Dissociative electron attachment to gas-phase 5-bromouracil

We report measurements of dissociative electron attachment (DEA) to gaseous 5-bromouracil (BrU) for incident electron energies between 0 and 16 eV. Low energy electron impact on BrU leads not only to the formation of a long lived parent anion BrU−, but also various anion fragments resulting from endo- and exo-cyclic bond ruptures, such as Br−, uracil-yl anions, i.e., (U-yl)−, OCN−, and a 68 amu anion tentatively attributed to H2C3NO−. The incident electron energy dependent signatures of either the Br− and (U-yl)− yields (at 0, 1.4, and 6 eV), or the OCN− and H2C3NO− yields (at 1.6 and 5.0 eV) suggests competing DEA channels for anion fragment formation. The production cross sections, at 0 eV incident electron energy, for BrU−, Br−, and (U-yl)− are estimated to be about 6×10−15, 6×10−14, and 1.0×10−15 cm2, respectively.