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  • 36.40.+d  (210)
  • Springer  (210)
  • 1990-1994  (210)
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  • Springer  (210)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Applied physics 55 (1992), S. 364-371 
    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.
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  • 2
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    Applied physics 56 (1993), S. 215-217 
    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.
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  • 3
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    Applied physics 57 (1993), S. 101-104 
    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.
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  • 4
    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.
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  • 5
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    Applied physics 58 (1994), S. 57-62 
    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.
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  • 6
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    The European physical journal 349 (1994), S. 219-222 
    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.
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  • 7
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    The European physical journal 15 (1990), S. 257-263 
    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.
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  • 8
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    The European physical journal 18 (1991), S. 409-412 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 35.80.+s
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The kinetics of cluster formation in supersonic jets is examined by numerical integration of the master equation system. Some general characteristics of cluster kinetics could be formulated. Excellent agreement between experimental curves of p-cresol (H2O)0, 1, 2, 3 formation as function of H2O pressure and the corresponding calculated curves were obtained assuming successive cluster formation. From the kinetic curves, an unambiguous assignment of cluster size was possible which agreed with mass-resolved REMPI measurements. The fit of the rate coefficients shows the formation of p-cresol (H2O)1 to be faster than p-cresol (H2O)2 and p-cresol (H2O)3.
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  • 9
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 34.60.+z ; 34.70.+e ; 35.20.Wg
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have studied electron transfer from state-selected Ar** (nd) Rydberg atoms to (CO2) m clusters for 12≦n≦48. The relative rate constant for the total negative ion formation reaches its maximum forn=21 and decreases towards lower and highern. From an accurate study of Penning ionization of nozzle beams with and without cluster formation we were able to derive the condensed fraction in our (CO2) m cluster beam and from a statistical analysis of cluster distributions we obtain an estimate for the absolute value of the effective rate constant for the total negative ion formation, which amounts to (4.5 ± 3) · 10−8 cm3/s for Ar** (21d).
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  • 10
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    The European physical journal 24 (1992), S. 247-275 
    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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  • 11
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    The European physical journal 19 (1991), S. 227-228 
    ISSN: 1434-6079
    Keywords: 33.60.Cv ; 35.20.Vf ; 36.40.+d
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Photoelectron spectra for neutral mercury clusters (up to a size of 109 atoms) and liquid mercury have been recorded for several different photon energies between 7.1 eV and 10.6 eV. For both large mercury clusters (Hg x ,x≥60) and liquid mercury a strong increase of the partial photoionization cross sections near threshold with decreasing photon energy is observed. This shows clearly that the local electronic structure of large mercury clusters is very similar to the electronic structure of the metallic bulk material.
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  • 12
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    The European physical journal 19 (1991), S. 385-387 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 34.50.Lf
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Reactivity of positively charged cobalt cluster ions (Co n + ,n=2−22), produce by laser vaporization, with various gas samples (CH4, N2, H2, C2H4, and C2H2) were systematically investigated by using a fast-flow reactor. The reactivity of Co n + with the various gas samples is qualitatively consistent with the adsorption rate of the gas to cobalt metal surfaces. Co n + highly reacts with C2H2 as characterized by the adsorption rate to metal surfaces, and it indicates no size dependence. In contrast, the reactions of Co n + with the other gas samples indicate a similar cluster size dependence; atn=4, 5, and 10−15, Co n + highly reacts. The difference can be explained by the amount of the activation energy for chemisorption reaction. Compared with neutral cobalt clusters, the size dependence is almost similar except for Co 4 + and Co 5 + . The reactivity enhancement of Co 4 + and Co 5 + indicates that the cobalt cluster ions are presumed to have an active site for chemisorption atn=4 and 5, induced by the influence of positive charge.
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  • 13
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    The European physical journal 22 (1992), S. 517-520 
    ISSN: 1434-6079
    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract Electron impact ionization of gas phase silver clusters Ag n ,n≦36 has been achieved in the threshold region. The vertical ionization potentials in this region clearly demonstrate the evidence of shell effects as well as a distinct even-odd oscillation up ton≃20. Their general size dependence is somewhat different from that of the alkali metal clusters due to the presence of thed-electrons.
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  • 14
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    The European physical journal 22 (1992), S. 521-527 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 34.90.+q
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The collisional velocity dependence of the cross sections for fragmentation of mass-selected (CO2) n + (n+2...7) clusters in collisions with Ar atoms is presented. Interesting structure can be observed in the cross sections which indicate that the collision occurs between the Ar atom and one CO2 molecule within the cluster. The results may be explained by assuming that the collision leads to either vibrational excitation of a loosely bound CO2 monomer which then leaves the cluster or excitation of the entire cluster to a dissociative state.
