bluuebunny/crossref_metadata_2025 huggingface dataset:
QUANTUM GROUP APPROACH TO A SOLUBLE VERTEX MODEL WITH GENERALIZED ICE RULE
Authors: SOW C.L. , TRUONG T.T.
Published: October 2004

Using the representation of the quantum group SL q(2) by the Weyl operators of the canonical commutation relations in quantum mechanics, we construct and solve a new vertex model on a square lattice. Random variables on horizontal bonds are Ising variables, and those on the vertical bonds take half positive integer values. The vertex is subjected to a generalized form of the so-called “ice rule,” its property is studied in detail and its free energy calculated with the method of quantum inverse scattering. Remarkably, in analogy with the usual six-vertex model, there exists a “free-fermion” limit with a novel rich operator structure. The existing algebraic structure suggests a possible connection with a lattice neutral plasma of charges, via the fermion-boson correspondence.
QUANTIZATION OF THE BIANCHI TYPE IX MODEL IN N=1 SUPERGRAVITY IN THE PRESENCE OF SUPERMATTER
Authors: MONIZ P.V.
Published: October 2004

The general theory of N=1 supergravity with supermatter is applied to a Bianchi type IX diagonal model. The supermatter is constituted by a complex scalar field and its [Formula: see text] fermionic partners. The Kähler geometry is chosen to be a two-dimensional flat one. The Lorentz-invariant ansatz for the wave function of the universe is taken to be as simple as possible in order to obtain new solutions. The set of differential equations derived from the quantum constraints are analyzed in two different cases: if the supermatter terms include an analytical potential or not. In the latter the wave function is found to have a simple form.
MULTIMATRIX MODELS: INTEGRABILITY PROPERTIES AND TOPOLOGICAL CONTENT
Authors: BONORA L. , NESTI F. , VINTELER E.
Published: October 2004

In this article, we analyze multimatrix chain models. They can be considered as multicomponent Toda lattice hierarchies subject to suitable coupling conditions. The extension of such models to include extra discrete states requires a weak form of integrability. The discrete states of the q-matrix model are organized in representations of sl q. We solve exactly the Gaussian type models, of which we compute several all-genus correlators. Among the latter models one can classify also the discretized c=1 string theory, which we revisit using Toda lattice hierarchy methods. Finally, we analyze the topological field theory content of the 2q-matrix models: we define primary fields (which are ∞q), metrics and structure constants, and prove that they satisfy the axioms of topological field theories. We outline a possible method for extracting interesting topological field theories with a finite number of primaries.
TRANSPORT PROPERTIES OF ANYONS
Authors: KHVESHCHENKO D. V.
Published: October 2004

We consider electromagnetic response as well as electrical and thermal transport in a normal state of anyon system at finite temperatures. We find the frequency and momentum dependences of electrical and thermal conductivities in the longwavelength limit. It is also shown that a pole of electric current and stress tensor correlation functions identified at zero temperature with a gapless sound-like mode becomes a diffusion above the critical temperature of the hypothetical superfluid anyon phase transition.
ENTREPRENEURIAL LEADERS IN FAMILY BUSINESS ORGANISATIONS
Authors: SHEH SEOW WAH
Published: October 2004

This research reports the findings of an empirical study into the behavioural attributes of the Chinese transformational leader in Singapore. The literature review reveals that the current research on transformational leadership only focuses on Western organisations. This research design used both qualitative and quantitative approaches. The qualitative research used the case study strategy as a primary instrument. This case study approach was to search for new themes and patterns across eight Chinese Chief Executives of medium to large-scale business enterprises. In the quantitative part of the research, the subordinates of the selected leader were identified to participate in the questionnaire survey – to rate their leaders' based on the presence and intensity of practice of the identified behavioural attributes. The six factors rotated uncovered a common list of behavioural attributes of the Chinese transformational leader that will facilitate the transformation process. Implications of the findings are discussed.
ENTREPRENEURIAL INTENTION AMONG INDONESIAN AND NORWEGIAN STUDENTS
Authors: KRISTIANSEN STEIN , INDARTI NURUL
Published: October 2004

This paper aims to identify determinants of entrepreneurial intention among young people. The empirical basis is formed by surveys among Indonesian and Norwegian students. The main objective is to compare the impact of different economic and cultural contexts. Independent variables in the study include demographic factors and individual background, personality traits and attitudes, and contextual elements such as access to capital and information. The individual perceptions of self-efficacy and instrumental readiness are the variables that affect entrepreneurial intention most significantly. Age, gender and educational background have no statistically significant impact. Generally, the level of entrepreneurial intention is higher among Indonesian students. The lower level of entrepreneurial intention among Norwegian students is explained by the social status and economic remuneration of entrepreneurs in comparison with those enjoyed by employees in the Norwegian context.
QUANTUM LEVEL STATISTICS USEFUL FOR MESOSCOPIC PHYSICS
Authors: HASEGAWA H. , MA J.-Z. , TAKAMI T.
Published: October 2004

We report on two results from our computational studies in quantum level statistics as a contribution to mesoscopic physics: (i) parametric motion of complex quantum levels and its dynamic treatment of second-derivative distribution for neighboring pairs (the so-called curvature distribution); (ii) intermediate statistics for long-range level correlation which exhibits a fractional power law, i.e., another manifestation of the fractional-power dependence like Sβ (0<β<1) familiar to Brody’s distribution, in the number variance and the Δ-statistics of Dyson-Mehta.
POTENTIAL-ENERGY SURFACES OF SODIUM CLUSTERS WITH QUADRUPOLE, HEXADECAPOLE, AND TRIAXIAL DEFORMATIONS
Authors: REIMANN S.M. , FRAUENDORF S.
Published: October 2004

