The influence of polarizability on the dielectric spectrum of the ionic liquid 1-ethyl-3-methylimidazolium triflate

Abstract

This work reports for the first time the computational, frequency-dependent dielec. spectrum of the polarizable mol. ionic liq. 1-ethyl-3-methylimidazolium triflate as well as its exptl. analog. In the frequency range from 500 MHz up to 20 GHz the agreement between the computational and the exptl. spectrum is quant. For higher frequencies up to 10 THz the agreement is still remarkably good. The exptl. asymptotic limit .vepsiln.∞ is 2.3. The difference in the computational value of 1.9 comes solely from the neglect of polarizability of the hydrogen atoms. For reasons of efficiency the simulations are based on the Lagrangian algorithm for the Drude oscillator model which cannot handle polarizable hydrogens. In the computational anal. the complete spectrum of the generalized dielec. const. is splitted into its translational and non-translational components, called dielec. cond. .vtheta.0(ν) and dielec. permittivity .vepsiln.(ν). For 1-ethyl-3-methylimidazolium triflate both components contribute with equal wt. and overlap in the complete frequency range. The inclusion of polarization forces, however, is quite different for the two components: the collective non-translational dynamics is accelerated and hence the dielec. permittivity is shifted to higher frequencies. The low frequency region of the dielec. cond. is also affected while its high frequency part remains almost unchanged. Inductive effects are not only visible at high frequencies but also contribute in the sub-GHz region. The computational peak found in this region correlates with the exptl. OKE-spectrum. It may be interpreted as the correlation between the induced dipole moment of the cations and the local elec. field exerted by the anionic cage.