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Simultaneous Orientational and Conformational Molecular Dynamics in Solid 1,1,2-Trichloroethane
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2018-02-22 00:00:00 , DOI: 10.1021/acs.jpcc.7b12469 Michela Romanini 1 , Efstratia Mitsari 1 , Pragya Tripathi 1 , Pablo Serra 2 , Mariano Zuriaga 2 , Josep Lluis Tamarit 1 , Roberto Macovez 1
The Journal of Physical Chemistry C ( IF 3.3 ) Pub Date : 2018-02-22 00:00:00 , DOI: 10.1021/acs.jpcc.7b12469 Michela Romanini 1 , Efstratia Mitsari 1 , Pragya Tripathi 1 , Pablo Serra 2 , Mariano Zuriaga 2 , Josep Lluis Tamarit 1 , Roberto Macovez 1
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The molecular dynamics in the ambient-pressure solid phase of 1,1,2-trichloroethane is studied by means of broadband dielectric spectroscopy and molecular dynamics simulations. The dielectric spectra of polycrystalline samples obtained by crystallization from the liquid phase exhibit, besides a space-charge relaxation associated with accumulation of charges at crystalline domain boundaries, two loss features arising from dipolar molecular relaxations. The most prominent and slower of the two loss features is identified as a configurational leap of the molecules which involves a simultaneous change in spatial orientation and structural conformation, namely between two isomeric forms (gauche+ and gauche–) of opposite chirality. In this peculiar dynamic process, the positions of the three chlorine atoms in the crystal lattice remain unchanged, while those of the carbon and hydrogen atoms are modified. This dynamic process is responsible for the disorder observed in an earlier X-ray diffraction study and confirmed by our simulation, which is present only at temperatures relatively close to the melting point, starting 40 K below. The onset of the disorder is visible as an anomaly in the temperature dependence of the dc conductivity of the sample at exactly the same temperature. While the slower relaxation dynamics (combined isomerization/reorientation) becomes increasingly more intense on approaching the melting point, the faster dynamics exhibits significantly lower but constant dielectric strength. On the basis of our molecular dynamics simulations, we assign the faster relaxation to large fluctuations of the molecular dipole moments, partly due to large-angle librations of the chloroethane species.
中文翻译：
固体1,1,2-三氯乙烷的同时取向和构象分子动力学
通过宽带介电谱和分子动力学模拟研究了1,1,2-三氯乙烷在常压固相中的分子动力学。通过液相结晶获得的多晶样品的介电谱，除了与电荷在晶畴边界处积累相关的空间电荷弛豫外，还显示了由偶极分子弛豫引起的两个损耗特征。这两个损失特征中最突出和最慢的特征是分子的结构跃迁，涉及空间方向和结构构象的同时变化，即两种同分异构形式（gauche +和gauche –）相反的手性。在这种特殊的动力学过程中，晶格中的三个氯原子的位置保持不变，而碳原子和氢原子的位置被修饰。这种动态过程是造成早期X射线衍射研究中观察到的无序现象的原因，并由我们的模拟结果证实，该无序现象仅在相对接近熔点的温度下（从40 K开始）存在。在完全相同的温度下，样品的直流电导率对温度的依赖性取决于异常的发生。尽管较慢的弛豫动力学（结合的异构化/重新取向）在接近熔点时变得越来越强烈，但较快的动力学表现出明显较低但恒定的介电强度。
更新日期：2018-02-22
中文翻译：
固体1,1,2-三氯乙烷的同时取向和构象分子动力学
通过宽带介电谱和分子动力学模拟研究了1,1,2-三氯乙烷在常压固相中的分子动力学。通过液相结晶获得的多晶样品的介电谱，除了与电荷在晶畴边界处积累相关的空间电荷弛豫外，还显示了由偶极分子弛豫引起的两个损耗特征。这两个损失特征中最突出和最慢的特征是分子的结构跃迁，涉及空间方向和结构构象的同时变化，即两种同分异构形式（gauche +和gauche –）相反的手性。在这种特殊的动力学过程中，晶格中的三个氯原子的位置保持不变，而碳原子和氢原子的位置被修饰。这种动态过程是造成早期X射线衍射研究中观察到的无序现象的原因，并由我们的模拟结果证实，该无序现象仅在相对接近熔点的温度下（从40 K开始）存在。在完全相同的温度下，样品的直流电导率对温度的依赖性取决于异常的发生。尽管较慢的弛豫动力学（结合的异构化/重新取向）在接近熔点时变得越来越强烈，但较快的动力学表现出明显较低但恒定的介电强度。
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