring silicon clusters (1989)
    Springer
    The European physical journal 14 (1989), S. 237-245 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20
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    Topics: Physics
    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)
    Springer
    The European physical journal 12 (1989), S. 11-13 
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    ISSN: 1434-6079
    Keywords: 07.75 ; 36.40 ; 34.80.G
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    Topics: Physics
    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)
    Springer
    The European physical journal 12 (1989), S. 53-59 
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    ISSN: 1434-6079
    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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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20
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    Topics: Physics
    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)
    Springer
    The European physical journal 11 (1989), S. 249-255 
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    ISSN: 1434-6079
    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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    ISSN: 1434-6079
    Keywords: 36.40 ; 47.55.E ; 61.14.F
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    Topics: Physics
    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)
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    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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    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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    Topics: Physics
    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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    Topics: Physics
    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)
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    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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    Topics: Physics
    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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    Topics: Physics
    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)
    Springer
    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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    Topics: Physics
    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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    Keywords: 36.40 ; 33.35.Ex
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    Topics: Physics
    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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    Topics: Physics
    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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    ISSN: 1434-6079
    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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    ISSN: 1434-6079
    Keywords: 31.20.N ; 36.40
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    Topics: Physics
    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)
    Springer
    The European physical journal 12 (1989), S. 395-397 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20.R
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    Topics: Physics
    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)
    Springer
    The European physical journal 12 (1989), S. 425-429 
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    ISSN: 1434-6079
    Keywords: 79.60 ; 36.40
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    Topics: Physics
    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)
    Springer
    The European physical journal 12 (1989), S. 435-437 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.20 ; 78.40
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    Topics: Physics
    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)
    Springer
    The European physical journal 12 (1989), S. 469-470 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 78.00
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    Topics: Physics
    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)
    Springer
    The European physical journal 12 (1989), S. 481-484 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.20
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    Topics: Physics
    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)
    Springer
    The European physical journal 12 (1989), S. 505-514 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 42.20 ; 78.00 ; 81.20 ; 81.40 ; 82.70
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    Topics: Physics
    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)
    Springer
    The European physical journal 13 (1989), S. 301-306 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    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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    Quantum chemical investigations of the latent image formation (1990)
    Springer
    The European physical journal 15 (1990), S. 79-86 
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    ISSN: 1434-6079
    Keywords: 31.20 ; 36.40 ; 82.65
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    Topics: Physics
    Notes: Abstract The alternating process of adsorption of Ag+ and trapping of a photoelectron on a (100) AgBr surface is investigated by quantum chemical calculations. The results give some insight into the initial steps of the photographic process (absorption of two photons which lead to the formation of a sublatent image).
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    Internal excitation effects in the photodissociation of size selected ethylene and methanol dimers (1991)
    Springer
    The European physical journal 18 (1991), S. 181-188 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 82.50.F
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    Topics: Physics
    Notes: Abstract The infrared photodissociation spectra of C2H4 and CH3OH dimers are measured for different internal excitation energies ΔE. The dimers are size-selected in a scattering process with He and the internal energy is varied by using (1) different collision energies, (2) different scattering angles and (3) by measuring the complete energy loss spectra with and without laser radiation by time-of-flight analysis of the scattered clusters. For (CH3OH)2 the width Γ of the spectrum increases strongly with ΔE, while the cross section at the maximum is constant, a normal behaviour for an inhomogeneously broadened system. For (C2H4)2 Γ is nearly constant after a sort of threshold and the cross section increases with increasing ΔE. These results are explained by hot band excitation and the coupling to the darkv 10-mode.
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    Sub-doppler-spectroscopy of Na3 (1991)
    Springer
    The European physical journal 18 (1991), S. 257-265 
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    ISSN: 1434-6079
    Keywords: 33.20 ; 35.20 ; 36.40
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    Topics: Physics
    Notes: Abstract Rotationally cold Na3-molecules are formed during the adiabatic expansion of an argon beam, seeded with 5% sodium vapor. With a single mode tunable dyelaser crossing the molecular beam perpendicularly within the ion source of a mass spectrometer the Na3-molecules are excited into levels of the2 A 2-state which are then ionized by acw argon-laser. Rotational lines of the electronic2 A 2 ←X 2 B 2 transition and their hyperfine structure could be resolved using an OODR-technique. A preliminary analysis of the measured spectra is discussed and a comparison of the experimental results with ab initio calculations is presented.
