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. 2006 Aug 14;125(6):61102.
doi: 10.1063/1.2232303.

Rotational Dynamics of a Diatomic Solute in the Room-Temperature Ionic Liquid 1-ethyl-3-methylimidazolium Hexafluorophosphate

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Rotational Dynamics of a Diatomic Solute in the Room-Temperature Ionic Liquid 1-ethyl-3-methylimidazolium Hexafluorophosphate

Youngseon Shim et al. J Chem Phys. .

Abstract

Reorientational time correlation functions C(l)(t)( identical withP(l)[cos theta(t)]) for a diatomic solute in 1-ethyl-3-methylimidazolium hexafluorophosphate (EMI(+)PF(6) (-)) are analyzed via molecular dynamics computer simulations, where <...> denotes an equilibrium ensemble average, P(l) the lth order Legendre polynomial and theta(t) the angle between the solute orientation at time t and its initial direction. Overall results are indicative of heterogeneous dynamics in EMI(+)PF(6) (-). For a small nondipolar solute, C(l)(t) are well-described as stretched exponential functions in wide time ranges. One striking feature is that after rapid initial relaxation, C(2)(t) decays more slowly than C(1)(t). As a result, the correlation time associated with the former is considerably longer than that with the latter. This is ascribed to solvent structural fluctuations, which allow large-amplitude solute rotations. As the solute size grows, relaxation of C(l)(t) approaches exponential decay.

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