Electron under irradiation

As may be expected oxyanions of molecules known as antioxidants were also found to produce solvated electrons under irradiation. Phenolate anion in water leads to aqueous electron photoejection under 254 nm irradiation [62] and to benzosemiquinone through phenoxy radicals as shown by CIDNP arguments [63], In the case of / -naphtholate [64] the electron is photoejected from the unrelaxed singlet state [65, 66] with a low quantum yield (see Table 3) [67],... 

Transformations of 5,6-dihydro-2//-pyrans 8 into the corresponding 3,4-dihydro-2//derivatives 9 under basic conditions (88KGS291 98TL2025), as well as the reverse conversion under irradiation [97H(46)451], have been explained by the intermediate formation of electron-delocalized heterocyclic systems, giving rise to two possible isomers. 

The single-electron transfer from one excited component to the other component acceptor, as the critical step prior to cycloaddition of photo-induced Diels Alder reactions, has been demonstrated [43] for the reaction of anthracene with maleic anhydride and various maleimides carried out in chloroform under irradiation by a medium-pressure mercury lamp (500 W). The (singlet) excited anthracene ( AN ), generated by the actinic light, is quenched by dienophile... 

On the other hand, Switzer et al. proposed a different model for the oscillation. They attributed the oscillation to repetitive build-up and breakdown of a thin CU2O layer, which is a p-type semiconductor and acts as a thin rectifying (passivating) layer [24]. Disappearance of the oscillation under irradiated condition supports this model. Light will generate electron-hole pairs in the CU2O and lower the rectifying barrier at the semiconductor/solution interface. 

The third fact that seemed to argue in favor of the occurrence of radicals 10 was the observation that reactions of a-tocopherol under typical radical conditions, that is, at the presence of radical initiators in inert solvents or under irradiation, provided also large amounts of two-electron oxidation products such as o-QM 3 and its spiro dimerization product 9 (Fig. 6.8).16,25,26 This was taken as support of a disproportionation reaction involving a-tocopheroxyl radical 2 and its hypothetical tautomeric chromanol methide radical 10, affording one molecule of o-QM 3 (oxidation) and regenerating one molecule of 1 (reduction). The term disproportionation was used here to describe a one-electron redox process with concomitant transfer of a proton, that is, basically a H-atom transfer from hypothetical 10 to radical 2. 

Later, an improved system for C02 photofixation was reported by the same authors.164 The new system consisted of 6.5 x 1(T5 M tris(2,2 -bipyridine)ruthenium(II), Ru(bpy)3, as the photosensitive electron donor, methyl viologen (MV2+, 20 mM) as the electron acceptor, and triethanolamine (TEOA, 0.6 M) as a sacrificial electron donor in a C02-saturated aqueous solution (Fig. 18). Under irradiation with a 300-W high-pressure Hg lamp with a CuS04 chemical filter (A > 320 nm), formic acid, which was detected by isotachophoresis, was produced in quantum yields of ca. 0.01%. Recently, however, Kase et al.165 have repeated this experiment using a 13C02 tracer and have claimed that the formic acid obtained was produced not by C02 reduction but rather by oxidative cleavage of TEOA. 

TABLE 6.4 Radiation Yields (G Values) of Stabilized Electrons in Organic Glasses Under /-Irradiation at 77 K... 

The two metal surfaces covered by SAMs are brought into contact by the use of a micro-manipulator in the presence of a liquid medium, such as hexadecane the presence of hexadecane transforms the defects of the SAMs into insulating sites. The use of a semitransparent solid surface (Au or Ag) allows (1) evaluation of the contact area by collecting the image of the contact area by a mirror and (2) electrical measurements under irradiation of the SAMs through the Au surface. The disadvantage of Hg-based junctions is related to the environmental unfriendly characteristics of Hg, which prevent any application. For this main reason, these junctions are valuable only as versatile test-beds for organic electronics. 

The ability of H2 photoproduction as a result of photoinduced electron transfer from Ti02 particles to hydrogenase was demonstrated in 1976 by Krasnovsky at al. [1], H2 was produced under irradiation of Ti02 suspension containing hydrogenase from T. roseopersicina,... 

