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 - + NO 2 (X 2 A 1 ) → NO 2 - → NO (X 2 Π) + O - ( 2 P)]. The long-term puzzling issues about the near-threshold dissociations of NO 2 - are settled. We suggest that three low-lying resonant states ( 1 B 1 , 3 B 1 , and 3 B 2 ) of NO 2 - contribute to the production of O - at attachment energies of <5 eV. Furthermore, B 1 and B 2 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.