The separation of the
maxima is about 1.3 ps, and so the Na atom takes that long
to swing out and be recaptured by the I atom. We can see
that the peaks progressively decrease in intensity, showing
that some Na atoms escape from their I atom partners on
each swing. It takes about 10 swings outward before an
Na atom can be sure of escaping. When sodium bromide
is studied by these methods, the sodium atom escapes after
about one swing, showing that an Na atom can escape more
readily from a Br atom than from an I atom.