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  • 36.40.+d  (210)
  • Springer  (210)
  • 2005-2009
  • 1990-1994  (210)
  • 1925-1929
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  • Springer  (210)
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  • 1
    Electronic Resource
    Electronic Resource
    Desorption of metal atoms with laser light of different polarization (1993)
    Springer
    Applied physics 57 (1993), S. 101-104 
    Details
    ISSN: 1432-0630
    Keywords: 73.20.Mf ; 82.65.Pa ; 82.50.−m ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract Laser-induced desorption of metal atoms from the surface of small metal particles has been investigated as a function of the shape of the particles and the polarization of the incident laser light. The particles were supported on LiF, quartz or sapphire substrates. In a first set of experiments, the shape of the particles was determined by recording optical transmission spectra with s- and p-polarized light incident under an angle of typically 40° with respect to the surface normal. The metal particles turn out to be oblate, the ratio of the axes perpendicular and parallel to the substrate surface being on the order of 0.5. This ratio decreases with increasing particle size. Also, the particles change shape if the temperature is raised. In further experiments, s- and p-polarized light has been used to stimulate desorption of atoms via surface plasmon excitation. It is found that the desorption rate markedly depends on the polarization of the light. This is explained by excitation of the collective electron oscillation along different axes of the non-spherical particles.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00331225
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  • 2
    Electronic Resource
    Electronic Resource
    The dimer sputtering mechanism of Cu(001) at low bombarding energy (1992)
    Springer
    Applied physics 55 (1992), S. 364-371 
    Details
    ISSN: 1432-0630
    Keywords: 79.20.N ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract The emission of dimers during bombardment of a Cu(001) surface by Cu atoms of 300 and 1000eV energy is studied. A molecular dynamics simulation method based on many-body potentials is employed. At 300eV bombarding energy, around 81% of the sputtered dimers originate from second-nearest neighbor sites. 58% of these are ejected in a collision sequence correlated by the projectile. These dimers lead to a second maximum in the kinetic energy distribution of emitted dimers at around 8eV, besides a maximum at 4eV. Only the latter is found at 1000eV bombarding energy. As in this case mostly next-neighbor surface atoms are sputtered, the specific emission mechanism found at 300eV is irrelevant. Finally, we show that the direction of the angular momentum of sputtered dimers is correlated with the original surface site of the dimers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00324086
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  • 3
    Electronic Resource
    Electronic Resource
    Orientational correlations and order in A3C60 (1993)
    Springer
    Applied physics 56 (1993), S. 215-217 
    Details
    ISSN: 1432-0630
    Keywords: 71.25.Mg ; 71.25.Rk ; 71.20.−b ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abstract A tight-binding method which has been previously applied to study the effect of uncorrelated orientational disorder on conduction-band properties is extended here to the case of systems with long-range order and/or short-range correlations. The density of states and conductivity are not highly sensitive to the specific short-range correlations, so long as the system is not too close to being fully ordered. Hence the strong effects of disorder found previously appear to be robust and should play an important role in the interpretation of normal-state properties of A3C60.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00539477
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  • 4
    Electronic Resource
    Electronic Resource
    RPA in nuclei and metal clusters (1994)
    Springer
    The European physical journal 349 (1994), S. 219-222 
    Details
    ISSN: 1434-601X
    Keywords: 21.60.Jz ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We discuss and compare the gross features of resonance excitations in nuclei and metal clusters. We point out the phenomenon of ”jellium scaling” which means that different materials for metal clusters all give similar resonance spectra and we discuss the various effects which determine the exact position of the resonance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01288962
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  • 5
    Electronic Resource
    Electronic Resource
    Nonlinear resonances and phase transitions of two-ion Coulomb clusters in a Paul trap: Calculations without laser cooling (1994)
    Springer
    Applied physics 58 (1994), S. 57-62 
    Details
    ISSN: 1432-0649
    Keywords: 32.80.Pj ; 42.50.Vk ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The mechanism responsible for transitions of laser-cooled trapped ions from an ordered “crystal” state to an irregular “cloud” state has been discussed controversially. A numeric and analytic study of the relative motion of two trapped ions without laser cooling is performed and compared with the results of previous simulations involving the laser. It turns out that the system without laser, in spite of its simplicity, already exhibits a non-monotonic dependence of crystal stability on trap parameters, which is linked to the presence of low-order nonlinear resonances.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01081714
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  • 6
    Electronic Resource
    Electronic Resource
    Resonant photoemission study ofK-derived valence-band states in K X C60 (1993)
    Springer
    The European physical journal 92 (1993), S. 347-351 
    Details
    ISSN: 1434-6036
    Keywords: 36.40.+d ; 74.75.+t ; 79.60.−i
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electronic structure of K-doped C60 was investigated by photoemission (PE) and X-ray absorption near-edge structure (XANES) studies at the C-1s and K-2p thresholds. In addition, information on the local K-derived partial density of states in superconducting K3C60 was obtained by resonant PE at the K-2p 1/2 threshold. The experimental observations support a complete charge transfer from K to C60 and we clearly observe a finite density of states atE F . From resonant PE, occupied states with K-p, d character could be identified in the binding-energy region from 1.5 to 8 eV below, but not directly at the Fermi level. This partial-density-of-states structure agrees well with the results of our band-structure calculations based on the local-density approximation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01308753
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  • 7
    Electronic Resource
    Electronic Resource
    Secondary ion mass spectra of gold super clusters up to 140000 dalton (1990)
    Springer
    The European physical journal 17 (1990), S. 73-76 
    Details
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 35.20.Wg ; 07.75.+h
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The bombardment of a two-shell gold complex (Au55(PPh3)12Cl6) with 10 keV Xe+-ions results in the formation of secondary ion masses up to 140000 u. These are by far the largest secondary ions observed under primary particle bombardment. The detection and identification of these ions with a Time-Of-Flight Secondary Ion Mass Spectrometer (TOF-SIMS) gives important information about the behavior of naked full-shell clusters. Au13 particles, generated from the Au55 cluster, serve as building blocks for a series of super-clusters up to (Au13)55. The results for keV-ion bombardment are compared to those for MeV-ion bombardment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437501
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  • 8
    Electronic Resource
    Electronic Resource
    Density of states and evaporation rate of helium clusters (1990)
    Springer
    The European physical journal 15 (1990), S. 257-263 
    Details
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 67.40.Kh ; 05.30.−d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The density of states of4He clusters is calculated on the assumption that only surface vibrations are thermally excited. Results for mixed3He-4He and3He clusters are also given. The Weisskopf procedure is used to calculate the evaporation rates and the cooling laws of helium clusters at low temperatures.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437187
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  • 9
    Electronic Resource
    Electronic Resource
    Production of C2H4Cl+ by dissociative photoionization of weak molecular complexes in C2H4+HCl mixtures (1990)
    Springer
    The European physical journal 16 (1990), S. 283-292 
    Details
    ISSN: 1434-6079
    Keywords: 34.50.Lf ; 36.40.+d ; 82.50.Fv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The photoionization efficiency (PIE) spectrum from 600 to 1200 Å for the production of the ion C2H4Cl+ by dissociative photoionization of the products of room-temperature jet expansions of a 1:4 mixture of C2H4 and HCl was measured at several nozzle pressures. The results were resolved into the PIE yield curve for the heterodimer process C2H4·HCl+hv→C2H4Cl++H+e. This reaction is necessarily characterized by a large change in geometry between neutral complex and ionic product. The observed spectrum exhibits an unusual and conspicuous peak at 15.2 eV that is characterized by a sharp cutoff to the high energy side. This feature points to the onset of strongly nonstatistical channels for the production of C2H4Cl+ at this energy such that product formation proceeds through very few states. The observed onset of C2H4Cl+ at 11.92±0.24 eV is 17±6 kcal mol−1 above the true threshold. An important conclusion is that at all energies above the onset the yield of dissociative ionization of the heterodimer to the cation C2H4Cl+ is determined by dynamical factors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01437532
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  • 10
    Electronic Resource
    Electronic Resource
    Electronic structure calculations of small Al n (n=2–8) clusters (1992)
    Springer
    The European physical journal 22 (1992), S. 641-644 
    Details
    ISSN: 1434-6079
    Keywords: 31.20.Ej ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electronic states of small Al n (n=2–8) clusters have been calculated with a relativistic ab-initio MO-LCAO Dirac-Fock-Slater method using numerical atomic DFS wave-functions. The excitation energies were obtained from a ground state calculation of neutral clusters, and in addition from negative clusters charged by half an electron in order to account for part of the relaxation. These energies are compared with experimental photo-electron spectra.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426366
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  • 11
    Electronic Resource
    Electronic Resource
    Mercury clusters: jellium-like mass spectra and threshold laws for electron impact ionisation (1991)
    Springer
    The European physical journal 19 (1991), S. 223-225 
    Details
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 71.30.+h
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mercury clusters have been ionised by impact of electrons of variable kinetic energy. For cluster sizesn≤540 a linear threshold law is observed, which allows an accurate identification of the ionisation energies. The differences to photo ionisation are discussed. Jellium like intensity variations are observed in the mass spectra, in a size region where the bonding in Hg clusters has not yet become metallic.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448297
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  • 12
    Electronic Resource
    Electronic Resource
    On the transition from localized to delocalized electronic states in divalent-metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 219-221 
    Details
    ISSN: 1434-6079
    Keywords: 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The transition from van der Waals to covalent bonding, which is expected to occur in divalent-metal clusters with increasing cluster size, is discussed. We propose a model which takes into account, within the same electronic theory, the three main competing contributions, namely the kinetic energy of the electrons, the Coulomb interactions between electrons, and thes ↔p intraatomic transitions responsible for van der Waals like bonding. The model is solved by taking into account electron correlations using a generalized Gutzwiller approximation (slave boson method). The occurrence of electron localization is studied as a function of the interaction parameters and cluster size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01448296
