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  • 36.40  (114)
  • Springer  (114)
  • American Meteorological Society
  • 1995-1999
  • 1990-1994  (114)
  • 1993  (55)
  • 1991  (59)
Collection
Keywords
Publisher
  • Springer  (114)
  • American Meteorological Society
Years
  • 1995-1999
  • 1990-1994  (114)
Year
  • 1
    Electronic Resource
    Electronic Resource
    Cluster emission under ion bombardment of metallic targets (1991)
    Springer
    Applied physics 52 (1991), S. 213-217 
    Details
    ISSN: 1432-0630
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Mass spectroscopic studies of the neutral particles sputtered by Ar+ ions at 8 keV from polycrystaline samples have been performed, using non-resonant laser ionization and subsequent time-of-flight mass spectroscopy. Besides sputtered atoms, also dimer and trimer contributions in the order of 10−1 to 10−2 and 10−3 to 10−4, respectively, are found in the sputtered flux. The data obtained here together with previously published data by other groups for different bombarding energies provide strong support for the validity of the recombination model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00324422
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  • 2
    Electronic Resource
    Electronic Resource
    Laser-stimulated desorption of potassium atoms (1991)
    Springer
    Applied physics 52 (1991), S. 445-447 
    Details
    ISSN: 1432-0630
    Keywords: 82.65 ; 36.40 ; 73.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Desorption of K atoms by laser-excitation of surface plasmons in small K particles is reported. The desorption rate has been measured for different laser wavelengths and particle sizes. Time-of-flight measurements reveal a kinetic energy of the desorbed atoms of Ekin=0.13(3) eV. From the experimental data it is concluded that the desorption mechanism is non-thermal in nature. Comparison of the results reported here with our earlier work on Na desorption is made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00323657
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  • 3
    Electronic Resource
    Electronic Resource
    Determination of C60/C70 ratios in fullerene mixtures and film characterization by scanning tunneling microscopy (1993)
    Springer
    Applied physics 56 (1993), S. 197-205 
    Details
    ISSN: 1432-0630
    Keywords: 36.40 ; 61.1.P ; 68.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Fullerene powder mixtures with different C60/C70 ratios have been analyzed by a variety of techniques, and results have been compared. The fullerence mixtures have been characterized as solutions in n-hexane by high-pressure liquid chromatography (HPLC) and UV-VIS spectroscopy. Thin films of fullerenes on Au(111) have been prepared from the mixtures by sublimation. The sublimation process has been studied by simultaneous thermogravimetric and differential thermal analyses. Thin fullerene films on Au(111) have been investigated by scanning tunneling microscopy (STM). The STM images show primarily two types of ballshaped molecules arranged in a lattice with hexagonal symmetry (fcc(111) face, nearest neighbour distance: 1 nm). The two species differ in diameter. STM images of films made of mixtures of different C60/C70 ratios show that C70 molecules display a larger apparent diameter (0.8 nm) and corrugation than C60 molecules (0.7 nm). The C60/C70 ratios obtained by counting the corresponding molecular species in the STM images of the thin films are compared to the C60/C70 ratios determined by HPLC on hexane solutions of the mixtures. The observed differences might be explained by different rates of sublimation for the two species. The STM images reveal film defects (vacancies and boundaries) and dynamic processes (displacement of C70 molecules and vacancies). In films prepared to have a C60 coverage of less than one monolayer, stable structural units of the C60(111) surface consisting of three or seven C60 molecules are revealed by STM. Occasionally, substructure within individual fullerene molecules is observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00539474
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  • 4
    Electronic Resource
    Electronic Resource
    Coherent raman spectroscopy of nitrogen molecules and clusters in supersonic jets (1991)
    Springer
    Applied physics 52 (1991), S. 84-89 
    Details
    ISSN: 1432-0649
    Keywords: 36.40 ; 42.65 ; 47.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Coherent Stokes and anti-Stokes Raman scattering CSRS and CARS have been employed to study the spectroscopy of nitrogen molecules and clusters in the expansion of a supersonic jet. In the vibrational spectrum, at strong stagnation conditions, an intense redshifted peak is observed which can be assigned to the intramolecular vibrations in large N2 clusters having adopted the β-phase structure. Another weak feature is assigned to nitrogen clusters in the α-phase. In the rotational region of the spectrum only monomer features have been observed. The failing to observe librational motions is consistent with the finding that the nitrogen clusters are predominantly in the orientationally unordered β-phase. The low rotational temperature suggests supercooling of the β-phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00357660
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  • 5
    Electronic Resource
    Electronic Resource
    Laser-fluorescence diagnostics for condensation in laser-ablated copper plasmas (1991)
    Springer
    Applied physics 53 (1991), S. 353-361 
    Details
    ISSN: 1432-0649
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We are investigating the thermodynamic conditions under which condensation occurs in laser ablated copper plasma plumes. The plasma is created by XeCl excimer laser ablation (308 nm, 300 mJ/pulse) at power densities from 500–1000 MW/cm2 into backing pressures of helium in the range 0–50 torr. We use laser-induced fluorescence (LIF) to probe velocity and relative density of both atomic copper and the copper dimer molecule, Cu2, which is formed during condensation onset. At low pressure (10 mtorr), the atomic Cu velocity peaks at approximately 2×106 cm/s. Copper dimer time-of-flight data suggest that condensation onset occurs after the Cu atoms have slowed very significantly. Excitation scans of the Cu2A-X (0,0) and (1,1) bands yield a rotational and vibrational temperature in the neighborhood of 300 K for all conditions studied. Such low temperatures support the theory that Cu2 is formed under thermally and translationally cold conditions. Direct laser beam absorption is used to determine the number density of atomic copper. Typical densities attained with 5 torr of helium backing gas are 6–8×1013 cm−3. Rayleigh scattering from particulate is easily observable under conditions favorable to particulate production.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00331827
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  • 6
    Electronic Resource
    Electronic Resource
    Structural stability and energetics of C, Si, and Ge microclusters: empirical many-body potential energy function calculation (1991)
    Springer
    The European physical journal 19 (1991), S. 423-425 
    Details
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The structural stability and energetics of carbon, silicon, and germanium microclusters containing 3−7 atoms have been investigated by using a recently developed empirical many-body potential energy function (PEF), which comprises two- and three-body atomic interactions. The PEF satisfies both bulk cohesive energy per atom and bulk stability exactly. It has been found that the most stable C3−4 microclusters are linear withD ∞h symmetry but C5−7 microclusters are planar withD nh symmetry. Silicon and germanium microclusters show similar structural stability. TheX n (X=Si, Ge;n=3−7) microclusters are found to be most stable in the following forms:X 3 is triangular withD 3h symmetry,X 4 is tetragonal withT d symmetry,X 5 is square pyramidal withD 4h symmetry,X 6 is bipyramidal square withO h symmetry, and finallyX 7 is square pyramidal having two atoms underneath withD 2h symmetry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448343
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  • 7
    Electronic Resource
    Electronic Resource
    C n carbon clusters (n=4−6, 60, 70): interesting cases of computation/observation comparisons (1991)
    Springer
    The European physical journal 19 (1991), S. 431-433 
    Details
    ISSN: 1434-6079
    Keywords: 35.20 ; 36.40 ; 82.30Q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Recent theoretical studies proved some of the small carbon clusters C n (n≈1−10) are represented by several isomeric structures. Evaluation of the isomer relative stabilities is necessary for comparison of theoretical data with observation, this being exemplified by the C4 and C6 cases. For the former cluster a new energy estimation has been suggested based on the isomerism reasoning. Relative-stability evaluation for clusters of different dimensions is discussed on the C60/C70 system, pointing out a strong pressure-dependency of the picture. The scheme is matched to the recent observations of Bethune and Meijer.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448345
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  • 8
    Electronic Resource
    Electronic Resource
    Reaction of small carbon clusters with hydrogen during laser vaporization of graphite (1991)
    Springer
    The European physical journal 19 (1991), S. 447-449 
    Details
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The hydrogen uptake for small carbon clusters C4 to C22 has been studied at high hydrogen pressure. This study indicate that both chain and ring structures exist in parallel.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448349
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  • 9
    Electronic Resource
    Electronic Resource
    Structural properties of 3-dimensional carbon clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 443-446 
    Details