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  • 15
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 35.20.Vf ; 33.80.Eh
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present resonant two-photon two-color photoionization (R2P2CI) spectra of a series of Aniline-Ar n complexes (n=1−6). An apparently anomalous blue shifted spectra for An-Ar3 is explained by a modified spectral shift additivity rule which assigns different shifts to different relative positions of the Ar with respect to aniline. Evidence is presented for the existence of several isomers of clusters withn≧2. It is shown that, by changing the nucleation conditions, it is possible to control the relative populations of the various isomers.
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  • 16
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    The European physical journal 22 (1992), S. 541-545 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 61.50.Cj
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    Topics: Physics
    Notes: Abstract Spherically averaged pseudopotential (SAPS) calculations have been done for Mg n clusters, withn up to 250 within the framework of density functional theory. The electronic structure is computed resorting to the Thomas-Fermi-Dirac-Weizsäcker (TFDW) approximation for the kinetic energy. The equilibrium geometries have been obtained by minimizing the total cluster energy with respect to the atomic positions using the steepest-descent method. The ground state geometries obtained in this way are formed by spherical atomic shells, the number of them increasing with cluster size, up to a number of four for the biggest sizes considered here. An analysis of the distribution of the interatomic distances shows that the more internal is the shell, the more contracted are the interatomic distances. This effect diminishes progressively with increasing cluster size. For the purpose of comparison, similar calculations have been done with Cs n clusters in the same size range, allowing us to reproduce previous results obtained using a more elaborated density functional technique (Kohn-Sham method). The inhomogeneous contraction of interatomic distances then appears as a general fact for simple metallic clusters and not only for alkaline ones.
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  • 17
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    The European physical journal 22 (1992), S. 547-551 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 79.20.Rf
    Source: Springer Online Journal Archives 1860-2000
    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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  • 18
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    The European physical journal 19 (1991), S. 283-286 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 73.40. Gk ; 61.16. Di
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Mechanism of the staircase like I–V curve observed recently in scanning tunneling spectroscopy (STS) of a metal fine particle supported on an oxide covered substrate is clarified based on theoretical simulations. It is discussed how the step structures are influenced by the coupling of the fine particle charge to the remaining degrees of freedom, such as induced charge in the surrounding medium. Relation between the characteristic features of single electron tunneling (SET) and the STS of micro-clusters is discussed
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  • 19
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    The European physical journal 25 (1993), S. 261-265 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 79.20.Kz
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    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.
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  • 20
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    The European physical journal 22 (1992), S. 641-644 
    ISSN: 1434-6079
    Keywords: 31.20.Ej ; 36.40.+d
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    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.
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  • 21
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    The European physical journal 26 (1993), S. 59-63 
    ISSN: 1434-6079
    Keywords: 79.70.+q ; 03.65.-w ; 36.40.+d ; 61.16.Di
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The quantized energy levels of electrons in supported nanometer-size Au clusters have been resolved at room temperature using field emission techniques. By studying the time dependence of the electron emission current from an individual supported cluster, information about the structural stability of the cluster can also be obtained. Studies show abrupt jumps between different emission rates that are revisited as time progresses. This phenomenon can be attributed to a rearrangement of the cluster structure and/or orientation on the substrate and provides new evidence of multiple ‘isomeric’ structures for small clusters of metallic atoms.
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  • 22
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    The European physical journal 26 (1993), S. 195-197 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 05.45.+b
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract The structure and long-time dynamics of (LiBr) n n=4,5,8 were studied by optimization and molecular dynamics. The ring structure, double ring stack for (LiBr)8, was found to be the energy minimum. They are dynamically flexible and, particularly for (LiBr)4 and (LiBr)5, hardly isomerise into other isomers determined by optimization. (LiBr)8 is probably a promising candidate to exhibit dynamic coexistence among a number of isomers.
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  • 23
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    The European physical journal 26 (1993), S. 201-203 
    ISSN: 1434-6079
    Keywords: 36.40.+d
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    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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  • 24
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    The European physical journal 26 (1993), S. 217-219 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 33.70.Jg ; 34.10.+x
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We present results of semiclassical simulations of the electronic spectra and dynamics of aniline-Arn (1≤n≤3) clusters. The spectral density formalism of Mukamel [3] is used to generate the spectra from the time dependent energy difference of the S0 and S1 states of aniline solvated by the argon atoms. A repulsive Ar-N interaction is incorporated in the Hamiltonian of the S1 state; this term permits a quantitative prediction of the origin shifts of the S1〈--S0 transition (both red and blue shifts) for all the clusters studied. The temperature dependence of the spectrum of aniline-Ar2 is correlated with the underlying dynamics of this cluster.
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  • 25
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    The European physical journal 26 (1993), S. 13-16 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 34.20.Gj ; 34.40.+n ; 34.70.+e
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    Topics: Physics
    Notes: Abstract We have measured absolute integral cross sections for low-energy collisions of atoms and molecules with neutral sodium clusters over a wide cluster size range (n=2–40). The cross sections are exceptionally large, reaching values of thousands of square angstroms. Consequently, the scattering involves long-range interactions. The van der Waals force, acting either alone (Nan+N2) or in concert with the inelastic charge-transfer “harpooning” channel (Nan+Cl2, Nan+O2) can describe the measurements. Using interaction parameters taken from spectroscopic studies of alkali clusters, we find very good agreement with the data. This provides a point of contact between beam scattering experiments and studies of cluster electromagnetic response properties.
