Molecular reorientation in ionic liquids:: A comparative dielectric and magnetic relaxation study

We have used H-2 magnetic relaxation to study the single-particle reorientation of the 1-ethyl-3-methylimidazolium ([emim](+)) ion in two prototypical low-viscosity ionic liquids comprising the bis(trifluoromethylsulfonyl)imide ([Tf2N](-)) and dicyanimide ([(CN)(2)N](-)) anions. Hydrodynamic analysis reveals extremely low ('subslip') coupling factors not captured by existing theories. Comparison with the microwave dielectric spectrum of [emim][Tf2N] shows that the dominant diffusive component of the dielectric response can be rationalized by single-particle reorientation of the cations. (C) 2007 Elsevier B.V. All rights reserved.