Electron-spin-resonance identification of a -CH2 -dot radical in irradiated amorphous SiO2:OH.
Electron-spin-resonance identification of a -CH2 -dot radical in irradiated amorphous SiO2:OH.
复制标题
电子自旋共振鉴定辐照无定形 SiO2:OH 中的 -CH2 -点自由基。
DOI：
10.1103/physrevb.54.15064
复制
发表时间：
1996
期刊：
影响因子：
--
通讯作者：
Leisure
中科院分区：
文献类型：
--
作者：
Austin;Leisure
一个三线电子自旋共振（ESR）光谱已观察到以下三个独立制造的火焰水解法（III型二氧化硅）的四个高纯度无定形二氧化硅样品的X射线照射。这一光谱的谱线间距约为18 G，以前被认为是由于一个未成对的自旋与氮的超精细相互作用。优化ESR参数和辐照程序已在本工作中获得前所未有的信号质量的光谱。在四种不同的二氧化硅样品中观察到三线ESR信号与两个碳自由基HC O·和CH 3·的存在或不存在的直接相关性。室温下缺陷浓度与X射线剂量关系的研究表明，三线缺陷与HC O·的衰变同时形成，先于CH 3·的出现。绝对自旋计数是一致的所有三个缺陷从一个单一的微量杂质的演变。提出三线谱是由两个等价的H1（I= 12）核自旋引起的超精细分裂而不是N14（I= 1）核自旋引起的.模拟的实验线的形状给出了良好的协议与双氢模型。这种外在的二氧化硅缺陷的超精细分裂的大小几乎是相同的，由于在甲醇中的C·H2 OH自由基的两个等效的氢。因此，三线缺陷被确定为a-CH 2·自由基，而不是之前所认为的氮缺陷。
A three-line electron-spin-resonance (ESR) spectrum has been observed following x irradiation in three of four high purity amorphous silica samples independently manufactured via the flame hydrolysis method (type-III silica). This spectrum, with a line separation of approximately 18 G, was previously attributed to an unpaired spin undergoing a hyperfine interaction with nitrogen. Optimization of ESR parameters and irradiation procedures have been employed in the present work to obtain spectra of unprecedented signal quality. A direct correlation of the three-line ESR signal with the presence or absence of two carbon radicals, HC O· and C H 3·, in the four different silica samples is observed. Studies of defect concentration vs x-ray dose at room temperature show that the three-line defect forms concurrently with the decay of HC O·, and prior to the appearance of C H 3·. Absolute spin counts are consistent with the evolution of all three defects from a single trace impurity. It is proposed that the three-line spectrum results from a hyperfine splitting due to the nuclear spins of two equivalent H 1 (I= 1 2), not N 14 (I= 1). Simulation of the experimental line shape gives excellent agreement with the two hydrogen model. The magnitude of the hyperfine splitting of this extrinsic silica defect is nearly the same as that due to the two equivalent hydrogens of the C· H 2 OH radical in methanol. Thus the three-line defect is identified as a-C H 2· radical, not a nitrogen defect as had been previously supposed.