Diffusive motions in liquid medium-chain n-alkanes as seen by quasielastic time-of-flight neutron spectroscopy.
Diffusive motions in liquid medium-chain n-alkanes as seen by quasielastic time-of-flight neutron spectroscopy.
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通过准弹性飞行时间中子能谱观察液体中链正构烷烃的扩散运动。
DOI：
10.1063/1.2990026
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发表时间：
2008
期刊：
影响因子：
--
通讯作者：
W. Petry
中科院分区：
文献类型：
--
作者：
T. Unruh;C. Smuda;S. Busch;J. Neuhaus;W. Petry
利用准弹性飞行时间中子能谱（QENS）研究了皮秒时间尺度上C（32）H（66）液体中的不同扩散运动。结果表明，在所有的观测时间，占主导地位的运动导致QENS信号的Q（2）比例，这表明一个菲克扩散机制。所观察到的运动可以通过观察时间依赖的表观扩散系数D（a）（t（o））来表征，其比分子自扩散系数D（s）大一个数量级。通过与分子动力学模拟的比较，所确定的运动归因于氢原子的位移，不仅反映了全球，而且也反映了局部分子轨迹。尽管棒状形状的分子，质量扩散的中心被认为是基本上各向同性的。给出了从CH（2）基团的快速翻滚到缓慢的长程分子扩散的扩散过程的相干图象。
Different diffusive motions in liquid C(32)H(66) on a picosecond time scale could be disentangled by resolution resolved quasielastic time-of-flight neutron spectroscopy (QENS). It is demonstrated that at all observation times, the dominating motion causes a Q(2) proportionality of the QENS signal, which indicates a Fickian diffusion mechanism. The observed motions can be characterized by an observation time dependent apparent diffusion coefficient D(a)(t(o)), which is up to one order of magnitude larger than the molecular self-diffusion coefficient D(s). By comparison with molecular dynamics simulations, the identified motions are attributed to displacements of hydrogen atoms reflecting not only global but also local molecular trajectories. Despite the rodlike shape of the molecules, the center of mass diffusion was found to be essentially isotropic. A coherent picture of the diffusional processes ranging from the fast tumbling of CH(2) groups to the slow long range molecular diffusion is presented.