Long-lived parent negative ions formed via nuclear-excited Feshbach resonances. Part 2.—Aromatic molecules other than benzene derivatives and non-aromatic organic structures

Abstract

Long-lived parent negative ions formed via nuclear-excited Feshbach resonances at thermal energies have been observed for 1-naphthaldehyde, 2-naphthaldehyde, benzoin, tetracyanoethylene, pentane-2,3-dione, acrolein, and acetic, adipic and malonic acids. The autodetachment lifetimes of these ions at thermal electron energies as determined by the slope method using a time-of-flight mass spectrometer are 15 ± 0.5, 7.6 ± 0.3, 10 ± 0.5, ∼60, 7 ± 0.3, 38 ± 3, 326 ± 30, 30 ± 3, and > 1 µs, respectively. The organic molecules benzil and quinoline formed long-lived parent negative ions whose autodetachment lifetimes at the peak of the negative ion resonances are 26 and 632 ± 74 µs, respectively, but for these two molecules the negative ion resonances peak at 0.7 and 0.6 eV, respectively, rather than at ∼0.0 eV. The autodetachment lifetimes of the benzil and tetracyanoethylene parent negative ions decrease with increasing electron energy. The measured lifetimes, as well as those reported by others on long-lived parent negative ions of organic molecules other than benzene derivatives, are summarized, discussed, and related to the respective molecular structures. From these data and those presented in Part 1, it can be concluded that NO₂-containing benzene derivatives, CN-substituted organic molecules, higher aromatic hydrocarbons, strained structures, and organic molecules containing the functional groups —COCO—, —COCH(OH)—, —COOH, and CHCHO, capture thermal electrons and form long-lived parent negative ions via nuclear-excited Feshbach resonances.