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首页> 外文期刊>Applied Magnetic Resonance >Electron spin relaxation of radicals in gamma-irradiated malonic acid and methyl malonic acid
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Electron spin relaxation of radicals in gamma-irradiated malonic acid and methyl malonic acid

机译：γ-丙二酸和甲基丙二酸中自由基的电子自旋弛豫

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摘要

Radicals generated by gamma-irradiation of malonic acid and methyl malonic acid were studied as a function of temperature by inversion recovery, echo-detected saturation recovery and electron-electron double resonance (ELDOR) at X-band, and by continuous-wave saturation recovery at X-band and S-band. ELDOR reductions for malonic acid radical in polycrystalline and single-crystal samples indicate that nuclear spin relaxation is faster than both electron spin relaxation and cross relaxation between 93 and 233 K. Deuteration of the carboxylate protons caused the maximum ELDOR reduction to shift from about 110 to 150 K, consistent with the assignment of the rapid nuclear spin relaxation to hydrogen-bonded proton dynamics. ELDOR enhancements for both radicals formed in methyl malonic acid indicate that cross relaxation is faster than both electron spin relaxation and nuclear spin relaxation between 77 and 220 K. Enhanced cross relaxation and electron spin relaxation are attributed to the rotation of methyl groups at a rate comparable to the electron Larmor frequency. The temperature dependence of the enhancement of 1/T-1e was analyzed to determine the activation energies for methyl rotation. The same radical is formed in irradiated methyl malonic acid and L-alanine, but the barrier to rotation of the alpha-methyl is 500 K in the methyl malonic acid host and 1500 K in the L-alanine host, which indicates a large impact of the lattice on the barrier to rotation. [References: 38]
机译：通过反演恢复，回波检测的饱和恢复和X波段电子双共振（ELDOR）以及连续波饱和恢复，研究了丙二酸和甲基丙二酸的伽马射线辐照产生的自由基与温度的关系。在X波段和S波段。多晶和单晶样品中丙二酸自由基的ELDOR还原表明，核自旋弛豫要快于电子自旋弛豫和交叉弛豫，介于93 K和233 K之间。羧酸盐质子的氘化导致最大ELDOR还原从约110转变为150 K，与快速核自旋弛豫与氢键质子动力学的分配一致。在甲基丙二酸中形成的两个自由基的ELDOR增强表明交叉弛豫比电子自旋弛豫和核自旋弛豫都快，介于77 K和220 K之间。增强的交叉弛豫和电子自旋弛豫归因于甲基的旋转速度相当电子拉莫尔频率。分析了1 / T-1e增强的温度依赖性，以确定甲基旋转的活化能。在辐照的甲基丙二酸和L-丙氨酸中会形成相同的自由基，但是α-甲基的旋转障碍在甲基丙二酸主体中为500 K，在L-丙氨酸主体中为1500 K，这表明旋转障碍物上的晶格。 [参考：38]

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