Mechanisms of Dissociative Electron Attachment to CO$_2$ and NH$_3$

Recent experiments at LBNL on the angular dependence of dissociative electron attachment (DEA) to CO$_2$ and NH$_3$ have raised new questions about the mechanism of DEA in both cases. In the case of CO$_2$, for attachment via the shape resonance at 4 eV, the angular distribution of O$^-$ is peaked along the axis of the incident direction of the electron, even though the resonance through which the electron is attached is of $^2\Pi$ symmetry. We present an explanation based on both the attachment amplitude from \textit{ab initio} complex Kohn scattering calculations and the identification of two conical intersections, one involving a $\Sigma/\Pi$ intersection, that may both be involved in the surprisingly complicated mechanism for this low energy DEA process. In NH$_3$, complex Kohn scattering calculations identify the $^2$A$'$ Feshbach resonance near 5 eV that produces both H$^-$ and NH$_2^-$ fragments in the experiment, also involving at least one conical intersection.