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  • 13
    Electronic Resource
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    Ab-initio study of localization of an excess electron in sodium halide clusters (1992)
    Springer
    The European physical journal 23 (1992), S. 91-98 
    Details
    ISSN: 1434-6079
    Keywords: 31.20.Di ; 31.20.Ej ; 31.90.+s ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The equilibrium geometries of Na n F n and Na n F n−1 are optimized forn=2, 3, 4 at the SCF level. The Na n F n molecules appear as formed by Na+ and F− ions. The paper studies the localization of the excess electron in the Na n F n−1 molecules. Na n F n−1 is obtained by removing from Na n F n a fluorine atom, and the excess electron takes the place of this lacking center, and allows a weak bond between the neighbouring Na atoms. Secondary minimum geometries, for which the excess electron has no defined place, are also studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01436708
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  • 14
    Electronic Resource
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    Effects of surface roughness on the electronic structure of metallic clusters (1992)
    Springer
    The European physical journal 24 (1992), S. 57-63 
    Details
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 31.20.Pv ; 05.40.+j
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study the electronic level density in spherical clusters. Due to the granularity of the ionic background the surface is irregular at the microscopical level. We show that this affects the shell structure and that the level statistics display from the bottom to the top of the spectrum a transition from a poissonian behaviour to one consistent with the predictions of random matrices theory.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01436604
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  • 15
    Electronic Resource
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    Analysis of the electronic structure of C60 doped withp-elements (1993)
    Springer
    The European physical journal 25 (1993), S. 175-180 
    Details
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 31.20.Sy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electronic structure of C60 doped with thep-elements B-F, Al-Cl and Ga-Br located at the centre of the cage has been analyzed within the local density approximation using the von Barth-Hedin exchange correlation potential. The calculations show the existence ofn- andp-type doped Buckminsterfullerene, where a partly occupied level occurs in the band gap, similar to the donor or acceptor levels in traditionally doped semiconductors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01450172
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  • 16
    Electronic Resource
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    EELS investigation of small gold clusters on mica substrates (1993)
    Springer
    The European physical journal 25 (1993), S. 261-265 
    Details
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 79.20.Kz
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Gold clusters with diameters from 2 to 10 nm are prepared by evaporation on mica substrates. They are investigated with low energy electron loss spectroscopy in the reflected beam and characterised in a transmission electron microscope. The energy loss spectra show a broadening of the plasma peak with decreasing particle size. The plasma frequency shifts to higher energies. The size dependence of the half width and of the plasma frequency is compared to known models. The results support the quantum box model of Genzel et al.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01426889
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  • 17
    Electronic Resource
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    Fragmentation and reaction processes in cluster-surface collisions (1993)
    Springer
    The European physical journal 26 (1993), S. 226-228 
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    ISSN: 1434-6079
    Keywords: 79.20.Rf ; 34.50.Lf ; 79.20.Nc ; 81.60.Cp ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We review the processes which have been observed from collisions between alkali-halide clusters and solid surfaces. Soft impact of nanocrystalline NanF n−1 + clusters against solid surfaces causes them to cleave along the lowest energy (100) plane. At higher collision energies (Ei〉1 eV/atom), an evaporative cascade occurs which is characteristic of a transformation of the nanocrystal to a molten state. Efficient F− transfer from the cluster to the surface can occur for the larger clusters (〉60 atoms) scattering from Si(111), in direct competition with the cleaving channel at low energies. In this regime, strong bonds can form between the F− and silicon surface. The reaction probability increases with cluster size indicating that an impact-initiated shock wave is needed to enhance the reactive process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429152
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  • 18
    Electronic Resource
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    Time-resolved studies of neutral and ionized Nan clusters with femtosecond light pulses (1993)
    Springer
    The European physical journal 26 (1993), S. 131-134 
    Details
    ISSN: 1434-6079
    Keywords: 33.80.-b ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The real-time dynamics of Nan (n=3–21) cluster multiphoton ionization and fragmentation has been studied in beam experiments applying femtosecond pump-probe techniques in combination with ion and electron spectroscopy. Three dimensional wave packet motions in the trimer Na3 ground state X and excited state B have been observed. We report the first study of cluster properties (energy, bandwidth and lifetime of intermediate resonancesNa n * ) with femtosecond laser pulses. The observation of four absorption resonances for the cluster Na8 with different energy widths and different decay patterns is more difficult to interpret by surface plasmon like resonances than by molecular structure and dynamics. Time-resolved fragmentation of cluster ions Na n + indicates that direct photo-induced fragmentation processes are more important at short times than the statistical unimolecular decay.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429122
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  • 19
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    Spectroscopy of size-selected neutral silicon clusters: Remarkably similar spectra for clusters containing between ∼15 and 70 atoms (1993)
    Springer
    The European physical journal 26 (1993), S. 147-149 
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    ISSN: 1434-6079
    Keywords: 78.40.Fy ; 36.40.+d ; 33.20.Kf ; 33.20.Lg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Absorption spectra have been recorded for gas phase, size-selected neutral silicon clusters using resonant one- and two-color photodissociation spectroscopy. We now have spectra between 0.94 – 5.58 eV for clusters containing up to 70 atoms. Starting at ∼15 atoms, the spectra are all amazingly identical. Comparisons of the silicon cluster spectra to those of various forms of bulk silicon show that the cluster spectra have much in common with the spectrum of the most stable diamond structure of bulk crystalline silicon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429127
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  • 20
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    A novel desorption mechanism of (AgnIn−1)+ cluster ions (1993)
    Springer
    The European physical journal 26 (1993), S. 181-183 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 82.30.Lp ; 82.80.Ms
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Silver iodide clusters have been generated by inert gas condensation technique, ionized via electron impact, and mass analyzed in a reflectron equipped time-of-flight mass spectrometer. The mass spectra are dominated by cluster ions of the composition (AgnIn−1)+. Additional kinetic energy analysis is applied to detect metastable decay of the cluster ions for n up to 30. In contrast to alkali halides, where halogen and monomer desorption had been observed, the main decay channel of silver iodide cluster ions is the loss of a neutral trimer Ag3I3.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01429137
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  • 21
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    Phase changes, nonwetting and coexistence: (KCI)32 (1993)
    Springer
    The European physical journal 26 (1993), S. 189-191 
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    ISSN: 1434-6079
    Keywords: 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Binary clusters of ionic substances exhibit several properties that make them quite different from homogeneous clusters representable by pairwise Lennard-Jones or Morse potentials. While the potential energy surfaces of clusters of a only a few or several pairs of ions can be explored in microscopic detail, clusters of the size of (KC1)32 must be examined statistically. The stable structures of (KC1)32 can be put into four useful categories: (1) the rocksalt-like ground state (2) slightly defective crystal-like structures (3) “non-wetting” structures that are partly rocksalt-like and partly amorphous and (4) the amorphous structures. A method is presented to estimate the density of configurational states as a function of energy and, from it, the partition function and thermodynamic properties of (KC1)32. Solid and liquid forms of this cluster can coexist in measurable quantities over a significant range of temperatures. However, the times required for the cluster to show ergodic exploration of solid-like and liquid-like regions of phase space is beyond the limits of conventional dynamic simulations.
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    URL: http://dx.doi.org/10.1007/BF01429140
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  • 22
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    Adsorption reactions of alkali-halide nanocrystals: Identification of an important surface defect (1993)
    Springer
    The European physical journal 26 (1993), S. 201-203 
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    ISSN: 1434-6079
    Keywords: 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The adsorption reactions of alkali-halide clusters have been investigated on a size-selected basis using flow-reactor methods. The reactivity of larger sodium-fluoride clusters [NanFn−1]+ toward polar molecules NH3 and H2O shows a distinctive pattern as a function ofn at ambient temperature. Comparison with computed structures shows that aparticular kind of defect greatly facilitates the initial adsorption process. This defect can be formed by removal of an ion-pair from the face of an otherwise perfect nanocrystal, to create a basket-like opening for the adsorbed molecule. It is shown that this kind of defect occurs as a most stable low-temperature structure only to a certain size, after which a less reactive defect takes its place. The implications of these findings for the adsorption reactivity of the surfaces of ionic solids are briefly discussed.
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    URL: http://dx.doi.org/10.1007/BF01429144
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  • 23
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    Is the B state of Na3 a case of Berry's phase? (1993)
    Springer
    The European physical journal 26 (1993), S. 270-272 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 33.20.Kf ; 35.20.Pa
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The B state of Na3 is often cited as an example of fractional quantization of the pseudorotational motion on the lower adiabatic surface of theE×e Jahn-Teller system. Recently, an alternative interpretation of the experimental results was given which is based on a pseudo-Jahn-Teller treatment and implies integer quantization. We present rotationally resolved spectra of a number of vibronic bands of the Na3 B-X system and believe that they can only be explained in terms of integer quantum numbersj of the vibronic angular momentum.