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Structural properties of 3d carbon clusters were calculated employing recently developed model potential energy functions for carbon. Primarily, spherical shell structures were included in the present investigation. Configurations corresponding to local energy minima were calculated for various shells of an icosahedron containing different number of C atoms. For C60, the two low-lying isomers, the buckminsterfullerene and truncated dodecahedron, were found to be almost isoenergetic. It was also found that fully relaxed structures of C90 and C120 have energies very comparable to that of C60. Furthermore, a systematic analysis carried out in this study for carbon clusters with varying dimensionalities, revealed an interesting relationship between the bond lengths and the distribution of bond angles. In all cases, shorter bond distances were found to be associated with larger bond angles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448348
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  • 10
    Electronic Resource
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    Symmetry substructures for MQ-NMR of [A]20 spin clusters of dodecahedranes, [13CH]20 or [13CD]20, metallic M @M20 and [H2O]+ @[H2O]20 exo-cage cluster molecules and their higher-n SO(3) ×l n spin algebras, within the context of mapping,l n -ITP algebras and number partitions (1993)
    Springer
    The European physical journal 25 (1993), S. 275-284 
    Details
    ISSN: 1434-6079
    Keywords: 76.60 ; 03.65.F ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract For both highern andI i ≧1 spin clusters, combinatorics provides powerful arguments with which to investigate the substructural forms of cluster spin algebras; this is especially so for SO(3) ×l n symmetries for 12≦n≦60 wherex (.) [λ] character tabulations become extensive. Bijective enumerative mappings over the combinatorialp-tuples (number partitions) afford insight into the general functionf(p,n) as well as into {|IM(I 1−I n [λ]〉} M -structure of spin algebras, even where the full details of the explicitx () [λ] (l n ) characters are not readily available. Both simply-reducible and higher aspects ofl n -inner tensor product (ITP) algebras are derived from dimensionality considerations, as part of combinatorial hooklength formalisms for $$\chi _{(1^n )}^{[\lambda ]} $$ . TheI i ≦3/2 forms of [A] n clusters forn≦20, (forp≦3, 4) of multiple-quantum NMR (MQ-NMR) are considered here as part of current interest in giant cage-clusters. In addition, the SU2 substructural hierarchy over Liouville space is derived for [A]20(l n ) (I i =1/2) spin cluster of the cage-cluster molecule dodecahedrane; aspects ofI i =1 spin cluster over {|IM (...)〉} space are derived as high temperature model of the exo-cage of [H2O]+ @[H2O]20 cluster ion; 20-fold higher-I i lusters provide models for M @M20 metal-clusters and further applications ofl 20-number partitions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426891
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  • 11
    Electronic Resource
    Electronic Resource
    Excitation and decay processes in helium clusters studied by fluorescence spectroscopy (1993)
    Springer
    The European physical journal 26 (1993), S. 175-177 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 67.90+Z ; 71.90+Q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Excitation and decay processes of helium clusters are investigated with fluorescence methods. The results differ remarkably from that obtained for the heavier rare gas clusters. They are discussed in view of the unusual structural and electronic properties of helium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429135
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  • 12
    Electronic Resource
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    Structural transitions and melting of copper clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 255-257 
    Details
    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Molecular dynamics is used to study the melting and structural transitions of small copper clusters. The melting temperature is found to be proportional to the average coordination number. Small icosahedral clusters melt at slightly higher temperatures than the cubic structures. Small cuboctahedral clusters are not stable but transform via a nondiffusive transition to icosahedral structure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429161
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  • 13
    Electronic Resource
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    Nuclear shell model applied to metallic clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 261-263 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We apply the nuclear shell model to jellium clusters of up to twenty-one Na atoms. Binding energies, ionization potentials, and photoabsorption cross sections are calculated and compared with mean-field results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429163
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  • 14
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    Surface melting in Ni55 (1993)
    Springer
    The European physical journal 26 (1993), S. 304-306 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The phenomenon of surface melting in a Ni55 cluster is predicted from results of molecular dynamics simulations.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429176
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  • 15
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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
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429180
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  • 16
    Electronic Resource
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    The evolution of electronic structure in AlnCom (1993)
    Springer
    The European physical journal 26 (1993), S. 322-324 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80.E
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The ionization potentials of AlnCom clusters (n〉m) have been bracketed using laser photoionization mass spectrometry. We find the electronic shell structure manifested in the ionization potentials of Aln for n≥7 is observed also for AlnCo and AlnCo2, and is consistent with cobalt contributing one electron to the conduction band of the cluster. However, with increasing number of cobalt atoms, this simple picture breaks down; all vestiges of aluminum cluster electronic shell structure are absent for m≥4.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429182
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  • 17
    Electronic Resource
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    Molecular dynamics studies of homogeneous nucleation in solid-state transitions (1993)
    Springer
    The European physical journal 26 (1993), S. 364-366 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 64.60.Qb ; 64.70.Kb ; 82.20.Wt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Simulations of clusters containing 100 to 250 molecules of TeF6 successfully reproduce the crystalline packing arrangements observed in electron diffraction investigations of large molecular clusters (∼ 104 molecules) of the same material. More remarkably, when the clusters are cooled step by step in MD computations at a rate of ca. 1011 K/s they spontaneously undergo the same bcc to monoclinic phase transition that has been observed experimentally in supersonic flow, despite the million-fold difference in the timescales involved. The existence of such a correspondence over so many orders of magnitude, in itself, imposes severe constraints on what type of molecular mechanism can underlie the transformation. Even more revealing evidence about the molecular behavior associated with the phase change is provided by the simulations. They show the formation of the actual transition complexes along the transition pathway, namely, the critical nuclei of the new phase. These nuclei, which are made up of approximately 20 molecules, can be recognized in the midst of the surrounding matter. Techniques based on molecular orientations, involving Pawley-Fuchs projections and orientational angular distribution functions, make it possible to estimate the size of critical nuclei. One noteworthy result established in the simulations is that the solid-state transition temperature from bcc to monoclinic depends upon particle size in the same manner as does the freezing point.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429196
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  • 18
    Electronic Resource
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    Excitation and decay processes in helium clusters studied by fluorescence spectroscopy (1993)
    Springer
    The European physical journal 26 (1993), S. 382-384 
    Details
    ISSN: 1434-6079
    Keywords: 36.40 ; 67.90+Z ; 71.90+Q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Excitation and decay processes of helium clusters are investigated with fluorescence methods. The results differ remarkably from that obtained for the heavier rare gas clusters. They are discussed in view of the unusual structural and electronic properties of helium.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429201
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  • 19
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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
    Source: Springer Online Journal Archives 1860-2000
    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.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01425612
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  • 20
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    Melting behavior of beryllium clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 134-136 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The melting properties of Ben, n=7−14, clusters have been studied using molecular dynamics simulations and an interatomic potential which contains two- and three-body terms, derived from local spin density calculations. The cluster meltinglike behavior has been studied calculating characteristic physical quantities like short-time averages of the kinetic energy per particle as a function of time, caloric curves and root-mean-square bond length fluctuations as a function of the cluster total energy. The meltinglike transition in Ben clusters shows more complex features than those found in van der Waals and ionic clusters. The estimated melting temperatures for n=11−14 are higher than the bulk value. This result indicates that the parameters of the cluster interaction potential could be inadequate to describe the thermodynamic properties of Ben clusters.
