Nondiffusive Rotational Jump Dynamics in Ethyl Ammonium Nitrate.

We examine the hydrogen bond jump mechanism in ionic liquid, ethyl ammonium nitrate (EAN), using classical molecular dynamics simulations. Hydrogen bond jump in EAN can occur through two different nondiffusive rotational jump mechanisms: N-H bond of ethyl ammonium can switch its hydrogen bond between two oxygen atoms of the same nitrate ion or it can break its hydrogen bond with the oxygen of a nitrate ion to form a new hydrogen bond with the oxygen atom of another nitrate ion. We observe the average magnitude of the jump angle of 30° in the first mechanism, whereas the jump angle for the second mechanism is 70°. The in-plane rotation of nitrate ion facilitates the H-bond switch in the first mechanism, whereas the rotation of the ammonium group of cation around the C-N bond facilitates the H-bond switch in the second mechanism. The jump angle observed in the second mechanism qualitatively agrees with experimentally observed large jump angle. We also investigate the effect of temperature on this nondiffusive rotational dynamics of ionic liquid to observe the changes in the jump angle and its distributions.