Fission metal cluster

Yannouleas C and Landman U 1995 Barriers and deformation In fission of charged metal clusters J. Phys. Chem. 99 14577... 

Vieira A and Flolhals C 1998 Shell effects on fission barriers of metallic clusters a systematic description Phys. Rev. B 57 7352... 

Combining the fusion-barrier calculated in this way with the heats of fission AHf (see Eq. 50) obtained from a classical metallic drop model, Garcias et al. obtained the fission barrier heights F for alkali metal clusters with charges... 

Dissociation, Fragmentation and Fission of Simple Metal Clusters... 

Under the general title of dissociation and fragmentation [7] processes in metal clusters, one usually distinguishes two classes of phenomena, i.e. (1) dissociation of neutral monomers and/or dimers, and (2) fission. The physical processes in the first class are most often referred to as evaporation of monomers and/or dimers, since they are endothermic processes and are usually induced through laser heating of the cluster. The unimolecular... 

Metal Cluster Fission and Nuclear Fission Similarities and Differences... 

These observations indicate that fission of metal clusters occurs when the repulsive Coulomb forces due to the accumulation of the excess charges overcome the electronic binding (cohesion) of the cluster. This reminds us immediately of the well-studied nuclear fission phenomenon and the celebrated liquid drop model (LDM) according to which the binding nuclear forces are expressed as a sum of volume and surface terms, and the balance between the Coulomb repulsion and the increase in surface area upon volume-conserving deformations allows for an estimate of the stability and fissility of the nucleus [12, 13]. 

In the following, we will present jellium-related theoretical approaches (specifically the shell-correction method (SCM) and variants thereof) appropriate for describing shell effects, energetics and decay pathways of metal-cluster fragmentation processes (both the monomer/dimer dissociation and fission), which were inspired by the many similarities with the physics of shell effects in atomic nuclei (Section 4.2). In Section 4.3, we will compare the experimental trends with the resulting theoretical SCM interpretations, and in addition we will discuss theoretical results from first-principles MD simulations (Section 4.3.3.1). Section 4.4 will discuss some of the latest insights concerning the importance of electronic-entropy and finite-temperature effects. Finally, Section 4.5 will provide a summary. 

Fission of doubly charged metal clusters, has attracted considerable attention in... 

In this section, we focus our discussion on recent trends in studies of binary fission processes in doubly charged metal clusters. 

The method we adopt in this section for further studying metal-cluster fission is the SE-SCM described in Section 4.2.2.6 (see also Ref. [43]). 

In addition to the present shape parameterization [43], other two-center shape param-eterizations (mainly in connection with KS-LDA jellium calculations) have been used [81-83] in studies of metal-cluster fission. They can be grouped into two categories, namely, the two-intersected-spheres jellium [81, 84], and the variable-necking-in parame-terizations [82, 83]. In the latter group. Ref. [82] accounts for various necking-in situations by using the funny-hills parameterization [85], while Ref. [83] describes the necking-in... 

The influence of the electronic entropy on the height of fission barriers has not been studied as yet, but it will undoubtedly be the subject of future research in metal-cluster physics. In any case, based on the results of this section, it is natural to conjecture that electronic-entropy effects will tend to quench the barrier heights, especially in the case of larger multiply charged clusters. 

In this three-variables parameterization, the B parameter controls the necking-in, the C parameter controls the distance, and the a parameter controls the asymmetry, leaving no freedom for the shapes of the parent or the emerging fragments to be varied. In particular, both fragments remain simultaneously either prolate-like or oblate-like, while final spherical shapes are excluded altogether. The weaknesses of the funny hills parameterization with respect to metal-cluster fission have been discussed in Ref. [24]. 

The 252(]f.pp) niajj spectrum of metal halides and oxides consists of a family cluster ions of these compounds extending to over mIz 10000, produced by the ejection of small domains of the crystal lattice in the region around the fission track. In addition, cluster ions are also observed that do not correlate with the composition of the crystal lattice, indicating that some of the cluster ions are involved in gas phase reactions in the desorption plume. One of the unique applications of 252(]f.pj) jg elucidation of the composition of large transition metal cluster compounds with values approaching 10. ... 

The effect has been observed for various atomic and molecular van der Waals clusters, hydrogen-bonded clusters and metal clusters. Seven-fold sodium clusters, for example, are not observed below 7 = 445. Under typical experimental conditions, multiply charged clusters are, like their singly charged counterparts, thermally excited they are found to evaporate atoms or molecules in a statistical, unimolecular process if their size is well above the appearance size. In the vicinity of the latter, however, fission competes with evaporation. Below the appearance size, the rate of fission greatly exceeds the time needed for mass spectrometric detection. The appearance size can be somewhat reduced if colder multiply charged clusters are generated. Ultimately, however, the clusters become unstable and the fission barrier vanishes. 

Naher U, Bjomhohn S, Frauendorf S, Garcias F and Guet C (1997) Fission of metal clusters. Physics Reports 285 245-320. 

Laser electrodispersion (LED) method makes possible to fabricate dense nanostmctured catalysts with unique catalytic properties. In contrast to earlier laser ablation techniques, where nanoparticles were synthesized from vaporized matter, LED is based on the cascade fission of hquid metalhc drops. Fabricated catalysts consist of ensembles of nanoparticles that are uniform in size and shape, amorphous and stable to coagulatioa The catalytic activity of these self-assembled Pt, Ni, Pd, Au and Cu catalysts with extremely low metal content (<10 mass.%) in hydrogenation and hydrodechlorination is several orders of magnitude higher compared to that for separated metal clusters, highly loaded metal films and supported catalysts prepared by usual methods. 

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