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    URL: http://dx.doi.org/10.1007/BF01425642
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  • 21
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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
    Source: Springer Online Journal Archives 1860-2000
    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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    URL: http://dx.doi.org/10.1007/BF01425653
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  • 22
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    Magic cluster ion distributions: (NO) 3 + (N2O)n and (NO) 3 + (CO2)n (1993)
    Springer
    The European physical journal 26 (1993), S. 183-185 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.80 ; 35.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Supersonic jet expansions of mixtures of nitric oxide with either nitrous oxide or carbon dioxide have been investigated over a wide range of relative concentrations. Mixed molecular cluster ions of the form (NO) m + (N2O)n and (NO) m + (CO2)n are detected following non-resonant two-photon ionization. Over a wide range of intermediate concentrations, the cluster ion distributions (NO) 3 + (N2O)n and (NO) 3 + (CO2)n with n≤30 are significantly more intense than clusters containing other numbers of nitric oxide molecules. The extra abundance of these species is attributed to their especially stable structures and several possible forms are discussed. An intriguing possibility involves a stable cyclic nitric oxide trimer (or ion) when combined with nitrous oxide or carbon dioxide clusters.
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    URL: http://dx.doi.org/10.1007/BF01425658
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  • 23
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    Reactions of carbon cluster ions stored in an RF trap (1993)
    Springer
    The European physical journal 26 (1993), S. 252-254 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Reactions of carbon clusterions with O2 were studied by using an RF ion trap in which cluster ions of specific size produced by laser ablation could be stored selectively. Reaction rate constants for positive and negative carbon cluster ions were estimated. In the case of the positive cluster ions, these were consistent with the previous experimental results using FTMS. Negative carbon cluster ions C n − (n=4−8) were much less reactive than positive cluster ions. The CnO− products were seen only in n=4 and 6.
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    URL: http://dx.doi.org/10.1007/BF01425681
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  • 24
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    Ring-stacking consideration on higher fullerene growth (1993)
    Springer
    The European physical journal 26 (1993), S. 258-260 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A hypothetical ring-stacking procedure combined with the isolated-pentagon rule(IPR) shows variety of formation pathways of many fullerene structures with a 5- and 6-membered ring carbon cage. Combining the ring-stacking procedure with energetic considerations, the numbers of possible reaction channels are dramatically reduced within the framework of the ring-stacking considerations. This, in turn, gives the results that only some specific isomers of large fullerenes are selectively produced. The resulting fullerene structures specified are surprisingly well consistent with the recent experimental results.
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    URL: http://dx.doi.org/10.1007/BF01425683
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  • 25
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    Electron energy loss spectroscopy of free C60 and C70 (1993)
    Springer
    The European physical journal 26 (1993), S. 294-296 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.80
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electron energy loss spectroscopy has been performed with samples of pure C60 and C70 using primary electron energies between 10 and 1100 eV. The experimental data could be explained in terms of optically forbidden and allowed transitions, and by collective excitations (plasmons), which could be distinguished by their dependence on the energy of the primary electron.
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    URL: http://dx.doi.org/10.1007/BF01425695
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  • 26
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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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    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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    STM observation of Au fine-particles on graphite (1991)
    Springer
    The European physical journal 19 (1991), S. 333-335 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.16.D ; 82.65.F
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    Topics: Physics
    Notes: Abstract Gold particles deposited on graphite in vacuum have been studied by STM observation in air. Liquid-like coalescence between small gold-particles has been observed near room temperature. Preparation of small particles in vacuum is discussed. Small particles are formed in nucleation process if the degree of coalescence of particles is reduced. Over 400 Au particles of 5 nm in diameters with a narrow size-distribution with FWHM 2 nm and a high density of 3×1012/cm2 is prepared by evaporating gold in a vacuum of about 2×10−5 Torr and at the substrate (HOPG) temperature of 20°C.
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    Adsorption — desorption kinetics on epitaxially oriented palladium clusters (1991)
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    The European physical journal 19 (1991), S. 347-351 
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    ISSN: 1434-6079
    Keywords: 82.65.Jv ; 36.40
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    Topics: Physics
    Notes: Abstract Palladium clusters with a low size dispersion and a single crystallographic shape have been obtained by epitaxial growth on (100) MgO. The isothermal adsorption — desorption kinetics of CO is obtained by a molecular beam method allowing the direct determination of the global adsorption probability and of the mean life time of CO molecules on the clusters. Three main results are deduced from these measurements: — an increase of the adsorption rate of CO on the clusters by the capture of CO molecules physisorbed on the substrate, — a faster desorption rate from (100) than from (111) facets at high coverage, — an increase of the adsorption energy for clusters smaller than 3 nm.
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    Thermionic emission from giant fullerenes (1991)
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    The European physical journal 19 (1991), S. 409-412 
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    ISSN: 1434-6079
    Keywords: 36.40
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    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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    Evidence of linear chain forn≧10 carbon negative ion clusters revealed by mass selected photodetachment spectroscopy (1991)
    Springer
    The European physical journal 19 (1991), S. 427-429 
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    Keywords: 36.40
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    Notes: Abstract Photodetachment spectra of negative carbon clusters are reported in the size range from 5 through 20 atoms. The clusters were prepared in a supersonic beam by laser vaporization and 2nd (2.3 eV) and 3rd (3.5 eV) harmonics of Nd-YAG laser were used for photodetachment. The resultant data indicate that carbon negative cluster ions in the 10–20 range take the forms of both linear chain and cyclic ring under a certain condition.