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    URL: http://dx.doi.org/10.1007/BF01429166
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  • 24
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    Time-resolved TPI spectroscopy of Na3-clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 276-280 
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    ISSN: 1434-6079
    Keywords: 33.80.−b ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The dynamics of excited states of cold Na3-clusters in a supersonic beam have been studied in time-resolved two-photon-ionization (TPI)-experiments, using picosecond pump&probe technique followed by mass-selective detection. In case of the electronically excited B-state for the first time the pseudorotational motion could be recorded as a temporal sequence. The time constant of pseudorotation was found to be 3ps. For the D-state, known to predissociate very rapidly, it was possible to directly ionize this excited electronic state. Decay times of the TPI-signal were estimated to be in the order of 2.7ps providing direct information of the fragmentation probability. Simultaneously the temporal evolution of the fragment signal Na 2 + was detected.
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    URL: http://dx.doi.org/10.1007/BF01429168
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  • 25
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    Energetics of aluminum-lithium clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 296-300 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 71.10.+x
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Energetics and structures of small aluminum-lithium clusters were investigated using structure-minimization and dynamic simulated annealing on the Born-Oppenheimer surface, calculated via local-spin-density functional method. A transition from atomic-based characteristics forn≤5 to a perturbed delocalized electronic cluster-shell behavior forn≥6, containing an AiLi5 “core”, is suggested.
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    URL: http://dx.doi.org/10.1007/BF01429174
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  • 26
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    ECP-CI study of electronic structure and geometry of small neutral and charged Ag n clusters; Predictions and interpretation of measured properties (1993)
    Springer
    The European physical journal 26 (1993), S. 287-289 
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    ISSN: 1434-6079
    Keywords: 31.20.Tz ; 31.50.+w ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The ground state geometries of small neutral Ag n (n=2–9) and charged Ag n ± (n=2–9) clusters have been determined in the framework of the SCF procedure employing a relativistic pseudopotential accounting for core-valence correlation effects (RECP-CVC). Similarities and differences between neutral and charged clusters have been found. Large scale CI for 5s electrons only has been carried out for determining stabilities, ionization potentials (IP) and vertical detachment energies (VDE) of anions. A comparison between predicted and measured observables allows for the tentative structural assignments. In addition, the low lying energies of excited states for the neutral species at the anionic geometries have been calculated to account fully for geometrical and spectroscopic assignment to the photodetachment measurements.
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    Nature of excitations in small alkali metal and other mixed clusters (1993)
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    The European physical journal 26 (1993), S. 17-22 
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    Keywords: 31.20.Tz ; 31.50.+w ; 36.40.+d
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    Topics: Physics
    Notes: Abstract The contribution of quantum chemicalab — initio studies of optical response in small metal clusters towards understanding of their specific electronic and structural properties has been presented. The role of cluster size, geometry, number of valence electrons and chemical composition has been pointed out. It has been shown that an appropriate many-electron description of excited states for stable cluster structures allows for the quantum molecular interpretation of the absorption spectra and other optical probles. The nature of excitations responsible for characteristic spectroscopic patterns has been discussed.
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    Observation of laser excitation of rhombic C4 using the coulomb explosion method (1993)
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    The European physical journal 26 (1993), S. 340-342 
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    Keywords: 36.40.+d
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    Notes: Abstract The combination of laser photodetachment of C 4 − and the Coulomb Explosion Imaging method was applied for the investigation of the structure of several C4 isomers and was correlated with their measured electron affinities.
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    Experimental studies on selenium cluster structures (1993)
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    The European physical journal 26 (1993), S. 352-354 
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    ISSN: 1434-6079
    Keywords: .64.70.Fx ; 36.40.+d ; 35.20.Vf
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    Notes: Abstract In this paper, we report properties of selenium clusters produced by vapor condensation technique. Impact electronic ionization is performed on clusters in the size range from 2 to 36 atoms. The measured ionization potentials exhibit small oscillation corresponding to the wiggles observed on the mass distribution. An attempt to connect these experimental observations with the geometrical structure of the molecules is made in the discussion.
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    The quadrupolar and hyperfine splittings in the metal cluster compound Au55(PPh3)12Cl6 (1993)
    Springer
    The European physical journal 26 (1993), S. 27-29 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 65.40.−f ; 76.80.+y
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    Topics: Physics
    Notes: Abstract There are 5 different Au-sites in the Au55 core of Au55(PPh3)12Cl6. The 13 inner atoms are almost identical to that of bulk gold. At the surface the attachment of the ligands is responsible for further differentiation. We have calculated the low temperature specific heat using the Mössbauer determined electrical quadrupolar splitting of the surface atoms. Due to too long a quadrupolar relaxation time, no such contribution is seen in the zero field results (down to 0.06 K) of Goll et al., Z. Phys. D 20, 329 (1991). The latter zero and in-field data are interpreted as the contribution of an electronic spin, hyperfine coupled to a nuclear spin 3/2. The effective abundance is about one spin per ten clusters.
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    The electronic contribution to the low temperature specific heat in the metal cluster compounds Au55(PPh3)12Cl6, Pt309Phen 36 * O30 and Pd561Phen37O200 - a comparison (1993)
    Springer
    The European physical journal 26 (1993), S. 30-32 
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    Keywords: 36.40.+d ; 65.40.Em
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    Notes: Abstract The low temperature specific heat of the metal cluster molecular compounds Au55(PPh3)12Cl6, Pt309 Phen 36 * O30 and Pd561Phen37O200, with resp. 55, 309 and 561 core atoms are compared. ForT ∼ 1 K, Pt309 and Pd561 show a linear contribution toC/R of about 1/3 of the bulk value. A Poisson distribution of the electronic energy levels is suggested as an explanation.
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    Valence band photoemission from deposited metal clusters: Case studies (1993)
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    The European physical journal 26 (1993), S. 54-57 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 79.60.−i ; 82.65.−i
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    Topics: Physics
    Notes: Abstract Metal clusters (Pb N ,Au N ) grow in a pulsed arc cluster ion source (PACIS). After supersonic expansion in the helium carrier gas the resulting beam is soft-landed under UHV conditions on either cold poly-cristalline silver,Si(111) or naturalSiO 2. Photoemission measurements with light from the synchrotron BESSY serve to investigate the electronic structure of the clusters. In this communication, valence band photoemission is presented forPb N onAg, Pb N onSi/SiO 2 andAu N onAg. After lead deposition, the valence band region exhibits only low, weakly structured intensity, whereas deposited gold clusters lead to the formation of a resolved narrow peak at 3.52 eV below ε F , which we attribute toAu 5d 5/2.
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    Dipole surface plasmon in large K N + clusters (1993)
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    The European physical journal 26 (1993), S. 95-97 
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    Keywords: 36.40.+d ; 33.20.Kf
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    Notes: Abstract The dipole surface plasmon forK N + clusters is analyzed using the RPA sum-rule technique within a semiclassical Density Functional Theory and the spherical jellium model. The theoretical frequencies are blue shifted as compared to the experimental ones. The discrepancies between theory and experiment are reduced when considering non-local energy contributions in the density functional and phenomenologically including atomic lattice effects by means of an electron effective mass and a static dielectric constant.
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    Mixed alkali microclusters (1993)
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    The European physical journal 26 (1993), S. 110-112 
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    Keywords: 36.40.+d ; 21.60.Cs
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    Notes: Abstract Under experimental conditions which do not favor delocalization of valence electrons alkali atoms remain neutral and are taken as atomic fermions. Thus, two neutral alkali component microclusters are treated by a two-fermion shell model producing two sets of magic numbers containing many common numbers.
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    Coexistence of electronic and atomic shells in microclusters (1993)
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    The European physical journal 26 (1993), S. 113-114 
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    Keywords: 36.40.+d ; 82.80.Ms
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    Notes: Abstract The present paper supports coexistence of electronic shells and shells of ion cores for large alkali clusters.
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    Photoionization of small silicon clusters: ionization potentials for Si2 to Si40 (1993)
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    The European physical journal 26 (1993), S. 204-206 
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    Keywords: 36.40.+d ; 34.50.Lf
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    Notes: Abstract Photoionization thresholds of Si n (n=2−40) were examined by vacuum UV radiation (5.7–8.5 eV) generated by stimulated Raman scattering of narrow-bandwidth 193-nm radiation in high pressure hydrogen and deuterium gases. A strong threshold energy dependence on cluster size is observed, featuring major maxima at 10 and 20. The magic behavior atn=10 is consistent with the results of the photofragmentation and CID experiments reported previously.
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    Electronic spectra of metal cluster molecules (1993)
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    The European physical journal 26 (1993), S. 4-7 
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    Keywords: 33.20.Kf ; 73.20.Mf ; 36.40.+d ; 82.70.Dd
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    Notes: Abstract The electronic absorption spectra (UV-visible-NIR) of a range of molecular metal cluster compounds, including new spectra of Pt309(phen*)36O28 in solution and Au55(PPh3)12Cl6 in the solid state, are discussed and compared with the spectra of colloidal particles of the corresponding metals. We consider frontier orbital separations, the development of ‘interband’ absorptions, the possible appearance of molecular plasma resonances, and charge-transfer in the solid state.