Combining a modified Nilsson-Clemenger model with the shell-correction method, the potential-energy surfaces of sodium clusters with sizes of up to N = 200 atoms are calculated, including nonaxial deformations. For spherical clusters, the model potential is fitted to the single-particle spectra obtained from microscopically self-consistent Kohn-Sham calculations using the jellium model and the localdensity approximation. Employing the Strutinsky shell-correction method, the surface energy of the jellium model is renormalized to its experimental value. The ground-state shapes are determined by simultaneous minimization of the deformation energies for quadrupole, hexadecapole, and triaxial cluster deformations.
PRODUCTION OF BINARY NANOPARTICLES (BiCu, BiTe, CdS) BY AEROSOL PROCESS: TREATMENT FOR ISOLATION AND CONCENTRATION
Authors: TOHNO S. , ITOH M. , KIMURA K.
Published: October 2004

We extended the modified gas-flow/cold-trap method to produce high-density and contact-free binary nanoparticles containing bismuth (BiCu, BiTe) and CdS particles. Binary nanoparticles were collected as stable dispersoids in hexane with a cationic surfactant. The electron micrographs showed individual clusters are separated from each other by surfactant thin layer and do not contact directly any other clusters even after the concentration process. The binary particles containing bismuth gave diffuse halo diffraction patterns characteristic of an amorphous state. Optical effects due to size quantization were observed for the CdS colloids.
SILICON-29 MAS-NMR AND ESR STUDY ON THE EFFECT OF HEAT TREATMENT ON THE STRUCTURE OF SiC−Si3N4 COMPOSITE ULTRAFINE PARTICLES
Authors: SUZUKI MASAAKI , LI XINGGUO , NAKATA YOSHINORI , NAGAI HIDEAKI , OKUTANI TAKESHI
Published: October 2004

The effect of heat treatment on the structure of SiC−Si3N4 composite ultrafine particles was studied by 29 Si MAS-NMR and ESR. 29 Si MAS-NMR and ESR results showed that the local structure changed a little below 1573 K, at which the XRD pattern did not change significantly, but slight increase in crystalline size were observed. When the SiC−Si3N4 powder was heat-treated at 1773 K, most nitrogen atoms dissolved into β-SiC lattice were removed from the β- SiC lattice, and the remaining nitrogens were considered to exist in the boundary layer between SiC crystals as SiC3N unit in the particle.
THE COMPLEXITY OF THE GROWTH AND OPTICAL PROPERTIES OF GERMANIUM NANOCLUSTERS
Authors: HAN MIN , GONG YANCHUN , MA JIANXIN , LIU FENGQI , WANG GUANGHOU
Published: October 2004

Germanium nanoclusters are prepared by means of the inert-gas condensation method. The growth, coalescence, and aggregation processes are investigated by means of TEM. It is found that the clusters can be either nanocrystals or amorphous-like. Furthermore, during the deposition, they can either randomly land on surface, keep isolated and finally form a cluster-assembled uniform film or aggregate with fractal structures and then form porous film, depending on their preparation condition. Spectropho-tometric measurements are recorded for these samples at room temperature in the ultraviolet, visible, and near-IR region, and show obvious blueshift of the band gap as large as 1.0–2.0 eV in comparison with those for the bulk specimens, which may be related to the quantum-confinement effect.
SPECIFIC HEAT IN THE THERMODYNAMICS OF CLUSTERS
Authors: BORRMANN PETER , GLOSKI DORIAN , HILF EBERHARD R.
Published: October 2004

The thermodynamic properties such as the specific heat are uniquely determined by the second moments of the energy distribution for a given ensemble averaging. However for small particle numbers the results depend on the ensemble chosen. We calculated the specific heat for both the canonical and the microcanonical ensemble for the same van der Waals clusters. The differences of the resulting thermodynamic observables for the two ensembles are calculated. We demonstrate how for increasing particle number these terms vanish for bulk material. For the calculation of the specific heat within the microcanonical ensemble we give a new method based on an analysis of histograms.
SUPERCONDUCTIVITY OF SMALL PARTICLES
Authors: MÜHLSCHLEGEL B.
Published: October 2004

Superconductivity in a small metallic particle means that pairing of electrons has to be included in the treatment of size-dependent properties. Here a model is reconsidered which applies to the small-size limit of conventional superconductors with a large intrinsic range of the pair coherence length. Mainly thermal equilibrium properties are discussed, but also some remarks about related phenomena and remaining problems are made.
MASS AND VELOCITY DISTRIBUTIONS OF AN IRON-CLUSTER BEAM GENERATED BY LASER VAPORIZATION
Authors: SAITO N. , IWATA Y. , KOYAMA K. , KITAMURA T. , TANIMOTO M.
Published: October 2004

The mass and velocity distributions of an iron-cluster beam generated by laser vaporization are measured by time-of-flight spectrometers to get information on the cluster growth inside the source. Only fast iron monomers are observed until 0.3 ms after the vaporization. The vaporized iron atoms are then cooled down enough to aggregate into clusters. The size of clusters become larger, up to 700 iron atoms, as the stagnation time in the source increases from 0.3 to 0.6 ms. The saturation of the cluster growth is observed later than 0.6 ms, suggesting the decrease in the density of the aggregating source particles.
PHOSPHORUS-CLUSTER CATIONS PRODUCED BY LASER ABLATION OF RED PHOSPHORUS
Authors: HUANG RONGBIN , LI HONGDI , LIN ZHENYANG , YANG SHIHE
Published: October 2004

