NIST Center for Neutron Research, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA.
McKetta Department of Chemical Engineering, University of Texas, Austin, Texas 78712, USA.
J Chem Phys. 2017 May 21;146(19):194501. doi: 10.1063/1.4983179.
In a recent paper [C. E. Bertrand et al., J. Chem. Phys. 145, 014502 (2016)], we have shown that the collective dynamics of methanol shows a fast relaxation process related to the standard density-fluctuation heat mode and a slow non-Fickian mode originating from the hydrogen bonded molecular associates. Here we report on the length scale dependence of this slow relaxation process. Using quasielastic neutron scattering and molecular dynamics simulations, we show that the dynamics of the slow process is affected by the structuring of the associates, which is accessible through polarized neutron diffraction experiments. Using a series of partially deuterated samples, the dynamics of the associates is investigated and is found to have a similar time scale to the lifetime of hydrogen bonding in the system. Both the structural relaxation and the dynamics of the associates are thermally activated by the breaking of hydrogen bonding.
在最近的一篇论文中[C. E. Bertrand 等人，J. Chem. Phys. 145, 014502 (2016)]，我们表明甲醇的集体动力学表现出一种与标准密度涨落热模式相关的快速弛豫过程，以及一种源自氢键合分子缔合物的缓慢非菲克模式。在这里，我们报告了这种缓慢弛豫过程的长度尺度依赖性。通过准弹性中子散射和分子动力学模拟，我们表明缓慢过程的动力学受到缔合物结构的影响，这可以通过极化中子衍射实验来实现。使用一系列部分氘代样品，研究了缔合物的动力学，发现其时间尺度与体系中氢键的寿命相似。结构弛豫和缔合物的动力学都通过氢键的断裂而被热激活。