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    Photoelectron spectroscopy and electronic structure of Ca@C60 (1993)
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    The European physical journal 26 (1993), S. 297-299 
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    Keywords: 36.40.+d ; 33.60.Cv
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    Notes: Abstract The electronic structure of an isolated Ca@C60 molecule was probed by photoelectron spectroscopy (PES) of Ca@C 60 − , generated by laser desorption of a preformed Ca@C60/fullerene thin film. The PES spectrum of Ca@C60 was found to be similar to that of C 60 − , except that Ca@C60 has an electron affinity of 3.0 eV, about 0.3 eV higher than that of C60. The spectrum suggests that Ca atom donates its two 4s electrons to the C60 t lu lowest unoccupied molecular orbital. Thus, the interaction between the central Ca atom and C60 is quite ionic, and Ca@C60 can essentially be expressed as Ca2+@C 60 2− .
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    Delayed ionization of IR-laser excited C60 (1993)
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    The European physical journal 26 (1993), S. 311-313 
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    Keywords: 36.40.+d ; 35.20.Wg
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    Notes: Abstract Using a pulsed CO2 laser we have desorbed C60 clusters from a solid target into an expanding He jet, coupled to a time-of-flight mass spectrometer. We observed self ionization of the excited clusters with a time delay of 120 ±20 µs. This is large compared to previously reported delays of up to 15 µs after laser excitation with visible or ultraviolet light. We suggest that the delayed ionization is caused by structural isomers of hot C60 clusters differing from the truncated-icosahedron structure.
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    Surface plasmons ofC 60 (1993)
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    The European physical journal 26 (1993), S. 282-284 
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    Keywords: 36.40.+d ; 71.45.−d ; 78.65.−s
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    Notes: Abstract We discuss the collective dipolar resonances of theC 60 molecule described by a spherically symmetric shell. The shell is modeled by a step in the radial direction. We present results for π and π+σ plasmons in good quantitative agreement with recent experiments. New features, like a monopole mode of oscillation, are predicted for theC 60 molecule.
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    Spectroscopy of DABCO-rare-gas and DABCO-DABCO van der Waals complexes (1993)
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    The European physical journal 27 (1993), S. 73-78 
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    Keywords: 33.20.Lg ; 36.40.+d
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    Notes: Abstract The excited electronic origin bands of several DABCO containing van der Waals complexes have been observed via (1+1) resonance enhanced multi-photon ionization. Sharp resonances with widths of about 3 cm−1 are seen for DABCO-Rg n=1,2,3 (Rg is Ar, Kr or Xe), for the DABCO-DABCO dimer and for DABCO-DABCO-Ar. The origins of the rare-gas complexes are blue shifted with respect to the monomer origin. Broad features originating from DABCO-Rg n complexes with highn, appear to higher energies than the complex origins, with widths of 120 cm−1.
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    Kinetic methods for quantifying magic (1991)
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    The European physical journal 21 (1991), S. 335-342 
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    Keywords: 36.40.+d ; 34.30.+h
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    Notes: Abstract Two methods are described for obtaining activation energies for evaporation from isolated clusters. They involve measurements of (1) kinetic energy distributions during evaporation and (2) metastable decay probabilities. The two methods supplement each other and can be applied to data garnered in the same apparatus. The methods are illustrated with applications to data in the literature on copper and carbon clusters. An even/odd alternation in evaporation energies from the copper clusters is consistent with a similar alternation in electron affinities, but not with elementary theory. Thermodynamic properties of carbon clusters are also deduced and discussed.
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    π plasmon modes inC 60 clusters (1993)
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    The European physical journal 27 (1993), S. 193-197 
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    Keywords: 36.40.+d ; 71.45.Gm
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    Topics: Physics
    Notes: Abstract We study collective excitations of π electrons in the fullerene molecule, by using the sum rule approach and linear response theory. The results for the excitation spectrum are discussed in relation to experimental data and to other theoretical approaches.
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    Direct fission versus sequential evaporation mechanism of sputtered caesium iodide cluster ions (1993)
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    The European physical journal 28 (1993), S. 339-343 
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    Keywords: 36.40.+d ; 35.20.Wg
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    Notes: Abstract A triple stage hybrid mass spectrometer was scanned for the trapping of the reaction intermediates of the over-all loss of two CsI-moieties from size-selected caesium iodide cluster ions of the general formula Cs (CsI)+ n . In addition to appropriate MS/MS/MS-methods an electrically floated collision cell has been applied to trap intermediates of unimolecular and collision-induced evaporations. In comparison with other experimental findings the features of the evaporation mechanism are discussed.
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    A tight-binding model for the optical properties of Au55-clusters (1994)
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    The European physical journal 29 (1994), S. 73-80 
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    Keywords: 36.40.+d ; 78.40
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    Notes: Abstract We have computed the electronic structure and the imaginary part of the dielectric function of the Au55 cluster using a tight-binding model which takes into account size and boundary effects. Besides the Drude behavior, we obtain anomalous absorption peaks in the infrared region due to the breakdown of the selection rule Δk=0. Taking into account surface coating effects, the onset of the interband absorption above 2.5 eV results to be red shifted, in agreement with the experimental data. As a consequence, we obtain a dramatic increase of the width of the plasmonic absorption peak, which accounts for the experimental optical spectra observed by Kreibig.
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    Effective magnetization of rotating free ferromagnetic metal clusters (1994)
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    The European physical journal 29 (1994), S. 67-72 
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    Keywords: 36.40.+d ; 75.60.Jp ; 76.50.+g
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    Topics: Physics
    Notes: Abstract The deflection of free magnetic metal clusters in a Stern-Gerlach magnetic field is studied. In particular we investigate magnetic resonance effects resulting from lattice anisotropy and cluster rotation. In analogy to small suspended particles in an oscillating magnetic field the anisotropy field fixed to the rotating atomic lattice of the cluster acts on the cluster magnetization like an rf field in NMR experiments. In our calculation we have used the Bloch equations and assumed different anisotropy field symmetries (uniaxial, cubic). A minimum in the magnetization as a function of the Stern-Gerlach field and also of the cluster size, as observed recently, is obtained under certain conditions. However, such a resonance behavior occurs only if the distribution of the rotation frequency ωrot is relatively narrow, while a broad distribution of ωrot yields an almost superparamagnetic behavior. In addition, the strength of the anisotropy field and the relaxation time are important variables which determine the magnetic behavior of the clusters.
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    Fullerene ionization dynamics after single photon excitation with synchrotron radiation (1994)
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    The European physical journal 29 (1994), S. 81-83 
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    Keywords: 33.80.Eh ; 36.40.+d ; 36.90.+f
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    Topics: Physics
    Notes: Abstract Ionization dynamics of free C60 is investigated after single photon excitation with synchrotron radiation in the energy range between 8.9 eV and 27.6 eV. Upper limits for the time constants describing possible delayed ionization are obtained from peak shape asymmetries in time of flight spectra as a function of excitation energy. The results clearly indicate that delayed ionization is not observed after single photon excitation in contrast to the results obtained in ns-laser MPI experiments.
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    Simulation of cluster impact fusion (1992)
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    The European physical journal 22 (1992), S. 547-551 
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    Keywords: 36.40.+d ; 79.20.Rf
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    Topics: Physics
    Notes: Abstract We report molecular dynamics simulations of the impact of TiD clusters on TiD targets. In each cluster collision the total fusion probability seems to be due to a single deuterium deuterium collision. The kinetic energies of incident deuterium atoms gradually level off around the initial cluster energy, but do not reach the high energy tail of a corresponding Maxwell-Boltzmann distribution. Neither any other support for a thermonuclear fusion mechanism was observed. On the contrary, our simulations imply that the enhanced fusion rate is rather due to channeled many atom collision cascade type mechanism.
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    Dynamics of the barium-molecule system within large argon clusters (1994)
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    The European physical journal 30 (1994), S. 45-52 
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    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract The effects of adding molecules on the LIF at 540 nm of a barium atom at the surface of an argon cluster (average size 420) has been investigated. We showed that molecules like ethanol,n-hexane and O2 from stable complexes with ground state barium. In the case of molecules like N2, CH4 and SF6, the collisional quenching of solvated Ba(1 P) is observed. The large quenching rates obtained are interpreted by a surface mobility of the collisional partners. Moreover, we showed that this collisional quenching leads to the ejection of free Ba(3 P 1).
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    Structures and spectra of Na(NH3) n=1,2 (1994)
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    The European physical journal 30 (1994), S. 69-75 
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    Keywords: 36.40.+d ; 33.80.Eh ; 82.30.Nr ; 82.40.Dm
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    Topics: Physics
    Notes: Abstract Geometric structures and the energies for the ground and several excited electronic states of a sodium atom bound with one or two ammonia molecules are presented. All self consistent field (SCF) calculations are performed with extended basis sets. Geometry optimization and one electron properties have been performed within the SCF approximation. Excited states have been calculated with the multi-configuration SCF (MCSCF) technique. This system may be viewed as a precursor to solvation in a macroscopic system. The excited state calculations provide important information for spectroscopic studies of these complexes.