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  • 26
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    The European physical journal 26 (1993), S. 343-345 
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    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract Absolute cross-sections for photodetachment of negative carbon clusters are reported for C n − (n=3,...,8). These measurements are made using different types of ion sources, which create different isomers. These new results indicate that various negative and neutral isomers exist, some with electron affinities as low as ∼1 eV.
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  • 27
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    The European physical journal 26 (1993), S. 352-354 
    ISSN: 1434-6079
    Keywords: .64.70.Fx ; 36.40.+d ; 35.20.Vf
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    Topics: Physics
    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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  • 28
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    The European physical journal 26 (1993), S. 373-376 
    ISSN: 1434-6079
    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract The paper presents an analytic model which is based on approximation of the catchment basins in cluster potential energy surface by structures of ash-tray type. In order to see how the quantities to be specified relate to those obtained by means of numerical computation, predictions for the Ar13 caloric curve are made and they are compared with computer simulation data.
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  • 29
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    The European physical journal 26 (1993), S. 388-390 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 05.45.+b
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    Topics: Physics
    Notes: Abstract The dynamics of clusters are revealed, in part, by the extent and nature of their chaotic and ergodic behavior. Conversely, small clusters offer opportunities to study the origins and evolution of chaotic and ergodic behavior. This investigation uses, as a probe, the time evolution of the distribution of sample values of the largest Liapunov exponent λmax. Two kinds of clusters are examined, Ar3 and Ar7. The distributionsg(λmax,E) allow inference of dynamical characteristics such as dwell times in the various potential minima and durations and frequencies of saddle crossings.
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  • 30
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    The European physical journal 26 (1993), S. 394-396 
    ISSN: 1434-6079
    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract Noble gas atoms trapped in the intracrystalline cavities of zeolites may form clusters. A classical-mechanical isoenergetic molecular dynamics simulation is performed to simulate the dynamical behavior of noble gas clusters in zeolite cavities. To implement the simulation, a model is adopted of a homogeneous spherical cavity with Morse interaction between the noble gas atoms and cavity walls. The results for Ar6 clusters indicate that the noble gas clusters in the cavity undergo the same solid/liquid phase changes as in free space, and, at high enough energies, a rapid exchange between atoms adsorbed on the inner surface and thosein the interior of the cavity. Mathematical quenching is used to investigated the multidimensional potential surface of Ar clusters in the cavity.
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  • 31
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 65.40.Em
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    Topics: Physics
    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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  • 32
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    The European physical journal 26 (1993), S. 113-114 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 82.80.Ms
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    Topics: Physics
    Notes: Abstract The present paper supports coexistence of electronic shells and shells of ion cores for large alkali clusters.
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  • 33
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    The European physical journal 26 (1993), S. 122-124 
    ISSN: 1434-6079
    Keywords: 73.20.Mf ; 36.40.+d ; 33.20Kf
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    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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  • 34
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    The European physical journal 26 (1993), S. 131-133 
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    Keywords: 36.40.+d ; 31.20.Sy ; 03.65.Sq
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    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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    The European physical journal 26 (1993), S. 143-145 
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    Keywords: 36.40.+d ; 31.20.Sy ; 71.30.+h
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    Topics: Physics
    Notes: Abstract Electronic structures of mercury clusters are studied by the self-consistent calculations. It is found that an icosahedral Hg13 cluster is characterized by the atomic nature with closed electronic shell configuration while a significant amount of thespd-hybridization is observed for a Hg19 cluster with a double-icosahedral shape. The electronic structure of a Hg12Ag cluster is also studied with a special focus on the electronic shell structure.
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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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    Topics: Physics
    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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  • 37
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    The European physical journal 27 (1993), S. 93-96 
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    Keywords: 36.40.+d ; 81.20.Sh
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    Notes: Abstract We have studied the low frequency vibrational modes and the structural rigidity of long graphitic carbon tubules consisting of 100, 200, and 400 atoms. Our calculations have been performed using an empirical Keating Hamiltonian with parameters determined from first principles. We have found the “beam bending” mode to be one of the softest modes in these structures. The corresponding beam rigity of a “bucky tube” is compared to an found to exceed the highest values found in presently available materials.
