Cluster production

Fig. 14 Potential energy profile for stepwise and concerted mechanisms with (solid lines) and without (dotted lines) an attractive interaction between the caged fragments in the product cluster. The case of the reduction of a neutral substrate is represented. It can be transposed for reductions of a positively charged substrate or for oxidations of neutral or negatively charged substrates.

In the preceding sections, interactions between radicals and ions in the product cluster have been neglected. There is little doubt that such interactions exist... 

Comparison with the case of a purely repulsive product profile [equation (3.17)] vs. equations (3.3) and (3.4) reveals that the effect of an attractive interaction between the fragments in the product cluster is not merely described by the introduction of a work term in the classical theory of dissociative electron transfer. Such a work term appears under the form of —AG p, but there is also a modification of the intrinsic barrier. With the same Ap, the change in the intrinsic barrier would simply be obtained by replacement of Dr by /Dr — /D )2. It is noteworthy that small values of DP produce rather strong effects of the intrinsic barrier. For example, if DP is 4% of Dr, a decrease of 20% of the intrinsic barrier follows. The fact that a relatively small interaction leads to a substantial decrease of the activation barrier is depicted in Figure 3.4. 

Extension of the model to take into account the bond bending effect and the interactions within the product cluster leads to the following modification of equations (6.209) and (6.210), in which the diabatic character of the surfaces is emphasized in the subscript notations ... 

Colja Laane is corporate science manager in the Life Science Products cluster at DSM. He is (co)author of over 120 papers and about 20 patents, mostly in the area of industrial biotechnology. He is a member or chairman of several committees involved in chemistry education and setting up life sciences startup companies in the Netherlands. He also chairs the Industrial Biotechnology section of the European Platform on Sustainable Chemistry. He graduated in biochemistry from the University of Groningen and holds a PhD from Wageningen. 

An additional motivation for investigations of binary cluster ions is the potential to understand the influence of the solvating component on the ion-molecule chemistry, that is, observe whether the product cluster ion sequences observed in mixed expansions are affected by the identity of the carrier gas. 

Examples include the manufacture of rapidly dispersible forms of concentrated food products (clusters, agglomerates) and of press feed for various ceramics applications. 

The product cluster ions can rapidly dissociatively recombine with electrons to produce excited neutrals. Three-body association reactions (10) become increasingly important as one descends from 90 km. Simultaneously, the electron density declines, increasing the lifetimes of the cluster ions. Below 80 km, positive and negative cluster ions become the most abundant charged species." ... 

The syntheses of the starting clusters ftj-MeCyCOiiCO) (ref. 6) and RuCo2(CO)i 1 (ref. 7) are well documented. The reagents Na[Mo(CjH5)(CO)3] (ref. 8) and [CsHsNi(CO)]2 (ref. 9) can be prepared according to publish procedures. 2-Butyne is commercially available. All intermediate and product clusters have been fully characterized including elemental analyses. 

The most prominent feature of the Dg Fd II cluster structure is its close adherence to the voided cubane configuration 3. It might have been expected that, in the process of removing one Fe atom from a cubane-type structure, the product cluster might relax or readjust to a more open or flattened arrangement. With reference to Fig. 10, this flattening would increase the angles at Fel and S3 from those at these atoms in the parent... 

All reactions in Fig. 24 afford products in which the coordination number at the unique subsite is 5 or 6. Of product clusters 49-55, 50 is the first organometallic derivative of a [4Fe-4Sp cluster, and 49, 51, and 55 are the initial examples of six-coordinate subsites. Another example of a substituted cluster identified by H NMR is provided by the spectrum in Fig. 25. Here 1 equivalent of tacn (1,4,7-triazacyclononane) reacts quantitatively with 37 to afford 49, the 4-Me, 5-H, and 6-Me resonances of which are substantially shifted from their positions in the chloride cluster. The spectrum is indicative of trigonal symmetry. Certain of the clusters 40-55 are considered in subsequent sections. 

Our observations and on results obtained in other systems (1), we favor an inner-sphere mechanism for Reaction 8. Assuming similar primary clustered products in all cases, it is evident that pyridine does not stabilize the primary product cluster, which undergoes fracture to give two discrete products, see Reaction 3. However, as noted earlier, coordinated pyridine does provide limited stability to the resulting Cu-O-Cu-O core. Polymerization of initiator species. Reactions 9 and 10, presumably is... 

Activity loss irreversible reaction with products (cluster formation) poisoning sintering of the metal crystallites poisoning... 

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