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Formation of Larger Species

The list of molecules in Table 1 contains species with as many as 13 atoms. Ion-molecule dominated syntheses for many of these species have been considered although many of the critical reactions have not been measured in the laboratory. [Pg.10]

Perhaps the synthesis of hydrocarbons is best understood. There are three main classes of reactions leading to complex hydrocarbons carbon insertion, condensation, and radiative association. Carbon insertion reactions are between C+ ions and smaller hydrocarbon neutrals viz., [Pg.11]

More saturated species can be formed via well-studied condensation reactions between hydrocarbon ions and neutrals viz., [Pg.11]

Neutral-neutral reactions are also involved in the synthesis of hydrocarbons, but here the evidence is less clear since, even for those systems studied in the laboratory, reaction products are rarely available. Unlike reactions involving O atoms, those involving C atoms and unsaturated hydrocarbons appear to be rapid, at least at room temperature and above.46,47 If the products of these reactions are analogous to ion-molecule insertion reactions, they can lead to molecular synthesis for example  [Pg.12]

Recent studies with a crossed-beam apparatus not only show that the products shown above are the correct ones, but that both the linear and cyclic isomers, each of which is a detected interstellar molecule, are formed.47 Crossed-beam studies also show that other reactions between C atoms and unsaturated hydrocarbons proceed to form similar products 48 [Pg.12]


The hydrolysis of metal alkoxides gives reactive M-OH bonds. It is followed by condensation and leads to the formation of larger species. Complexation leads to non reactive M-OX bonds which prevent condensation and favor the formation of smaller species. A large variety of oligomeric species can then be obtained upon hydrolysis and condensation. Molecular clusters or colloidal particles can be synthesized depending on the relative amount of hydrolysis (h=H20AI) and complexation (x=X/M). More condensed species are obtained as x decreases and h increases as shown by the following examples. [Pg.664]

To test this hypothesis, the solvent dependence of the aggregation process was examined by light scattering measurements, where the formation of larger species (aggregates) could be shown. In accordance... [Pg.235]

Quantities AiT are enthalpies of formation of the species the densitiese of S1H2 and SiH species in the plasma have been shown to be larger than other species. [Pg.358]

It is thought that small additions of hydrocarbon solvents tend to enhance the formation of Ru(C0)3, whereas larger concentrations seriously decrease the dielectric constant of the solvent so that the formation of ionic species in solution is suppressed. [Pg.327]

This section reviews the developments in the chemistry of monoborane complexes of the transition metals especially borohydride and hydridoborate complexes. Although such complexes are not strictly metallaboranes in the sense that they are not cluster species, they are included here as they share many similarities with polyborane species of the transition metals such as three-center two-electron bonding. Additionally, as will be shown in Section 3.04.3.1 borohydride species can also be intermediates in the formation of larger M By clusters. In this chapter, three-coordinate monoborane species, which are best considered as cr-complexes between a transition metal and HBR2 or metal-boryl (M-B) species, are not considered. [Pg.134]

The major issue is the formation of silver clusters in situ in the presence of the biomolecule to be labeled. On one hand, this problem is due to the fact that only a few scaffolds are suitable systems providing the proper environment for the formation of these very small species and preventing the formation of larger silver nanoparticles. On the other hand, the biomolecules might be harmfully... [Pg.323]

The rate constants involved in the formation of larger clusters are described in terms of the RRK theory, which states that the substimtion reaction rate for the addition of the strongly bound component is much faster than for the addition of the more weakly bound component. This gives rise to the experimental observation that the composition of the clusters does not reflect the composition of the vapor phase from which they are formed. Instead, during the formation stage of the clusters, a non-statistical enrichment toward the more strongly bound species occurs. ... [Pg.158]

The apoproteins of HDL are secreted by the liver and intestine. Much of the lipid comes from the surface monolayers of chylomicrons and VLDL during lipolysis. HDL also acquire cholesterol from peripheral tissues in a pathway that protects the cholesterol homeostasis of cells. In this process, free cholesterol is transported from the cell membrane by a transporter protein, ABCA1, acquired by a small particle termed prebeta-1 HDL, and then esterified by lecithin cholesterol acyltransferase (LCAT), leading to the formation of larger HDL species. The cholesteryl esters are transferred to VLDL, IDL, LDL, and chylomicron remnants with the aid of cholesteryl ester transfer protein (CETP). Much of the cholesteryl ester thus transferred is ultimately delivered to the liver by endocytosis of the acceptor lipoproteins. HDL can also deliver cholesteryl esters directly to the liver via a docking receptor (scavenger receptor, SR-BI) that does not endocytose the lipoproteins. [Pg.789]

In aggregation the species retain their identity but lose their kinetic independence since the aggregate moves as a single unit. Aggregation of droplets may lead to coalescence and the formation of larger droplets until the phases become separated. In coalescence, on the other hand, the original species lose their identity and become part of a new species. Kinetic stability can thus have different meanings. An... [Pg.117]

During direct reduction, the creation of a mobile species at -150 °C results in large Pt particles. In addition, calcination-reduction at higher temperatures leads to the formation of larger Pt particles. QEXAFS shows that PtOx is formed after calcination. It is most likely that also PtOx particles have the ability to sinter39 and ultimately form larger Pt particles. [Pg.31]

At normal deposition pressures, the mean free path of the gas molecules is 10" -10" cm and is much smaller than the dimensions of the reactor, so that many intermolecular collisions take place in the process of diffusion to the substrate. An understanding of the growth is made particularly difficult by these secondary reactions. In a typical low power plasma, the fraction of molecular species that is radicals or ions is only about 10" , so that most of the collisions are with silane. An important process is the formation of larger molecules, for example... [Pg.30]

Unsaturated residue formed during catalytic reactions that produced paraffins and olefins is the source of alkyl aromatics and nonvolatile residue. When HZSM-5 catalyst is employed, aromatic alkyl chain sizes are restricted to C4 or smaller. The pores of HZSM-5 are large enough to allow formation of small alkyl aromatics by cyclization and dehydrogenation of surface species, but formation of fused unsaturated coke precursors are inhibited. Unlike HZSM-5, larger HY pores facilitate the formation of larger nonvolatile unsaturated coke precursors. [Pg.54]


See other pages where Formation of Larger Species is mentioned: [Pg.10]    [Pg.534]    [Pg.1137]    [Pg.10]    [Pg.534]    [Pg.1137]    [Pg.1192]    [Pg.218]    [Pg.59]    [Pg.138]    [Pg.148]    [Pg.315]    [Pg.69]    [Pg.70]    [Pg.125]    [Pg.779]    [Pg.141]    [Pg.100]    [Pg.139]    [Pg.557]    [Pg.344]    [Pg.182]    [Pg.284]    [Pg.224]    [Pg.653]    [Pg.60]    [Pg.12]    [Pg.325]    [Pg.75]    [Pg.94]    [Pg.51]    [Pg.140]    [Pg.165]    [Pg.536]    [Pg.169]    [Pg.7]    [Pg.167]   


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Formate species

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