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    Stability, structures and a hypothetical growth mechanism of carbon 5/6 network (1993)
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    The European physical journal 26 (1993), S. 69-73 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract A novel picture of growth of fullerene and fullerene-like structures is proposed. The ring stacking model have been studied in detail in connection with the stability, structures and growth mechanism of carbon 5-and 6-membered ring network. Combining the model with energetic considerations, the selective formation of sizes and isomers of large fullerenes has successfully been described.
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    Collision-induced reactions of size-selected molecular cluster anions (1993)
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    The European physical journal 26 (1993), S. 223-225 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.90
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    Topics: Physics
    Notes: Abstract Collision-induced reactions of size-selected cluster anions, (CO2) n − and (N2O)nO− with He and Kr atoms were studied at collision energies from 0.1 to 2.0 eV (center-of mass) by means of a tandem mass-spectrometer equipped with a pair of octapole ion guides. The dominant process was evaporation of the constituent molecules from the parent cluster ion. The absolute cross section for the evaporation was measured as functions of the size of the parent cluster ion and the collision energy. The reaction was explained by collisional excitation of the parent cluster ion followed by its unimolecular dissociation. The observed cross sections which correspond to those for the collisional excitation agree with those calculated in terms of charge-induced dipole and induced dipole-induced dipole interactions between the parent cluster ion and the target atom. The distributions of the product ions resulting from the unimolecular dissociation were reproduced by a simple calculation based on RRK theory. In the collision of (CO2) n − , the cross sections for (CO2) 10 − and (CO2) 14 − were significantly small and their abundances in the product ion distributions were particularly large. These findings indicate that (CO2) 10 − and (CO2) 14 − are stable species. On the other hand, stable species in (N2O)nO− was found to be (N2O)5O−.
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    Electron energy loss spectroscopy of van-der-Waals clusters (1991)
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    The European physical journal 20 (1991), S. 35-38 
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    Keywords: 36.40 ; 34.80 ; 71.35
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    Notes: Abstract A method to measure electron energy loss spectra (EELS) of clusters with a high resolution (30 meV) has been developed and has been applied to some van der Waals clusters (Ar n , Kr n ). Structures have been found which relate to the excitation of atoms on the surface and inside the cluster. An influence of the cluster size on the spectra has been observed.
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    On the nature of bulk and surface excitations in Argon clusters (1991)
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    The European physical journal 20 (1991), S. 39-42 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 71.90 ; 78.40
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    Notes: Abstract Absorption spectra of Ar clusters containing between 10 and 106 atoms are dominated by strong transitions into bulk and surface states. The intensity variation of bulk and surface excitations is analyzed within a model, which divides the cluster into a surface layer and into an interior part. The thickness of the surface layer is determined by the intensity ratio of bulk and surface excitations. For then=2, 2′ excitons a reasonable value ranging between the radius of then=2 exciton and the nearest neighbour distance is obtained. In case of then=1 excitons the thickness of the surface layer is much smaller than the nearest-neighbour distance indicating that then=1 surface excitons might be interpreted as excitations of atoms on the cluster surface.
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    Theory for excess electrons in clusters of rare gas atoms (1991)
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    The European physical journal 20 (1991), S. 53-55 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract An exact theory for excess electrons in clusters of rare gas atoms is limited to small sizes,n 〈 20, because of many body polarization interactions which make it necessary to solve a large system of linear equations. We present a simple dielectric screening approximation, which avoids this difficulty and which is in very good agreement with the exact calculation. This approximation can be used to examine the excitation energies of excess electrons and exciton energies in large clusters. A new atomic structure is proposed for a cluster of 12 Xe atoms, resulting in an increased binding energy for the excess electron, which is larger than the electron affinity of a cluster of 13 atoms. This might explain the relatively large abundance of Xe 12 − observed in the experiment.
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    Liquid drop model of multiply charged metal cluster fission (1991)
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    The European physical journal 20 (1991), S. 111-113 
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    Keywords: 36.40 ; 61.25
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    Topics: Physics
    Notes: Abstract Qualitative similarities and differences between metal cluster and nuclear fission are discussed in terms of the liquid drop model. Points covered include the dependence onz 2/n of the relative fission rate, the critical size, and the competition between fission and evaporation.
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    The relation of cluster ion distributions to neutral cluster distributions in cluster beam experiments (1991)
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    The European physical journal 20 (1991), S. 115-118 
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    Keywords: 36.40 ; 33.80 ; 82.30
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    Notes: Abstract One of the major problems in cluster beam experiments with uncharged clusters is to relate the detected distribution of cluster ions to the original distribution of the neutrals. Fragmentation of the clusters, differences in ionization efficiencies, and desorption of ligands for chemically reacted clusters distort the initial distribution. In this contribution the abundances of the neutral and the ionized particles will be related by rate equations in terms of phenomenological rate constants. Two approaches are chosen. In the more simple one the ionization and decay processes are fast and take place during the excitation pulse. In the second approach delayed processes are also allowed. In both cases recursion formulas are derived as analytical solutions of the coupled rate equations for the time evolution of the neutral and ionized cluster intensities. The general solutions contain a considerable number of parameters which have to be reduced by experimental conditions and observations. Applications are discussed.
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    Photofragmentation of cluster ions: the visible photoabsorption spectrum of Ar2N 2 + (1991)
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    The European physical journal 20 (1991), S. 153-155 
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    Keywords: 36.40 ; 33.80 ; 33.20
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    Topics: Physics
    Notes: Abstract The absolute cross section for photodissociation of Ar2N 2 + was measured as a function of wavelength in the 470–550 nm range. A structureless broad band was observed; the cross section has a maximum of ∼ 210 × 10−18 cm2 at ∼ 500 nm. The measurement of the photofragment time-of-flight spectrum shows that(1) N 2 + , Ar+ and Ar 2 + are produced in the photodissociation of Ar2N 2 + in the wavelength range studied, and that(2) the observed visible absorption band is ascribable to a parallel-type transition of Ar2N 2 + , which possibly retains a linear geometry.
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    On the structure and stability of Ar n and Ar n + clusters at finite temperature (1991)
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    The European physical journal 20 (1991), S. 147-151 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 71.10 ; 77.30
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    Topics: Physics
    Notes: Abstract For Ar2–29 and Ar 2–29 + clusters at 20 K in the polarization model presented here the electrodynamical dipole-dipole many-body problem is solved selfconsistently with the Monte-Carlo method (MC) at 20 K, i.e. the instantaneous dipole-dipole interaction is solved to infinite perturbation order and in cluster expansion to the order of the cluster size. The long range many-body dipole-dipole interaction is coupled to exchange interaction by a modified effective dipole polarizability. This model will be compared to the dimer model and classical MC simulation of Ar n . The resulting different magic numbers in the binding energies are discussed in this connection with different experimental techniques of cluster ionization. By the mean square cluster diameter a shape parameter is introduced and it is found that with this parameter structural form transition in cluster growth can be resolved, and surprisingly do not correlate with the magic numbers.