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  • 38
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    Keywords: 81.30.-t ; 61.14.-x ; 36.40.+d
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    Notes: Abstract Solid-liquid transition of fine tin particles having diameter of 2–10 nm is studied in-situ by high-resolution transmission electron microscopy under a ultra-high vacuum condition. Melting temperature is confirmed to decrease with the decrease of particle diameter. The particles less than the critical size, 2r c⋍5 nm, are found to have a specific phase between the solid and the liquid phase. The particle in this “pseudo-crystalline” phase contains crystalline embryos in it. Particles larger than the critical size have sharp liquid-solid transition, which completed within the time resolution of our microscope observation, 33 ms upon heating or cooling process. Large solid particles have Wulff's polyhedron, while particles around the critical diameter have rather spherical shape. Structural anomaly at the critical size occurs all over the outer most surface layer slightly below the melting temperature. Origin of the “pseudo-crystalline” phase and surface pre-melting phenomena are discussed.
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  • 39
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    The European physical journal 20 (1991), S. 97-99 
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    Keywords: 36.40.+d
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    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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    The European physical journal 20 (1991), S. 123-125 
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    Keywords: 36.40.+d
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    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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    The European physical journal 23 (1992), S. 269-274 
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    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract In the framework of the jellium model an algorithm is presented to calculate the electrostatic energy of charged metal clusters of arbitrary shape. Explicit expressions are given for some special shapes.
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  • 42
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    The European physical journal 28 (1993), S. 223-234 
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    Keywords: 36.40.+d ; 31.90.+s
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    Notes: Abstract Fission of doubly charged silver clusters is investigated by the method of shell corrections. The following fission events are considered: Ag 22 2+ → Ag n + + Ag 22 −n + , (n=11, 10, 9, 8); Ag 21 2+ → Ag n + + Ag 21 −n + , (n=10, 9, 8, 7); Ag 18 2+ → Ag n + + Ag 18 −n + , (n=9, 8, 7, 6). It is found that the shell correction energy is comparable to or larger than the deformation energy of the liquid drop. Threshold energies for the fission events are calculated and compared with the experimental abundance spectra obtained by Katakuse et al. (1990). Correspondence between the calculated threshold energies with the shell corrections and the experimental abundance is very good, showing products from lower threshold fission channels yield more abundance. The threshold energies without the shell corrections are almost constant irrespective of the fission channels and cannot explain the experimental abundance. Abundance of some products are too small to be accounted for only by the threshold energies. The low abundance of those products may be explained by the presence of competing fission channels that have similar minimal energy paths. It is found in fission of Ag 18 2+ that the shell correction overwhelms the Coulomb energy and the fission channel to Ag8 + Ag 10 2+ is preferred over the fission channel to Ag 8 + + Ag 10 + .
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  • 43
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    The European physical journal 28 (1993), S. 247-255 
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    Keywords: 36.40.+d ; 61.16.Di
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    Notes: Abstract Multislice calculations have been performed for Ag, Pd and Au clusters in the size range of ≃ 5.0 nm diameter of cuboctahedral, icosahedral and decahedral structures. It could be shown that tilt series are necessary for the classification of the structures. Particularly for arbitrary orientations, i.e. deviations from main directions such as 2-, 3- and 5-fold axes, the performance of computer simulations is mandatory. The influence of absorption is also studied for the case of a 100 kV microscope by introducing a complex potential.
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    The European physical journal 20 (1991), S. 1-7 
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    Keywords: 36.40.+d
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    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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  • 45
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    The European physical journal 20 (1991), S. 329-331 
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    Keywords: 36.40.+d ; 65.40.−f
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    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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  • 46
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    The European physical journal 20 (1991), S. 333-335 
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    Keywords: 36.40.+d ; 76.60.Es
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    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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    The European physical journal 20 (1991), S. 349-352 
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    Keywords: 36.40.+d ; 61.50.Cj ; 68.35.−p
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    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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    The European physical journal 20 (1991), S. 357-359 
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    Keywords: 35.20.W ; 36.40.+d ; 68.40
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    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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    The European physical journal 20 (1991), S. 361-363 
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    Keywords: 36.40.+d ; 71.50.+t ; 31.20.Pv
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    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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    The European physical journal 29 (1994), S. 241-243 
    ISSN: 1434-6079
    Keywords: 21.60.Jz ; 36.40.+d ; 71.10.+x
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    Topics: Physics
    Notes: Abstract Numerical Hartree-Fock calculations on the2S+1 L states arising from 1s 2 1 pv and 1s 2 1p 6 1 pμ open-shell configurations of Nan-type (n≦20) jellium spheres are reported for the first time. TheL, S multiplet energy spread is substancially larger than that expected from earlier estimates of exchange interaction energies. A new way of considering cluster abundance structures in mass spectra emerges from the results.