We report the generation of phosphorus-cluster cations containing up to 35 atoms by direct laser ablation of red phosphorus for the first time without supersonic expansion. Bare-cluster cations with an odd nymber of phosphorus atoms are preferentially produced. For even-number phosphorus atom clusters, the cluster cations with an odd number of hydrogens (present in trace amount in the source) are easily produced.
DYNAMIC OBSERVATION OF LASER-ABLATED CARBON PARTICLES USING TIME-RESOLVED X-RAY ABSORPTION SPECTROSCOPY
Authors: MIYASHITA A. , OHYANAGI T. , YODA O. , MURAKAMI K.
Published: October 2004

Time- and space-resolved characteristics of laser-ablated carbon particles were studied by x-ray absorption spectroscopy. Absorption peaks from the 1s→2p transition of neutral carbon atom ( C 0), C −, C +, and C 2+ ions were observed, An absorption peak from 1s→π* and a broad absorption maximum from the 1s→σ* transition of small clusters were also observed. Neutral carbon, C −, C +, and small carbon clusters were emitted from the sample long after laser irradiation. Spatial distributions of laser-ablated carbon particles in the localized helium-gas environment were measured. In the helium-gas environment, the ablation plume was depressed by the helium cloud generated on the top of the ablation plume.
PRODUCTION OF SULFUR-SELENIUM MIXED CLUSTERS BY THE SUPERSONIC JET EXPANSION METHOD
Authors: YAO M. , NAGAYA K. , HAYAKAWA T. , ENDO H.
Published: October 2004

The mass spectrum for S, Se, and S−Se mixed vapor has been measured. From the dependence of the relative intensity of [Formula: see text] clusters on the electron-impact energy E e it is suggested that neutral S 2 dimer may be evaporated from [Formula: see text] clusters. The E e dependence of the relative intensity of [Formula: see text] clusters is more complicated. The spectrum for S−Se mixed vapor suggests that a S atom may be replaced by a Se atom in S-rich clusters.
FORMATION OF HELIUM-CLUSTER IONS CO2Hen+ (n≤15) IN A DRIFT TUBE COOLED BY LIQUID HELIUM
Authors: TANUMA H. , SAKAMOTO M. , KOBAYASHI N.
Published: October 2004

The formation of helium-cluster ion CO 2 He n+ (n≤15) has been observed when CO2+ ions are injected into a drift tube filled with helium gas cooled by liquid helium. The cluster sizes n = 5 and 14 are found to be magic numbers based on the drift-field dependence of the cluster size distribution. The structure of CO 2 He 14+ cannot be considered as the icosahedron, which is proposed as the structure of the cluster ions having twelve helium atoms surrounding the ionic core in our previous papers.
EFFECTS OF ELECTRON CORRELATIONS ON SMALL CLUSTERS OF HYDROGEN-LIKE ATOMS
Authors: EBINA K. , KAWARABAYASHI H. , KABURAGI M.
Published: October 2004

We develop a simple procedure to calculate the electronic structure of a cluster of hydrogen atoms, taking into account the electron correlations analogously to the induced covalent-bond scheme. The results for H 3 are in fairly good agreement with the precise quantum-chemistry calculations. For H 4 we calculate the ground and excited states of the electron system for various spin states and for various nuclear configurations. We discuss our results by comparing with those for a more simplified Hamiltonian, where the electronic degrees of freedom are represented by the quantum spin operators.
SHAPE ISOMERISM OF SODIUM CLUSTERS WITH QUADRUPOLE, OCTUPOLE, AND HEXADECAPOLE DEFORMATIONS IN THE STRUCTURE-AVERAGED JELLIUM MODEL
Authors: HIRSCHMANN TH. , BRACK M. , MONTAG B. , REINHARD P.-G. , MEYER J.
Published: October 2004

Multidimensional deformation energy surfaces of singly charged sodium clusters with 8≤ Z ≤50 valence electrons have been calculated including quadrupole, octupole, and hexadecapole shapes for the ionic background. We solve the Kohn-Sham equations in the local-density approximation with preserved axial symmetry on a two-dimensional lattice. In addition to the diffusivity of the jellium surface, the structure-averaged jellium model (SAJM) which yields the empirical bulk properties and surface tension of sodium is successfully applied to deformed systems. Discussing the systematics of shape transitions, we find good agreement with recent experimental dipole resonance splittings found in the photoabsorption cross sections and confirm the oblate shape of the first neighboring clusters above the closed 2p shell ( Z =40) provided that left-right asymmetry is enabled.
SIZE EFFECTS AND THE ROLE OF NONADDITIVE FORCES IN NEUTRAL AND ANIONIC SILVER-CLUSTER STABILITY
Authors: KAPLAN I.G. , SANTAMARÍA R. , NOVARO O.
Published: October 2004

The precise quantum-chemical study of neutral and anionic silver clusters manifests the pronounced size effect for the vertical ionization potential (VIP), vertical detachment energy (VDE), and atomic detachment energy (ε1). The additive and nonadditive contributions to the binding energy of clusters are calculated and their role in the cluster stability is discussed.
MOLECULAR DYNAMICS SIMULATION FOR THE CLUSTERING PROCESS BY TEMPERATURE CONTROL
Authors: IKESHOJI T.
Published: October 2004

The clusterization process from gas states of Lennard–Jones (L–J) potential atom and water molecule of the TIP4P model was simulated by the molecular dynamics calculation with a constant-temperature thermostat at 0.1 (reduced unit) for the L–J atom system and at 200 K for the water molecule. The linear relationship between the logarithm of the populatlon and the cluster size was observed with no significant peak. The inner temperature of clusters was higher than the system temperature. Structure parameters derived from the inertia of clusters gave the following information on the structure. Clusters grow at first in linear or planar structure. Dipole interaction of water molecules favors more linear structure at the beginning of the cluster formation. Clusters around 13 L–J atoms become highly spherical and water clusters of 3–5 members become rings, after lowering of the temperature.
STRUCTURES AND STABILITIES OF ${\rm H}_3^+ ({\rm H}_2)_n$ CLUSTERS (n=1–11)
Authors: DIEKMANN B. , BORRMANN P. , HILF E.R.
Published: October 2004