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    Evaporation of Lennard-Jones clusters (1991)
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    The European physical journal 20 (1991), S. 163-166 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract Extensive molecular dynamics simulations have been done to study the evaporation of a 13-atom Lennard-Jones cluster. The survival probability and the evaporative lifetime are calculated as a function of the cluster total energy from a classical trajectory analysis. The results are interpreted in terms of the RRK theory of unimolecular dissociation. The calculation of the binding energy of the evaporated species from the evaporation rate and the average kinetic energy release is discussed.
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    IR-photodissociation of size selected molecular clusters and their structures (1991)
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    The European physical journal 20 (1991), S. 177-180 
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    Keywords: 36.40 ; 82.50.F
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    Notes: Abstract Infrared photodissociation spectra of (CH3NH2) n clusters were measured fromn=2 ton=6 near the monomer absorption of the C-N stretching mode at 1044 cm−1 using a cw-CO2 laser. The clusters were size-selected by scattering from a helium beam. The spectrum of cold dimers shows a red (1038 cm−1) and a blue (1048 cm−1) shifted peak which is attributed to the non-equivalent position of the C-N in the open dimer structure. The larger clusters exhibit only one peak between 1045.4 cm−1 and 1046.0 cm−1 caused by the equivalent position of the C-N in the cyclic structures of the larger clusters. Structure calculations confirm these results. Secondly, the mixed complexes C2H4-CH3COCH3 and C2H4-(CH3COCH3)2 were investigated. The dimer spectrum, measured around the monomer frequency of the out-of-plane bending mode of C2H4 at 949 cm−1, shows two peaks at 946.2 cm−1 and 961.3 cm−1. This splitting is attributed to two different isomers that are found in configuration calculations. A similar behaviour is found for the trimer.
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    Fragmentation by electron impact ionization and intracluster reactions of size selected (N2H4) n and (OCS) n clusters (1991)
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    The European physical journal 20 (1991), S. 181-183 
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    Keywords: 36.40 ; 34.80.G
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    Notes: Abstract The hydrogen-bonded (N2H4) n clusters and the van der Waals (OCS) n clusters are size selected in a scattering experiment with a He beam up to the cluster sizen=6. By measuring the angular distributions of the scattered clusters the complete fragmentation pattern of electron impact ionization is obtained. For Hydrazine the two main fragment masses are the protonated species (N2H4) n−1H+ and with somewhat weaker intensities also the nominal ion mass (N2H4) n + . The largest intensity is observed for the monomer ion N2H 4 + to which clusters up ton=5 fragment. For carbonylsulfide, completely different results are obtained. Aside from the fragments of the OCS monomer and the van der Waals cluster fragments (OCS) 2 + and (OCS) 3 + signals at mass S 2 + , S 3 + and S2OCS+ are detected. This indicates a fast chemical reaction in the cluster according to: S + OCS → CO + S2 which occurs for clusters of sizen ≥ 2. Peaks at S 3 + and S2OCS+ are seen for the first time forn ≥ 5 according to a further reaction of S2 in the cluster.
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    Energy transfer rates in inhomogeneous van der Waals clusters (1991)
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    The European physical journal 20 (1991), S. 185-187 
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    Keywords: 33.65 ; 33.80E ; 36.40
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    Topics: Physics
    Notes: Abstract The internal energy exchanges inside an inhomogeneous van der Waals cluster are investigated by means of molecular dynamic calculations. The very long time scales for relaxation of the high frequency degrees of freedom are examined within the framework of Nekhoroshev's theorem.
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    Production and stability of oxygen cluster cations and anions, revisited (1991)
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    The European physical journal 20 (1991), S. 201-203 
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    Keywords: 36.40
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    Notes: Abstract Stoichiometric and non-stoichiometric, positive and negative oxygen cluster ions (n up to 70) have been produced in a crossed neutral beam/electron beam ion source. The abundance and stability of the ions formed have been analyzed with a double focussing sector field mass spectrometer in a series of experiments. Positive and negative ion mass spectra observed exhibit distinct abundance anomalies, however, at different cluster sizes. Abundance maxima and minima correlate with correspondingly small and large metastable fractions of (O2) n + and (O2) n − ions, respectively. (O2) n + ions may also lose up top=(n−1) monomers by collision induced dissociation with monotonously decreasing probability with increasingp. Metastable fractions determined for (O2) n − ions produced with appr. zero eV electrons are in general larger than those for ions produced with appr. 7 eV electrons. (O2) n − ions are also observed to decay via autodetachment, with lifetimes increasing with increasing cluster size. Finally, here we were able to prove that an apparent loss of the monomer fragment O (and higher homologues) observed in the metastable time regime is due to ordinary metastable monomer evaporation in the acceleration region. Moreover, we will also present here some new data and interpretation concerning the electron attachment cross section function for O2 clusters.
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    Metal carbide clusters formed by laser ablation of metal oxide-graphite systems (1991)
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    The European physical journal 20 (1991), S. 89-91 
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    Keywords: 36.40 ; 34.80 ; 33.80
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    Notes: Abstract The laser ablation of solid targets made of mixtures of simple components yields cluster ions of various composition. In this paper, positive cluster ions formed by laser ablation of metal oxide and graphite systems are reported. The formation of Me m C n + cluster ions indicate a chemical reaction in the surrounding area hit by the laser beam.
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    Metastable decay of Ar n + involving single monomer evaporation and the loss of peculiar numbers of monomers (1991)
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    The European physical journal 20 (1991), S. 157-159 
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    Keywords: 36.40
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    Notes: Abstract Production and stability of Ar n +* ions (withn up to 420) formed by electron impact ionization of a supersonic Ar cluster beam were investigated with a double focussing sector field mass spectrometer. The present study confirms previous magic number determinations up to the 4th icosahedral shell. A systematic study of metastable dissociations (monomer evaporation, magic number evaporation) for singly charged cluster ions as a function of cluster size, internal excitation energy and time elapsed since ion formation gives new insight into the ionization process and subsequent reactions of the ions formed. At a well-defined threshold energy ofca. 28 eV, the magic number loss mechanism occurs simultaneously with the well known single monomer evaporation process which proceeds at all energies. The new mechanism is the first known example of cluster ion metastability showing an exponential dependence on time, providing further evidence that the precursor parent cluster ion is produced in a specific energy state.
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    Melting of gold microclusters (1991)
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    The European physical journal 20 (1991), S. 235-238 
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    Keywords: 36.40
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    Notes: Abstract The transition from solid-like to liquid-like behavior in Au n ,n=6, 7, 13, clusters is studied using molecular dynamics simulations. A Gupta-type potential with all-neighbour interactions is employed to incorporaten-body effects. The melting-like transition is described in terms of short-time averages of the kinetic energy per particle, root-mean-square bond length fluctuations and mean square displacements. A comparison between melting temperatures of Au n and Ni n clusters is presented.
