gamma. -irradiated hydrocarbon crystals. Yields, decay, and photoreactions of radicals: carbanion formation. [4/sup 0/K, 77/sup 0/K]
gamma. -irradiated hydrocarbon crystals. Yields, decay, and photoreactions of radicals: carbanion formation. [4/sup 0/K, 77/sup 0/K]
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伽玛。
DOI：
10.1021/j100518a008
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发表时间：
1977
期刊：
影响因子：
--
通讯作者：
J. Willard
中科院分区：
文献类型：
--
作者：
D. Wilkey;H. W. Fenrick;J. Willard
我们在这里报告的实验设计，以回答有关自由基的性质和电荷载流子的命运在γ-辐照结晶和多晶烷烃的问题。这些问题对于加深对这些体系的辐射化学和固态化学的理解是重要的，它们包括：（1）烷烃链长与自由基产率之间是否存在相关性？(2)相位对产量有什么影响？当一种化合物在相同的温度下可以以玻璃或晶体的形式获得时，产率是否相同？(3)为什么多晶碳氢化合物中自由基的衰变动力学与玻璃态碳氢化合物中的不同（即，随温度逐步变化）？(4)在某些烷烃玻璃中观察到的光诱导去除有限部分的捕获自由基，也发生在多晶烷烃中吗？(5)自由基的光致异构化和过程的热逆转而不损失自由基浓度，是否发生在结晶烃中，就像在玻璃中一样？(6)光响应不同的自由基种群在ESR饱和特性上是否不同？(7)在γ-辐照的结晶碳氢化合物中是否存在碳负离子形成的电荷稳定作用？这些数据是在固体碳氢化合物的早期研究的背景下得到的，包括：（1）芳香族化合物产生的陷阱化合物的G值（每吸收100 eV产生的自由基）比烷烃或烯烃产生的自由基低10倍以上。2这被解释为2表明键断裂的概率与相对于键强度的最低电子激发态的能量有关。(2)从烷烃侧链到芳香族基团的分子内能量转移的证据，3分子间能量转移到溶质，在thesolute分子中产生选择性键断裂，4和转移到甲苯溶质，随后从甲苯发光。玻璃态支链烷烃的5（3）G（R·）一致低于多晶正构烷烃（~ 5.0）（~ 3.0）。6a，B（4）氘代玻璃态烃和多晶烃中的G（R·）比质子化烃中的G（R·）均匀地低30%或更多，6ab和n-C10 H22中的键断裂的定位不同于n-C10 D22。7（5）某些化合物的不同固态相经7次辐照形成不同的自由基。46（6）捕获的氢原子不是通过7照射烃晶体和玻璃形成的，66而不是CH 4。(7)300 -400 nm范围内的光吸收，8 a，B光激励发光，8 c，d和光激电导率86· 5表明烃玻璃中碳负离子的形成和光电离（8）烃玻璃辐解产生的自由基表现出相对快速的时间依赖性一级衰减（~ 50%），这是由内部自由基-自由基反应引起的，由于随机遭遇而导致的秩序衰减。9（9）当温度升高到连续更高的温度时，由多晶烃的7辐照产生的自由基经历逐步衰减，表明不同尺寸的微晶的选择性软化，或不同尺寸的自由基捕获位点。
We report here experiments designed to answer ques-tions about the properties of radicals and the fate of charge carriers in 7-irradiated crystalline and polycrystalline alkanes. These questions, which are important to im-proved understanding of the radiation chemistry and solid state chemistry of these systems, include the following:(1) Is there a correlation between alkane chain length and radical yield?(2) What are the effects of phase on yield? When a compound can be obtained as either a glass or crystal at the same temperature, are the yields the same?(3) Why are the decay kinetics of radicals in polycrystalline hydrocarbons different (ie, stepwise with temperature) than in glassy hydrocarbons?(4) Does the photoinduced removal of a limited fraction of trapped radicals, which has been observed in some alkane glasses, also occur in polycrystalline alkanes?(5) Does photoisomerization of radicals and thermal reversal of the process without loss of radical concentration occur in crystalline hydrocarbons as it does in glasses?(6) Do radical populations which differ in their photoresponse differ in ESR saturation characteristics?(7) Does charge stabilization by carbanion formation occur in 7-irradiated crystalline hydrocarbons? These data have been sought against the background of earlier work on solid hydrocarbons which includes:(1) Evidence that the G values (radicals produced per 100 eV absorbed) of trappedradicals produced from aromatic compounds are more than tenfold lower than for radicals produced from alkanes or alkenes. 2 This has been interpreted2 as indicating that the probability of bond rupture is related to the energy of the lowest electronic excited state relative to the bond strength.(2) Evidence for intramolecular energy transfer from alkane side chains to aromatic groups, 3 for intermolecular energy transfer to solutes with resultant selective bond rupture in thesolute molecules, 4 and for transfer to toluene solute with subsequent luminescence from the toluene. 5 (3) G (R·) in glassy branched chain alkanes is uniformly lower (~ 3.0) than in polycrystalline n-alkanes (~ 5.0). 6a, b (4) G (R·) in deuterated glassy and polycrystalline hydrocarbons in uniformly 30% or more lower than in protiated hydro-carbons, 6ab and the localization of bond rupture is different in n-Ci0H22 than n-C10D22. 7(5) Different radicals are formed by 7 irradiation of different solid state phases of some compounds. 46 (6) Trapped hydrogen atoms are not formed by the 7 irradiation of hydrocarboncrystals and glasses, 66 other than CH4.(7) Optical absorption in the300-400-nm range, 8a, b photostimulated luminescence, 8c, d and photostimulated conductivity86· 5 indicate carbanion formation and photoionization in hydrocarbon glasses (8) Radicals produced by 7 radiolysis of hydrocarbon glasses show a relatively rapid time-dependent first-order decay (-~ 50%) resulting from intraspur radical-radical reaction and a slower second-order decay resulting from random encounters. 9 (9) Radicals produced by 7 irradi-ation of polycrystalline hydrocarbons undergo stepwise decay as the temperature is raised to successively higher temperatures, indicating selective softening of crystallites of different sizes, or radical trapping sites of different