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    Intermolecular interactions: basis set and intramolecular correlation effects on semiempirical methods. Application to (C2H2)2, (C2H2)3 and (C2H4)2 (1994)
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    The European physical journal 30 (1994), S. 327-340 
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    Keywords: 34.20.−b ; 36.40.+d ; 31.20.Ej
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    Notes: Abstract A detailed study of the intrinsic consistency of the semiempirical method of P. Claverie namely, the effects of the basis set and intramolecular correlation on the multipole distributions of molecular subunits and the influence of the electronic population of each atom in the molecular subunit on its van der Waals radius, is performed on some van der Waals dimers. The validity, limits of this model and the appropriate way to use it is established. In particular, the dependence of the geometry and the interaction energy on the basis set chosen and the intramolecular correlation shows that the multipole distribution involved in the calculation of the electrostatic and polarization terms must be derived from a correlated wave function within an extended basis set. Associated to non local methods for finding stationary points, the method of P. Claverie reproduce reliably the intermolecular geometrical parameters observed for the equilibrium structures and the transition states of the dimer and trimer of acetylene. In addition, a study of the equilibrium structures of the ethylene dimer is presented, the aim of being to clarify the considerable uncertainty in their number and their geometry.
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    Atomic and electronic structure of Na10K10Cs n clusters (1994)
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    The European physical journal 30 (1994), S. 349-356 
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    Keywords: 36.40.+d ; 61.55.Hg ; 68.35.Dv
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    Topics: Physics
    Notes: Abstract Density functional theory is used to study the atomic and electronic structures of Na10K10Cs n clusters with up to sixty atoms. The simplifying approximation has been made of replacing the external potential of the ionic background by its spherical average about the cluster centre in the iterative process of solving the Kohn-Sham equations for each geometry tested. The search for the equilibrium geometry is performed by employing the technique of simulated annealing. We have always found segregation of Cs atoms to the surface as well as a rather neat separation of different species in different (radial) regions of the cluster. This layering effect appears to be consistent with a tendency to maximize electronegativity differences. When the cluster is big enough, Cs atoms begin to appear also inside the cluster. Those geometrical effects do not perturb the electronic magic numbers well known for pure alkali metal clusters.
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    Collision induced dissociation of stored gold cluster ions (1994)
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    The European physical journal 30 (1994), S. 341-348 
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    Keywords: 36.40.+d ; 34.50.−s ; 35.20.Gs
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    Topics: Physics
    Notes: Abstract The stability of gold cluster ions Au n + (2≦n≦23) has been investigated via collision induced dissociation in a Penning trap. Threshold energies and dissociation channels have been determined. The cluster stability exhibits a pronounced odd — even alternation: Clusters with an odd number of atoms,n, are more stable than the even-numbered ones. Enhanced stabilities are found for Au 3 + , Au 9 + , and Au 19 + in accordance with the Clemenger-Nilsson and the deformed jellium model of delocalized valence electrons. Excited odd cluster ions withn≦15 predominantly decay by evaporation of dimers; all others decay by monomer evaporation. From the dissociation channels estimates of the binding energies are deduced.
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    Collisional process involving atomic cluster ions (1994)
    Springer
    The European physical journal 31 (1994), S. 187-189 
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    ISSN: 1434-6079
    Keywords: 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Collision of Ar cluster ions, Ar n + (n=3−16), with He and Ne atoms was investigated by use of mass spectroscopic techniques. The cross sections for the production of Ar n′ + (n′〈n) were measured as functions of the size of the parent cluster ion and the collision energy (0.1–10 eV in the center-of-mass frame). These results were analyzed in the scheme of hard-sphere spectator collision with RRK theory. It was concluded that the reaction proceeds via collisional excitation of the parent cluster ion and following sequential loss of the constituent Ar atoms.
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    Superfluid effects in rotating helium clusters (1990)
    Springer
    The European physical journal 16 (1990), S. 299-301 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 67.40.−w
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We study the response of Bose4He clusters to an external field corresponding to a rotation with frequency ω. An explicit form for the normal (nonsuperfluid) fraction of the system as a function of the temperatureT and of the mass numberN of the cluster is obtained under the assumption that only surface modes are thermally excited. The critical behaviour of4He clusters at high rotational frequencies is also investigated.
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    Evolution of bulk-like properties in mercury microclusters (1990)
    Springer
    The European physical journal 17 (1990), S. 309-312 
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    ISSN: 1434-6079
    Keywords: 71.30.+h ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The transition from non-metallic to metallic behavior of mercury microclusters, Hg n , withn ranging from 2 to 79, is investigated using first principles tight-binding linear muffin-tin orbital method. Then dependence of the ionization potential, the cohesive energy, the energy gap, and the nature of the bonding indicates metallic behavior for Hg n withn≧80. The average bond length of Hg clusters is found to be larger than that of the bulk. Our results are in good agreement with experiments.
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    Photoionization studies of free sodium ammonia clusters (1992)
    Springer
    The European physical journal 22 (1992), S. 651-658 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 33.80.Eh ; 82.40.Dm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Free sodium ammonia clusters Na(NH3) n up ton=45 were generated in a pickup source by injecting a beam of neutral sodium atoms into the expansion zone of a piezo driven pulsed nozzle. The clusters thus formed are studied by one-photon ionisation in the region of 266 nm to 520 nm, time-of-flight mass spectrometry as well as photoelectron spectrometry. Ionisation thresholds for clusters up ton=18 and dissociation energies for the neutral Na(NH3) n up ton=6 are reported.
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    Gas phase reactivity of thermal metal clusters (1991)
    Springer
    The European physical journal 19 (1991), S. 343-346 
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    ISSN: 1434-6079
    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract Reaction kinetics of metal cluster ions under well defined thermal conditions were studied using a flow tube reactor in combination with laser vaporization. Aluminum anions and cations were reacted with oxygen, and several species which are predicted jellium shell closings, were found to have special stability. Metal alloy cluster anions comprised of Al, V and Nb were also seen to react with oxygen. Alloy clusters with an even number of electrons reacted more slowly than odd electron species, and certain clusters appeared to be exceptionally unreactive. Copper cation clusters were observed to associate with carbon monoxide with reactivities that approach bulk behavior at surprisingly small cluster size. These reactions demonstrate how the rate of reaction changes with cluster size.
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    Cluster size effects (1992)
    Springer
    The European physical journal 24 (1992), S. 247-275 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 31.20.Ej ; 35.20-i ; 33.80.-b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract In this paper we address some of the unique, novel and basic features of clusters, which involve the physical and chemical consequences of their large surface/volume ratio and the size dependence of the properties of large finite systems. Energetic, quantum, electronic, spectroscopic, and electrodynamic size effects in clusters were quantified by cluster size equations (CSEs), which describe the gradual “transition” from the large finite cluster to the infinite bulk system, with increasing the cluster size. Some progress was also accomplished in the description of the “transition” from cluster microsurfaces to macrosurfaces, which can be described in terms of surface CSEs. The analysis implies a nonuniversality principle for cluster size effects, with different physical properties being described in terms of distinct CSEs. The CSEs provide a quantitative answer to a central question in the area of cluster chemical physics: What is the minimal cluster size for which its properties become size invariant and do not differ in any significant way from those of the macroscopic sample of the same material? A unified (but not universal) description is advanced for the merging between the properties of microscopic large finite systems and those of a macroscopic bulk material.
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    Molecular dynamics of 300 keV (D2O)100 clusters on Ti-D (1992)
    Springer
    The European physical journal 24 (1992), S. 385-394 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 52.20.Hv ; 79.20.Nc
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    Topics: Physics
    Notes: Abstract We use the molecular dynamics code DAMSEL to predict the velocity distributions for beam and lattice atoms after bombardment of Ti-D “foils” of thickness 20.86 Å by 300 keV (D2O)100 cluster ions. From these distributions we estimate the D-D nuclear fusion yield. We find that cluster bombardment reduces the overall energy deposition of the beam in the lattice compared to that of the individual beam atoms of the same velocity. However, a small portion of lattice atoms (〈1%), and a larger percentage of beam atoms (∼30%), have energies above the maximum present in the case of bombardment by individual D or O atoms. The folding of the standard D-D fusion cross sections over the relative velocity distributions produced by beam and lattice deuterons produce a fusion yield estimate of ∼1×10−21 fusions per cluster, with the high-energy distributions of beam deuterons playing the most important role. This is nine orders of magnitude lower that the data of Beuhler et al. While transient (∼10 fs) atom densities 50% higher than that of the initial lattice are recorded in the course of the simulation, the average energy transferred per lattice atom — 23 eV — is insufficient to support any “collision spike” explanation of the observed fusion yield.
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    Absorption spectra of small niobium and gold clusters measured by photodepletion of their rare gas van der Waals complexes: some preliminary experiments (1993)
    Springer
    The European physical journal 26 (1993), S. 36-40 
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    ISSN: 1434-6079
    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract The optical absorption spectra of small niobium clusters have been determined over the wavelength range 260 – 740 nm by photodetaching Krypton atoms from the corresponding neutral van der Waals, vdW, complexes, NbnKrm, n=5–15, m=1–3. Cross sections for small gold clusters were determined by photodetachment experiments oncharged vdW complexes [AunXem]+, m=1, 2. The absorption cross sections are observed to increase monotonically with decreasing wavelength. At the long wavelength end of the range, the cross section is practically independent of the cluster nuclearity, n; whereas, at the short wavelength end of the range, the cross section increases monotonically with n.
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    Size dependence of the solid-solid phase transition in CdSe nanocrystals (1993)
    Springer
    The European physical journal 26 (1993), S. 56-58 
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    ISSN: 1434-6079
    Keywords: 68.35.Md ; 36.40.+d ; 64.60.-i ; 62.50.+p
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract High pressure optical absorption spectra are presented for CdSe nanocrystals as a function of size. The spectra show a transition to a high pressure Rock Salt type phase at pressure greatly elevated from the bulk. The size dependence of the transition pressure can be explained in part by an increased surface tension in the Rock Salt phase relative to the low pressure tetrahedral phase.