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    Structural and dynamical properties of transition metal clusters (1991)
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    The European physical journal 20 (1991), S. 239-242 
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    Keywords: 36.40
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    Notes: Abstract Results of molecular dynamics simulation studies of structural and dynamical properties of 12-, 13-, and 14-atom transition metal clusters are presented. The calculations are carried out using a Gupta-like potential expressed in reduced units. The transformation to absolute units involves two size-dependent parameters which effectively convert the potential into a size-dependent one. The minimum energy geometries of the clusters are obtained through the technique of simulated thermal quenching. A melting-like transition is observed as the energy of the clusters is increased. A novel element of the transition is that it may involve a premelting state.
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    Size effects in the solid phase transition of SF6 clusters (1991)
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    The European physical journal 20 (1991), S. 251-253 
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    Keywords: 36.40 ; 61.14F ; 64.70K
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    Topics: Physics
    Notes: Abstract The structure of SF6 clusters produced in a free jet expansion is studied by electron diffraction methods. A solid phase transition is known to occur when clusters are warmed up by changing several experimental conditions in the expansion of a Ne + SF6 mixture. In the present study, the total stagnation pressure and the SF6 mole fraction are varied in order to understand how these parameters influence the structural state of the clusters and further to observe the phase transition for different cluster sizes. When the stagnation pressurep 0 is larger than about 10 bar, a given mole fraction results in clusters with identical structure and probably identical temperature. Whenp 0 is decreased below 10 bar, identical structures are found for lower and lower mole fractions. This structural behaviour suggests that for small clusters, containing less than about 500 molecules, the transition steps occur at temperatures lower than those observed for larger clusters. The possibility of detecting a temperature variation in the diffraction patterns of small cubic clusters is discussed.
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    Kinetics of phase changes in large molecular clusters (1991)
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    The European physical journal 20 (1991), S. 255-257 
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    Keywords: 36.40 ; 61.14.F ; 64.60.Q ; 82.20.M
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    Topics: Physics
    Notes: Abstract A method has been devised to study the kinetics of phase changes in an unfamiliar regime of extreme undercooling and rate of transformation. We show how electron diffraction can monitor the time evolution of phase changes in molecular clusters condensed from the vapor in supersonic flow. Transitions taking place in microseconds are readily followed. Examples include solid state transformations as well as the freezing of liquid clusters. Aspects of the experiment making it possible to observe familiar transitions under highly unusual conditions will be discussed along with some advantages of the new technique.
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    Theory of the structural fluctuation of Au55 clusters (1991)
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    The European physical journal 20 (1991), S. 259-261 
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    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract Stabilities and structural fluctuations of both neutral and charged Au55 clusters are examined and discussed in relation to recent experimental observations of small gold particles with an electron microscope. Transition probabilities between the icosahedral and cuboctahedral structures are calculated according to the transition state theory using a model potential consisting of attractive many-body, repulsive pairwise and Coulomb parts. It is shown that for a neutral cluster the cuboctahedral structure has too short life time to be observed around room temperature and that, on the other hand, for more than 6-fold multiply charged clusters, both structures have life times of the order of 0.1 s around room temperature and, therefore, the transition between them can be observed.
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    Optical plasmon losses in stabilized Au55 clusters (1991)
    Springer
    The European physical journal 20 (1991), S. 297-300 
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    ISSN: 1434-6079
    Keywords: 33.20.K ; 36.40 ; 42.20 ; 78.40 ; 82.70
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Au55 cluster compounds are investigated by optical spectroscopy and TEM. The optical spectra appear to be rather structureless, neither showing a collective excitation resonance nor exhibiting distinct absorption bands known from lower nuclearity clusters. We discuss changes of the electronic properties compared to larger Au clusters affecting both, 6sp electrons and5d-6sp interband transitions, the cluster-ligand-interaction being considered as a charge transfer process. We additionally report on a low temperature instability of the cluster compound, which results in changed optical extinction spectra. A characteristic absorption feature at λ=400 nm is attributed to small, ligand-free Au cluster fragments.
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    Negative ion photoelectron spectroscopy of solvated electron cluster anions, (H2O) n − and (NH3) n − (1991)
    Springer
    The European physical journal 20 (1991), S. 9-12 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.60 ; 33.80.E
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The photodetachment spectra of (H2O) n =2−69/− and (NH3) n =41−1100/− have been recorded, and vertical detachment energies (VDEs) were obtained from the spectra. For both systems, the cluster anion VDEs increase smoothly with increasing sizes and most species plot linearly withn −1/3, extrapolating to a VDE (n=∞) value which is very close to the photoelectric threshold energy for the corresponding condensed phase solvated electron system. The linear extrapolation of this data to the analogous condensed phase property suggests that these cluster anions are gas phase counterparts to solvated electrons, i.e. they are embryonic forms of hydrated and ammoniated electrons which mature with increasing cluster size toward condensed phase solvated electrons.
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    Photoemission on gold-55-clusters derived from gold-phosphine AuP(C6H5)3Cl (1991)
    Springer
    The European physical journal 20 (1991), S. 377-379 
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    ISSN: 1434-6079
    Keywords: 79.60 ; 71.20 ; 36.40
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    Topics: Physics
    Notes: Abstract We measured XPS and UPS spectra of gold clusters with 55 atoms, embedded in an electrically isolating phosphine matrix, and of gold-phosphine, from which the clusters were chemically derived. Compared to the spectra of bulk gold the valence band spectrum and the core level spectra of the clusters showed shifts of the peaks and the fermi level to higher binding energies. The shift of the peaks could qualitatively be interpreted by a final state effect. We succeeded in a separation of bulk and surface contributions to the core level spectra and in a reasonable quantitative analysis of the valence band spectrum of the clusters. The Au 4f core level spectrum of gold-phosphine showed two peaks at 1.5 eV higher binding energies than the corresponding peaks of the clusters.
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    Electronic structure of Cr clusters on graphite (1991)
    Springer
    The European physical journal 20 (1991), S. 387-390 
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    ISSN: 1434-6079
    Keywords: 79.20 ; 73.20 ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electronic structure of small chromium clusters deposited by evaporation onto clean polycrystalline graphite has been studied by means of Auger, X-ray Photoemission (XPS) and Electron Energy Loss (EELS) spectroscopies. The XPS results show an increase in the binding energy of both core levels and valence band reducing the cluster size. The EELS measurements show a variation of the intensity ratio of L3-to-L2 ionization core edges. We interpret this change as due to different redistribution, within the clusterd-band, of the empty states above the Fermi level. As a consequence the XPS results may also be attributed to sizeable change of the electronic structure of the small clusters.
