Rotational motion in the molecular crystals meta- and ortho-carborane studied by deuteron nuclear magnetic resonance.
Rotational motion in the molecular crystals meta- and ortho-carborane studied by deuteron nuclear magnetic resonance.
复制标题
通过氘核磁共振研究分子晶体间碳硼烷和邻碳硼烷的旋转运动。
DOI：
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发表时间：
2005
影响因子：
4.4
通讯作者：
H. Zimmermann
中科院分区：
文献类型：
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作者：
M. Winterlich;R. Böhmer;G. Diezemann;H. Zimmermann
用质子核磁共振技术测量了正碳硼烷和偏碳硼烷分子晶体的自旋晶格和自旋自旋弛豫时间、一维和二维谱以及二和四时间关联函数。研究发现，这些晶体在非立方相中表现出高度的各向异性运动。为了能够定量描述碳硼烷的运动几何结构，建立了几个随机模型。通过模型计算和实验结果的比较，发现这些准二十面体形状的分子的动力学受复合重取向过程的支配。在这里，分子围绕分子固定的轴进行三次跳跃，该轴本身可以相对于晶体固定的轴倾斜四个不同的方向。随着温度的升高，倾角显著增大。在四次受激回波函数测量的基础上，讨论了动态非均质性的含义，并与过冷液体进行了比较。
Spin-lattice and spin-spin-relaxation times, one- and two-dimensional spectra as well as two- and four-time correlation functions were measured for the molecular crystals ortho- and meta-carborane using deuteron nuclear magnetic resonance. It is found that in their noncubic phases these crystals exhibit highly anisotropic motions. In order to allow for a quantitative description of the motional geometry of the carboranes several stochastic models are formulated. By comparison of the model calculations with the experimental results it is found that the dynamics of these quasi-icosahedrally shaped molecules is governed by a composite reorientation process. Here the molecules perform threefold jumps around a molecule-fixed axis which itself can be tilted in four different directions with respect to a crystal-fixed axis. The tilt angle increases significantly with increasing temperature. On the basis of measurements of four-time stimulated-echo functions, implications for dynamic heterogeneity also in comparison with that of supercooled liquids are discussed.