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    Small can be different (1993)
    Springer
    The European physical journal 26 (1993), S. 119-125 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 31.20.Sy ; 32.80.Dz ; 71.10.+x
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Theoretical investigations of size evolutionary patterns for multiply charged anionic metal clusters and solvation of sodium in water clusters are discussed. For Na N Z- clusters, energetic stability and electron decay channels are determined. Formation of a “surface Rydberg-like state” in Na(H2O) N , correlating with calculated and measured ionization potentials, is analyzed.
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    The optical absorption spectra of small Silver clusters (n=8–39) embedded in rare gas matrices (1993)
    Springer
    The European physical journal 26 (1993), S. 138-140 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 33.20.Lg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The optical absorption of small mass selected Agn-clusters (n=8–39) embedded in solid Ar, Kr and Xe has been measured. Strong absorption has been found between 3 and 4.5 eV. The absorption spectra show 1 to 3 major peaks depending on the cluster size. The width of these peaks is smaller than in gas phase photodepletion experiments of silver ions, most likely due to the low and well defined temperature of the clusters in the matrix. The results are compared to a simple model based on a Drude metal, taking into account the spillout of the electrons and allowing for a deviation of the cluster from a spherical shape. Absorption cross sections scale with the number of valence electrons.
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    Ion solvation in water clusters (1993)
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    The European physical journal 26 (1993), S. 166-168 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 61.22.Pg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We describe here molecular dynamics computer simulations performed to study the solvation of ions (Cl− and Na+) in water clusters. Our simulations show that the calculated structure and dynamics of the clusters is very sensitive to the potential model which is used to describe the interactions. From the comparison with thermodynamic data and data from the photoelectron spectra we conclude that in Cl−(H2O)n (n≤20) clusters the ion is located on the surface of the cluster.
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    Electronic structure and bonding of the metal cluster compound Au55(PPh3)12Cl6 (1993)
    Springer
    The European physical journal 26 (1993), S. 162-165 
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    ISSN: 1434-6079
    Keywords: 31.10.+z ; 36.40.+d ; 33.45.+x ; 33.60.-q
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    Topics: Physics
    Notes: Abstract We discuss the electronic structure, bonding and physical properties of the gold cluster compound Au55(PPh3)12Cl6. Results from our experimental measurements, including EXAFS, specific heat, Mössbauer, UV-visible and photoelectron spectroscopy, are combined with those of other work to form a consistent physical picture of the system. The bonding in Au55(PPh3)12Cl6 is much more delocalised and non-directional than in smaller gold cluster molecules. The Au55 cluster exhibits a substantial degree of metallic bonding, while displaying some of the characteristics of a discrete energy level spectrum.
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    Quantum molecular dynamics simulations of fullerenes and graphitic microtubules (1993)
    Springer
    The European physical journal 26 (1993), S. 74-78 
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    ISSN: 1434-6079
    Keywords: 31.70.Ks ; 36.40.+d ; 71.20Hk ; 31.20.Sy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We describe the results of extensiveab initio molecular dynamics calculations of the properties of fullerenes and microtubules. Our finite temperature quantum MD simulations for solid C60 are in excellent agreement with NMR, photoemission and neutron scattering data. The C60 isomer containing two pairs of adjacent five-fold rings has a binding energy only 1.6 eV smaller than that of perfect C60, but the transformation between these two structures is hindered by a 5.4 eV barrier. It thus requires high temperatures and long annealing times. High temperatures are also needed for the transformation of the lowest energy C20 isomer, a dodecahedron, to a corannulene structure, which can be thought of as a fragment of C60. The corannulene structure is a natural precursor for the formation of C60. Simulations of reactions show that C2 can insert into C58, perfect C60, and defect C60 fullerenes without an activation barrier, while C3 attaches only to their surfaces. Evaporative fragmentation of carbon clusters during annealing is unlikely, but atom and fragment exchange during collision favor "locally" most stable structures, such as C60. These results may explain the large increase in the abundance of C60 and C70 when carbon clusters are annealed at high density. We have also carried out calculations for paradigmatic microtubules, both reflection-symmetric and chiral. We find that the optimized geometries of the tubules are close to the ideal ones. It is possible to fabricate tubules with direct band gaps away from the Γ point by exploiting the similarities between the projected band structure of graphite and that of the tubule. The semiconducting tubules can be doped n- and p-type by substitutional N and B, respectively.
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    Cluster-molecule systems: Analysis and tuning of the interaction potential (1993)
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    The European physical journal 26 (1993), S. 110-114 
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    ISSN: 1434-6079
    Keywords: 34.10.+x ; 36.40.+d ; 82.20. Fd ; 82.20. Wf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The interaction (modelled by a LEPS potential) of a D2 molecule with an icosahedral Ni13 cluster is mapped and analyzed in the form of equipotential contour plots. The topological features of the map correlate with the energetic and dynamical characteristics of the dissociative adsorption of the molecule on the cluster, which were extracted from quasiclassical trajectory simulations. A modification of the LEPS potential used originally is introduced. It brings the calculated reactivity of the cluster into agreement with the experimental data.
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    Nonlinear optical properties of confined excitons in clusters (1993)
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    The European physical journal 26 (1993), S. 126-130 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 42.65.-k ; 73.20.Dx
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    Topics: Physics
    Notes: Abstract Size effects in femtosecond photon echo spectroscopy of neat clusters are calculated using a quasiparticle representation of the nonlinear response. We extend our previous study of cooperative effects on the nonlinear response of assemblies of two level molecules [J. A. Leegwater and S. Mukamel, Phys. Rev. A46, 452 (1992)] to allow for nuclear motion and to have an s-p model of polarizable atoms. Photon echos in Benzene/Argon clusters are calculated using a semiclassical phase averaging procedure [L. E. Fried and S. Mukamel, Adv. Chem. Phys. (in Press)].
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    Optical spectra of size-selected matrix-isolated silicon clusters (1993)
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    The European physical journal 26 (1993), S. 141-143 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 61.50.Lt
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    Topics: Physics
    Notes: Abstract Size selected silicon clusters have been isolated in rare gas matrices and studied by optical absorption spectroscopy. The clusters were produced in a pulsed laser vaporization source, size selected with a quadrupole mass spectrometer and deposited at low energies into a cocondensed krypton matrix held at T〈20 K. A comparison of the optical spectra of ten atom wide bands (Si25-Si35, Si35-Si45 and Si45-Si55) shows the general size evolution of the optical properties. Single cluster sizes have also been isolated and show somewhat sharper spectra than the bands. The measured spectra show similarities to spectra calculated using Mie theory and bulk optical constants. Cluster-cluster agglomeration was studied by evaporating the inert gas matrix. The results suggest that the clusters agglomerate into larger particles even under the mildest "soft landing" conditions.
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    Time-resolved spectroscopy of Nan-cluster fragmentation (1993)
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    The European physical journal 26 (1993), S. 33-35 
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    ISSN: 1434-6079
    Keywords: 33.80.-b ; 36.40.+d
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    Topics: Physics
    Notes: Abstract Using picosecond pump&probe technique followed by mass-selective detection, the dynamics of excited states of cold Nan=3...8-clusters in a supersonic beam — excited at λ=422nm — have been studied in time-resolved two-photon-ionization (TPI)-experiments. With growing cluster size a monotonous decrease of the decay times is observed except in the case of Na7 known to be a very symmetric cluster.
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    Simulation of silicon clusters from “quantum” Langevin molecular dynamics (1993)
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    The European physical journal 26 (1993), S. 51-55 
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    ISSN: 1434-6079
    Keywords: 71.10.+x ; 36.40.+d
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    Topics: Physics
    Notes: Abstract We present a simulation method to determine from first principles the structure of low symmetry atomic systems. Our method is based on Langevin molecular dynamics and quantum mechanical interactions derived fromab initio pseudopotential calculations. The molecular dynamics time step with this approach can be one to two orders of magnitude larger than in the Car-Parrinello method, compensating for the time required for self-consistency at each step. Moreover, because the simulation is constrained to reside on the Born-Oppenheimer surface, this method can be used for insulating as well as metallic and charged systems. Application will be made to small silicon clusters.
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    Structure, dynamics and thermodynamics of small particles and inorganic clusters (1993)
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    The European physical journal 26 (1993), S. 105-109 
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    ISSN: 1434-6079
    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract This invited review attempts to draw together recent advances in the structural characterisation of clusters and our theoretical understanding of dynamics, especially coexistence phenomena. It is now possible to characterise the potential energy surface of a small cluster in great detail, both in terms of local minima and transition states. A selection of results is collected includingab initio calculations on main group ligated clusters and a wide variety of systems bound by model analytic potentials. Useful comparisons may be made between the rearrangement mechanisms supported by the various potential energy surfaces. Furthermore, knowledge of transition states enables us to explain the results of dynamical simulations in great detail, and make comparisons with thermodynamic models. For larger systems, however, the number of stationary points is daunting, yet progress is still possible in terms of the underlying potential energy surface using the harmonic superposition approximation.
