Probing the Potential Energy Surfaces of BrCN^- by Dissociative Electron Attachment

State coupling certainly determines the topologic features of the molecular potential energy surface (PES) and potentially diversifies chemical reaction pathways. Here we report the new PESs of BrCN^- in the low-lying electronic states that are distinctly different from the previous predictions in the short Br-CN bond region but validated by the high-resolution ion velocity imaging measurements of low-energy dissociative electron attachment (DEA) to BrCN. Besides the vibrating CN^- ions produced in the fast Br-CN bond stretching motions, we confirm that the ro-vibrating CN^- ions with a nearly isotropic angular distribution are produced by receiving a torque in the combinational motion of Br-CN bond bending and stretching. The latter process is closely related to the potential well of BrCN^- at the first excited state A²Π_3/2 that arises from the Π-Σ state couplings. Our findings not only suggest that the PESs of other anionic cyanogen halides are in dire need of reexamination but also show that ion velocity imaging of the DEA process is a powerful experimental method for evaluating the theoretical PESs of molecular anions.