Cluster polymerization

Very recently Fontijn and Rosner145a have offered another explanation for the upper-atmosphere and wind-tunnel experiments. They propose that when the NO is adiabatically expanded, clustering (polymerization and perhaps condensation) occurs. Thus the third-order reaction (81) behaves as a second-order reaction, and has a correspondingly larger third-order rate constant. 

The hexanuclear molybdenum halide clusters (Mo6Xs)X4, i.e. (Mo6X 8)CP2CF 4/2, are known to react with some transition metal halide compounds forming two different types of cluster polymeric clusters with bridging outer halide ligands (X ) and discrete clusters with terminal halide ligands (X ). 

The study of gas phase and cluster polymerization is an important intellectual and technological frontier which promises unique results not only for a fundamental understanding of polymerization reactions, but also for the development of new materials with unique properties. In the past it has been almost impossible to study gas phase chain polymerization because the involatile product molecules condensed out of the gas phase. The application of microgravity to the study of gas phase polymerization is expected to result in a better control of the process and may also lead to important technological advances. 

Figure Bl.19.13. (a) Tliree STM images of a Pt(l 11) surface covered witli hydrocarbon species generated by exposure to propene. Images taken in constant-height mode. (A) after adsorption at room temperature. The propylidyne (=C-CH2-CH2) species that fomied was too mobile on the surface to be visible. The surface looks similar to that of the clean surface. Terraces ( 10 mn wide) and monatomic steps are the only visible features. (B) After heating the adsorbed propylidyne to 550 K, clusters fonn by polymerization of the C H...

In the preceding section we observed that both the rate of polymerization and the degree of polymerization under stationary-state conditions can be interpreted to yield some cluster of the constants kp, kj, and k j. The situation is summarized diagramatically in Fig. 6.4. The circles at the two bottom corners... 

A fascinating variety of discrete (or occasionally polymeric) polynuclear halogeno complexes of As, Sb and Bi have recently been characterized. A detailed discussion would be inappropriate here, but structural motifs include face-shared and edge-shared distorted (MXe) octahedral units fused into cubane-like and other related clusters or cluster fragments. Examples (see also preceding paragraph) are ... 

AgPh is a colourless solid [144] that is rather insoluble in non-donor solvents and appears to be polymeric (AgPh) (n > 10) in addition mixed compounds (AgPh) .AgN03 (n = 2,5) can also be obtained that involve silver clusters. Mesitylsilver is a thermally stable (but light-sensitive) white crystalline solid in the solid state it is tetrameric (in contrast to the pentameric copper and gold analogues) ... 

From the earliest days of radiation chemistry it has been known that acetylene polymerizes to a cuprene-like ( alprene ) solid (5, 6,25,28). The characteristics of the polymerization—e.g., lack of effect of temperature, doso rate, and pressure on polymer yield and negligible effect of radical scavengers—led Lind (24) to postulate an ion cluster mechanism. 

Abstract Molecular spectroscopy is one of the most important means to characterize the various species in solid, hquid and gaseous elemental sulfur. In this chapter the vibrational, UV-Vis and mass spectra of sulfur molecules with between 2 and 20 atoms are critically reviewed together with the spectra of liquid sulfur and of solid allotropes including polymeric and high-pressure phases. In particular, low temperature Raman spectroscopy is a suitable technique to identify single species in mixtures. In mass spectra cluster cations with up to 56 atoms have been observed but fragmentation processes cause serious difficulties. The UV-Vis spectra of S4 are reassigned. The modern XANES spectroscopy has just started to be applied to sulfur allotropes and other sulfur compounds. 

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