Bond Formation and Bond Scission Dynamics in Polyatomic Molecules Revealed by Momentum Imaging Experiments and Electron Scattering Calculations.

We present combined experimental and theoretical studies of dissociative electron attachment (DEA) dynamics in methane and ammonia. DEA in each of these systems proceeds through electronic Feshbach resonances, where a valence electron is excited and captured with the incident electron in the lowest unoccupied orbital. In methane, one triply-degenerate resonance undergoes Jahn-Teller splitting through molecular distortions, leading to four observed final states, each having a 2-body and a 3-body dissociation with anionic products H$^{\mathrm{-}}$ and CH$_{\mathrm{2}}^{\mathrm{-}}$ and neutrals CH$_{\mathrm{3}}$, CH$_{\mathrm{2}}$, H$_{\mathrm{2}}$ or H. In ammonia, one resonance leads to H$^{\mathrm{-}} \quad +$ NH$_{\mathrm{2}}$ and NH$_{\mathrm{2}}^{\mathrm{-}} \quad +$ H, the latter resulting from non-adiabatic charge transfer. A higher energy resonance leads directly to H$^{\mathrm{-}} \quad +$ NH$_{\mathrm{2}}$* and indirectly to NH$_{\mathrm{2}}^{\mathrm{-}} \quad +$ H. We examine the dynamics of the transient anion in each of these processes.