Negative ion formation by low energy electron attachment to gas-phase 5-nitrouracil

Dissociative electron attachment (DEA) to gas phase 5-nitrouracil (5NU) is studied using a double focusing sector field mass spectrometer and a hemispherical electron monochromator (HEM) combined with a quadrupole mass spectrometer (QMS). Besides the formation of the long-lived parent anion 5NU−, low energy electron impact (<20 eV) leads to a number of anionic fragments. The ion yield for all observed negative ions has been recorded as a function of the incident electron energy. The most dominant negative ion observed was (5NU–NO2)−, which is produced directly in the ion source and also weakly as a product of a metastable decay of 5NU−. These experiments were supported by quantum chemical calculations based on the density functional theory to calculate the electrostatic potential and molecular orbitals.