  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.
