Structure and Dynamics of Acetonitrile: Molecular Simulation and Neutron Scattering
Structure and Dynamics of Acetonitrile: Molecular Simulation and Neutron Scattering
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DOI：
10.1016/j.molliq.2021.118423
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发表时间：
2021-12
影响因子：
6
通讯作者：
S. Cohen;M. Plazanet;S. Rols;D. Voneshen;J. Fourkas;B. Coasne
中科院分区：
文献类型：
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作者：
S. Cohen;M. Plazanet;S. Rols;D. Voneshen;J. Fourkas;B. Coasne
我们研究了散装液体乙腈中组织和动力学之间的相互作用。利用从分子模拟中得到的角分辨径向分布函数g(r,θ)，我们确定了一个复杂的微观结构，其中大多数液体分子与一个或多个相邻分子以反平行的“八极子配对”配置和/或偏移，头对尾配置相关联。对这些结构基序的详细分析表明，头尾偏移二聚体是最普遍的。一个时间依赖的配对分析证实了这幅强有力的分子关联有利于头对尾二聚体，其持续时间比反平行二聚体更长。这种组织与配对时间（~ ps）比典型的旋转时间常数长有关，不能在二聚体中的库仑相互作用的基础上解释，因此必须来自既不强也不特定的集体效应。最后，利用中子散射技术和分子模拟，我们研究了液体乙腈在时间尺度上的动力学，范围从亚皮秒（状态的振动密度）到皮秒（旋转/平移运动和广义状态密度）到几十皮秒（菲克体系中的自扩散率）。
We examine the interplay between organization and dynamics in bulk liquid acetonitrile. Using angularly resolved radial distribution functions,g(r,θ), derived from molecular simulations, we identify a complex microscopic structure in which most liquid molecules are associated with one or more neighboring molecules in an antiparallel, “octupole-paired” configuration and/or an offset, head-to-tail configuration. A detailed analysis of these structural motifs reveals that the offset head-to-tail dimers are the most prevalent. A time-dependent pairing analysis corroborates this picture of robust molecular associations favoring head-to-tail dimers, which last longer than antiparallel dimers. This organization, which is associated with pairing times (∼ps) longer than the typical rotational time constant, cannot be explained on the basis of the Coulomb interactions in the dimer, and so must arise from collective effects that are neither strong nor specific. Finally, using both neutron-scattering techniques and molecular simulations, we study dynamics in liquid acetonitrile over time scales ranging from subpicosecond (the vibrational density of states) to picosecond (rotational/translational motions and the generalized density of states) to tens of picoseconds (self-diffusivity in the Fickian regime).