Showing papers on "Cluster (physics) published in 1982"
TL;DR: In this article, a molecular dynamics computer simulation method for calculating equilibrium constants for the formation of physical clusters of molecules is presented, which is based on Hill's formal theory of physical clustering.
Abstract: We present a molecular dynamics computer simulation method for calculating equilibrium constants for the formation of physical clusters of molecules. The method is based on Hill’s formal theory of physical clusters. In the method, a molecular dynamics calculation is used to calculate the average potential energy of a cluster of molecules as a function of temperature, and the equilibrium constants are calculated from the integral of the energy with respect to reciprocal temperature. The method is illustrated by calculations of the equilibrium constants for the formation of clusters of two to five water molecules that interact with each other by an intermolecular potential devised by Watts. The method is compared with other procedures for calculating the thermodynamic properties of clusters.
3,263 citations
377 citations
TL;DR: In this article, the main thrust of a review is to develop several useful criteria for identifying homogeneously catalyzed reactions as being cluster-catalyzed, including catalytic concentration studies where the turnover frequency increases with increasing catalyst concentration are indicative of cluster catalysis.
114 citations
TL;DR: In this article, the formation of (H2O)N (N ≤ 40) has been investigated using a neutral free jet expansion with modulated molecular beam, and the existence of reproducible features at small cluster sizes involving well-defined structures similar to those occurring in bulk-ice crystals are explained on the basis of simple RRK arguments and internal energy considerations.
108 citations
TL;DR: In this article, the effect of configuration on the interactions of clusters with an electron gas and in collisions with single atoms (vicinage effect) was explored using a classical harmonic-oscillator model and with quantum-mechanical perturbation theory.
Abstract: The excitation of electronic transitions in matter by a group of swift ions traveling close together and at nearly the same velocity may depend on the spatial configuration of ions making up the cluster. We have studied theoretically the effect of configuration on the interactions of clusters with an electron gas and in collisions with single atoms (vicinage effect). The latter case is explored using a classical harmonic-oscillator model and with quantum-mechanical perturbation theory. We discuss similarities between the vicinage function for energy loss of a swift cluster in the electron gas and that for the same cluster colliding with a system of noninteracting atoms at condensed-matter density. The aligning effect of the wake potential on the trailing ion of a dicluster penetrating a solid target, as first observed by Gemmell et al., is not expected to occur in cluster collision with single atoms, and does not occur in collision with gases at ordinary pressures. Aligning forces comparable with those in solids require target densities of the same order of magnitude as those occurring in condensed matter. The data of Lurio, Anderson, and Feldman taken in a search for vicinage effects in inner-shell excitation are discussed. The effect of wakemore » fluctuations on cluster energy loss is shown to be negligible under ordinary conditions. We evaluate the effect of residual molecular ionic structure on cluster energy loss.« less
79 citations
TL;DR: In this paper, a thermal flow surce is used to generate continuous beams of refractory metals by a high-temperature oven for metal vaporization and a liquid-nitrogen-cooled quench cell for condensation and cluster growth.
Abstract: Generation of continuous beams of clusters of refractory metals by a thermal flow surce is described. The source consists of a high-temperature (up to 2000/sup 0/C) oven for metal vaporization and a liquid-nitrogen-cooled quench cell for condensation and cluster growth. Various flow gases are used to vary the distribution of clusters produced. The operation of the source and the characterization of cluster beams of Al, Cr, Ni, Cu, and Ag are discussed.
69 citations
68 citations
66 citations
TL;DR: In this article, the reported discrepancy between Hartree-Fock and Xα densities of states for metal clusters (2-9 atoms) by LCAO Xα calculations are reported.
62 citations
TL;DR: In this paper, the authors present experimental conditions for electrochemical studies of cluster electrochemistry and present a new redox series with nickel-cyclopentadienyl clusters and a new series of capped trinuclear clusters.
58 citations
TL;DR: In this article, a cluster model of the glass transition was developed, treating the relative size of the cluster as an order parameter, which accounts for some of the features of the transition.
