甲烷团簇与氘团簇的团簇源特性比较

利用瑞利散射法测量了特定喷嘴产生的甲烷团簇及氘团簇的大小随背压的变化曲线。将团簇大小的实验值与Hagena理论进行了比较,当背压超过3MPa时,两种团簇的实验值都明显高于理论值。实验发现,特定喷嘴在相同的背压下,常温(298K)甲烷团簇尺寸小于低温(80K)氘团簇尺寸,而甲烷团簇中氢原子数至少是氘团簇中氘原子数的1.98倍。     

Formation of polaron clusters

The formation of spherical polaron clusters is studied within the Fröhlich polaron theory. In a dilute polaron gas, using the non-local statistical approach and the polaron pair interaction obtained within the Pekar strong coupling theory, the homogeneous phase results to be unstable toward the appearance of polaron clusters. The physical conditions of formation for the clusters are determined calculating the critical values of electron-phonon interaction for which bound states in the collective polaron potential develop. Finally the sequence in the filling of the states is found and the stability of the clusters is assessed.Received: 6 May 2004, Published online: 12 October 2004PACS: 71.38.-k Polarons and electron-phonon interactions     

Simulation of the interaction of bipartite bimetallic clusters with low-energy argon clusters

Molecular-dynamics simulation of the evolution of bipartite bimetallic clusters consisting of 390 atoms during bombardment by Ar_n (n = 1, 2, 13) clusters with initial energies from 1 eV to 1.4 keV is performed. Binary Cu–Au and Ni–Al clusters consisting of equal atomic fractions of corresponding elements were used as a target. As a result of simulation, the temperatures, changes in the potential energy, sputtering yields, and intensities of collision-stimulated displacement of atoms through the interface of monometallic parts of binary clusters, depending on the size and energy of incident particle, are obtained.

     

Condensation of beryllium clusters

An original technique is proposed for describing the condensation of clusters in the situation where the interaction of a cluster with the surrounding clusters is very weak but cannot be ignored. It is demonstrated using beryllium clusters as an example that the proposed method is an efficient tool for calculating the energy band structure of clusters. It is shown that an increase in the number of beryllium atoms in a cluster leads to an increase in its stability.     

Protonated water clusters

A complete set of protonated water clusters conformers up to n = 8 have been evaluated by ab-initio Hartree-Fock method in 6-311G** molecular orbitals basis set and with quadratic complete basis set method. Configurations of ground-state conformers are in a good accord with those available in literature but present dissociation energies for the light clusters agree better with experimental values. A tentative analysis of experimental conditions for observation of certain clusters is presented in comparison to selected formation paths of clusters. Dissociation energies show a broad range of values.     

Multiply charged clusters

We review progress made in understanding Coulomb explosion of multiply charged atomic clusters. Their collision with highly charged atomic ions leads to clusters in charge states as high as z=10 with little vibrational excess energy; these systems approach the Rayleigh limit. Phase transitions become evident at higher excess energies. Numerous studies have been devoted to C^z+₆₀, like collisions with surfaces, multi-coincidence fragmentation analysis and gas-phase reactions. Stability and decay of highly charged micrometer-sized droplets and of metal di- and trianions have been monitored in ion traps. Excitation by femtosecond laser pulses allows to unravel properties of highly charged transient cluster ions. To cite this article: O. Echt et al., C. R. Physique 3 (2002) 353–364.     

Polytetrahedral clusters.

By studying the structures of clusters bound by a model potential that favors polytetrahedral order, we find a previously unknown series of "magic numbers" (i.e., sizes of special stability) whose polytetrahedral structures are characterized by disclination networks that are analogous to hydrocarbons.     

仲氢及正氘团簇的量子定域和超流动性研究

本文采用路径积分Monte Carlo (PIMC)方法研究仲氢团簇和正氘团簇的结构和超流体性质.比较仲氢团簇(分子数N≤40)在T=0.4 K,T=1.6 K的临近能量差和超流比例(superfluid fractions),发现仲氢团簇在T=0.4 K时出现"量子熔化"(quantum melting);研究了仲氢团簇的量子定域(quantum localization)和 "量子熔化"的关系,对T=0.4 K时仲氢及正氘团簇的量子定域与超流动性 关键词： 团簇 量子定域 量子熔化 超流比例     

Trianionic gold clusters

Using Penning-trap experiments and a shell-correction method incorporating ellipsoidal shape deformations, we investigate the formation and stability patterns of trianionic gold clusters. Theory and experiment are in remarkable agreement concerning appearance sizes and electronic shell effects. In contrast to multiply cationic clusters, decay of the trianionic gold clusters occurs primarily via electron autodetachment and tunneling through a Coulomb barrier, rather than via fission. Received 9 January 2001     

Experiments on clusters

In this contribution we discuss four different types of experiments that have been conducted at molecular beams of neutral clusters. The size of particularly stable sodium chloride clusters and their corresponding geometrical structure is inferred from intensity anomalies in mass spectra. This information is obtained either for charged or for neutral clusters depending on whether the clusters are ionized by electron impact or by multiphoton absorption. The important role of fragmentation in mass spectrometry of xenon clusters is revealed by multiphoton ionization; dissociative reactions occurring on the time scale of 10⁻⁷ s with respect to the ionizing event can be analyzed. The solvation energy of negatively charged carbon dioxide clusters as a function of cluster size is obtained from electron attachment spectra. A resonance in the ion yield close to zero eV electron energy signifies that all clusters except for the monomer feature a positive electron affinity. An analysis of the kinetic energy of fragment ions, originating from delayed dissociation of triply charged carbon dioxide clusters, reveals that the size distribution of their fission fragments is extremely symmetric.     

The role of small clusters in the transformation of two-ring clusters into fullerenes

Possible reactions by which small carbon molecules C₂ and C₃ can join a cluster at an intermediate assembly stage from a two-ring cluster to a fullerene are considered. For analysis of the separate stages of this type of reaction, methods of quantum chemistry are used. The generalized reaction probabilities obtained are then included into the general scheme of assembly kinetics alongside monomolecular reactions. It has been shown that at a small cluster concentration of about 10¹⁴ cm⁻³ the assembly time drops severalfold. Also given are generalized results of the effect on the assembly time of the multiplicity of paths of fullerene assembly from two-ring clusters.