Radiolytic yield

In dibenzothiophene-S,S-dioxide the S atom is in a ring, and hence more constrained. The yield of SOz in the radiolysis is linear with the dose to about 13 Mrad after which it levels off as in p,p -ditolyI sulfone. However, the yield of S02 in this case is much lower (a factor of 25) than in the case of p,p -ditolyl sulfone (G = 0.002 compared to G = 0.05). This stability of the dibenzothiophene sulfone could be partially due to back reaction to reform the parent sulfone and partially due to more efficient energy delocalization. The expected biphenylene product was not detected due to limitations of the analytical method. Bowmer and O Donnell70 studied the volatile products in y-radiolysis of dialkyl, alkyl aryl and diaryl sulfones. Table 2 gives the radiolytic yields of S02 and of the hydrocarbon products of the alkyl or aryl radicals. The hydrocarbon products are those obtained either by H atom abstraction or by radical combination. The authors69 suggested the mechanism... 

The effect of the temperature is an exponential increase in the radiolytic yield of the volatile products for each poly(olefin sulfone). If the logarithm of G(volatile products) is... 

It was found that Zs levels off at dose > 20 krad. The cross-linking process in dioxane occurs at times longer than several milliseconds. Similar results were obtained for PHS in dioxane, however the radiolytic yield of scission, G(S), measured from the initial slope of the plot of Zs vs. D, is different for the two polymers G(S) is about 12 for PBS and about 4 for PHS, in contrast to irradiation of the pure polymers, where for both at 30° G(S) 1080. 

Kemp and coworkers employed the pulse radiolysis technique to study the radiolysis of liquid dimethyl sulfoxide (DMSO) with several amines as solutes [triphenylamine, and N, A, A, N -tetramethyl-p-phenylenediamine (TMPD)]. The radiolysis led to the formation of transient, intense absorptions closely resembling those of the corresponding amine radical cations. Pulse radiolysis studies determine only the product Ge, where G is the radiolytic yield and e is the molar absorption. Michaelis and coworkers measured e for TMPD as 1.19 X 10 m s and from this a G value of 1.7 is obtained for TMPD in DMSO. The insensitivity of the yield to the addition of electron scavenger (N2O) and excited triplet state scavenger (naphthalene) proved that this absorption spectrum belonged to the cation. 

TABLE 3. Radiolytic yields of the final products of the radiolysis of cyclic oligoenes I. Liquid phase... 

Primary processes, reactions of positive ions and radiolytic yields... 

Linear Energy Transfer. The concept of linear energy transfer (LET) has been a useful one in rationalising the variation in radiolytic yields found for different types of radiation. It is still widely... 

Due to the accurate knowledge of the dose used, a control of the progressive extent of the radiolytic reduction was achieved. However, quite often, puzzling data were reported when the zero-valent metal was formed, such as an induction time for precipitation, a sensitivity of the radiolytic yields to the initial presence of added particles, and an unusually weak reproducibility [9,10]. Moreover, oxidation of silver atoms by molecular oxygen was observed [7], although the process was thermodynamically improbable for a noble metal such as silver. 

Schmidt KH, Flan P, Bartels DM (1995) Radiolytic yields of the hydrated electron from transient conductivity improved calculation of the hydrated electron diffusion coefficient and analysis of some diffusion-limited (e )aq reaction rates. J Phys Chem 99 10530-10539 Schoneich C, Aced A, Asmus K-D (1991) Halogenated peroxyl radicals as two-electron-transfer agents. Oxidation of organic sulfides to sulfoxides. J Am Chem Soc 113 375-376 Schuchmann Fl-P, von Sonntag C (1981) Photolysis at 185 nm of dimethyl ether in aqueous solution Involvement of the hydroxymethyl radical. J Photochem 16 289-295 Schuchmann Fl-P, von Sonntag C (1984) Methylperoxyl radicals a study ofthey-radiolysis of methane in oxygenated aqueous solutions. Z Naturforsch 39b 217-221 Schuchmann Fl-P, von Sonntag C (1997) Heteroatom peroxyl radicals. In Alfassi ZB (ed) Peroxyl radicals. Wiley, Chichester, pp 439-455... 

After irradiation with 3.3 MGy of a DCH18C6 solution in 1 mol L 1 nitric acid containing 20 g I. of uranyl nitrate, compounds 2 and 4 (presented in Figure 8.15 with their radiolytic yields) were shown to be the main products of radiolysis nevertheless, 50% of DCH18C6 remained unchanged. In these conditions, the disappearance yield G(-DCH18C6) was estimated to be 0.72 molecule/100 eV (7). 

SCHEME 4.1 Schematics of radiolysis and reducing species. As a result of ionization of the water molecule, hydroxyl radicals and hydrated electrons are formed. The final radiolytic yield depends on the secondary reactions in spurs and on the presence of other compounds. See Refs 25,26,190, and 191 for the detailed discussion and references. Solvated electrons are mobile enough to escape spurs and to react with the heme protein complexes even at 77K. All other reactive products of radiolysis are immobilized in the solid solvent matrix, or trapped by radical quenchers. 

The radiolytic yields are always expressed by the G value, which is defined as the number of particles (molecules, radicals, ions) produced or consumed per 100 eV of energy absorbed in the system. 

Kovalev and coworkers77 studied the effect of methanol on the radiolysis of liquid CC14. In pure CC14, y-radiolysis leads to the formation of Cl2 and C2C16 with a radiolytic yield of G = 0.70 0.03. When methanol is added, the yield of the first product falls to zero already at 2 x 10"3 M methanol, while G(C2C16) increases to 4.8 0.5. New products found are... 

In a slightly more detailed study of dry styrene, Metz et al. (23) have reported similar observations. They tentatively identified a species with broad absorption maximum at 370 m/x, decaying with a first-order half-life of approximately 4 /xsec., extremely sensitive to water, sensitive to oxygen, insensitive to N20, and formed with an apparent radiolytic yield (measured immediately after a 0.2-/xsec. pulse) of G 0.15, as the styryl radical anion. 

The radiolytic yields of these species are now well established and are 0.28,... 

A new generation of cross-linked hyaluronic acids, termed Hylans, is now available [96]. It would be expected that such aggregated molecules, which consist of several hyaluronic acid chains linked via methoxy bridges to a protein core, should be more resistant to free radical-induced depolymerisation. The results of initial studies to determine the radiolytic yield of chain scission... 

Radiolytic yields expressed in terms of 10 7 mol J l for oxygen consumption and the formation of superoxide radical anions, peroxides and carbon dioxide in the steady-state g-radiolysis of N2O/O2 (4/1) saturated solutions of hyaluronic acid (1 x 10-3 mol dm-3). Hyaluronic acid concentrations are in terms of dimeric subunits... 

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