TL;DR: The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 1108 as discussed by the authors, and the full manuscript of the complete manuscript is available in:
Abstract: The complete manuscript of this communication appears in: Angew. Chem. Suppl. 1982, 1108. DOI:10.1002/anie.198211080
TL;DR: In this article, a general equation for the energy balance in a liquid containing a cluster of cavities is used to derive the collapse equations for specific cluster configurations, and the influence of temperature on the cavity cluster formation and collapse is considered.
Abstract: A general equation for the energy balance in a liquid containing a cluster of cavities is used to derive the collapse equations for specific cluster configurations. These equations contain as parameters the volume fraction of cavities β and a coefficient γ for the energy transfer into the cluster due to collapse of the individual cavities. The influence of γ and β and of the spatial distribution of β is calculated. Experimental studies of the plane, one-dimensional collapse of a cavity layer are compared with the theoretical results. In this connection the influence of temperature on the cavity cluster formation and collapse is considered.
TL;DR: This paper introduces a new procedure, based on probability profiles, for judging the validity of clusters established from rank-order proximity data, and explains the background from graph theory and cluster analysis needed to treat cluster validity.
TL;DR: In this article, the first example of a cluster compound with a metal atom incorporated into the centre of a puckered ring of like metal atoms was presented. But the analysis of this compound was performed using a single crystal X-ray analysis of [Au9{P(p-C6H4OMe)3}8]-(BF4)
Abstract: The single crystal X-ray analysis of [Au9{P(p-C6H4OMe)3}8]-(BF4)3; has provided the first example of a cluster compound with a metal atom incorporated into the centre of a puckered ring of like metal atoms.
TL;DR: In this article, methods of cluster analysis based on maximizing or minimizing certain criteria are examined and the effect of adding a single point to the data casts light on the properties of the methods.
Abstract: SUMMARY Methods of cluster analysis based on maximizing or minimizing certain criteria are examined. The effect of adding a single point to the data casts light on the properties of the methods.
TL;DR: In this paper, the acceleration and deflection fields of a reversed Nier-Johnson geometry double focusing mass spectrometer were decoupled by decoupling the mass spectrum of C3H8 and the cluster species (NH3)2, NH3)3, and CO2)2.
Abstract: Metastable decay reactions occurring in the mass spectrum of C3H8 and the cluster species (NH3)2, (NH3)3, and (CO2)2 were investigated by decoupling the acceleration and deflection fields of a reversed Nier–Johnson geometry double‐focusing mass spectrometer. It is shown that the present experimental setup (molecular beam‐electron impact ion source‐deflection optics) permits a clean separation of molecular beam processes from background processes. The general reliability of our instrument is demonstrated by the study of the well‐characterized metastable ions in propane, which corrobated and extended previous measurements. Moreover, the ability to differentiate and study quantitatively both collision‐induced and unimolecular decay processes with the combined techniques of our instrument is demonstrated. Our tentative conclusion from the present study of ammonia and carbon dioxide clusters is that small cluster ions should be described by a loosely coupled oscillator model. The simple dissociation of (CO2)+2...
TL;DR: In this article, an irreversible stochastic model for the growth of clusters on a square lattice is formulated and studied by Monte Carlo simulation, and the growth rate has a nonlinear nonlocal dependence on the density of occupied sites, qualitatively similar to that of crystallization governed by surface tension and diffusion.
Abstract: An irreversible stochastic model for the growth of clusters on a square lattice is formulated and studied by Monte Carlo simulation. The growth rate has a nonlinear nonlocal dependence on the density of occupied sites, qualitatively similar to that of crystallization governed by surface tension and diffusion. The density and Hausdorff dimension of the clusters are estimated. These results are compared with data for percolation clusters and with recent results for diffusion-limited growth.
01 Jan 1982
TL;DR: In this paper, it is shown that the variety of stable transition metal-hydrogen bonding modes in known metal-boron cluster compounds greatly exceeds that found in pure (nonboron) metal cluster hydrides.