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    Calculation of photoionization cross sections of Na2–8 and K2–8 clusters (1991)
    Springer
    The European physical journal 18 (1991), S. 267-280 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80E
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    Topics: Physics
    Notes: Abstract Analysis of free metal clusters studied with photoionization mass spectrometry or photoelectron spectroscopy requires theoretical predictions of the photoionization cross sections to gain a deeper physical understanding. Calculated energy-dependent photoionization cross sections of Na2–8 and K2–8 clusters are presented in this study. The ground state electronic structure of the clusters are calculated using the Local Spin Density method (LSD) which is also the starting point for the cross section calculation with the continuum multiple scattering method. A basic analysis of the photoionization process is given within the independent electron picture. Strong resonances are predicted in the UV cross sections (5–10 eV) of K3–8 but not for Na3–8, interpreted as shape resonances, i.e. quasibound states in which electrons are trapped by a potential barrier. Unfortunately experimental data are only known close to the ionization threshold and a comparison between our values and experimental data in a broad energy range is not possible.
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    Computer simulations of small semiconductor and metal clusters (1991)
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    The European physical journal 19 (1991), S. 31-36 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract A brief survey is presented of recent simulations of small clusters, made with both ab-initio and classical approaches, with particular emphasis on the application of the Car-Parrinello method. The discussion mainly focusses on the structural properties of a variety of materials and on the effects of temperature.
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    The influence of shells, electron thermodynamics, and evaporation on the abundance spectra of large sodium metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 47-50 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20.Wg ; 03.65.-w
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    Topics: Physics
    Notes: Abstract Measurements of the mass abundance spectra of sodium clusters containing up to 600 atoms are presented. The clusters are produced in a seeded supersonic expansion of Ar or Kr gas, and the spectra are obtained by a time-of-flight technique. The sawtooth features in the spectra are interpreted as evidence of a regular spherical shell structure with magic numbers,N 0, scaling approximately with the cube root of the number of sodium atoms. Altogether twelve shell closings are observed,N 0=2, 8, 20, 40, 58, 92, 138, 196, 260, 344, 440 and 558. There is also a pronounced odd-even staggering all the way up toN=70. The experimentally observed intensity changes for the clusters around the magic numbers are discussed in terms of the electronic free energy,F(N), calculated at finite temperature, and the second differences of the free energy Δ2 F(N)=F(N−1)−2F(N)+F(N+1). The processes behind the non-uniform abundance distributions, and the thermodynamics of finite electron systems with non-uniform level spacings are discussed on this basis.
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    Semiclassical variational study of size effects in neutral and charged jellium droplets (1991)
    Springer
    The European physical journal 19 (1991), S. 55-58 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20
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    Topics: Physics
    Notes: Abstract An analytic expression for the total energy of metallic clusters composed ofN identical atoms of valencev and with net chargeQ is obtained by means of a variational solution of the Thomas-Fermi-Weizsäcker energy density functional within the spherical jellium model. The minimum energy is given as an expansion in decreasing powers of the cluster radiusR=r s Z 1/3, withZ=vN andr s the radius per electron of the bulk metal. The coefficients are obtained as functions ofr s . Terms of volume (R 3), surface (R 2), curvature (R), constant (R 0), (1/R) and (1/R 2) are clearly separated in the formula, as well as the different contributions (kinetic, coulombic and exchange-correlation) to each of them. The asymptotic values (R→∞) for the work functions,W(r s ), and surface energies σ(r s ), are compared to analogous semiclassical and Kohn-Sham calculations of jellium-like surfaces and to the experimental values. The size dependent behaviour of chemical potentials, μ(R), electron affinities,AF(R), and ionization potentials,IP(R), are easily obtained for any kind of metallic clusters. In particular we discuss the Coulomb and quantum corrections to the coefficients β, δ in the asymptotic formulae:IP≃W+β/R andAF≃W+δ/R.
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    Absolute cross sections for electron impact ionization of Ag2 (1991)
    Springer
    The European physical journal 19 (1991), S. 77-79 
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    ISSN: 1434-6079
    Keywords: 34.80G ; 36.40 ; 35.20V
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    Topics: Physics
    Notes: Abstract The previously measured relative cross section function for electron impact ionization (EII) of neutral Ag2 has now been calibrated quantitatively by combining the electron impact ionization with in situ non resonant two photon ionization (NR2PI). By comparing the NR2PI saturation intensities measured for Ag 2 + and Ag+ with the corresponding EII intensities, the ratio between the electron impact ionization cross sections (EIICS) of neutral Ag2 and Ag was determined to be σAg2/σAg=1.53 for an electron energy of 46 eV. This result agrees well with the geometricn 2/3-rule $$(\sigma X_n \sim n^{2/3} )$$ commonly proposed for the dependence of the EIICS of clustersX n on the cluster sizen.
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    Thermal broadening of plasmon absorption in potassium cluster ions (1991)
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    The European physical journal 19 (1991), S. 85-87 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 78.40-q
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    Topics: Physics
    Notes: Abstract The optical absorption spectrum around the surface plasmon peak is presented for K 21 + . Hot, charged potassium clusters are produced by an adapted liquid metal ion source. The plasmon is found to be slightly red shifted from and distinctly broader than the one reported in an experiment on colder clusters by Bréchignac et al. [3]. Mechanisms responsible for the temperature dependence of the width and position of the surface plasmon in small metal clusters are discussed.
