We report the results of {\em ab initio} calculations on dissociative electron attachment (DEA) to water that demonstrate the importance of including three-body breakup in the dissociation dynamics. While three-body breakup is ubiquitous in the analogous process of dissociative recombination, its importance in low-energy dissociative electron attachment to a polyatomic target has not previously been quantified. Our calculations, along with our earlier studies of DEA into two-body channels, indicate that three-body breakup is a major component of the observed O- cross section. The local complex potential model provides a generally accurate picture of the experimentally observed features in this system, reproducing some quantitatively, others qualitatively, and one not at all.

The angular dependence of dissociative electron attachment (DEA) to polyatomic targets is formulated in the local complex potential model, under the assumption that the axial recoil approximation describes the dissociation dynamics. An additional approximation, which is found to be valid in the case of H2O but not in the case of H2S, makes it possible to describe the angular dependence of DEA solely from an analysis of the fixed-nuclei entrance amplitude, without carrying out nuclear dynamics calculations. For H2S, the final-vibrational-state-specific angular dependence of DEA isobtained by incorporating the variation of the angular dependence of the entrance amplitude with nuclear geometry into the nuclear dynamics. Scattering calculations using the complex Kohn method and, for H2S, full quantum calculations of the nuclear dynamics using the Multi-Configuration Time-Dependent Hartree method, are performed.

The potential energy surfaces corresponding to the long-lived fixed-nuclei electron scatering resonances of H$_2$O relevant to the dissociative electron attachment process are examined using a combination of ab initio scattering and bound-state calculations. These surfaces have a rich topology, characterized by three main features: a conical intersection between the $^2A_1$ and $^2B_2$ Feshbach resonance states; charge-transfer behavior in the OH ($^2\Pi$) + H$^-$ asymptote of the $^2B_1$ and $^2A_1$ resonances; and an inherent double-valuedness of the surface for the $^2B_2$ state the C$_2v$ geometry, arising from a branch-point degeneracy with a $^2B_2$ shape resonance. In total, eight individual seams of degeneracy among these resonances are located.