Electrical Conductivity. Measurements of the electrical conductivity of materials under Irradiation, particularly time-resolved conductivity following a pulse of electrons, can provide Information on mobilities and trapping mechanisms, free electron yield, and thermal1sat Ion times and path lengths. Some measurements have been done on polymers (45-47) particularly because of their technological Importance in the electronics Industry (37). More fundamental work Is needed. 

From the data of literature it is known that water-soluble derivatives of fullerenes are able to be localized in mitochondria and influence their state as well as enzyme system (Foley et al., 2002). Such intracellular localization of fullerenes C60 could explain biologic effects under irradiation, because generation of free oxygen radicals in the cells occurs during emission of electrons from electron-transport chain of mitochondria. 

D. Ugarte, Curling and closure of graphitic networks under electron-beam irradiation. ... 

The enantioselective oxidative coupling of 2-naphthol itself was achieved by the aerobic oxidative reaction catalyzed by the photoactivated chiral ruthenium(II)-salen complex 73. 2 it reported that the (/ ,/ )-chloronitrosyl(salen)ruthenium complex [(/ ,/ )-(NO)Ru(II)salen complex] effectively catalyzed the aerobic oxidation of racemic secondary alcohols in a kinetic resolution manner under visible-light irradiation. The reaction mechanism is not fully understood although the electron transfer process should be involved. The solution of 2-naphthol was stirred in air under irradiation by a halogen lamp at 25°C for 24 h to afford BINOL 66 as the sole product. The screening of various chiral diamines and binaphthyl chirality revealed that the binaphthyl unit influences the enantioselection in this coupling reaction. The combination of (/f,f )-cyclohexanediamine and the (R)-binaphthyl unit was found to construct the most matched hgand to obtain the optically active BINOL 66 in 65% ee. 

LDPE and EVA were blended in a 80/20 ratio and the non-crosslinked foam thereof was exposed to various doses of electron beam irradiation in air. The foam was made using isobutane as blowing agent. It was found that foam with uniform cell structure was not achieved in the case of pre-crosslinked foam with more than 40% gel fraction. Non-crosslinked foams were, however, easily crosslinked to a gel content of about 57% with electron beam irradiation under optimum conditions. The gel... 

Both of the bisfullerene compounds 19 and 23 undergo the intramolecular [2-1-2] reaction in chloroform and in ODCB, respectively, to give 24 [38] and 25 [41 ] quantitatively under irradiation by visible light. In these newly formed bisfullerene compounds, the electronic interaction between two Cgo cages was found to be greater than that in 19 and 23, as examined by electrochemical measurements, due to the closely fixed geometry. 

The application of HRTEM and ED can be difficult, however, because of the tendency of the catalysts to become amorphous under the beam. Use of higher accelerating voltages (to minimize the production of inelastic collisions which are primarily responsible for the structural disintegration of the sample), better vacuum in the sample chamber and, when possible, dealumination of the aluminosilicate (by replacing AP+ with in the framework) without losing structural integrity avoids these problems. These studies have indicated that Al-O bonds are more susceptible to rupture under electron-beam irradiation than Si-O bonds. 

We have just seen that there is evidence that aluminum ions can migrate under thermal pretreatment and this is also observed with sodium ions whose migration is favored by the presence of water (76). These processes are important since clusters of sodium ions can be formed and become efficient traps for electrons to produce F centers under irradiation, i.e.,... 

Although radical cations are generated in some electron-irradiated monomers (e.g., vinyl ethers or epoxies), efficient cationic polymerization is not observed. Under certain conditions (addition of iodonium, sulfonium, or sulfoxonium salts, cationic polymerization with the use of electron beam irradiation can be induced. Several studies on radiation cross-linking of elastomers support the concept of ionic mechanism. ... 

Electron beam damage effects followed the general rule that molecular groups in intimate contact with the metal substrate and aromatic groups appear relatively stable. Thus in the monolayer, alanine, with a methyl group likely sticking out from the surface, was the only molecule found to be unstable. In multilayer films, only tryptophan with the aromatic indole group to stabilize the molecule was found to yield multilayers stable under electron beam irradiation. 

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