Dissociative electron attachment to p-fluoranil and p-chloranil

The processes of formation and decay of negative molecular ions (NMI) of p-fluoranil [2,3,5,6-tetrafluoro-1,4-benzoquinone (FA)] and p-chloranil [2,3,5,6-tetrachloro-1,4-benzoquinone (CA)] in the gas phase were investigated. In both cases, long-lived NMIs were found in two resonances, at thermal electron energies and in the region of 0.8-0.9 eV, with lifetimes relative to electron ejection of τ_a ∼ 600 µs. The dissociation of molecular NIs with the formation of fragment ions [M-COF₂]^-, [M-CO]-, and Cl^- proceeds at microsecond times, which is confirmed by the registration of the corresponding metastable ions. It is shown that the dependence of the lifetime of MNIs on the electron energy can be explained by the presence of a transition state at an energy of ∼0.5 eV.