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    Synchrotron radiation study of silver and chromium particles supported on graphite (1991)
    Springer
    The European physical journal 20 (1991), S. 391-394 
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    ISSN: 1434-6079
    Keywords: 79.60 ; 36.40
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    Topics: Physics
    Notes: Abstract Silver and chromium particles in the size range 10 nm to 25 nm formed by deposition in ultra-high vacuum on graphite have been studied using synchrotron radiation. We have determined the island size by measuring the spectral dependence of the reflectivity of each sample using light in the photon energy range 35 eV to 190 eV. Comparing this measurement to a calculation of the reflectivity modified by the size-dependent extinction, determined using Mie theory, gives the average particle radius. Using this sizing technique we find that, for the growth of silver at room temperature, the average radius increases linearly with the cube root of evaporation time. Deposition with the substrate at elevated temperatures produces, for similar coverages, an increase in the average size for temperatures between 200°C and 225°C followed by a rapid decrease above 225°C. Chromium shows size effects in the photoemission spectra from the 3s and 3p core levels and the 3d valence band. With decreasing radius a decrease in the multiplet splitting of the 3s core level and a large change in the relative intensity among the 3p multiplets occurs indicating increased electron correlation as the system becomes smaller. A narrowing of the valence band also occurs which we attribute to a structural change at the surface of the particles.
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    High resolution MW spectroscopy of Rydberg clusters for the studies of small metal cluster ions: a preliminary experiment (1991)
    Springer
    The European physical journal 20 (1991), S. 407-409 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 33.40. Hp ; 32.30. Bv
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    Topics: Physics
    Notes: Abstract Microwave spectroscopy in highly excited Rydberg states is proposed for structure determination of small metal cluster ions. An experimental setup for microwave optical triple resonance is developed and tested for Yb atom. Many microwave transitions are measured with the line width less than 1 MHz (HWHM).
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    Formation of silver clusters in nozzle expansions (1991)
    Springer
    The European physical journal 20 (1991), S. 425-428 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.50.C
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The first successful experiments to generate continuum silver cluster beams from nozzle expansions are described. A mixture Ar/Ag expands out of a conical nozzle (0.35 mm dia., 10° cone angle, length 17 mm). At 2150 K, total pressure 300 kPa, silver partial pressure 8 kPa the silver intensity measured with a rate meter 479mm away from the source is 1.8 nm/s, or 0.02 g m−2s−1. The data for the onset of clustering confirm the predictions of the scaling laws developed to compare condensation in nozzle expansions of metal vapors with that of rare gases.
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    An electron diffraction apparatus for small particle beams (1991)
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    The European physical journal 20 (1991), S. 457-459 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 61.14
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    Topics: Physics
    Notes: Abstract An electron diffraction apparatus is described which has been developed for use with small particle beams. The apparatus features a pulsed 100 kV electron beam and on-line parallel measurement of the diffraction pattern using linear charge coupled devices. Preliminary results on a molecular beam of small silver particles are presented.
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    Concluding remarks (1991)
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    The European physical journal 20 (1991), S. 465-467 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract Viewing cluster science as the embryology of the full-grown forms of matter we encounter in our surroundings, makes it appear to a relative newcomer as a highly dynamic discipline. Lines of attack showing marked progress or potential promise are briefly reviewed, and a sketch of the vast field of still-open problems is presented.
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    Electron transfer collisions between sulfur dioxide clusters and laser-excited Rydberg atoms (1991)
    Springer
    The European physical journal 21 (1991), S. 177-184 
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    ISSN: 1434-6079
    Keywords: 34.50.g ; 34.70. ; 35.20.W ; 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Electron attachment to SO2 clusters is studied in a pulsed crossed beam apparatus, using laser-excited nf Rydberg atoms as a low energy electron source. The results are interpreted as an attachment to a dimer subcluster followed by a rapid impulsive dissociation of the nascent dimer anion. The remaining cluster anions possess a large amount of internal energy. At low principal quantum numbersn, the influence of the Rydberg ionic core leads to an important evaporation process interpreted with simple model calculations.
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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
    Source: Springer Online Journal Archives 1860-2000
    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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    Interaction of CO with silver clusters: Dependence on cluster size (1993)
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    The European physical journal 26 (1993), S. 162-164 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract The interaction of matrix-isolated silver clusters with CO has been investigated for clusters containing as few as 100 atoms/cluster. A vibrational mode at a monolayer coverage, which is found on bulk silver at 2110 cm−1, is present even for these small particles. For these small-sized particles however, an additional, broad, unresolved band at 1950 cm−1 appears, which does not exist for larger clusters. Whether this band has its origin in a modified chemical behaviour for particles smaller than 100 at/cl is not clear.
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    Threshold electron spectra of semiconductor cluster ions (1993)
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    The European physical journal 26 (1993), S. 216-218 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract A simple threshold electron analyzer was constructed and laser photodetachment threshold electron spectra of Si− and Si 4 − were measured.
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    Electronic and geometrical structure of noble metal clusters (1993)
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    The European physical journal 26 (1993), S. 12-14 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract We investigate the electronic and structural properties of small (N ≲ 20) and medium sized (N ≲ 500) clusters of Cu, using the first principles Tight-Binding Linear Muffin-Tin Orbitals (TB-LMTO) method in connection with the real-space recursion scheme. We find the electronic structure resembling the one of simple alkali metal clusters: Pronounced shell closing effects can be identified in the ionization potentials as well as in the HOMO-LUMO gaps for the magic sizesN=8, 20, 34 and 40. The low-energy equilibrium geometries show considerable Jahn-Teller distortions, just as in the case of alkali metals.
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    Two dimensional detection of size selected and focused neutral carbon clusters using image intensified charge coupled device (ICCD) system (1993)
    Springer
    The European physical journal 26 (1993), S. 317-319 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract An apparatus for getting size selected and focused neutral carbon clusters was developed. Using image intensified charge coupled device (ICCD) system, the beam profiles of C 10 − and C10 were investigated. The results indicated that the beam density of C10 surpasses that of C 10 − of space charge limit.
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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 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20.Gm ; 31.20.D ; 82.40.We
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    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.
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    Two maxima dependencies of isomerism contribution to heat capacity of N2O-HCN & CO-C2H2 systems in low temperature region (1993)
    Springer
    The European physical journal 26 (1993), S. 338-340 
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    ISSN: 1434-6079
    Keywords: 35.20 ; 36.40
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    Topics: Physics
    Notes: Abstract Temperature effects on heat capacity in four and three component systems N2O-HCN and CO-C2H2, respectively, were computed. Structural and vibrational parameters originated from the second order Møller-Plesset perturbation treatment with the 6-31++G** basis set while relative energies were of a still advanced nature. Isomerism contribution to heat capacity exhibits two temperature maxima at 43 and 205 or 15 and 83 K in N2O-HCN or CO-C2H2. The highest reported isomeric enhancement of the total heat capacity is about 27 %.
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    Clustering in expanding nozzle flows (1993)
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    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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    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 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 34.70.+e
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    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.
