Water rotational jump driven large amplitude molecular motions of nitrate ions in aqueous potassium nitrate solution

TL;DR

This study uses molecular dynamics simulations to uncover complex nitrate ion rotational motions driven by large amplitude jumps, which are coupled with water molecule jumps, revealing new insights into electrolyte solution dynamics.

Contribution

The paper introduces a new time correlation function to analyze coupled jump dynamics and identifies two distinct mechanisms of ion-water motion coupling in aqueous potassium nitrate.

Findings

Large amplitude angular jumps significantly influence ion and water motions.

Coupled jump motions are associated with hydrogen bond rearrangements.

Two distinct mechanisms of coupled dynamics are identified, both linked to density fluctuations.

Abstract

Molecular dynamics simulations of aqueous potassium nitrate solution reveal a highly complex rotational dynamics of nitrate ions where, superimposed on the expected continuous Brownian motion, are large amplitude angular jumps that are coupled to and at least partly driven by similar large amplitude jump motions in water molecules which are associated with change in the hydrogen bonded water molecule. These jumps contribute significantly to rotational and translational motions of these ions. We explore the detailed mechanism of these correlated (or, coupled) jumps and introduce a new time correlation function to decompose the coupled orientational- jump dynamics of solvent and solute in the aqueous electrolytic solution. Time correlation function provides for the unequivocal determination of the time constant involved in orientational dynamics originating from making and breaking of hydrogen bonds. We discover two distinct mechanisms-both are coupled to density fluctuation but are of different types.