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    The European physical journal 20 (1991), S. 437-439 
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    Keywords: 07.75.+h ; 35.20.Wg ; 36.40.+d
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    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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    The European physical journal 24 (1992), S. 385-394 
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    Keywords: 36.40.+d ; 52.20.Hv ; 79.20.Nc
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    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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    The European physical journal 21 (1991), S. 65-81 
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    Keywords: 36.40.+d ; 31.20.Sy ; 05.30.−d ; 65.50.+m
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    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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    The European physical journal 25 (1993), S. 253-259 
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    Keywords: 36.40.+d ; 32.80.pj ; 42.50.vk
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    Topics: Physics
    Notes: Abstract The ordered structures of two-species ions stored in a Paul trap are simulated by minimizing the total effective potential energy of the ion system. It is shown that the homo-charged two-species ion clusters display separating and mixing structures for different mass and charge ratios. The hetero-charged ion clusters consisting of one light negatively (positively) charged ion and three to six heavy positively (negatively) ions are found to exist stably, and the stability conditions obtained through the perturbative analysis indicate that the ion cluster consisting of more heavy ions has a looser limitation on mass and charge ratios of two-species ions.
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    The European physical journal 21 (1991), S. 163-175 
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    Keywords: 03.65. ; 36.40.+d ; 21.60.-n
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    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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    The European physical journal 26 (1993), S. 226-228 
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    Keywords: 79.20.Rf ; 34.50.Lf ; 79.20.Nc ; 81.60.Cp ; 36.40.+d
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    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.
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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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    The European physical journal 26 (1993), S. 128-130 
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    Keywords: 36.40.+d ; 35.20.VF
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    Notes: Abstract Ionization Potentials of LinHm clusters have been measured by photoionization. As in Lin, odd-even alternations and shell closing effects are observed. In a first approximation, we find that LinH clusters behave like Lin−1 and LinH2 like Lin−2. The results may be interpreted by assuming that the bonding of one hydrogen localizes one electron and that the other electrons remain delocalized.
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    The European physical journal 26 (1993), S. 137-139 
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    Keywords: 36.40.+d ; 35.20.Vf ; 33.80.Eh
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    Notes: Abstract Laser photoionization experiments have been performed on a large size range of indium and thallium clusters. The metal clusters were produced by laser vaporization technique and analyzed after laser ionization by standard time-of-flight mass spectrometry. For the indium clusters, individual ionization potentials (IP) are deduced for N≤132. Abrupt decreases in the IP values are observed, which correspond to the openings of new electronic shell as predicted by the spherical jellium model. For larger indium clusters, the unresolved mass spectra present small but reproducible oscillations. Interpretations in terms of either electronic shell structure or cluster geometry remain undecided for the moment. Our results on thallium clusters are less abundant and only qualitative. Nevertheless, they show that thallium behaves more like a monovalent element than like a trivalent one.
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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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    The European physical journal 26 (1993), S. 255-257 
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    Keywords: 36.40.+d ; 31.90.+s ; 71.45.Nt
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    Notes: Abstract A local-density approximation calculation is performed on various M8C12 structures, including Ti8C12, V8C12, VTi7C12 and ScTi7C12. It is found that the magic numbers observed during the experimental discovery of these species does not depend on the details of the electronic structure, but rather can be described as a chemical system derived from ethylene.
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    The European physical journal 21 (1991), S. 349-356 
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    Keywords: 36.40.+d ; 75.60.Jp
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    Topics: Physics
    Notes: Abstract We discuss the magnetic properties of small neutral transition-metal clusters like Fe n and Co n deduced from Stern-Gerlach deflection experiments. We claim that the asymmetric Stern-Gerlach deflection profiles are due to a transfer from electronical angular momentum to the cluster rotation, allowing for a depopulation of the high energy magnetic levels. For finite temperatures we consider two limiting cases. First, the cluster magnetization is assumed to be tied to the random orientation of the cluster easy axes due to the lattice anisotropy. This causes a surprisingly small magnetization for small external magnetic fields. For larger fields and also for increasing temperatures the magnetization is released from the cluster geometry and allowed to align itself parallel to the field. In the second case the clusters are treated as an ensemble of superparamagnetic particles. Here, the effect of the anisotropy is less visible. The cluster lattice anisotropy per atom is expected to decrease for increasing cluster size. Preliminary results support this.
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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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    The European physical journal 25 (1993), S. 175-180 
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    Keywords: 36.40.+d ; 31.20.Sy
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    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.
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    The European physical journal 28 (1993), S. 163-167 
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    Keywords: 36.40.+d ; 76.60.Es
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    Notes: Abstract A model based on resonant spin-rotation coupling is used to reproduce the magnetization of free iron clusters experimentally observed by Stern-Gerlach deflections. Due to the interaction with the rotating magnetocrystalline anisotropy field, the dynamics of the magnetic moment of the clusters cannot be explained only in terms of thermal relaxation. As in magnetic resonance experiments, modified Bloch equations can describe the interaction of the particle spin with the deflecting field and the rotating anisotropy field. The dependence of the magnetization on the rotational temperature of the clusters and the relaxation time is discussed.
