Effects of various types of molecular dynamics on 1D and 2D (2)H NMR studied by random walk simulations
Effects of various types of molecular dynamics on 1D and 2D (2)H NMR studied by random walk simulations
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通过随机游走模拟研究各种分子动力学对 1D 和 2D (2)H NMR 的影响
DOI：
10.1006/jmre.2000.2160
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发表时间：
2000
影响因子：
2.2
通讯作者：
Rossler
中科院分区：
文献类型：
--
作者：
Vogel;Rossler
通过随机行走模拟，系统地研究了各种复杂分子动力学对固体中（2）H NMR实验的影响。更准确地说，我们计算一维（1D）（2）H NMR谱和二维（2D）（2）H NMR实验的结果在时域中，考虑到各向同性以及高度限制的运动，涉及不同的有限角度的旋转跳跃。虽然选择的动力学模型来模拟过冷液体和玻璃中的初级和次级弛豫，我们不打算定量描述实验结果，而是显示复杂的重新取向出现的一般效果。我们仔细研究了时域中的2D（2）H NMR，其最初设计用于测量超低速运动（τ>/= 1 ms）的相关时间，是否也可以用于获得更短的τ。它表明，扩展的时间窗口τ>/= 10 s是可能的，当处理指数松弛，但它会失败，如果有一个分布的相关时间G（lgtau）。反之亦然，我们表明，1D（2）H NMR光谱，通常记录看动力学与tau在微秒制度，也适用于研究超低速运动提供的损失的相关性是逐步实现的。因此，同时进行一维和二维核磁共振实验，以揭示复杂的分子运动机制是有用的。此外，我们表明，高度受限的动态可以清楚地观察到在一维光谱和二维核磁共振在时域中，如果长的固体回波延迟和大的演变时间，分别。最后，意想不到的意见，出现在后一个实验时，考虑非常广泛的分布G（lgtau）。由于这些影响，所考虑的运动的时间尺度和几何形状不能从实验结果的直接分析中提取。版权所有2000学术出版社。
By carrying out random walk simulations we systematically study the effects of various types of complex molecular dynamics on (2)H NMR experiments in solids. More precisely, we calculate one-dimensional (1D) (2)H NMR spectra and the results of two dimensional (2D) (2)H NMR experiments in time domain, taking into account isotropic as well as highly restricted motions which involve rotational jumps about different finite angles. Although the dynamical models are chosen to mimic the primary and secondary relaxation in supercooled liquids and glasses, we do not intend to describe experimental results quantitatively but rather to show general effects appearing for complex reorientations. We carefully investigate whether 2D (2)H NMR in time domain, which was originally designed to measure correlation times of ultraslow motions (tau >/= 1 ms), can be used to obtain shorter tau, too. It is demonstrated that an extension of the time window to tau >/= 10 &mgr;s is possible when dealing with exponential relaxation, but that it will fail if there is a distribution of correlation times G(lgtau). Vice versa, we show that 1D (2)H NMR spectra, usually recorded to look at dynamics with tau in the microsecond regime, are also applicable for studying ultraslow motions provided that the loss of correlation is achieved step by step. Therefore, it is useful to carry out 1D and 2D NMR experiments simultaneously in order to reveal the mechanism of complex molecular motions. In addition, we demonstrate that highly restricted dynamics can be clearly observed in 1D spectra and in 2D NMR in time domain if long solid-echo delays and large evolution times are applied, respectively. Finally, unexpected observations are described which appear in the latter experiment when considering very broad distributions G(lgtau). Because of these effects, time scale and geometry of a considered motion cannot be extracted from a straightforward analysis of experimental results. Copyright 2000 Academic Press.