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Showing papers on "Cluster (physics) published in 2000"


Journal ArticleDOI
TL;DR: In this paper, the magnetic field strength and distribution over a sample of 16 ''normal'' low redshift (z < 0.1) galaxy clusters was investigated. But the results showed that the hot intergalactic gas within these clusters is permeated with a high filling factor by magnetic fields at levels of = 5-10 (l/10 kpc)^{-1/2} microGauss.
Abstract: Results are presented of a new VLA-ROSAT study that probes the magnetic field strength and distribution over a sample of 16 ``normal'' low redshift (z < 0.1) galaxy clusters. The clusters span two orders of magnitude in X-ray luminosity, and were selected to be free of (unusual) strong radio cluster halos, and widespread cooling flows. Consistent with these criteria, most clusters show a relaxed X-ray morphology and little or no evidence for recent merger activity. Analysis of the rotation measure (RM) data shows cluster-generated Faraday RM excess out to ~0.5 Mpc from cluster centers. The results, combined with RM imaging of cluster-embedded sources and ROSAT X-ray profiles indicates that the hot intergalactic gas within these ``normal'' clusters is permeated with a high filling factor by magnetic fields at levels of = 5-10 (l/10 kpc)^{-1/2} microGauss, where l is the field correlation length. These results lead to a global estimate of the total magnetic energy in clusters, and give new insight into the ultimate energy origin, which is likely gravitational. These results also shed some light on the cluster evolutionary conditions that existed at the onset of cooling flows.

543 citations


Journal ArticleDOI

449 citations


Journal ArticleDOI
TL;DR: FESER et al. as discussed by the authors proposed a framework for applied regional cluster analysis based on the National Industry Clustering Template (NICST) framework, which can be used in a growing number of cities, states and regions in the US.
Abstract: FESER E. J. and BERGMAN E. M. (2000) National industry cluster templates: a framework for applied regional cluster analysis, Reg. Studies 34, 1‐19. A growing number of cities, states and regions in...

438 citations


Journal ArticleDOI
TL;DR: In this paper, a Schottky junction formed at the interface of ITO and zinc phthalocyanine was investigated to study the influence of the metal particles on the optical extinction spectra and on the short circuit photocurrent spectra of such constructed organic solar cells.

422 citations



Journal ArticleDOI
TL;DR: In this paper, the authors present atomically resolved scanning tunneling microscopy measurements of the cluster surfaces and an atomic model of the strong metal support interaction (SMSI) state, characterized by complete encapsulation of the clusters with a reduced titanium oxide layer.
Abstract: Nanosized platinum clusters were grown on a TiO2(110) surface and annealed in ultrahigh vacuum at high temperatures. This leads to the so-called strong metal-support interaction (SMSI) state, characterized by a complete encapsulation of the clusters with a reduced titanium oxide layer. We present atomically resolved scanning tunneling microscopy measurements of the cluster surfaces and an atomic model of the SMSI state. The ability to resolve the cluster surface geometry with atomistic detail may help to identify the active sites responsible for the SMSI.

338 citations



Book ChapterDOI
01 Jan 2000
TL;DR: Cluster analysis as discussed by the authors is a family of statistical procedures specifically designed to discover classifications within complex data sets, such that objects within one cluster share more in common with one another than they do with the objects of other clusters.
Abstract: Publisher Summary This chapter provides an overview of the uses of cluster methods and describes the procedures involved in conducting cluster analyses. Cluster analysis is a term used to describe a family of statistical procedures specifically designed to discover classifications within complex data sets. The objective of cluster analysis is to group objects into clusters such that objects within one cluster share more in common with one another than they do with the objects of other clusters. Thus, the purpose of the analysis is to arrange objects into relatively homogeneous groups based on multivariate observations. Furthermore, the chapter discusses the uses for cluster analysis. Clustering methods are useful whenever the researcher is interested in grouping together objects based on multivariate similarity. Cluster analysis can be employed as a data exploration tool as well as a hypothesis testing and confirmation tool. The most frequent use of cluster analysis is in the development of a typology or classification system. However, cluster analysis is not a single standardized procedure, and there are pitfalls associated with its improper use, therefore, care is required in its application.

