Dissociative Electron Attachment to H$_2$O and H$_2$S

Dissociative electron attachment (DA) to H$_2$O is of direct importance for both biological and techological systems. The calculations on H$_2$O and H$_2$S presented comprise the first \textit{ab initio} treatment of DA to a polyatomic molecule employing the full dimensionality of nuclear motion. Cross sections obtained for DA via the $^2$B$_1$ state of H$_2$O agree well with experiment, reproducing the high degree of vibrational excitation of the OH fragment. Several interesting features of the $A'$ manifold of resonances for H$_2$O have been discovered, including a conical intersection between the $^2$A$_1$ and $^2$B$_2$ Feshbach resonances and a branch-point degeneracy between the $^2$B$_2$ shape and Feshbach resonances. This latter feature has no analogue in bound-state theory. We show results of recent calculations on the Renner-Teller coupled $^2$A$_1$ and $^2$B$_1$ surfaces, and on electronically coupled diabatic $^2$A$_1$ and $^2$B$_2$ surfaces. The angular dependence of the H$^-$ + OH channel for the $^2$B$_1$ state of H$_2$O and that of the analagous channel and state of H$_2$S have been calculated by incorporating the mixing of different partial waves into the entrance amplitude, and for H$_2$S, the variation of this mixing with geometry.