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首页> 外文期刊>Physical chemistry chemical physics: PCCP >Dynamics and spin relaxation of tempone in a host crystal. An ENDOR, high field EPR and electron spin echo study
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Dynamics and spin relaxation of tempone in a host crystal. An ENDOR, high field EPR and electron spin echo study

机译：主体晶体中的tempone动力学和自旋弛豫。 ENDOR，高场EPR和电子自旋回波研究

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摘要

We studied in the temperature range 4-300 K the dynamics and the electron spin echo decay of the radical 4-oxo-2,2,6,6,-tetramethyl-1-piperidinyloxyl (tempone) doping substitutionally a single crystal of the diketone 2,2,4,4-tetramethyl-cyclobutan-1,3-dione. Electron nuclear double resonance (ENDOR) and high field electron paramagnetic resonance (EPR) spectra (110 GHz) displayed three types of motion: interconversion between twisted-crossover conformations, rotation of the methyl groups and libration of the radical in the crystal matrix. At room temperature all the motions are fast. and they reach the slow motion regime each at a different temperature, being all slow below 80 K. An approximate value of 9 kJ mol~(-1) for the energy barrier hindering the rotation of the tempone methyl groups is estimated. At low temperature their motion is too slow to give any contribution to the echo decay. The echo decays as a linear exponential in the range 100-300 K, due to the radical motions. At T < 100 K the interaction with the methyl protons of the matrix is the dominant dephasing mechanism, and the echo decays as a gaussian. At T < 20 K it depends on the square root of the time. Echo decays and electron spin echo envelope modulations (ESEEM) are simulated by using the available theoretical models. A damping of ESEEM superimposed to the echo decay is discussed.
机译：我们研究了在4-300 K的温度范围内自由基4-oxo-2,2,6,6，-tetramethyl-1-piperidinyloxyl（tempone）取代掺杂二酮单晶的动力学和电子自旋回波衰减2,2,4,4-四甲基-环丁烷-1,3-二酮。电子核双共振（ENDOR）和高场电子顺磁共振（EPR）光谱（110 GHz）显示三种运动：扭曲交叉构象之间的相互转化，甲基的旋转和晶体基质中自由基的释放。在室温下，所有运动都是快速的。它们分别在不同的温度下达到慢动作状态，在低于80 K时都变慢。据估计，能量阻隔的大约9 kJ mol〜（-1）阻碍了tempone甲基的旋转。在低温下，它们的运动太慢，无法对回声衰减做出任何贡献。由于激进运动，回波在100-300 K范围内衰减为线性指数。在T <100 K时，与基质甲基质子的相互作用是主要的移相机制，回波以高斯衰减。在T <20 K时，它取决于时间的平方根。回波衰减和电子自旋回波包络调制（ESEEM）通过使用可用的理论模型进行仿真。讨论了叠加在回声衰减上的ESEEM阻尼。

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