294 citations


Journal ArticleDOI
27 Jul 2000-Nature
TL;DR: The observation of so-called ‘localized clusters’—periodic antiphase oscillations in one part of the medium, while the remainder appears uniform—in the Belousov–Zhabotinsky reaction–diffusion system with photochemical global feedback is reported.
Abstract: Oscillatory clusters are sets of domains in which nearly all elements in a given domain oscillate with the same amplitude and phase1,2,3,4. They play an important role in understanding coupled neuron systems5,6,7,8. In the simplest case, a system consists of two clusters that oscillate in antiphase and can each occupy multiple fixed spatial domains. Examples of cluster behaviour in extended chemical systems are rare, but have been shown to resemble standing waves9,10,11,12,13, except that they lack a characteristic wavelength. Here we report the observation of so-called ‘localized clusters’—periodic antiphase oscillations in one part of the medium, while the remainder appears uniform—in the Belousov–Zhabotinsky reaction–diffusion system with photochemical global feedback. We also observe standing clusters with fixed spatial domains that oscillate periodically in time and occupy the entire medium, and irregular clusters with no periodicity in either space or time, with standing clusters transforming into irregular clusters and then into localized clusters as the strength of the global negative feedback is gradually increased. By incorporating the effects of global feedback into a model of the reaction, we are able to simulate successfully the experimental data.

254 citations


Journal ArticleDOI
TL;DR: It is demonstrated that tin cluster ions with 10-30 atoms remain solid at approximately 50 K above the melting point of bulk tin.
Abstract: The fact that the melting points of nanoparticles are always lower than those of the corresponding bulk material is a paradigm supported by extensive experimental data for a large number of systems and by numerous calculations. Here we demonstrate that tin cluster ions with 10--30 atoms remain solid at $\ensuremath{\sim}50$ K above the melting point of bulk tin. This behavior is possibly related to the fact that the structure of the clusters is completely different from that of the bulk element.

248 citations


Journal ArticleDOI
TL;DR: The dynamical cluster approximation (DCA) as mentioned in this paper is based on an iterative self-consistency scheme on a finite-size periodic cluster, which is obtained by taking the cluster to a single site (the thermodynamic limit).
Abstract: We recently introduced the dynamical cluster approximation (DCA), a technique that includes short-ranged dynamical correlations in addition to the local dynamics of the dynamical mean-field approximation while preserving causality. The technique is based on an iterative self-consistency scheme on a finite-size periodic cluster. The dynamical mean-field approximation (exact result) is obtained by taking the cluster to a single site (the thermodynamic limit). Here, we provide details of our method, explicitly show that it is causal, systematic, Phi derivable, and that it becomes conserving as the cluster size increases. We demonstrate the DCA by applying it to a quantum Monte Carlo and exact enumeration study of the two-dimensional Falicov-Kimball model. The resulting spectral functions preserve causality, and the spectra and the charge-density-wave transition temperature converge quickly and systematically to the thermodynamic limit as the cluster size increases.

Journal ArticleDOI
TL;DR: The melting point of the investigated tin clusters was found to be lowered by 125 K and the latent heat of fusion per atom is reduced by 35% compared to bulk tin.
Abstract: The melting of isolated neutral tin cluster distributions with mean sizes of about 500 atoms has been investigated in a molecular beam experiment by calorimetrically measuring the clusters' formation energies as a function of their internal temperature. For this purpose the possibility to adjust the temperature of the clusters' internal degrees of freedom by means of the temperature of the cluster source's nozzle was exploited. The melting point of the investigated tin clusters was found to be lowered by 125 K and the latent heat of fusion per atom is reduced by 35% compared to bulk tin. The melting behavior of the isolated tin clusters is discussed with respect to the occurrence of surface premelting.