Geometries and energies for [Formula: see text] clusters (n=0,…, 11) have been calculated using standard ab-initio methods. Up to the clusters with n=6, three different Pople basis sets (DZ, TZ, TZP) have been used in the calculations. For larger cluster sizes, the calculations have been carried out with one basis set (DZ) using the HF/CISD method. We discuss here only the nice counterplay of polarization effects between the central [Formula: see text] ion and the adsorbed H2 molecules, which naturally governs both the geometric structure and energy of the clusters.
STABLE TRAJECTORY OF CHARGED PARTICLE IN PAUL TRAP: APPLICATION OF BAND THEORY
Authors: KABURAGI M. , FUKUDA Y. , KOHMOTO T.
Published: October 2004

The purpose of this study is to develop a theory for the motion of a charged particle in a trap with general rf trapping field. We first show that the equations of motion for a charged particle in the trap are equivalent to Schrödinger equation for a one-dimensional system with periodic potential. Applying the band theory to the equation, we analyze the region in a so-called (a, q) parameter-space with stable trajectory. It is shown that the stable region is roughly divided into two regimes, namely the nearly free regime and the tight-binding regime. The a-q relations for the boundaries of each regime are obtained in explicit formula. Using these results, we discuss the effects of the waveform of the rf trapping field on the motion of a charged particle, aiming to obtain a wider stable region in the parameter space for experimental studies.
NEW GEOMETRIC SHELL STRUCTURES
Authors: MARTIN T.P. , ZIMMERMANN U. , MALINOWSKI N. , NÄHER U. , FRANK S. , TAST F. , WIRTH K.
Published: October 2004

Clusters often grow by adding concentric layers of atoms in such a way that the overall symmetry of the cluster is left unchanged. Icosahedral shell structure was first envisioned by Mackay1 while working on the difficult geometric problem of sphere packing. Shells with icosahedral symmetry have since been identified in clusters composed of inert-gas atoms,2–4 metal atoms,5,6 and even complex molecules. In this report experimental evidence will be presented for shell structures based on geometries other than the Mackay icosahedra. The results which will be discussed include: (a) octahedral shells in Al and In clusters, (b) non-Mackay-like icosahedral shells of metal deposited expitaxially on a C60 molecule and (c) new data on very large cubic shells of alkali halides. In all these cases, the evidence for shells consists of mass spectrometric anomalies that appear periodically when plotted on a (mass)1/3 scale. Each geometry is associated with a unique periodicity.
VALENCE- AND INNER-SHELL SPECTROSCOPY ON RARE-GAS CLUSTERS
Authors: BJÖRNEHOLM O. , FEDERMANN F. , JOPPIEN M. , FÖSSING F. , KAKAR S. , VON PIETROWSKI R. , MÖLLER T.
Published: October 2004

An overview of the present status of valence- and inner-shell spectroscopy on rare-gas clusters is given. Fluorescence excitation, time-of-flight ion and photoelectron spectroscopy with synchrotron excitation was used to study the electronic level structure of rare-gas clusters. Ne and Ar clusters covering the size range from the monomer up to a few thousand atoms/cluster are used as examples. Specific advantages and limitations of different methods of the study of electronic level structure as well as geometrical structure are discussed. A wealth of information on the evolution of electronic level structure has already been obtained. Nevertheless, several interesting questions concerning the evolution of energy-level shifts remain unresolved. Prospects for future work and experimental developments are given.
USING CLUSTERS TO RELATE TOPOGRAPHY AND DYNAMICS OF MULTIDIMENSIONAL POTENTIALS
Authors: KUNZ B. , BERRY R.S. , ASTAKHOVA T.
Published: October 2004

Striking results obtained recently for (KCl)32 indicate that clusters undergoing cooling can find their way to regular structures under statistically unfavorable odds as large as 1012:1 even when all energy is removed in only about 25 vibrational periods.1,2 To understand what characteristics of potential surfaces are responsible for such “focusing” character, we have undertaken a series of statistical analyses of a moderately complex system, the van der Waals cluster of 19 atoms held by pairwise Lennard–Jones forces. The analysis can be done hierarchically, first in terms of the distributions of minima and of saddles, then of pairs of successive wells and intervening saddles, and then in terms of whole sequences of pathways to different basins. The goals are an interpretation of what make a complex surface “focusing” or glass-forming, and a means to quantify the optimal cooling schedule to achieve either a structure of a selected (and physically attainable) type, or an arbitrary, presumably amorphous structure.
ELECTRONIC PROPERTIES AND MAGNETISM OF Rh AND Pd CLUSTERS
Authors: YANG JINLONG , TOIGO F. , WANG KELIN
Published: October 2004

The electronic structure and magnetism of Rh43, Rh55, Pd43, and Pd55 clusters with possible icosahedral and octahedral geometries are studied using the discrete-variational local-spin-density functional method. All clusters are shown to have magnetic ground states. An anomalous symmetry dependence of the Rh cluster magnetism is found: the total magnetic moment of the icosahedral Rh clusters is smaller than that of the octahedral Rh clusters. The calculated moments of the Rh and Pd clusters are in good agreement with a recent experiment. The density-of-state profiles of octahedral Rh55 and Pd55 show the features characteristic of the bulks.
SIZE AND DENSITY DEPENDENCES OF THE SCREENING EFFECT IN METAL CLUSTERS
Authors: SONODA KOHJI , SHIMOJO FUYUKI , HOSHINO KOZO , WATABE MITSUO
Published: October 2004

