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The present work combines experiment and theory to reveal the behavior of bromo-substituted-biphenyls after an electron attachment. We experimentally determine anion lifetimes using an electron attachment–magnetic sector mass spectrometer instrument. Branching ratios of dissociative electron attachment fragments on longer timescales are determined using the electron attachment–quadrupole mass spectrometer instrument. In all cases, fragmentation is low: Only the Br− and [M–Br]− ions are detected, and [M–H]− is observed only in the case of 4-Br-biphenyl and parent anion lifetimes as long as 165 µs are observed. Such lifetimes are contradictory to the dissociation rates of 2- and 4-bromobiphenyl, as measured by the pulse radiolysis method to be 3.2 × 1010 and >5 × 1010 s−1, respectively. The discrepancy is plausibly explained by our calculation of the potential energy surface of the dissociating anion. Isolated in vacuum, the bromide anion can orbit the polarized aromatic radical at a long distance. A series of local minima on the potential energy surface allows for a roaming mechanism prolonging the detection time of such weakly bound complex anions. The present results illuminate the behavior recently observed in a series of bromo-substituted compounds of biological as well as technological relevance. [ABSTRACT FROM AUTHOR]

The electron-induced reactivity of 5-(4-chlorophenyl)-1H-tetrazole and 5-chloro-1-phenyl-1H-tetrazole was studied using a trochoidal electron monochromator quadrupole mass spectrometer experimental setup. 5-(4-chlorophenyl)-1H-tetrazole underwent dissociative electron attachment to form Cl−, [M–HCl]−, and [M–H]−. 5-chloro-1-phenyl-1H-tetrazole underwent associative electron attachment to form the parent anion and dissociative electron attachment to form Cl−, CN2Cl−, [M–N2–Cl]−, and [M–HCl]−. For each anion product, the ion yield was measured as a function of incident electron energy. Density functional theory calculations were performed to support the experimental results with estimates of the energetic thresholds for the different reaction pathways. While the tetrazole group is susceptible to electron-induced ring opening in both molecules, this process was only observed for 5-chloro-1-phenyl-1H-tetrazole, indicating that this process is influenced by the structure of the molecule. [ABSTRACT FROM AUTHOR]