Journal ArticleDOI
TL;DR: In this paper, the authors investigate the amount of excess energy required in intracluster gas in order to reproduce the observed X-ray cluster properties, and study the excess energies obtained from supernovae in a semi-analytic model of galaxy formation.
Abstract: The strong deviation in the properties of X-ray clusters from simple scaling laws highlights the importance of non-gravitational heating and cooling processes in the evolution of protocluster gas. We investigate this from two directions: by finding the amount of ‘excess energy’ required in intracluster gas in order to reproduce the observed X-ray cluster properties, and by studying the excess energies obtained from supernovae in a semi-analytic model of galaxy formation. Using the insights obtained from the model, we then critically discuss possible ways of achieving the high excess specific energies required in clusters. These include heating by supernovae and active galactic nuclei, the role of entropy, and the effect of removing gas through radiative cooling. Our model self-consistently follows the production of excess energy and its effect on gas haloes. Excess energy is retained in the gas as gravitational, kinetic and/or thermal energy. The density profile of a gas halo is then selected according to the total energy of the gas. Our principal assumption is that in the absence of non-gravitational processes, the total energy of the gas scales as the gravitational energy of the virialized halo – a self-similar scaling law motivated by hydrodynamic simulations. This relation is normalized by matching the model to the largest observed clusters. We model the gas distributions in haloes by using a two-parameter family of gas profiles. In order to study the sensitivity of results to the model, we investigate four contrasting ways of modifying gas profiles in the presence of excess energy. In addition, we estimate the minimum excess energy required in a fiducial cluster of around 2 keV in temperature by considering all available gas profiles. We conclude that the excess energies required lie roughly in the range 1–3 keV particle−1. The observed metallicities of cluster gas suggest that it may be possible for supernovae to provide all of the required excess energy. However, we argue that this scenario is only marginally acceptable and would lead to highly contrived models of galaxy formation. On the other hand, more than enough energy may be available from active galactic nuclei.

Journal ArticleDOI
TL;DR: In this paper, the isomers of B12N12, a ring, a graphitic sheet, and a fullerene-like cage of four-and six-membered rings are examined by theoretical means.
Abstract: A number of recent studies have explored the energetics of intermediate-sized clusters, such as small fullerenes. For example, the isomer energies of C20 have proven difficult to ascertain as different theoretical methods give widely varying results. For cluster sizes around 20−30 atoms, it is not immediately clear whether a monocyclic, graphitic, or fullerene structure is energetically preferred. In the present work, the isomers of B12N12, a ring, a “graphitic” sheet, and a fullerene-like cage of four- and six-membered rings, are examined by theoretical means. The energies of the three isomers are calculated using Hartree−Fock theory and density functional theory (DFT) in local and gradient-corrected forms. The Dunning correlation-consistent basis sets are used, with geometries optimized up to the triple-ζ level and energies calculated at the quadruple-ζ level. The effects of the basis set, as well as the effects of local versus nonlocal DFT, are discussed. The results are compared to those of similar st...

Journal ArticleDOI
TL;DR: In this article, the most important steps in preparing supported nano-assembled model catalysts and investigating their size-dependent catalytic properties are outlined, on the basis of specific examples taken from our laboratory.
Abstract: The present review outlines, on the basis of specific examples taken from our laboratory, the most important steps in (i) preparing supported nanoassembled model catalysts and (ii) investigating their size-dependent catalytic properties. We describe the cluster generation and present evidence for softlanding of the clusters onto solid surfaces. Subsequently, the growth and the characterization of the cluster support material, thin magnesium oxide films, are discussed, including the role of surface defects. Then the thermal stability of Cu clusters and the individual electronic structure of small Ag and Cu clusters on MgO are addressed. Finally, two examples of cluster size-dependent heterogeneous catalytic reactions are presented, (i) the cyclotrimerization of acetylene on nanoassembled Pd catalysts, and (ii) the CO oxidation on nanoassembled Au catalysts. We show experimentally and together with first-principle calculations that the interaction of such small metal clusters with the oxide surface strongly changes their catalytic properties. In contrast to large particles an additional electron in localized valence states of small clusters represents a major change. It is this charge transfer which turns inactive gold and palladium clusters into active model catalysts opening new perspectives to tune catalytic processes on the nanoscale.

Journal ArticleDOI
TL;DR: In this paper, the authors used the embedded-atom method (EAM) to model the energy and mobility of self-interstitial atom (SIA) clusters in bcc α-iron.

Journal ArticleDOI
28 Feb 2000-Chaos
TL;DR: Experiments on chaotically oscillating arrays of 64 nickel electrodes in sulfuric acid found that external resistors in parallel and series are added to vary the extent of global coupling among the oscillators without changing the other properties of the system.
Abstract: Experiments on chaotically oscillating arrays of 64 nickel electrodes in sulfuric acid were carried out. External resistors in parallel and series are added to vary the extent of global coupling among the oscillators without changing the other properties of the system. The array is heterogeneous due to small variations in the properties of the electrodes and there is also a small amount of noise. The addition of global coupling transforms a system of independent elements to a state of complete synchronization. At intermediate coupling strengths stable clusters, or condensates of elements, form. All the elements in a cluster follow the same chaotic trajectory but each cluster has its own dynamics; the system is thus temporally chaotic but spatially ordered. Many cluster configurations occur under the same conditions and transitions among them can be produced. For values of the coupling parameter on either side of the stable cluster region a non-stationary behavior occurs in which clustered and synchronized...