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    Response properties of sodium clusters within a jellium-like model with finite surface thickness (1991)
    Springer
    The European physical journal 19 (1991), S. 93-96 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 71.45.G
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    Topics: Physics
    Notes: Abstract The usual spherical jellium model of alkaline clusters is generalized to allow for a finite surface thickness in the positive background distribution. Static (relative stability, ionization potentials) and response properties have been calculated and the results show a better agreement with experiments.
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    The elastic scattering on jellium clusters (1991)
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    The European physical journal 19 (1991), S. 97-99 
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    ISSN: 1434-6079
    Keywords: 34.80.B ; 36.40
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    Topics: Physics
    Notes: Abstract The following calculations are based on the local density approximation potential (LDA) of W. Ekardt for the spherical jellium-background model (SJBM). Taking into account the smooth shape of the potential, the WKB approximation was used to calculate the energy and angular dependence of the electron scattering cross-sections fo rsmall Na clusters. The number of phase shifts needed to describe the scattering in the range of energies 〈4.5 eV increases with the size of cluster. The calculated elastic electron scattering cross-sections for the Na clusters, corresponding to the shell closings (8, 20, 40), are exhibiting a pronounced peak structure, correlated with resonance states. The computed peaks of the angular dependences of the cross-sections on energy are shifted to small angles with increasing the cluster size. The absence of fragmentation at these small electron energies presents a challenge for the experimentalists.
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    Bimetallic cluster cations ejected from a liquid metal ion source: Li-Na and Li-Mg (1991)
    Springer
    The European physical journal 19 (1991), S. 129-131 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 79.70 ; 35.20X
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    Topics: Physics
    Notes: Abstract Cluster ions of alloys (Li-Na, Li-Mg) have been produced by a liquid metal ion source (LMIS), and analyzed by mass spectrometry. For the Li-Na system, bimetallic clusters with various compositions were formed, and dominant bimetallic species were Na2Li+, NaLi+, NaLi 2 + and NaLi 8 + with this sequence of ion intensity. These clusters are systems containing 2 or 8 valence electrons except for NaLi+. For the Li-Mg, observed bimetallic clusters were limited to only three species (MgLi+, MgLi 2 + and Mg2Li+), but unexpectedly small multiply charged homonuclear clusters, Mg 2 2+ and Mg 3 2+ , were observed.
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    Enthalpies of formation of gaseous Zintl-molecules over sodium-tellurium alloys (1991)
    Springer
    The European physical journal 19 (1991), S. 181-184 
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    ISSN: 1434-6079
    Keywords: 05.70 ; 07.75 ; 36.40
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    Topics: Physics
    Notes: Abstract The vapor over sodium-tellurium alloys was investigated using Knudsen effusion mass spectrometry. The stoichiometries of the molecules in the gas phase are compared with the stoichiometries of those appearing in liquid ammonia. Enthalpies of formation for the gaseous molecules are obtained using van't Hoff plots and third law evaluations.
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    Magic numbers in sims of Mn similar to those of charged Ar clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 189-190 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20X ; 79.20X
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    Topics: Physics
    Notes: Abstract Manganese cluster ions Mn k + (k≲60) have been produced by 7 keV Xe ion bombardment and analyzed by a double-focusing mass spectrometer. Discontinuous variations of intensity are found atk=5, 14, 16, 29, 34, 45 and 54. Most of these magic numbers coincide with or differ by only one from those observed in Ar k + . The similarity in magic numbers between Mn k + and Ar k + indicates that the bonding nature in the charged Mn clusters is similar to that in the charged Ar clusters; The polarization force between a positive ion in the center of a cluster and surrounding neutral atoms is dominant binding force.
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    A diatomics-in-molecules model for singly ionized neon clusters (1992)
    Springer
    The European physical journal 23 (1992), S. 171-179 
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    ISSN: 1434-6079
    Keywords: 31.20.G ; 36.40 ; 34.20
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    Topics: Physics
    Notes: Abstract A minimum-basis diatomics-in-molecules (DIM) model previously developed for singly-ionized argon clusters is applied to neon clusters, Ne n + , forn=3, 4,...,22. A search for the global minimum energy of each cluster yields structures with the positive charge localised on a dimer-ion. This appears to be due largely to the linear unsymmetrical configuration which the model finds for Ne 3 + . For this reason, the structures of the clusters at their minimum energy are different from those for Ar n + computed with the same model. On the other hand, the behaviour of the charge distribution as a function of the geometrical configuration is similar to that for Ar n + , as are the overall shapes of the potential energy surfaces. The results are discussed in terms of the charge distributions and the ratios of equilibrium properties of the dimers and dimer-ions which constitute the input to the model.
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    URL: http://dx.doi.org/10.1007/BF01436741
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