期刊
JOURNAL OF CHEMICAL PHYSICS
卷 148, 期 19, 页码 -出版社
AMER INST PHYSICS
DOI: 10.1063/1.5017797
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资金
- CSIR, India
- TUE-CMS project at the centre [SR/NM/NS-29/2011(G)]
- CSIR Project [01/2811/14/EMR-II]
Reorientational dynamics of the constituent ions in a room temperature ionic liquid, 1-butyl-3methylimidazolium hexafluorophosphate ([BMIM][PF6]), are explored via molecular dynamics simulations, and several features of orientation dynamics are summarized. The anion, [PF6](-), not only exhibits a higher propensity to orientation jumps than the cation, [BMIM](+) but also accesses a wider jump angle distribution and larger peak-angle. Jump and waiting time distributions for both the ions depict power-law dependences, suggesting temporally heterogeneous dynamics for the medium. This heterogeneity feature is further highlighted by the finding that the simulated first rank (l = 1) and second rank (l = 2) average reorientational correlation times reflect a severe break-down of Debye's (l + 1) law for orientational diffusion in an isotropic homogeneous medium. Simulated average H-bond lifetime resides between the mean orientation jump and waiting times, while the structural H-bond relaxation suggests, as in normal liquids, a pronounced presence of translational motion of the partnering ions. Average simulated jump trajectories reveal a strong rotation-translation coupling and indicate relatively larger changes in spatial and angular arrangements for the anion during an orientation jump. In fact, a closer inspection of all these results points toward more heterogeneous dynamics for [PF6](-) than [BMIM](+). This is a new observation and may simply be linked to the ion-size. However, such a generalization warrants further study. Published by AIP Publishing.
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