Journal ArticleDOI
TL;DR: In this paper, a physical description of the fundamental plane of Galactic globular clusters is presented, which explains all empirical trends and correlations in a large number of cluster observables and provides a small but complete set of truly independent constraints on theories of cluster formation and evolution in the Milky Way.
Abstract: This paper develops a physical description of the fundamental plane of Galactic globular clusters that explains all empirical trends and correlations in a large number of cluster observables and provides a small but complete set of truly independent constraints on theories of cluster formation and evolution in the Milky Way. In a very good first approximation, the internal structures and dynamics of Galactic globulars are described by single-mass, isotropic King models and are thus characterized by four nominally independent physical parameters. Within this theoretical framework, it is shown that (1) 39 regular (non-core-collapsed) globulars with measured central velocity dispersions all share a common core mass-to-light ratio, V,0 = 1.45 M☉ L, and (2) 109 regular globulars both with and without direct observations of V,0 show a very strong correlation between global binding energy and total luminosity, regulated by Galactocentric position: Eb = 7.2 × 1039 ergs(L/L☉)2.05(rgc/8 kpc)-0.4. The observational scatter about either of these two constraints can be attributed fully to random measurement errors, making them the defining equations of a fundamental plane (FP) to which real clusters are confined in the larger, four-dimensional parameter space of general King models. They are shown to underlie a pair of bivariate correlations first found, and used to argue for the existence of a globular cluster FP, by Djorgovski. A third, weaker correlation, between clusters' total luminosities and King-model concentration parameters, is related to the (nonrandom) distribution of globulars on the FP. With L, V,0, Eb, and the central concentration c thus chosen as the four physical quantities that define any single globular cluster, the FP equations for V,0 and Eb(L,rgc) are used to derive expressions for any other observable in terms of only L, rgc, and c. Results are obtained for generic King models and applied specifically to the globular cluster system of the Milky Way.

Journal ArticleDOI
TL;DR: In this paper, the effects of the oxygen gas flow rate during deposition, temperature, and cluster size on the coercivity and hysteresis loop shift induced by field cooling were measured.
Abstract: Monodispersed Co/CoO cluster assemblies with the mean cluster sizes of 6 and 13 nm have been prepared by a plasma-gas condensation type cluster beam deposition apparatus. We measured the effects of the oxygen gas flow rate during deposition, temperature, and cluster size on the coercivity and hysteresis loop shift induced by field cooling. The large exchange bias field (10.2 kOe) and coercivity (5 kOe) were observed at 5 K for the monodispersed Co/CoO cluster assembly with $d=6\mathrm{nm}.$ The correlations between unidirectional anisotropy and uniaxial anisotropy, training effect and magnetic relaxation can be interpreted by the hypothesis of a spin disorder in the interfacial layer between the antiferromagnetic CoO shell and the ferromagnetic Co core.

Journal ArticleDOI
TL;DR: In this paper, a fourteen-metal (Me3tacn)8Cr8Ni6(CN)24]12+ cluster was constructed by using a blocking ligand on only one of the mononuclear reaction components.
Abstract: The synthesis of high-nuclearity metal-cyanide clusters presents a possible means of controlling magnetic properties in the design of new single-molecule magnets. Previous work employed tridentate blocking ligands in directing the assembly of a cubic [(tacn)8Co8(CN)12]12+ (tacn = 1,4,7-triazacyclononane) cluster; an improved crystal structure now confirms the lack of a guest water molecule inside the cluster cage. The ability to generate larger clusters by using a blocking ligand on only one of the mononuclear reaction components is demonstrated with the synthesis of a fourteen-metal [(Me3tacn)8Cr8Ni6(CN)24]12+ cluster. The geometry of this cluster consists of a cube of eight Me3tacn-ligated CrIII ions connected via bridging cyanide ligands to six square-planar NiII ions situated just above the center of each cube face. Surprisingly, no guest species are evident within the 284 A3 cavity defined by the rigid metal-cyanide cage. Assembly of the cluster in boiling aqueous solution involves a linkage isomeriz...

Journal ArticleDOI
TL;DR: In this article, the capacitance-probe measurements of instantaneous local solid concentrations in a 15 cm diameter fast fluidized beds (FFB) were used to investigate the effect of particle size and gas velocity on the formation of clusters.