We employ a jellium sphere as a model for a metal cluster and calculate the change in the electronic states when an extra positive point charge is introduced at its center, by solving the Kohn–Sham equation in the local-density approximation and in the local-spin-density approximation with the self-interaction correction, and by solving the Hartree–Fock equation. The screening charge density around the extra charge is estimated by subtracting the charge induced near the cluster surface from the total induced charge density. It is found that, even for small clusters with the number of atoms N=20, 40, and 58, the screening effect is similar to that in the bulk jellium and that the screening charge distributions for larger clusters with N=92 almost coincide with that in the bulk. The density dependence of the screening charge is also investigated by calculating the screening charge for rs=3.0, 4.0, and 5.0. It is shown that the period of oscillation of these screening charge distributions can almost be scaled by rs and it is close to that of the Friedel oscillation. The results obtained by three methods are compared with special attention to the effect of the self-interaction.
ELECTRONIC STRUCTURES OF HEAVY-METAL CLUSTERS
Authors: ISHII Y. , WATARI N. , OHNISHI S.
Published: October 2004

The electronic structures of small Hg and Pb clusters are studied by the first-principle calculations within the local density-functional approximation. It is found that the stable structure of Hg19 cluster is not polyicosahedral but hexagonal close-packed although the bonding nature is still atom-like with no significant sp-hybridization. The stability of a doubly charged Pb cluster is discussed in connection with the electronic shell-model description. We conclude that the stability of Pb clusters is determined by complicated correlation between the atomic and electronic structures, and the electronic shell model cannot be applied straightforwardly.
STRUCTURES OF BENZENE CLUSTERS
Authors: LI ZHIQIANG , OHNO KAORU , KAWAZOE YOSHIYUKI , MIKAMI MASUHIRO , MASUDA YUJI
Published: October 2004

The structures of small benzene clusters ( C 6 H 6)n (n=2–8) have been calculated using the discrete variational method (DVM) in the framework of local-density functional approximation (LDA) and molecular dynamics (MD) simulations. The structure of benzene dimer by our calculation is in good agreement with the Hartree–Fock studies. The structure of trimer is first optimized by MD with the intermolecular potential obtained from ab-initio study, and the intramolecule force field of Dreiding. Further calculations are carried out by DVM. We obtain the structure of benzene trimer from first principles calculation, and the optimized structure is a triangle having bloodstrain constructed from the T-type benzene dimer which is expected to be stable experimentally. The structures of tetramer to octamer molecules are obtained by MD and compared with previous calculations and experiments. Consistent structure patterns stemming from the fundamental T-shape dimer are found for all clusters.
STUDY OF SMALL SEMICONDUCTOR CLUSTERS USING ANION PHOTOELECTRON SPECTROSCOPY: GERMANIUM CLUSTERS (Gen, n=2−15)
Authors: BURTON GORDON R. , XU CANGSHAN , NEUMARK DANIEL M.
Published: October 2004

The technique of anion photoelectron spectroscopy has been used at 266, 355, and 416 nm to study small germanium clusters, [Formula: see text], n=2–15. The electron affinities for these cluster anions have been determined from the photoelectron spectra. The spectra for [Formula: see text] and [Formula: see text] show well-resolved vibrational structure.
COMPARISON OF PHOTOELECTRON SPECTRA OF ${\rm Cu}_n^-$, ${\rm Ag}_n^-$, AND ${\rm Na}_n^-$: MOLECULAR ORBITALS VERSUS ELECTRONIC SHELLS
Authors: GANTEFÖR G. , HANDSCHUH H. , MÖLLER H. , CHA CHIA-YEN , BECHTHOLD P.S. , EBERHARDT W.
Published: October 2004

The photoelectron spectra of [Formula: see text] clusters are compared to the results of quantmn-chemical ab-initio calculations (n=2-9) and to the predictions of the shell model. The shell model yields qualitative assignments of the dominant features in the spectra to photoemission from occupied electronic shells. These correspond to the exact quantitative assignments to transitions into various electronic states of the neutral clusters according to the quantum-chemical calculations. The photoelectron spectra of [Formula: see text] and [Formula: see text] clusters exhibit certain similarities to the Ag data in agreement with the basic idea of the shell model.
PHOTOELECTRON SPECTROSCOPY OF SILICON–CARBON CLUSTER ANIONS
Authors: NAKAJIMA A. , TAGUWA T. , NAKAO K. , GOMEI M. , KISHI R. , IWATA S. , KAYA K.
Published: October 2004

Photoelectron spectra of [Formula: see text] cluster anions (3≤n, m≤6) were measured at the photon energy of 3.49 eV, by using a magnetic-bottle electron spectrometer having ~60-meV resolution. The [Formula: see text] clusters were produced by laser vaporization of a carbon–silicon mixture rod in a He carrier gas. The spectra of the [Formula: see text] clusters are similar to those of pure [Formula: see text] clusters in the peak positions and their envelopes, which is attributed to the similarity in electronic structure of Si and C atoms, leading to a similar geometry. In contrast, the similarity in the photoelectron spectra is not observed between [Formula: see text] and [Formula: see text] clusters, which is attributed to a change in their geometry; from chain to ring.
STUDY OF IRON–CARBON MIXED CLUSTERS FeCn (n=2−5): A POSSIBLE LINEAR-TO-CYCLIC TRANSITION FROM FeC3 TO FeC4
Authors: WANG LAI-SHENG
Published: October 2004