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    Resonant two-photon ionization spectroscopy of C6H6-(SF6)1,2 (1993)
    Springer
    The European physical journal 26 (1993), S. 213-216 
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    ISSN: 1434-6079
    Keywords: 33.20.Lg ; 36.40.+d
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    Topics: Physics
    Notes: Abstract Vibrationally resolved electronic spectra of heteroclusters C6H6-SF6 and C6H6-(SF6)2 were studied in the spectral regions near the S0-S1, 0 0 0 and 6 0 1 transitions of the benzene monomer. A nonvanishing 0 0 0 vibrational band has been observed for C6H6-SF6 with a C3v symmetry. For both clusters we have determined the ionization potentials as well as the binding energies in the electronic ground state and the ionization state. The fragmentation of larger clusters (C6H6)n(SF6)m is restricted to the loss of SF6 molecules while the emission of C6H6 molecules have not been observed.
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    Aluminum and gallium clusters — a comparative study using simulated annealing (1993)
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    The European physical journal 26 (1993), S. 23-27 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 31.20.Sy
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    Topics: Physics
    Notes: Abstract Density functional calculations with simulated annealing have been performed for clusters of aluminum and gallium with up to 10 atoms. There are many local minima in the energy surfaces and numerous stable isomers. As cluster size increases, there is a transition from planar to non-planar structures atn=5. All structures show regular patterns of bond and dihedral angles similar those found in the bulk materials. The bonds in gallium clusters are consistentlyshorter than those in clusters of the lighter element aluminum.
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    High resolution laser spectroscopy of the Na3 B — X system (1993)
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    The European physical journal 26 (1993), S. 273-275 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 33.20.Kf ; 35.20.Pa
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    Topics: Physics
    Notes: Abstract The B-X system of Na3 has been investigated at rotational resolution by using cw resonant two photon ionization spectroscopy. Model calculations of the spectra were performed with bond angles and distances as adjustable parameters. In this way, information on the geometry of the ground state and the B state of the sodium trimer was derived.
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    Molecular dynamics simulation of thin film formation by energetic cluster impact (ECI) (1993)
    Springer
    The European physical journal 26 (1993), S. 229-231 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 81.15.Jj ; 81.15.Rs
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    Topics: Physics
    Notes: Abstract Langevin Molecular Dynamics Simulations have been performed in order to understand thin film formation by impact of energetic clusters. The impact of Mo1024 clusters on a Mo surface is simulated at kinetic energies between 1 and 10 eV per atom. The results are in qualitative agreement with the experiments. Due to the high temperature induced locally at the impact zone, the method can be used to form compact, smooth, and strongly adhering thin films on room temperature substrates.
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    Spectroscopy of free sodium-ammonia clusters (1991)
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    The European physical journal 20 (1991), S. 65-67 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 33.80.Eh ; 82.30.Nr ; 82.40.Dm
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Neutral sodium ammonia clusters are formed in apickup source by injecting a beam of sodium atoms into the expansion zone of a pulsed nozzle beam of neat ammonia gas. The clusters are studied by one-photon ionisation in the range of 266 nm to 500 nm with pulsed lasers and Time-of-Flight mass spectroscopy. Na(NH3) n cluster ion signals up ton=35 are observed. The ionisation potentials of complexes up ton=9 are reported.
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    Photoelectron spectroscopy of negative ions solvated in clusters (1991)
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    The European physical journal 20 (1991), S. 69-72 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 33.60.Cv
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    Topics: Physics
    Notes: Abstract We have measured the photoelectron spectra of Cl−, Br− and I− complexed with water molecule and of I−·(CO2) n clusters wheren=1−7. The significance of these measurements to the understanding of solvation phenomena is discussed.
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    A REMPI study of solvation of small Hg n clusters by polar molecules (1991)
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    The European physical journal 20 (1991), S. 73-75 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 35.20.VF
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Free Hg n (DME) m clusters (where DME=dimethyl-ether,n=1, 2, 3,m=1÷5) formed in a supersonic expansion were studied by the REMPI (Resonance-Enhanced Multi-Photon Ionization) technique. A large decrease of ionization energies due to solvation of Hg n clusters is observed. Preliminary results are discussed in terms of different equilibrium configurations of the electronic ground, excited and ionic states of clusters.
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    URL: http://dx.doi.org/10.1007/BF01543941
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    Mass spectrometric study of MgO clusters produced by the gas aggregation technique (1991)
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    The European physical journal 20 (1991), S. 97-99 
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    ISSN: 1434-6079
    Keywords: 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Gas phase (MgO) n + and (MgO) n Mg+ clusters were produced in a gas aggregation source and studied by using laser-ionization time-of-flight mass spectrometry. A MgO molecule apparently serves as the nucleus for cluster growth, to which Mg and O atoms add. The heat generated by the formation of metal-oxygen bonds, and that added to the cluster by ionization leads to the production of clusters with the stoichiometry of the stable high-temperature oxide. The abundance maxima observed in the mass spectra indicate that the clusters form compact cubic structures similar to pieces of the MgO crystal lattice. The primary fragmentation channel responsible for the observed patterns is probably the loss of MgO monomers.
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    Evaporation of atoms from metal clusters (1991)
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    The European physical journal 20 (1991), S. 123-125 
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    ISSN: 1434-6079
    Keywords: 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The evaporation of atoms from metal clusters following photon absorption has been investigated by comparing the predictions of the statistical Weisskopf approach with the one of macroscopic kinetic theory. The consequences on the evaporation rate due to finite size effects in the separation energy and to the initial temperature of the cluster are also discussed.
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    Hot tungsten clusters: competition between atom ejection and thermionic emission (1991)
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    The European physical journal 20 (1991), S. 127-129 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 79.40.+z
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract This is a first report concerning the thermionic emission of electrons from hot metal clusters. Tungsten clusters were exposed to a 10 ns laser pulse, and the delayed emission of electrons from the clusters was recorded as a function of time after the excitation. A large yield of W n + cluster ions, which were born as late as microseconds after the laser pulse, has been detected forn〉4. Tungsten cluster ions created via thermionic emission show no measurable metastable decay during the flight time in the mass spectrometer. This indicates that they are colder than expected, if evaporative cooling after prompt ionization would prevail.
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    Optical properties and electronic excitations of rare gas clusters (1991)
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    The European physical journal 20 (1991), S. 1-7 
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    ISSN: 1434-6079
    Keywords: 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The electronic structure of rare gas clusters has been probed with time- and spectrally resolved fluorescence methods. The character of different electronic excitations of pure (Ar, Kr, Xe) and doped (XeAr n ) clusters containing up to 105 atoms is discussed and investigated as a function of the cluster size. Surface, bulk, Rydberg-and cluster-type excitations are responsible for absorption bands below the ionisation limit. A very important parameter within this context is the ratio of the cluster-radius and the radius of the electronic excitation. Modified solid state concepts are very suitable for the description of the unrelaxed excitations of the clusters. The interpretation of the decay and relaxation processes requires a molecular approach. Clusters containing a few hundred atoms show cluster specific excitations, which up to now cannot be explained within these two traditional concepts.
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    NMR in metal cluster compounds compared to glasses (1991)
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    The European physical journal 20 (1991), S. 333-335 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 76.60.Es
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The field and temperature dependence of the31P nuclear spin lattice relaxation rate in the metal cluster compound Ru55(P(t-Bu)3)12Cl20 follows a power law: 1/T 1 ∝T n B −m , withn=1.5±0.1 at 3.25 T andn=1.3±0.1 at 6.45 T;m ⋍ 1.4. Such dependences have so far only been observed in inorganic glasses and been attributed to two level systems. The correspondence suggests that the relaxation rate is due to interaction of theP-nuclear moment with electronic spins of stochastically moving charge carriers, which are thought to be responsible for the electrical conductivity through hopping between neigboring cluster molecules.
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    Low-temperature specific heat of the cluster compound Au55 (P(C6H5)3)12Cl6 (1991)
    Springer
    The European physical journal 20 (1991), S. 329-331 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 65.40.−f
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Specific-heat measurements on the cluster compound Au55(P(C6H5)3)12Cl6 at temperatures 0.06 K ≤T≤3 K and in magnetic fields 0≤B≤6 T are reported. While above 0.6 K the specific heatC is dominated by the inter-cluster vibrational contribution observed previously, an anomalous increase ofC towards lowT is observed below 0.3 K, withC ∼T −2. This contribution develops into a Schottky-like anomaly forB≥0.4 T, indicating that it might be attributed to local moments which are also observed in ESR measurements. From the height of the anomaly one can infer that approximately one tenth of the Au55 clusters carry a magnetic moment. For 0.6 K≤T≤1 K andB=0 our data indicate the absence of a linear electronic specific-heat contribution expected for bulk Au. This possibly constitutes the first direct observation of the quantum-size effect on electronic energy levels in the specific heat.
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    An atomic-scale model offcc crystal-growth (1991)
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    The European physical journal 20 (1991), S. 349-352 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 61.50.Cj ; 68.35.−p
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Nearly perfectfcc growth may be simulated by the application of a simple growth-algorithm — only sites that are at least 4-coordinated are occupied — to a selected seed. The seed is a 22-atom cluster, being the smallest close-packed structure with two crossing stacking-faults. The stacking-faults produce active surface-sites, that can not be exhausted by occupation; they are arranged in non-vanishing steps, similar to those produced by screw-dislocations. The algorithm prevents further stacking-faults, and ensuresABC-stacking of close-packed (111)-layers, characteristic of thefcc structure. The same algorithm would not produce further growth ofperfect fcc clusters or of Mackay icosahedra. It is proposed that the ability to grow fast under near-equilibrium conditions is a better criterion to select clusters as precursors of the bulk-structure than their cohesive energy. The crystal structure problem of the rare gases — whyfcc, nothcp? — is discussed in connection with the apparent impossibility to simulatehcp growth by an analogous procedure.