Abstract: Transition metal hydride chemistry has experienced enormous growth and impact in recent decades,(1) accelerated by the widespread interest in these species as homogeneous and heterogeneous catalysts. This work has paralleled the rapid development of metallaborane and metallacarborane chemistry,(2) and it was inevitable that the two fields would overlap and that metal-boron clusters having metal-hydrogen bonds would be discovered. What was not really foreseen, however, was the vast scope of structures and chemistry that has emerged in this area. Indeed, it is the case that in terms of isolable monomeric species, the variety of stable transition metal-hydrogen bonding modes in known metal-boron cluster compounds greatly exceeds that found in “pure” (nonboron) metal cluster hydrides. The reasons would seem to be, first, that boron frameworks in general provide inherently stable matrices in which metal atoms with hydrogen ligands can reside; second, that borane and metallaborane cages tend to be hydrogen-rich, setting the stage for metal-hydrogen interactions; and third, that hydrogen bridging is a common feature in electron-deficient boron clusters, and the involvement of metals in such systems can be seen (at least in retrospect) as a natural extension of this phenomenon.
TL;DR: In this paper, the electronic stucture of Bel, Mgm and Can (1⩽ 7, m and n ⩽ 5) metal clusters has been investigated by means of an ab initio pseudopotential method followed by multireference double-excitation configuration interaction (PP MRD CI).
TL;DR: In this paper, a formalism was presented for estimating critical cluster size as defined in classical models for nucleation phenomena, which combines Bennett's Monte Carlo technique for determining free-energy differences for clusters containingn andn- 1 atoms with the steady state nucleation rate formalism.
Abstract: A formalism is presented for estimating critical cluster size as defined in classical models for nucleation phenomena. The method combines Bennett's Monte Carlo technique for determining free-energy differences for clusters containingn andn- 1 atoms with the steady state nucleation rate formalism. A simple form for the free energy of formation of then cluster [including a termA (n)n2/3] is used to predict critical cluster size and critical supersaturation ratio, S*. This approach is applied to Lennard-Jones vapor clusters at 60 K. Results for free-energy differences for the 13, 18, 24, and 43 clusters predict a critical cluster size of 70 ± 5 atoms at a critical supersaturation ratio given bylnS*=2,45 0.15. This method is intended to provide estimates of critical cluster size for more ambitious attempts to calculate cluster free energies or for initializing conditions in microscopic simulations of nucleating systems.
TL;DR: In this paper, the effects of the kinetic energy of the ionized cluster on the initial stage of film formation and the resulting properties of the deposited films are discussed with microscopic and macroscopic observations.
TL;DR: The most extensively studied higher cluster compound of osmium is the hexanuclear carbonyl, 0s6(CO)18, as this has produced in high yields (80%) by pyrolysis of 0s3(CO)/12 as discussed by the authors.
Abstract: Hexanuclear carbonyls The nost extensively studied higher cluster compound of osmium is the hexanuclear carbonyl, 0s6(CO)18, as this has produced in high yields (80%) by pyrolysis of 0s3(CO)12. Scheme I suimrises some of the chemistry observed for this compound. The majority of reactions with nucleophiles proceed via the fission of metal-metal bonds and the formation of a new cluster unit. This in-plies that the LUMO contains a large degree of M-M bonding character. In certain instances the reactions are reversible involving the reformation of the starting compound [Os6(0o)18/12)] (Ref. 2). The structural variation within the series of cluster compounds )s6(CO)15J, [HOs6(CO)18and H20s6(CO)18 is of interest (Ref. 3). As predicted by Wade's Rules the two ions are octahedral, based on an octahedron of oh syimtry in contrast to the compound 0s6(CO)18 which is also octahedral but based on a C2v syntretry. Acidification to H20s6(CO)18 leads to a new cluster geanetry based on the capping of a triangular face of a square based pyramid, although the total number of electrons within the cluster bonding remains constant. This illustrates the potential for mere than one metal stereochemical arrangement within a given electron distribution. We have recently been able to obtain an unstable isomer of H20s6(cO)18 (Ref. 4), by reaction of the anion with hydrogen chloride gas in methylene chloride, to give a red solid 1120s6(CO)18. This
TL;DR: In this article, a simple empirical rule for cluster stability relating bond energy of the neutral cluster to Coulomb energy is given, which predicts cluster stabilities for the reported metals and other elements mentioned in the literature, as well as providing evidence for charge explosion of certain doubly charged trimeric clusters.