Small Fe/C mixed clusters, [Formula: see text], are studied by anion photoelectron spectroscopy at 3.49-eV photon energy. The spectra of [Formula: see text] and [Formula: see text] show well-resolved features and are consistent with linear-to-linear detachment transitions. The [Formula: see text] spectrum is quite broad, suggesting large geometry change from the anion to the neutral. Since [Formula: see text] is known to be linear, our data suggest that neutral FeC4 may have a cyclic structure. The spectrum of [Formula: see text] exhibits both sharp and broad features, consistent with the existence of both a linear and a cyclic isomer. A linear-to-cyclic structural transition is thus suggested to take place for the neutral FeCn clusters from n=3−4; for n<4 they are linear and for n≥4 they can be both linear and cyclic. This is similar to the linear-to-cyclic transition occurring for pure carbon clusters from n=9−10 (Ref. 10) but at a much smaller cluster size due to the presence of the Fe atom.
MAGNETIC PROPERTIES OF SODIUM CLUSTERS
Authors: FRAUENDORF S. , PASHKEVICH V.V. , REIMANN S.M.
Published: October 2004

Axial and triaxial shapes of Na clusters are determined by means of the shell-correction method.1 The orbital paramagnetism and the diamagnetism of small Na clusters are calculated. Odd axial clusters may have substantial orbital paramagnetic moments, which are quenched for triaxial shapes. Even clusters show diamagnetism, which is maximal for spherical and attenuated for deformed shape.
EXACT MANY-BODY APPROACH TO MAGNETISM AND CLUSTER STRUCTURE
Authors: PASTOR G.M. , HIRSCH R. , MÜHLSCHLEGEL B.
Published: October 2004

The magnetic and structural properties of small clusters having N≤8 atoms were determined rigorously in the framework of the Hubbard model by performing the exact many-body electronic calculations together with a complete geometry optimization. We discuss the resulting interplay between electron correlations, magnetism, and cluster structure at T=0, as well as the stability of cluster ferromagnetism against temperature-induced electronic excitation and structural changes.
PROTON TUNNELING IN THE S1 STATE OF TROPOLONE–M1(M=Ar, Kr, Xe, CH4, CD4, N2) CLUSTERS
Authors: SEKIYA H. , HAMABE H. , NAKAJIMA T. , NISHIMURA Y.
Published: October 2004

The S 1← S 0 fluorescence excitation spectra of jet-cooled tropolone–M1(M= Ar , Kr , Xe , CH 4, CD 4, N 2) clusters have been measured to investigate the effect of intermolecular interactions on proton tunneling. It has been found that the [Formula: see text] tunneling splittings of tropolone–CH4/CD4 and tropolone–N2 are significantly smaller than that of tropolone.
LASER-INDUCED OPTICAL-EMISSION STUDIES OF NIOBIUM CLUSTERS
Authors: FRENZEL U. , KALMBACH U. , KREISLE D. , RECKNAGEL E.
Published: October 2004

The laser-induced optical emission of niobium clusters generated via the standard laser-vaporization technique is studied in the wavelength range from 350 to 750 nm. Particles with a radius of approximately 4 nm were heated by pulsed Nd:YAG laser operating at the fourth harmonic at 266 nm. The emission spectra are recorded as a function of delay time after the excitation and show a broad structureless continuum similar to blackbody radiation. Using the emissivity of a small spherical particle given by the Mie theory together with Planck’s law the experimental spectra can be reproduced quite well by varying the temperature of the particle. Thus temperatures can be deduced from the spectra. Increasing delay time leads to decreasing temperature of the particles which can be attributed to radiation cooling.
OPTICAL RESPONSE OF SMALL CLOSED SHELL Cs-CLUSTER IONS
Authors: ELLERT CHRISTOPH , SCHMIDT MARTIN , SCHMITT CHRISTINA , HABERLAND HELLMUT
Published: October 2004

The absolute photoabsorption cross sections of [Formula: see text] and [Formula: see text] have been measured at two temperatures (evaporative ensemble, 115 K). The maximum of the observed resonance is nearly independent of the temperature and agrees within 5% with the Mie plasmon resonance as calculated from the bulk electron density of cesium. This is in contrast to the sodium case, where the plasmon is redshifted by about 20%. For n=9 and 21 the integrated oscillator strength amounts to 89% [Formula: see text] and 73% [Formula: see text] per valence electron in the energy range 1.5 eV<hν<3.0 eV.
EVIDENCE FOR THERMIONIC EMISSION FROM SMALL AGGREGATES
Authors: KLOTS C.E. , COMPTON R.N.
Published: October 2004

The delayed emission of electrons from small isolated aggregates has been reported now by several laboratories. When the emission is from a negative ion, it can plausibly be identified with the vibrational autoionization which has been known for many years from ions such as [Formula: see text]. Whether delayed emission from neutral species should be called “thermionic” is more problematic. Do these aggregates sample all of the available phase space prior to emission? We examine the experimental evidence which bears on this question. Particular reference is made to studies of “metallic” aggregates and of caged carbon clusters. Tantalizing evidence for the thermionic paradigm is noted, although recent experiments with niobium clusters can only be understood by postulating that they have unusual thermodynamic properties. Finally, Schottky’s expression for the effect of an externally applied electric field on a work function is extended to aggregates of arbitrary size.
A NEW APPROACH OF THE SIMS METHOD FOR METAL CLUSTERS
Authors: KATAKUSE I. , ICHIHARA T. , ITO H. , SAKURAI T. , MATSUO T.
Published: October 2004

The size distributions of ( CsI )n Cs +, [Formula: see text], and [Formula: see text] (M: alkali metal, j=1, 2, 3, 4, 5) clusters were obtained using secondary-ion mass spectrometry. The sizes of stable neutral clusters ( CsI )n and ( Hg )n clusters were determined from the mass spectra of cluster ions ( CsI )n Cs + and ( Hg )nM+. The magic numbers of [Formula: see text] clusters were identical to those of van der Waals type clusters. It is believed that the shell closing cluster [Formula: see text] is at the center of complex clusters [Formula: see text]. The [Formula: see text] clusters were believed to have electronic shell structures from the magic numbers.
IONIZATION-INDUCED FRAGMENTATION OF SMALL Hgn CLUSTERS: A MOLECULAR DYNAMICS STUDY
Authors: REICHARDT D. , GARCIA M.E. , BENNEMANN K.H.
Published: October 2004

