Indicator radiolysis

The total yield of OH radicals is 6.0 and hence the yield of sulfinic acid of G = 2.7 indicates that 45% of the OH radical produced in the radiolysis attack the sulfinyl group of MTMSO. The authors48 said that the residual 55% attack the sulfide S—C bond, but this claim ignores completely other routes, such as hydrogen abstraction, which was found for other sulfoxides45. 

The most radiation-stable poly(olefin sulfone) is polyethylene sulfone) and the most radiation-sensitive is poly(cyclohexene sulfone). In the case of poly(3-methyl-l-butene sulfone) there is very much isomerization of the olefin formed by radiolysis and only 58.5% of the olefin formed is 3-methyl-l-butene. The main isomerization product is 2-methyl-2-butene (37.3% of the olefin). Similar isomerization, though to a smaller extent, occurs in poly(l-butene sulfone) where about 10% of 2-butene is formed. The formation of the olefin isomer may occur partly by radiation-induced isomerization of the initial olefin, but studies with added scavengers73 do not support this as the major source of the isomers. The presence of a cation scavenger, triethylamine, eliminates the formation of the isomer of the parent olefin in both cases of poly(l-butene sulfone) and poly(3-methyl-1-butene sulfone)73 indicating that the isomerization of the olefin occurred mainly by a cationic mechanism, as suggested previously72. 

Bowden and Thompson83 studied the degradation of thin films of various poly(olefin sulfone)s of low olefins due to radiolysis by electron beams at 20 °C. All samples decreased in thickness, indicating scission and depropagation. 

Phenomenological evidence for the participation of ionic precursors in radiolytic product formation and the applicability of mass spectral information on fragmentation patterns and ion-molecule reactions to radiolysis conditions are reviewed. Specific application of the methods in the ethylene system indicates the formation of the primary ions, C2H4+, C2i/3+, and C2H2+, with yields of ca. 1.5, 1.0, and 0.8 ions/100 e.v., respectively. The primary ions form intermediate collision complexes with ethylene. Intermediates [C4iZ8 + ] and [CJH7 + ] are stable (<dissociation rate constants <107 sec.-1) and form C6 intermediates which dissociate rate constants <109 sec. l). The transmission coefficient for the third-order ion-molecule reactions appears to be less than 0.02, and such inefficient steps are held responsible for the absence of ionic polymerization. 

Field and Lampe (23) established the occurrence of the hydride transfer reaction in the gas phase in 1958 by detecting secondary ions of mass one unit lower than the parent compound. Subsequently, Futrell (24, 25) attempted to account for most lower hydrocarbon products formed in the radiolysis of hexane and pentane by assuming that hydride transfer reactions play a dominant role in radiolysis. More recently, Ausloos and Lias (2) presented experimental evidence which indicated that some of the products in the radiolysis of propane are, in... 

Table III shows that in the gas phase at a pressure of 40 torr the relative rates of the H2 transfer reactions from the cyclopentane ion to the various additives differ drastically from those derived from liquid phase radiolysis experiments. This indicates that the changes in density may profoundly affect the relative rates of the two competitive reactions, Reactions 22 and 28. Experimental results, which will be described in a later publication, indicate that in the liquid phase an increased importance of the H2 transfer reaction to some of the additives occurs at the expense of the H atom transfer reaction, Reaction 23.

Sumiyoshi and coworkers studied the radiolysis of aqueous solution of methyl methylthiomethyl sulfoxide [ H3S(0) H2S H3 MTMSO] at various pH by pulse radiolysis. They found that the reaction of e with MTMSO (in the presence of 1M t-butyl alcohol to scavenge OH" radicals) leads to formation of a transient with a broad absorption band of = 375 nm. The absorbance at 375 nm as a function of pH are of S shape, indicating an equilibrium due to reaction with H. Similar to the finding in dimethyl sulfoxide they suggested the scheme. 

The optical absorption spectra of sulfonyl radicals have been measured by using modulation spectroscopy s, flash photolysis and pulse radiolysis s techniques. These spectra show broad absorption bands in the 280-600 nm region, with well-defined maxima at ca. 340 nm. All the available data are summarized in Table 3. Multiple Scattering X, calculations s successfully reproduce the experimental UV-visible spectra of MeSO 2 and PhSO 2 radicals, indicating that the most important transition observed in this region is due to transfer of electrons from the lone pair orbitals of the oxygen atoms to... 

The pulse radiolysis of ODN conjugated with Py and Ptz showed a transient absorption spectrum with a peak at 470 or 520 nm, assigned to Py+ or Ptz + respectively (Fig. 9). The formation rates of Py+ and Ptz+ obtained for Py-1 and Ptz-1 were almost identical to that of the decay of TIOH+ and no secondary formation was observed. These results indicate that a hole migrates from... 

The structures under consideration are indicated in Inserts VI and VII. Such radicals are usually secondary products of radiolysis, formed, for example, by extraction of hydrogen from a R2C(H)-precursor. However, closely related radicals can be formed, for example, by electron-loss from vinyl- or allyl- derivatives (66,67) or from substituted aromatic cations (68,69) [see, for example, VIII-X]. 

At least seven modes of dissociation are theoretically possible below the ionization threshold, although their total yield in radiolysis is small (Platzman, 1967). The dissociation products are H, H2, O, and OH, where the first two are in their ground (electronic) states but the last two may be either in ground or excited states. Only two modes of dissociation, H20 -H + O and H20 H + OH, are possible for all excitation energies UV photolysis indicates that the latter process is by far (90%) the most likely. Accordingly, in radiolysis there is a tendency to lump the decay of all excited states of the water molecule into H and OH. 

The pKa of the "OH radical is 11.9. The basic form is O ", which predominates at PH 12. Von Sonntag and coworkers14 found that the absorption at 310 nm of pulse radiolysis of pH = 13 N2O saturated solution of 1,4- or 1,3-cyclohexadiene indicates that 0 " anion radical only abstracts hydrogen atoms but does not add to the double bond. 

Using basic pH leads to higher plateau rate constants, indicating that the ratedetermining step is reaction 18. Reaction 17 must be at least as fast as the rate of 02 addition in the highest 02 concentration used, kn 8 x 105 s 1, which is the limit of the instrument measurement. The G of benzene in pulse radiolysis was found to be equal to that of the nitroform anion (1.6 x 10-7 molJ-1) as can be expected from reactions 17-19. Since the yield of the cyclohexadienylperoxyl radical is 2.9 x 10-7 mol. 1 1 it means that only a fraction (ca 60%) of the cyclohexadienylperoxyl radicals eliminates HO2. The H02 elimination occurs by H-transfer of the allylic hydrogen to the oxygen... 

This conclusion is supported by results of detailed study on the decay of hydroxyhexa-dienylperoxyl radicals, formed by addition of OH to benzene, followed by addition of dioxygen molecule. It was found that in the high dose rate of pulse radiolysis, hydro-quinone is the major product whereas catechol was not observed, indicating that only the 1,3-isomer loses HO2" and hence does not lead to dihydroxybenzene. The observation that the yield of 02 is 60% of the yield of the cyclohexadienyl radicals indicates that when dioxygen molecules react with the cyclohexadienyl radical, the radical is 60% trapped in the mesomeric form of 5b, whereas the results from the final products of dimerization in /-radiolysis show that 60% react in the form 5a. 

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