Generation of reactive species

The various reagents may be created in several ways. They may be obtained by photolysis, pyrolysis or discharge of a suitable precursor. Refractory substances, such as metals and metal salts, can be produced in the gas phase by direct vaporisation or, more recently, by laser 

A wide range of ground and excited state atoms and radicals has been produced by laser photolysis. Lin and McDonald [9] have recently reviewed the production of such species by photolysis and they list the many kinetically important atoms and free radicals that can be produced. As the range of available lasers increases, we can expect laser photolysis to become one of the major sources of reactive species for kinetic studies. 

A very recent, but less commonly used, photolysis source is the continuously tuneable far-ultraviolet (5—lOOnm) synthrotron radiation. Despite the fact that the photon output of a storage ring at a given 

The generation of reactive species by a fast pre-reaction is a well established process in kinetics, particularly in flow systems, although this technique is now being used in molecular beam sources [see (f), below]. As atoms are commonly generated by thermal or microwave dissociation (see above), reactions are mainly used to produce radicals. However, some atoms may be produced by reaction as a more convenient alternative to direct vaporisation or dissociation. Scandium and yttrium atoms have been generated [25] by the reaction 

Many reactive radicals have been generated by reaction, usually in discharge flow systems where the reaction generally involves an atom produced by microwave or radio frequency discharge. Clyne and Nip [17] present an account of such methods. One feature of the radicals produced by reaction is that they may be formed in excited states, usually vibrational or electronic. For example, the OH radical may be generated [27] in low vibrational levels (v 3) by the reaction 

Many reactive radicals have been generated by reaction, usually in discharge flow systems where the reaction generally involves an atom produced by microwave or radio frequency discharge. Clyne and Nip 

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In combustion experiments, there are two key considerations first, generating a flame and second, detecting the species of interest. Gaseous flows in a flame can be classified as laminar (streamlined layers) or turbulent. While these flames can be analyzed directly, it is less confounding to study flame chemistry through controlled generation of reactive species in one of a wide variety of experimental apparata. 

The process of generation of reactive species by high-energy electrons. (Garratt, P. G., Strahlenhartung, Curt R. Vincentz Verlag, Hannover, p. 61 (1996). In German. Reprinted with permission from Vincentz Network.)... 

In general, upon exposure to UV radiant energy, a photoinitiator can generate free radicals or ions, as pointed out earlier. These are generated at a rapid rate, and their depth profile corresponds to the inverse photon penetration profile. Similar to electron penetration, the final cure profile often deviates from the initial radical or ion distribution, since they can live much longer than the exposure time. The mechanisms of the processes for the generation of reactive species are discussed in detail in Davidson. ... 

Spectral outputs of some metal halide lamps compared with that of a standard mercury lamp Spectral output of commercial micro-wave-driven lamps The process of generation of reactive species. 

Generation of reactive species (free radicals or ions)... 

II. GENERATION OF REACTIVE SPECIES IN THE ELECTRON-DONOR-ACCEPTOR SYSTEM... 

The ring strain associated with the three-membered ring facilitates the generation of reactive species such as biradicals (cyclopropanes) and ylides (oxiranes and azir-idines) upon photoexcitation. These intermediates can undergo cycloaddition reaction with olefins to give five-membered rings. Selected examples from each reactive intermediate are presented in this section. 

As indicated above, the photolysis of Fe(III)-carboxylate and aminocarboxy-late complexes may result in oxidative degradation of the ligand and reduction of the metal centre to Fe(II). In addition, these complexes may play a significant role in the photochemical generation of reactive species such as 02 , H2O2 and OH [28,51,64], The degradation of a variety of organic con-... 

Electrooxidation of halide salts is quite useful for the generation of reactive species of halogen atoms under mild conditions. Functionalization of alkenes involving the formation of halohydrins, 1,2-halides, a-halo ketones, epoxides, allylic halides and others has been achieved by electrochemical reactions and is well documented in the literature. On the other hand, electrogenerated carbenium ions can be captured by nucleophilic halide anions, providing a new route to halogenated compounds... 

Generation of Reactive Species via Photoinduced Electron Transfer. 303... 

Aslan, M., Barnes, S., Kirk, M., Rosenfeld, S., Townes, T., Ryan, T., and Freeman, B.A., Nitric oxide-dependent generation of reactive species in sickle cell disease renal and hepatocellular actin tyrosine nitration, J. Biol. Chem., 278, 4194, 2003. 

The effect of the rubber modifier on the cure rate can be attributed in part to interactions between the rubber and the PCI. These interactions may result in the rubber acting as a screen or quencher to the PCI, inhibiting the generation of reactive species that lead to cure. The decrease in degree of cure can in turn be associated with the acrylonitrile content of the modifier due to an increase in interactive sites and/or enhanced compatibility with the resin (increased solubility... 

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