Pair-trapped species

A triplet exciton localized at such a pair would be expected to spend, on average, fifty percent of its time at the molecule which originally absorbed the exciting photon and fifty percent at the partner site. Thus, triplet-triplet annihilation involving interaction of a second exciton with this pair-trapped species will, with equal probability, produce a DF photon nearly co-1 inear with the excitation polarization or else randomly oriented with respect to it. 

Theoretical studies performed by Grimes et al. (1992) on the basis of the solution energies of different species in the fuel yielded dependence of the chemical states of both iodine and cesium on the fuel stoichiometry. According to their results, in UO2-X the fission products exist as Csl pairs trapped at neutral trivacan-... 

The low efficiency of exchange in water can be explained by postulating that the ion-molecule pair (8.13 in Scheme 8-10) is almost completely trapped by water molecules, i.e., the first intermediate reacts so easily with this more strongly nucleophilic species that the reaction of the second intermediate (8.14) with N2 is not detectable. Therefore, the reaction coordinate diagrams for the dediazoniation in TFE and in water may be visualized as shown in Figure 8-4. 

Species such as 5 and 6 are called benzynes (sometimes dehydrobenzenes), or more generally, arynes, and the mechanism is known as the benzyne mechanism. Benzynes are very reactive. Neither benzyne nor any other aryne has yet been isolated under ordinary conditions, but benzyne has been isolated in an argon matrix at 8 where its IR spectrum could be observed. In addition, benzynes can be trapped for example, they undergo the Diels-Alder reaction (see 15-58). It should be noted that the extra pair of electrons does not affect the aromaticity. The... 

In our experiment, photocatalytic decomposition of ethylene was utilized to probe the surface defect. Photocatalytic properties of all titania samples are shown in table 2. From these results, conversions of ethylene at 5 min and 3 hr were apparently constant (not different in order) due to the equilibrium between the adsorption of gaseous (i.e. ethylene and/or O2) on the titania surface and the consumption of surface species. Moreover it can be concluded that photoactivity of titania increased with increasing of Ti site present in titania surface. It was found that surface area of titania did not control photoactivity of TiOa, but it was the surface defect in titania surface. Although, the lattice oxygen ions are active site of this photocatalytic reaction since it is the site for trapping holes [4], this work showed that the presence of oxygen vacancy site (Ti site) on surface titania can enhance activity of photocatdyst, too. It revealed that oxygen vacancy can increase the life time of separated electron-hole pairs. 

The mobile charge carrier species may either recombine or reach the semiconductor surface, where they can be trapped by the surface adsorbates or other sites. The lifetime of electron-hole (e /h+) pairs that are generated is important in determining the reaction yield. The holes are mainly trapped by water molecules or hydroxyl ions, giving rise to very reactive hydroxyl radicals ... 

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