Journal ArticleDOI
TL;DR: In this article, only one ubiquitous polyoxocation in these sols has ever been unambiguously characterized: Al 13O4(OH)24+x(H2O)12-x (Al 13), an -Baker-Figgis isomer of the Keggin cluster.
Abstract: Speciation in partially neutralized aluminum solutions is of interest to many fields aside from chemistry, including environmental science and biology where issues such as the toxicity and transport of Al are important. 1,2 A well-known class of catalysts is derived from using polyoxoaluminum species as pillaring agents for layered clays and inorganic oxides (PILCs). 3 They are also a major component of alumina sols and act as precursors for a multitude of ceramic and catalytic materials. 4,5 Despite over 50 years of research, only one ubiquitous polyoxocation in these sols has ever been unambiguously characterized: Al 13O4(OH)24+x(H2O)12-x (“Al 13”), an -Baker-Figgis isomer of the Keggin cluster. 6-9 Only circumstantial evidence exists for other species. 10

Journal ArticleDOI
TL;DR: In this paper, an analytic model describing the cluster wind flow that results from the multiple interaction of the stellar winds produced by the stars of a dense cluster of massive stars is presented.
Abstract: We present an analytic model describing the cluster wind flow that results from the multiple interaction of the stellar winds produced by the stars of a dense cluster of massive stars. The analytic solution (obtained by matching an inner and an outer solution at the radius of the stellar cluster) can have asymptotically subsonic or supersonic behavior, the latter possibility being appropriate for the case of a cluster surrounded by a low-pressure environment. We also present a three-dimensional numerical simulation of such a cluster wind. We find that the behavior of the mean flow computed from the numerical simulation quite closely follows the flow properties deduced from the analytic model. Finally, we discuss the observational properties of the cluster wind produced by dense clusters such as the Arches cluster close to the center of our Galaxy. In particular, we predict that the X-ray emission from the intracluster gas in this stellar cluster could be detectable.

Journal ArticleDOI
TL;DR: In this article, the authors used the analysis of local stress to understand the physical origin of amorphization in gold nanoclusters, and found that the compact ordered structures, which are very stable for pair potentials, are destabilized by the tendency of metallic bonds to contract at the surface, because of the decreased coordination.
Abstract: Knowledge of the structure of clusters is essential to predict many of their physical and chemical properties. Using a many-body semiempirical Gupta potential (to perform global minimizations), and first-principles density functional calculations (to confirm the energy ordering of the local minima), we have recently found [Phys. Rev. Lett. 81, 1600 (1998)] that there are many intermediate-size disordered gold nanoclusters with energy near or below the lowest-energy ordered structure. This is especially surprising because we studied ''magic'' cluster sizes, for which very compact-ordered structures exist. Here, we show how the analysis of the local stress can be used to understand the physical origin of this amorphization. We find that the compact ordered structures, which are very stable for pair potentials, are destabilized by the tendency of metallic bonds to contract at the surface, because of the decreased coordination. The amorphization is also favored by the relatively low energy associated to bondlength and coordination disorder in metals. Although these are very general properties of metallic bonding, we find that they are especially important in the case of gold, and we predict some general trends in the tendency of metallic clusters towards amorphous structures. (c) 2000 The American Physical Society.

Journal ArticleDOI
TL;DR: In this paper, the conformation of a previously observed ice-like water cluster in the solid state proves to be robust to geometric changes in its surrounding, and the hydrogen bonded arrangement is finally revealed in detail.

Journal ArticleDOI
TL;DR: The point-centered domain decomposition algorithm is implemented in the new program Opal p using a standard message passing library, so that it runs on both shared memory and massively parallel distributed memory computers.

Journal ArticleDOI
TL;DR: In this article, the cationic, neutral, and anionic charge states of the B13 cluster were examined through the use of density functional theory and an intriguing atom-in-a-cage structure was found.
Abstract: The cationic, neutral, and anionic charge states of the B13 cluster are examined through the use of density functional theory. Several different isomers are studied and compared with a special emphasis given to the electronic structure of the lowest lying isomers. Included among the isomers are three which have been proposed earlier and a pair of new ones. While no minima that corresponded to a filled icosahedron could be found for the cluster, an intriguing atom-in-a-cage structure was found that is a local minimum on the cationic, neutral, and anionic surfaces. The structure found for the anionic cluster has D3h symmetry, and the 12 external boron atoms are arranged as three six-membered rings back-to-back. The planar and quasi-planar structures are seen to be more stable than three-dimensional isomers, but the ordering by stability of the planar and quasi-planar structures changes depending on the charge. Relative energies, selected geometric features, ionization potentials, and electron affinities are...