The time evolution of small Hg n clusters immediately after ionization is studied by performing molecular dynamics simulations for different cluster sizes and different initial cluster structures. The potential-energy surface and the forces are determined self-consistently from a microscopic electronic theory, which takes into account the interplay between delocalization of the hole and polarization energy. We study the energy-transfer processes within the cluster and also estimate melting and fragmentation times for some particular cases. The short-time behavior of the kinetic energy, charge and dipole distributions is analyzed. The role of the initial temperature of the clusters is discussed.
METASTABLE DECAY OF MERCURY/CESIUM COMPLEX CLUSTER
Authors: SAKURAI T. , ITO H. , MATSUO T. , KATAKUSE I.
Published: October 2004

Metastable decay of mercury/cesium complex cluster, Hg n Cs +, was measured by using a time-of-flight mass spectrometer of Osaka University. The TOF spectrometer is comprised of four electrostatic analyzers (ESAs). By scanning the applied voltage of the ESAs, MS/MS spectra and MS/MS/MS spectra can be obtained. The product-ion spectra generated from metastable decay of the complex cluster were obtained by MS/MS analysis. The product ions of the decay were determined as Cs+ and Hg n Cs +. Sequential decays were also observed with the MS/MS/MS analysis mode of the spectrometer. The position occurring metastable decay producing detected ion can be selected with the TOF spectrometer. To compare the product-ion yield generated at two different positions, the rate constant of the decay can be estimated. In preliminary experiments using glycerin-trimer ion, [3g+H]+, as a precursor, the obtained rate constant of the decay is 2.0×104 l/s.
FROM ABUNDANCE SPECTRA TO CLUSTER ENERGIES
Authors: HANSEN KLAVS
Published: October 2004

We derive a simple but accurate relation between evaporative activation energies and abundances in ensembles of large, hot clusters. The relation is compared with simulated abundance spectra.
PHOTOELECTRON SPECTROSCOPY OF BINARY CLUSTER ANIONS
Authors: KAYA KOJI , NAKAJIMA ATSUSHI
Published: October 2004

Photoelectron spectra of Al nSm− and [Formula: see text] were measured using magnetic-bottle-type photoelectron spectrometer. Sulfur atoms were found to perturb the structural factor of Al clusters and several magic number clusters such as AlS − and Al 3 S 3− were newly observed. Sodium atoms perturb the electronic factor of Si clusters with small disturbance of the geometries of the genuine clusters.
RHODIUM-CLUSTER REACTIVITY: STICKING PROBABILITIES OF SOME DIATOMIC MOLECULES
Authors: ANDERSSON M. , HOLMGREN L. , ROSÉN A.
Published: October 2004

The reactivity of neutral rhodium clusters towards D 2, N 2, O 2, CO , and NO has been investigated and the absolute sticking probability (S) of the first molecule on Rh 10– Rh 50 ( Rh 10– Rh 35 for D 2) was determined. For O 2, the absolute sticking probability of the second molecule was measured. The reactions were made under single-collision-like conditions where the clusters make only one or a few collisions with reactive gas molecules. All molecules but N 2 react with a high sticking probability on most cluster sizes. N 2 molecules adsorbed on clusters produced in a liquid-nitrogen-cooled cluster source, while cooling the cluster source did not significantly change S for the other molecules. The sticking probability of O 2 and NO on Rh n looked almost the same, monotonically increasing from 0.2/0.4 at n=10 to 0.8/0.9 at n=25, and the high S also remains for larger clusters. The sticking probability of CO shows small variations around S=0.6 over the entire size range. The sticking probability is somewhat lower for D 2 and substanitially lower for N 2 (also on cool clusters), and these two molecules display the most distinct variations in S as a function of cluster size, often with coinciding maxima and minima.
ELECTRONIC STRUCTURE OF Si20 FULLERENE AND SOLID Si20
Authors: SAITO SUSUMU
Published: October 2004

The electronic structure of the dodecahedral Si 20 fullerene obtained in the density-functional theory is discussed. In addition, the Si 46 lattice, which is known to be the real geometry of the Si atoms when crystallized with metal atoms, is pointed out to be essentially solid Si 20, and its geometrical and electronic properties are also discussed. The novel pentagonal bond network in these materials is found to have strong influence on their electronic structure. In the case of Na 2 Ba 6 Si 46, which is the ideal phase of superconducting-doped solid Si 20, the high Fermi-level density of states due to the hybridization between the Ba states and the Si 46 conduction-band states is considered to be important for the observed superconductivity.
EVALUATION OF THE MOLECULAR LINEAR POLARIZABILITY, OSCILLATOR STRENGTHS FOR FREE C60, AND OPTICAL CONSTANTS FOR FILMS OF C60
Authors: ROSÉN ARNE , WESTIN ERIK
Published: October 2004

Ground-state local-density calculations have been performed to evaluate the free response of the wave-length dependent microscopic linear polarizability for the C60 molecule using a sum-over-states approach. The influence of screening of the electromagnetic field was determined by applying external static electric fields in separate self-consistent-field calculations to evaluate the induced dipole moment. The polarizability calculated in the static limit was used to determine an effective screening parameter which was in turn used together with an RPA approach to calculate the wavelength dependent microscopic polarizability. Inclusion of screening was found to give an optical spectrum shifted about 0.4 eV from the experimentally determined absorption spectrum of C 60 in solution. Furthermore, after introduction of Lorentz local-field factors, the evaluated dielectric function ε(ω) was compared with experimental data for films of C 60 determined using ellipsometry in the 2–6 eV energy range and EELS techniques in the 0–30 eV energy range. The calculations compare reasonably well with experimental data except for a uniform shift of 0.4 eV in the 2–6 eV energy range and a shift of 2–3 eV in the 15–30 eV energy range.
HIGH-RESOLUTION HEIGHT-PROFILE ANALYSIS AND LASER-IONIZATION CHARACTERIZATION OF A WIDE RANGE OF FULLERENES IN LAMINAR DIFFUSION FLAMES
Authors: SIEGMANN K. , HEPP H. , SATTLER K.
Published: October 2004

