The rotational dynamics and the geometry of a light and flexible impurity molecule like methyl, matrix isolated in van der Waals solid, are supposed to be sensitive to the host molecule dynamics and order alterations of the matrix. In addition, the location of the impurity and its interaction with the matrix molecules is of prime importance. Large energy gaps between rotation levels of quantum rotators allow precise investigation of temperature-assisted quantum tunneling effects. The molecular rotation of methyl radicals isolated in the deuterated solid methane isotopomer, CD₄, was investigated both by experimental and theoretical electron paramagnetic resonance (EPR) methods. The reduction of the quantum rotation frequency evident from the EPR spectrum of methyl radical at liquid-He temperatures was explained and connected to the irregular ratio of the central doublet to the outer quartet hf transitions. The involvement of temperature in the alteration of methyl symmetry between the C₃ and D₃ groups and the molecular host–host and guest–host interaction strengths were also examined by constructing temperature profiles of the rotation correlation times in the three phases of solid methane. The present study proves the deep impact that a van der Waals matrix may have on the geometry and the rotation levels of a substitutionally trapped quantum impurity rotor, effects that are yet very little known. This close correlation between dynamics of an impurity particle and the matrix molecules has great potential in developing sensitive physicochemical probes for van der Waals solids.

中文翻译：

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量子转子矩阵中的量子杂质转子：固体CD ₄矩阵中CH _3的电子顺磁共振动力学

轻质和灵活的杂质分子（如甲基）的旋转动力学和几何形状（范德华固体中分离出的基质）被认为对基质分子动力学和基质的阶跃变化敏感。此外，杂质的位置及其与基质分子的相互作用至关重要。量子旋转器的旋转水平之间的巨大能隙使得可以精确研究温度辅助的量子隧穿效应。氘化固体甲烷同位素异构体CD _4中分离的甲基自由基的分子旋转，通过实验和理论电子顺磁共振（EPR）方法进行了研究。解释了从液氦温度下甲基自由基的EPR谱可明显看出的量子旋转频率的降低，并将其与中心双峰与外部四重峰hf跃迁的不规则比率相关。温度参与C ₃和D ₃之间甲基对称性的改变还通过构建固态甲烷三相中旋转相关时间的温度分布图，研究了各基团以及分子主体-主体和客体-主体之间的相互作用强度。本研究证明范德华矩阵可能对替代俘获的量子杂质转子的几何形状和旋转水平产生深远的影响，但所产生的影响却鲜为人知。杂质粒子动力学与基质分子之间的这种紧密联系在开发用于范德华固体的灵敏理化探针方面具有巨大潜力。