Journal ArticleDOI
TL;DR: In this paper, scanning tunneling microscopy (STM) was used to monitor the morphological changes of oxide-supported metal clusters upon exposure to reactants at elevated pressures.
Abstract: Deposition of metals onto planar oxide supports provides a convenient methodology for modeling important aspects of supported metal catalysts. In this work, scanning tunneling microscopy (STM), in conjunction with traditional surface-science techniques, is used to monitor the morphological changes of oxide-supported metal clusters upon exposure to reactants at elevated pressures. Of special concern is the relationship between catalytic activity/selectivity and surface structure, e.g., metal–support interaction and intrinsic cluster size effects. Au and Ag clusters were vapor-deposited onto TiO2(110) under ultrahigh vacuum (UHV) conditions. Characterization of cluster size and density as a function of metal coverage is correlated with catalytic reactivity. Oxygen-induced cluster ripening occurs upon exposure of Au/TiO2(110) and Ag/TiO2(110) to 10.00 Torr O2. The morphology of the metal clustering induced by O2 exposure implies the chemisorption of O2 onto the metal clusters and the TiO2 substrate at room temperature. Ag and Au clusters exhibited a bimodal size distribution following O2 exposure due to Ostwald ripening, i.e., some clusters increased in size while other clusters shrank. A volatile oxide species is proposed to form at high oxygen pressures, accelerating intercluster atom transport. The oxide substrate was found to play a role in the kinetics of cluster ripening. STM shows that oxide-supported metal clusters are very reactive to O2 and that nanoclusters are particularly susceptible to adsorbate-induced restructuring.

Book ChapterDOI
01 Jan 2000
TL;DR: In this article, a detailed treatment of the third-order nonlinear optical properties of transition metal nanocluster composites is presented, in which cluster concentration is below percolation limit (dispersed clusters).
Abstract: Publisher Summary This chapter is concerned with metal nanocluster composites formed by transition metal clusters embedded in silicate glasses, in which cluster concentration is below percolation limit (dispersed clusters); in particular, the systems are in the condition of quasi-static regime, where cluster radius is much smaller than the wavelength of the light used to probe its response and–most of all–the light used in a MNCG-based optoelectronic device. Composite materials formed by transition metal clusters embedded in glass matrices exhibit peculiar optical properties. The development of the cluster-matter field assumed a strong impact owing to the experimentalavailability of selected cluster beams and time-of-flight mass spectrometry techniques. In general, the problem of the modelization of the cluster behavior has followed either atomistic (bottom-up) approaches, which exploits ab initio techniques of the quantum chemistry, or top-down approaches, describing the cluster as a mesoscopic piece of bulk to be treated in the solid-state or statistical physics framework. This work gives particular emphasis to the third-order nonlinear optical properties, because their technological implications as well as their peculiarity in MNCGs deserve this detailed treatment. One of the greatest challenges for optics is the development of computer systems based on all-optical photonic switching devices replacing electronic ones, that is, with short time and energy consumption per switch.

Journal ArticleDOI
TL;DR: In this article, the authors used a polarizable water potential to simulate the structure and spectra of a 1000 molecule cluster of cubic cubic ice structures and showed that the resulting lower energy structure includes disordered surface layer and an interior that retains a degree of oxygen order.
Abstract: Infrared spectra have been determined for aerosol ice samples with particles that vary in average diameter down to ∼2 nm. The aerosol spectra, obtained at 100 K, show that the crystalline core of the average particle decreases rapidly with decreasing particle size and vanishes near 4 nm (or 1000 molecules). Consequently, the combined FT-IR spectrum of the surface and subsurface regions has been observed directly for the first time and observed to be nearly invariant to ∼3 nm. Using a polarizable water potential, the structure and spectra of a 1000 molecule cluster has been simulated. The starting point was an approximately spherical cubic ice structure, which was subjected to relaxation by molecular dynamics. The resulting lower energy structure includes a disordered surface layer and an interior that clearly retains a degree of oxygen order. The simulated spectrum of the cluster is separable into components resembling the surface, subsurface, and core ice experimental spectra. The combined results suppor...