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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >High-resolution ESR study of the H center dot center dot center dot CH3, H center dot center dot center dot CHD2, D center dot center dot center dot CH2D, and D center dot center dot center dot CD3 radical pairs in solid argon
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High-resolution ESR study of the H center dot center dot center dot CH3, H center dot center dot center dot CHD2, D center dot center dot center dot CH2D, and D center dot center dot center dot CD3 radical pairs in solid argon

机译：固体氩气中H中心点中心点中心点CH3，H中心点中心点中心点CHD2，D中心点中心点中心点CH2D和D中心点中心点中心点CD3自由基对的高分辨率ESR研究

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High-resolution electron spin resonance (ESR) spectra of radical pairs of a hydrogen atom that coupled with a methyl radical (H center dot center dot center dot CH3, H center dot center dot center dot CHD2, D center dot center dot center dot CH2D, and D center dot center dot center dot CD3) were observed for X-ray irradiated solid argon containing selectively deuterium-labeled methanes, CH4, CH2D2, and CD4, at 4.2 K. The double-quartet H-1-hyperfine (hf) splittings of ca. 26 and 1.16 mT at the Delta m(s) = +/- 1 and Delta m(s) = +/- 2 transitions, which are one-half of the isotropic H-1-hf splittings of an isolated H-atom and a CH3 radical, were attributed to the H center dot center dot center dot CH3 pair. The H-1-hf splittings at the Delta m(s) = +/- 1 transition were further split by the fine structure (fs) due to the electron dipole-dipole coupling. Because of the high-resolution spectra, three different sets of the fs splitting, d, are clearly resolved in the spectra of both the H center dot center dot center dot CH3 and the D center dot center dot center dot CD3 pairs. The separation distance (inter-spin distance), R, between the H-atom and the CH3 radical being in pairs was evaluated from the d values based on a point-dipole interaction model. For the case of the H center dot center dot center dot CH3 pair, the observed d values of 4.2, 4.9, and 5.1 mT yield the respective separations, R = 0.87, 0.83, and 0.82 nm, to probe the trapping site of the pair in an Ar crystalline lattice (fcc). For the pair with R = 0.87 nm, for example, we propose that the CH3 radical occupies a substitutional site and the counter H-atom occupies either the interstitial tetrahedral sites directed away from the CH3 radicals by a distance of 0.87 nm or the interstitial octahedral sites by a distance of 0.88 nm. When a mixture of CH4 and CD4 in a solid Ar matrix was irradiated, only two different radical pairs, H center dot center dot center dot CH3 and D center dot center dot center dot CD3, were observed. This result clearly demonstrates that the hydrogen atom and methyl radicals, which undergo a pairwise trapping, can originate from the same methane molecule.
机译：与甲基（H中心点中心点中心点CH3，H中心点中心点中心点CHD2，D中心点中心点中心点CH2D）耦合的氢原子的自由基对的高分辨率电子自旋共振（ESR）光谱，和D中心点中心点中心点CD3）在4.2 K下观察到含有选择性氘标记的甲烷CH4，CH2D2和CD4的X射线辐照的固体氩气。约分裂在Delta m（s）= +/- 1和Delta m（s）= +/- 2跃迁处分别为26和1.16 mT，这是一个孤立H原子的各向同性H-1-hf分裂的一半。一个CH3基团，归因于H中心点中心点中心点CH3对。由于电子偶极-偶极耦合，在δm（s）= +/- 1跃迁处的H-1-hf分裂被精细结构（fs）进一步分裂。由于具有高分辨率的光谱，在H中心点中心点中心点CH3和D中心点中心点中心点CD3对的光谱中清楚地分辨出三组不同的fs分裂d。基于点-偶极相互作用模型，由d值评估成对的H原子与CH 3自由基之间的分离距离（自旋间距离）R。对于H中心点中心点中心点CH3对，观察到的d值4.2、4.9和5.1 mT产生各自的间隔R = 0.87、0.83和0.82 nm，以探测该对的俘获位点在Ar晶格（fcc）中。例如，对于R = 0.87 nm的那对，我们建议CH3自由基占据一个取代位点，反H原子占据与CH3自由基相距0.87 nm的间隙四面体位点或间隙八面体距离为0.88 nm。当照射固体Ar基体中的CH4和CD4的混合物时，仅观察到两个不同的自由基对，即H中心点中心点中心点CH3和D中心点中心点中心点CD3。该结果清楚地表明，经历成对捕集的氢原子和甲基自由基可源自相同的甲烷分子。

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