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  • 66
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    Keywords: 36.40.+d ; 34.10.+x
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    Notes: Abstract The dynamics of C60-rare gas collisions is studied using molecular dynamics with empirical two- and three-body forces. The carbon potential is chosen to be able to reproduce the experimentally determined bond lengths and cluster radius of C60 as well as the structure of small carbon clusters. The reaction channels observed can be divided into four categories: deep inelastic scattering, fragmentation, capture and inelastic scattering. The temperature dependence of the threshold energy for capture is studied and compared with available experimental data. The calculations predict a maximum in the lowest tail of the kinetic-energy distribution of the projectile with a transition from a single- to a double-humped maximum with increasing collision energy and, in addition, may provide a natural interpretation for the, as yet unexplained, structure in the experimental shapes.
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  • 67
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    Keywords: 36.40.+d
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    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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  • 68
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    The European physical journal 26 (1993), S. 51-55 
    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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  • 69
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    The European physical journal 26 (1993), S. 56-58 
    ISSN: 1434-6079
    Keywords: 68.35.Md ; 36.40.+d ; 64.60.-i ; 62.50.+p
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    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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  • 70
    ISSN: 1434-6079
    Keywords: 31.70.Ks ; 36.40.+d ; 71.20Hk ; 31.20.Sy
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    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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  • 71
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    The European physical journal 26 (1993), S. 110-114 
    ISSN: 1434-6079
    Keywords: 34.10.+x ; 36.40.+d ; 82.20. Fd ; 82.20. Wf
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    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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  • 72
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    The European physical journal 26 (1993), S. 126-130 
    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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  • 73
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    The European physical journal 26 (1993), S. 138-140 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 33.20.Lg
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    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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  • 74
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    The European physical journal 28 (1993), S. 331-337 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 33.20.Ea
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    Topics: Physics
    Notes: Abstract Infrared photodissociation spectra of (CH3OH) n clusters (n=2, 3 and 6) and the mixed dimer C2H4 · CH3COCH3 are presented. The clusters are generated in a supersonic jet expansion and size selected by scattering from a helium atomic beam combined with mass spectrometric detection. Continuous CO2-lasers are used to vibrationally excite the molecules in the cluster leading to rapid dissociation of the complex. Various dissociation peaks that are found in single-laser dissociation spectra can be assigned unambigously in a pump-probe experiment with two lasers to either different isomers (acetone-ethene dimer) or splitted lines of one isomer (methanol hexamer). For size distributions, the method is able to select contributions of single masses which is demonstrated for mixtures of methanol dimers and trimers.
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  • 75
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    The European physical journal 26 (1993), S. 8-12 
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    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract The change of the cohesive energy and the optical absorption spectra of small singly sized Hg clusters is discussed. The cohesive energy allows one to determine the different regimes of chemical bonding. The optical spectra show an abrupt transition to a collective, plasmon-like absorption as a function of increasing cluster size. The position of the one plasmon peak is: 1) independent of the charge state, 2) nearly independent of cluster size, and 3) agrees with that of the classical Mie plasmon calculated from the experimental dielectric constants. The width of the plasmon peaks is discussed. A strong influence of electronic correlations on the cluster size dependence of the oscillator strength is observed.
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  • 76
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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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    Topics: Physics
    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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  • 77
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    The European physical journal 26 (1993), S. 349-351 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 31.20.Sy ; 61.55.Dc
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    Topics: Physics
    Notes: Abstract The combination of density functional (DF) theory with molecular dynamics (MD) allows one to simulate dynamical processes in solids, clusters and molecules without requiring a parameterization of the forces in the system. The method can also be used with the strategy of “simulated annealing” to determine structural isomers. We demonstrate the capabilities of the scheme in the case of the structure of neutral and charged phosphorus clusters, and discuss relationship between these structures and those of bulk systems (crystalline and amorphous). The results show clearly the tendency of phosphorus structures to have threefold coordination as well as “tubular” structures similar to that found in Hittorf's phosphorus (H-P). We discuss the interplay between electronic and geometric structure.
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  • 78
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    The European physical journal 26 (1993), S. 355-357 
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    Keywords: 36.40.+d ; 73.20.Dx ; 63.20.Dj
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    Topics: Physics
    Notes: Abstract We use low temperature (10K) optical hole-burning and fluorescence line narrowing spectroscopy to investigate the electronic properties of CdSe nanocrystallites (quantum dots) as a function of crystallite diameter (20–80Å). We discuss how the homogeneous linewidth of the HOMO-LUMO transition, the energy shift between the absorbing and emitting state, and the LO phonon frequency vary with nanocrystallite size.
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  • 79
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    The European physical journal 26 (1993), S. 377-381 
    ISSN: 1434-6079
    Keywords: 33.10.-n ; 33.70.Jg ; 36.40.+d
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    Topics: Physics
    Notes: Abstract Spectral lineshapes of the electronic origin of tetracene·Arn (n=1–3,19) clusters have been simulated by the semiclassical spectral density method [L. E. Fried, S. Mukamel, J. Chem. Phys.96, 116 (1992)]. Information is obtained concerning the spectral shifts, the homogeneous linewidths and their temperature dependence.
