Dissociation Dynamics of Anionic Nitrogen Dioxide in the Low-Lying Resonant States

Experimental studies of the dynamics near the molecular dissociation threshold are frequently frustrated, due to the small cross sections and the demand for identification of close-lying electronic states or nuclear motions with multiple degrees of freedom. Using the high-resolution anion velocity map imaging technique, here we report a dynamics study of the dissociations of anionic nitrogen dioxide in low-lying resonant states formed by electron attachment [e^- + NO₂ (X²A₁) → NO₂^- → NO (X²Π) + O^- (²P)]. The long-term puzzling issues about the near-threshold dissociations of NO₂^- are settled. We suggest that three low-lying resonant states (¹B₁, ³B₁, and ³B₂) of NO₂^- contribute to the production of O^- at attachment energies of <5 eV. Furthermore, B₁ and B₂ symmetries of the resonant states lead to different anisotropies of the O^- angular distribution. At the relatively high electron attachment energies, a prompt fragmentation in the molecular bent conformation competes with an indirect dissociation in the straightened conformation.