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    Shell structure and level spacing distribution in metallic clusters (1993)
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    The European physical journal 26 (1993), S. 28-32 
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    ISSN: 1434-6079
    Keywords: 36.40
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    Topics: Physics
    Notes: Abstract The lattice gas Monte Carlo and tight binding method is used to study the electronic shell structure in large metallic clusters. The average density of states of a large ensemble of deformed clusters shows the same shell structure as the most spherical geometry. The level spacing distribution at the Fermi level is a Wigner distribution.
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    Interplay between collective and single electron excitations in large metal clusters (1993)
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    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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    Structural models for intermediate-sized Si clusters (1993)
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    The European physical journal 26 (1993), S. 346-348 
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    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)
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    The European physical journal 26 (1993), S. 367-369 
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    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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    Supported Pdn (n=1−20) cluster reactivity : CO chemisorption (1993)
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    The European physical journal 26 (1993), S. 64-66 
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    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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    Ionization potential of clusters in liquids (1993)
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    The European physical journal 26 (1993), S. 82-86 
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    Keywords: 82.50 ; 36.40 ; 35.20.V
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Time-resolved observations of the fast electron transfer from an electron donor to metal ions adsorbed on metal clusters in solution have shown that a critical size of the cluster is required to make it capable of accepting electrons. The threshold is attributed to a size dependent redox potential of the cluster, increasing with the nuclearity (in contrast with the ionization potential in the gas phase which decreases when n increases): it corresponds to the nuclearity for which the cluster redox potential becomes more positive than the potential of the electron donor acting as a monitor. New data of redox potentials (or IP) of Agn clusters (hydroquinone as monitor) and Cun cluster (sulfonatopropylviologen anion as monitor) are derived. The influence of n and of the solvation or the ligand is discussed.
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    The role of Ga-droplet formation in nanometer-scale GaAs cluster synthesis from organometallic precursors (1993)
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    The European physical journal 26 (1993), S. 219-221 
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    Keywords: 36.40
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    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.
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    The optical extinction of ligand-stabilized Au13- and Au55-clusters: The vanishing of the Mie-resonance (1993)
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    The European physical journal 26 (1993), S. 1-3 
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    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.
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    URL: http://dx.doi.org/10.1007/BF01425599
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    Reactivity of carbon cluster ions with Ar, O2 and D2 (1993)
    Springer
    The European physical journal 26 (1993), S. 305-307 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Carbon cluster ions generated by laser evaporation have been reacted with atoms (Ar) and molecules (O2, D2). In order to vary the reaction conditions for the cluster ions two gas inlets at different locations have been added to the cluster source. Addition of D2 increased the line width in the TOF-spectrum indicating the appearance of reaction products of the type CmDn. Both O2 and D2 proved very effective in removing the odd numbered carbon cluster ions in the vicinity of C60. Application of O2 produced a significant effect: depending on the gas pressure it reacted with small cluster ions forming products like CnO+ and CnO2 +. Such reaction channels are not found for n〉12 thus indicating a change in cluster geometry. Another sequence of experiments has been undertaken by adding Ar atoms to the carbon cluster ions. Some stable ionic reaction products like ArC+,..., ArC4 +, ArC5 + can be detected. It is known from previous studies that the ArC+ is a stable ion with an dissociation energy of about 1 eV.
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    URL: http://dx.doi.org/10.1007/BF01425698
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    Dynamics of cluster-surface interaction: Evidence of structural isomers of C 60 − (1993)
    Springer
    The European physical journal 26 (1993), S. 320-322 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Collision induced electron detachment of the fullerene C 60 − and the other C 60 − produced through the laser vaporization of a carbon rod was studied. Both of C 60 − showed quite different behavior for the process. It was suggested that the laser vaporized C 60 − has a different structure from the fullerence C 60 − .
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    Quantum mechanical study of the structure and stability of molecular van der Waals' clusters II: (NH3)nHCN (1993)
    Springer
    The European physical journal 26 (1993), S. 329-331 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 31.20.D
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The structures and stabilities of small mixed clusters of ammonia with hydrogen cyanide have been studied usingab initio electronic structure calculations at the Hartree Fock and Møller Plesset levels of theory. Stable structures for (NH3)nHCN, n=1, 2, 3 have been located. Two stable structures and a transition state for the heterodimer are described.
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    Exchange effects on electronic states in jellium clusters (1993)
    Springer
    The European physical journal 28 (1993), S. 73-80 
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    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.
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    URL: http://dx.doi.org/10.1007/BF01437457
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    Modified Nilsson model for large sodium clusters (1993)
    Springer
    The European physical journal 28 (1993), S. 235-245 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20.Wg ; 71.45.Nt
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We propose a modified Nilsson model for spheroidal sodium clusters and investigate the modification of shell structure by deformation for sizes up toN=850. For spherical clusters, our potential is fitted to the single-particle spectra obtained from microscopically selfconsistent Kohn-Sham calculations using the jellium model and the local density approximation. Employing Strutinsky's shell-correction method, the surface energy of the jellium model is renormalized to its experimental value. We find good agreement between our theoretically predicted deformed magic numbers and the experimentally observed ones extracted from recent sodium mass abundance spectra.
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    URL: http://dx.doi.org/10.1007/BF01437890
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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
    Source: Springer Online Journal Archives 1860-2000
    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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    URL: http://dx.doi.org/10.1007/BF01429138
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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
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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)
    Springer
    The European physical journal 19 (1991), S. 31-36 
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    ISSN: 1434-6079
    Keywords: 36.40
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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
    Source: Springer Online Journal Archives 1860-2000
    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)
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    The European physical journal 19 (1991), S. 189-190 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 35.20X ; 79.20X
    Source: Springer Online Journal Archives 1860-2000
    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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    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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    Studies of Sb and Bi cluster produced by laser desorption (1991)
    Springer
    The European physical journal 19 (1991), S. 203-206 
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    ISSN: 1434-6079
    Keywords: 36.40 ; 79.20
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Direct production of cations and anions of metal clusters of Sb and Bi by laser evaporation in a vacuum has been studied. Bulk sample substrates are irradiated by 1064, 532 and 355 nm beams at variable intensity, and the ions produced are accelerated and identified by time-of-flight mass spectrometry. At 1064 nm, the cation distributions show that Sb 3 + and Bi 3 + are the most abundant species, while the monomer and dimer cations are almost non-existent. The anion spectra indicate very low yields of Sb− and Bi− with dominant dimer anion species. These patterns persist with laser power variation within the stable operation domain. With lower incident laser wavelength, the mass distributions are modified, favouring the production of the light cluster ions. In no circumstances were Sb and Bi ions withn〉5 observed. Many of the observed phenomena can be explained if one assumes that for these elements, clusters withn〈6 are formed on the substrate surface. Cluster ions are produced via a prompt desorption process, and are subjected to photon induced reactions due to the same incident laser beam. However, more detailed investigation of the desorption properties will be necessary to confirm such a desorption mechanism.
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    URL: http://dx.doi.org/10.1007/BF01448292
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