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  • 80
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    The European physical journal 26 (1993), S. 391-393 
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    Keywords: 36.40.+d ; 05.45.+b
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    Topics: Physics
    Notes: Abstract We have computed the local Kolmogorov entropy of molecular dynamics trajectory segments near the potential energy saddles of model Ar3 and Ar5 clusters. In the case of Ar3 clusters bound with a Lennard-Jones potential, the local Kolmogorov entropy of the cluster is significantly smaller in the saddle region than in other areas of the potential surface. This behavior indicates an increase in the degree of nearly quasiperiodic motion near the Ar3 saddle due to the partial decoupling of the cluster's vibrational modes there. Lennard-Jones Ar5 clusters do not exhibit similar behavior, but Ar5 clusters bound with a short-range Morse potential do. This suggests that the “regularizing” effect of saddle regions is strongly dependent on the shape of the energy surface near the saddle. From these observations, we can determine which features of the saddle are most important in this respect; the flatness of the saddle region seems to be one such feature.
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  • 81
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    The European physical journal 29 (1994), S. 139-145 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 34.10.+x ; 82.20.Rp
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    Topics: Physics
    Notes: Abstract In this article, the dynamics of fragmentation of highly excited van der Waals clusters are analyzed. An approach to the characterization of complex cluster fragmentation is described, based on a combination of structural and dynamical analysis of classical trajectories. In this method, the final fragmentation pattern is analyzed by a depth-first search algorithm based on graph theory, which provides a partitioning of the system into intact fragments of various sizes: monomers, dimers, trimers, and higher multimers. With knowledge of the final products, a dynamical analysis is accomplished by tracing back the time dependence of the relevant fragment energies. A transition from oscillatory to constant behavior of these energies indicates that the fragment has become energetically isolated from the parent cluster. This allows an unambiguous definition of the dissociation time of the fragment. The method is applied to the characterization of cluster fragmentation of chemically activated I2Ar 12 * formed in the association reaction I+I(Ar)12→I2+12 Ar. It is found that cluster decomposition channels, leading to the formation of at least one multi-atom fragment, play an important role in the evaporative cooling of I2, in addition to monoatomic sequential evaporation.
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  • 82
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 61.14.−x ; 61.16.Di
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    Topics: Physics
    Notes: Abstract The structures of unsupported ultrafine silver particles in a molecular beam, produced by the inert-gas-aggregation technique, have been studied by electron diffraction. The dependence of particle structure on evaporation-source temperature (1260 °C ≤ Tc ≤ 1400 °C) has been investigated. Particles in the beam are found to divide into: a dominating proportion of small, decahedral particles, and a small proportion of unexpectedly large icosahedral particles, larger than any previously reported free icosahedra. The mean diameters are 2–3 nm and 7–10 nm, respectively. F.c.c. particles, with an average diameter of ∼6 nm, appear in significant numbers when Tc≥1350 °C. The particles' mean sizes and distribution widths increase with Tc. Electron microscope observations of particles collected from the beam support these findings.
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  • 83
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    The European physical journal 26 (1993), S. 87-88 
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    Keywords: 61.16.Di ; 78.65.Ez ; 36.40.+d
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    Topics: Physics
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  • 84
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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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    Topics: Physics
    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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  • 85
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    The European physical journal 26 (1993), S. 110-112 
    ISSN: 1434-6079
    Keywords: 36.40.+d ; 21.60.Cs
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    Topics: Physics
    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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  • 86
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    The European physical journal 31 (1994), S. 191-197 
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    Keywords: 36.40.+d
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    Topics: Physics
    Notes: Abstract Highly charged metal clusters can be easily produced using the technique of multi-step photoionization. The critical sizes at which fission occurs are reported here for alkali metal clusters having charges as high as +7. An interpretation within the framework of the liquid droplet model reveals that the fission process is strongly asymmetric and thermally activated.
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  • 87
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    The European physical journal 26 (1993), S. 146-149 
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    Keywords: 36.40.+d ; 33.60.Cv ; 07.77.+p
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    Topics: Physics
    Notes: Abstract Bismuth cluster anions are produced in a new type of source (PACIS). For Bismuth the intensity is estimated to be 10 times higher than that of a laser vaporization source. UV-photoelectron spectroscopy serves to study the electronic level structure of the cluster anions. In the photoelectron spectra of Bi 2 − , Bi 3 − and Bi 4 − the main transitions agree with earlier results of LIF investigations on the neutral species as well as with recent theoretical and experimental data. Here we present a first extension to higher photon energies.
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  • 88
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    The European physical journal 26 (1993), S. 15-17 
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    Keywords: 68.35.Bs ; 36.40.+d ; 35.20.Bm
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    Topics: Physics
    Notes: Abstract Rigorous analytical formulae for mean nearest-neighbour coordination numbers in clusters as a function of cluster size have been derived for a range of geometries: the tetrahedron, octahedron, cuboctahedron, icosahedron and bcc rhombic dodecahedron. Formulae for outer-neighbour coordination numbers are also reported, including a complete analysis of interatomic distances and mean coordination numbers in icosahedra. The formulae will find application in studies of electronic structure and interpretation of EXAFS data.
