  Based on the trajectories of the separation between water molecule pairs from
MD simulations, we investigate the bond breakage dynamics in bulk water. From
the spectrum of mean first-passage times, the Fokker-Planck equation allows us
to derive the diffusivity profile along the separation coordinate and thus to
unambiguously disentangle the effects of free-energy and local friction on the
separation kinetics. For tightly coordinated water the friction is six times
higher than in bulk, which can be interpreted in terms of a dominant reaction
path that involves additional orthogonal coordinates.