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    Particle size effects of clusters and crystallites (1991)
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    The European physical journal 20 (1991), S. 357-359 
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    ISSN: 1434-6079
    Keywords: 35.20.W ; 36.40.+d ; 68.40
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Size effects of pair distance, cohesive energy, surface stress, and compressibility have been calculated for shell-like structurated particles Y N ofn complete shells (units Y: rare gases, molecules, ion pairs). The influence of surface definition on size effects has been discussed.
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    Molecular statistical description of small thermodynamic systems: problems and possibilities (1991)
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    The European physical journal 20 (1991), S. 365-368 
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    ISSN: 1434-6079
    Keywords: 63.90.+t ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Thermodynamic quantities of small systems like pressure, the inner energy and the average number of particles of the system can be evaluated using the grand canonical ensemble. Such calculations were carried out for a Bragg-Williams lattice gas in the potential field of a micropore.
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    Localization in small fcc-particles with surface irregularities and disorder (1991)
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    The European physical journal 20 (1991), S. 361-363 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 71.50.+t ; 31.20.Pv
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A numerical eigenvector analysis is used to investigate Anderson localization in small fcc-particles ofN=309 andN=147 atoms. Special attention is given to the way size and surface roughness of the particles influence the localization behavior. States begin to localize in a non-exponential regime several lattice spacings from the center of localization and finally converge to a fully exponentially-localized regime for strong disorder. For smooth surface particles, it is found that the states localize first at the band bottom and a mobility edge can clearly be defined for increasing disorder. This doesn't seem to be the case for the rougher particles, where the band middle and the band bottom show similar behavior towards localization. Although particles with surface irregularities show an onset of localization for smaller values of the disorder than smooth particles, the localization length is greater.
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    Electronic structure of deposited monosized metal-clusters (1991)
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    The European physical journal 20 (1991), S. 385-386 
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    ISSN: 1434-6079
    Keywords: 79.60.Cn ; 36.40.+d ; 73.20.Dx
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Monosized Pt- and Au-clusters deposited on silica substrates are analyzed by photoelectron spectroscopy. The 4f-core-level energies and the valence electronic states depend on the cluster size and on the element. Au shows more uniform behavior for cluster sizes between 1 and 7 atoms than Pt does. Both materials are not yet metallic for clusters containing only a few atoms.
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    URL: http://dx.doi.org/10.1007/BF01544017
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    An improved laser vaporization cluster source and time-of-flight mass spectrometer (1991)
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    The European physical journal 20 (1991), S. 437-439 
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    ISSN: 1434-6079
    Keywords: 07.75.+h ; 35.20.Wg ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We briefly describe an improved laser vaporization cluster source, which produces intense, stable and cold cluster beams, and a new time-of-flight mass spectrometer, which in several respects is more versatile and better suited for cluster studies than traditional designs. The mass spectrometer has a high resolution mode with a very large effective ionization region as well as position and velocity sensitive detection modes.
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    URL: http://dx.doi.org/10.1007/BF01544031
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    Molecular dynamics calculation of half-lives for thermal decay of Lennard-Jones clusters (1991)
    Springer
    The European physical journal 21 (1991), S. 57-64 
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    ISSN: 1434-6079
    Keywords: 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Molecular dynamics has been used with a Lennard-Jones (6–12) potential in order to study the decay behavior of neutral Argon clusters containing between 12 and 14 atoms. The clusters were heated to temperatures well above their melting points and then tracked in time via molecular dynamics until evaporation of one or more atoms was observed. In each simulation, the mode of evaporation, energy released during evaporation, and cluster lifetime were recorded. Results from roughly 2000 simulation histories were combined in order to compute statistically significant values of cluster half-lives and decay energies. It was found that cluster half-life decreases with increasing energy and that for a given value of excess energy (defined asE=(E tot −E gnd)/n), the 13 atom cluster is more stable against decay than clusters containing either 12 or 14 atoms. The dominant decay mechanism for all clusters was determined to be single atom emission.
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    URL: http://dx.doi.org/10.1007/BF01426618
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    Thermal properties of the valence electrons in alkali metal clusters (1991)
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    The European physical journal 21 (1991), S. 65-81 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 31.20.Sy ; 05.30.−d ; 65.50.+m
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The finite-temperature density functional approach is applied for the first time to calculate thermal properties of the valence electron system in metal clusters using the spherical jellium model. Both the canonical and the grand canonical formalism are applied and their differences are discussed. We study the temperature dependence of the total free energyF(N) (including a contribution from the ionic jellium background) for spherical neutral clusters containingN atoms. We investigate, in particular, its first and second differences, Δ1 F =F (N − 1) −F (N) and Δ2 F =F(N + 1) +F(N − 1) − 2F(N), and discuss their possible relevance for the understanding of the mass abundance spectra observed in cluster production experiments. We show that the typical enhancement of magic spherical-shell clusters withN=8, 20, 34, 40, 58, 92, 138, 186, 254, 338, 398, 440, 508, 612..., most of which are well established experimentally, is decreasing rather fast with increasing temperatureT and cluster sizeN. We also present electronic entropies and specific heats of spherical neutral clusters. The Koopmans theorem and related approximations for calculating Δ1 F and Δ2 F atT 〉 0 are discussed.
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    Shell-structure and octupole instability in fermion systems (1991)
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    The European physical journal 21 (1991), S. 163-175 
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    ISSN: 1434-6079
    Keywords: 03.65. ; 36.40.+d ; 21.60.-n
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Simulating the one-particle spectra of the infinite-well potential by a model, we study the symmetry and the shell-structure of octupole deformations as well as the possible occurrence of octupole (and quadrupole) instabilities. Among various types of octupole deformations investigated theY 32-type deformation is found to have a strong shell-structure as well as a very interesting symmetry which leads to the occurrence of highly-degenerate single-particle levels. One particle spectra of the octupole-coupled two-level model (withl andl + 3) are analytically studied in the limit of large angular-momentum,l.
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    URL: http://dx.doi.org/10.1007/BF01425595
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    Finite size effects in the evaporation rate of3He clusters (1991)
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    The European physical journal 21 (1991), S. 185-188 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 67.50.Dg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have computed the density of states and the evaporation rate of3He clusters, paying special attention to finite size effects which modify the3He level density parameter and chemical potential from their bulk values. Ready-to-use liquid-drop expansions of these quantities are given.
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    Calculations of the dynamical Debye-Scherrer electron diffraction pattern from small particles of gold and silver (1993)
    Springer
    The European physical journal 26 (1993), S. 73-75 
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    ISSN: 1434-6079
    Keywords: 61.14.−x ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Calculations of the dynamical Debye-Scherrer electron diffraction pattern for ultrafine gold and silver particles have been performed using the multislice method. Two cluster sizes, 31 and 55 Å in diameter (923 and 5083 atoms, respectively), of both f.c.c. and icosahedral structures were used, at incident voltages of 40 kV and 100 kV.
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    Shell effects in large AlN clusters (1993)
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    The European physical journal 26 (1993), S. 92-94 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 03.65.Sq ; 33.80.Eh ; 35.20.Vf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Neutral aluminum clusters have been produced by laser vaporization technique, ionized by a low-power near-threshold laser light and detected using standard TOF spectrometric methods. Ionization potentials have been deduced in the low size range. In the large size range 250〈N〈1400 the patterns of the mass spectra exhibit a regular and continuous oscillation, originating from size-dependent ionization threshold effects. The period, constant on a Ne 1/3 scale (Ne=3N is the number of valence electrons), is approximately two times shorter than the one observed in alkali experiments. This feature is analyzed in terms of shell structure.
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    Collective excitations of embedded potassium clusters (1993)
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    The European physical journal 26 (1993), S. 122-124 
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    ISSN: 1434-6079
    Keywords: 73.20.Mf ; 36.40.+d ; 33.20Kf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The collective surface-plasmon excitation of potassium clusters embedded in different dielectric matrices has been studied within the time-dependent local-density-approximation and the jellium model. The matrix has been taken into account through a static dielectric constant ε in both the cluster ground state and in the determination of the dynamical susceptibility. We conclude that the change in the residual electron-electron interaction when the cluster is introduced in a matrix is a basic effect for the determination of the static polarizabilities and plasma frequencies. As we increase ε the surface-plasmon energy is shifted to the red and a tendency to saturation is obtained. The red shift is in good agreement with electron-energy-loss spectroscopy experiments.
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    URL: http://dx.doi.org/10.1007/BF01425638
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    A non local approach for the exchange energy. Selfconsistent implementation in metal clusters (1993)
    Springer
    The European physical journal 26 (1993), S. 131-133 
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    ISSN: 1434-6079
    Keywords: 36.40.+d ; 31.20.Sy ; 03.65.Sq
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Starting from the Hartree-Fock exchange energy density of a spin saturated system and using the Density Matrix Expansion we have built a non local Energy Density Functional without problems of divergence in the large gradient limit. We have applied this functional to the study of ground state properties and the dipole excitation energies of some metallic clusters in the quantal and semiclassical approaches.
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    URL: http://dx.doi.org/10.1007/BF01425641
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