Picosecond dynamics initiated by electron photodetachment in Cl-...H2O and Br-...H2O
complexes is explored using classical Wigner trajectories which correctly map 
the initial quantum vibrational state of the systems. The three lowest potential 
energy surfaces of the neutral clusters reached after electron photodetachment are 
constructed by the ab initio Fock-Space Coupled Cluster method and then quantitatively 
fitted to a Diatomics-in-Molecule model which also allows 
for a simple inclusion of spin-orbit interactions. 
Due to large differences between the shapes of the anionic and neutral
potential energy surfaces, and due to the presence of light hydrogen atoms an unusual dynamical
behavior is observed. Although the vertical photodetachment process places the systems above the
dissociation threshold, the clusters do not dissociate directly. Instead, relatively long-lived
vibrational resonances are observed. This is due to a strong excitation of the 
non-dissociative (internal) water rotation and only a weak excitation of the dissociative 
intermolecular stretch upon photodetachment. Implications of the observed 
dynamics for the interpretation of experimental vibrationally resolved ZEKE spectra are discussed.