Neutral fullerenes are detected online in laminar, atmospheric pressure methane diffusion flames using time-of-flight mass spectrometry combined with laser ionization. The intensity of the C 60 signal shows a quadratic dependence of the laser-pulse energy, which is consistent with two-photon ionization. Poly-cyclic aromatic hydrocarbons (PAH) are also found in these flames. Height profiles of fullerenes are compared with height profiles of PAH and it is found that the concentration of fullerenes most strongly at a height where the concentration of PAH decreases the most. This height in the flame probably marks the burnout of the available hydrogen. Since all fullerenes, independent of their number of carbons, peak at the same height above burner, we conclude that fullerenes in flames do not grow by the addition of small molecules.
MICROSCOPIC STRUCTURE OF THE SURFACE PLASMON IN FULLERENES
Authors: PACHECO J.M.
Published: October 2004

The microscopic structure of the surface plasmon is investigated in the fullerenes C 60 and C 70, in particular the contribution to its line shape and linewidth arising from the coupling to the normal modes of vibration of the ions, both at zero and at finite temperature. This coupling is found to be negligible in C 60 at all temperatures, but sizeable for C 70 already at T=0, evidencing a weak temperature dependence, a feature which is due to the lower equilibrium symmetry of C 70. As a result, Landau damping is found to be the dominant relaxation mechanism contributing to the large width observed experimentally.
DETECTION OF BLACK-BODY RADIATION FROM LASER-DESORBED C60
Authors: MITZNER R. , CAMPBELL E.E.B.
Published: October 2004

The optical emission spectrum of laser-desorbed C 60 has been investigated as a function of laser fluence for desorption with a KrF excimer laser (pulse length 20 ns). The observed spectra show close similarities to black-body radiation and can be fitted with the Planck black-body formula, thus giving information on the temperature of the fullerene beam. The temperatures of approximately 3000 K which are obtained are in good qualitative agreement with previous, indirect temperature estimates.
DELAYED IONIZATION OF FULLERENES AND FULLERENE DERIVATIVES UPON LASER DESORPTION AND SURFACE COLLISION
Authors: BECK R.D. , WEIS P. , ROCKENBERGER J. , KAPPES M.M.
Published: October 2004

Delayed electron emission has been observed upon laser desorption for several fullerenes, endohedral metallofullerenes, and large carbon clusters formed by coalescence reactions. Odd-numbered carbon clusters and fullerene derivatives with exohedral functional groups do not show delayed ionization under similar conditions, presumably due to lower dissociation energies. Thus, delayed electron emission is suggested to be a characteristic indicator for strongly bound fullerene structures. Measurements of the rate of delayed electron emission are used together with structural information from other sources to calculate ionization potentials for these species. Selective observation of delayed electron emission from scattered [Formula: see text] after surface impact and neutralization of [Formula: see text] on graphite confirms an earlier report of this process by Whetten et al.6
PHOTOIONIZATION THRESHOLD STRUCTURE OF FULLERENES: VIBRATIONAL EXCITATION
Authors: STEGER H. , VRIES J. de , HIELSCHER A. , KAMKE W. , HERTEL I.V.
Published: October 2004

The threshold region of the photoionization spectra of fullerenes shows distinct changes of slope which are typical for the opening of additional channels due to vibrational excitation. Typically, after evaporation from a hot oven, C 60 is excited in all its vibrational modes. Through coupling with the ionization transition only the two highly symmetric modes (breathing mode and tangential stretch mode) can be excited or de-excited. An analysis of the C 60 data reveals very good agreement of the observed structure with the expected energetic positions of various combinations of excitation and de-excitation of these two modes.
FORMATION OF ODD-NUMBERED FULLERENE-FRAGMENT IONS IN THE COALESCENCE REACTIONS OF FULLERENES
Authors: ZHU LEI , WANG SHENYI , LI YUFEN
Published: October 2004

We found that the coalescence reactions of fullerenes occur more efficiently for chemical adduct compounds of C 60 than pristine C 60 by the laser-desorption ionization technique. Under specific conditions, not only the even-numbered daughter fullerenes by successive C 60 losses or captures appeared, but also odd-numbered carbon-cluster anions [Formula: see text](51≤N≤65) were detected in the chemical fusion processes. The result suggests a new way to open fullerene cages, and the possible mechanism involved is discussed.
C2-LOSS FRAGMENTATION OF HIGHER FULLERENES AND METALLOFULLERENES
Authors: WAKABAYASHI T. , SHIROMARU H. , SUZUKI S. , KIKUCHI K. , ACHIBA Y.
Published: October 2004

Photofragmentation investigations were performed by using chromatographically isolated pure samples of higher fullerenes and metallofullerenes. Quite similar distributions of fragments were commonly observed for five different fullerenes, and this fact supports the presence of a “scrambled-cage” structure in a highly excited fullerene cage. An enhancement of the C 60 and C 70 signals was also observed as a result of “delayed C 2-loss” fragmentation within a time scale of about 60 µs after photoexcitation. Photodissociation study of mono- and di-metallofullerenes revealed the qualitative difference in the fragment distributions between them, suggesting that LaC 82 would possess an endohedral, and Sc 2 C 84 an exohedral, form.