Resonance electron attachment and long-lived negative ions of phthalimide and pyromellitic diimide

Resonance attachment of low energy (0-15 eV) electrons to imide-containing molecules, phthalimide (PTI) and pyromellitic diimide (PMDI), was investigated in the gas-phase by means of Electron Transmission Spectroscopy (ETS) and Dissociative Electron Attachment Spectroscopy (DEAS). Among a variety of low intensity negatively charged fragments formed by DEA, in both compounds the dominant species was found to be a long-lived (μs) parent molecular anion formed at zero energy. In addition, in PMDI long-lived molecular anions were also observed at 0.85 and 2.0 eV. The experimentally evaluated detachment times from the molecular anions as a function of incident electron energy are modeled with a simple computational approach based on the RRKM theory. The occurrence of radiationless transitions to the ground anion state, followed by internal vibrational relaxation, is believed to be a plausible mechanism to explain the exceptionally long lifetime of the PMDI molecular anions formed above zero energy.