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  • 89
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    The European physical journal 16 (1990), S. 293-297 
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    Keywords: 36.40.+d ; 32.80.Pj ; 42.50.Vk
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    Topics: Physics
    Notes: Abstract We prove that stable Coulomb clusters consisting of ions of both signs of charge exist in a Paul trap.
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  • 90
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    Keywords: 34.50.Lf ; 36.40.+d ; 82.50.Fv
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    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.
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  • 91
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    The European physical journal 16 (1990), S. 299-301 
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    Keywords: 36.40.+d ; 67.40.−w
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    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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  • 92
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    The European physical journal 17 (1990), S. 69-72 
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    Keywords: 36.40.+d ; 21.10.-k
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    Topics: Physics
    Notes: Abstract The electronic properties of small metal particles within the recently proposed self-consistent spheroidal jellium model [1] are further explored and compared to recent experimental data. Physical properties investigated include ionization potentials, electron affinities and the binding energy of neutral monomers to cationic clusters. The formalism is applied within the size-range 2≦N≦41, but could easily be extended beyondN=41. Finally, we discuss briefly the implications for the study of the dynamical response of open-shell clusters. In sharp contrast to earlier studies the functional is now corrected for self-interaction error, in a way first proposed by Pedew and Zunger [2]. This enables us to calculate reliable values for the electron affinities within ajellium-based model. This has the advantage, that we can calculate the affinities for Cu for all particle numbers for which experimental data are available. In all cases investigated we obtain excellent agreement with experiment, with pronounced shell-effects both for the electron affinities and for the binding energies, confirming in this way that the abundances map the relative stability of (Me) N clusters, with Me being a sp-metal atom (Na, K, Li, Cu, Ag, Au etc.).
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    The European physical journal 17 (1990), S. 73-76 
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    Keywords: 36.40.+d ; 35.20.Wg ; 07.75.+h
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    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.
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    The European physical journal 19 (1991), S. 219-221 
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    Keywords: 36.40.+d
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    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.
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    The European physical journal 26 (1993), S. 33-35 
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    Keywords: 33.80.-b ; 36.40.+d
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    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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  • 96
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    The European physical journal 22 (1992), S. 645-650 
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    Keywords: 36.40.+d ; 35.20.Wg
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    Notes: Abstract Rare gas ions Ne+, Ar+ and Kr+ are injected into a drift tube which is filled with helium gas and cooled by liquid helium. Helium cluster ions RgHe x + (Rg=Ne, Ar and Kr,x≦14) are observed as products. Information regarding the stability of RgHe x + is obtained from drift field dependence of the size distribution of the clusters, and magic numbers are determined. The magic numbers arex=11 and 13 for NeHe x + andx=12 for ArHe x + and KrHe x + . NeHe x + , Ar+ and Kr+ are proposed as the core ions for NeHe 13 + , ArHe 12 + and KrHe 12 + , respectively.
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    The European physical journal 22 (1992), S. 651-658 
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    Keywords: 36.40.+d ; 33.80.Eh ; 82.40.Dm
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    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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    The European physical journal 22 (1992), S. 659-666 
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    Keywords: 74.20.Fg ; 36.40.+d
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    Notes: Abstract Motivated by the experimental finding of oddeven alternations in the mass spectra and ionization potentials of metal clusters, we have investigated the possibility of interpreting these results as evidence for pairing correlations among the electrons. For the present exploratory calculations, we have used a spherical BCS model which we have applied, as an example, to some Al clusters. Additional model calculations have been carried out for Na N with 34〈N〈100 in order to illustrate a possible systematics.
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  • 99
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    Keywords: 36.40.+d ; 33.35.-q ; 33.25.-j
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Fullerenes containing metal atoms and clusters can be formed by the arc-vaporization method. The electronic structure of these metallofullerenes can be probed using magnetic resonance techniques. Electron paramagnetic resonance (EPR) spectra of LaC82, YC82, ScC82 and Sc3C82 have been obtained. Metallofullerenes containing a single metal atom (MC82 with M = La, Y, or Sc), have small hyperfine couplings and g-values close to 2, implying that they can be described as + 3 metal cations within — 3 fullerene radical anion cages. In the La and Y cases, additional EPR active MC82 species have been found. The EPR spectrum of Sc3C82 shows that the metal atoms are equivalent, suggesting that they may form a triangular molecule. No EPR spectrum is found for Y2C82 or for Sc2C2n species (with 2n = 82,84,86), suggesting that they are diamagnetic. Sc NMR spectra of a solution containing Sc2C2n species have been obtained which confirm the diamagnetism of the discandium metallofullerenes.
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  • 100
    Electronic Resource
    Electronic Resource
    Springer
    The European physical journal 26 (1993), S. 181-183 
    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
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