Stabilization, fragmentation and rearrangement reactions in low-energy electron interaction with tetrafluoro-para-benzoquinone: a combined theoretical and experimental study

Abstract

Quinones are a class of organic compounds whose extraordinary electron transfer properties are fundamental in ubiquitous processes such as the ATP production and the photosynthesis. Here, we report a combined theoretical and experimental study to shed some light on low-energy electron interaction with tetrafluoro-para-benzoquinone (TFQ) and para-benzoquinone (p-BQ). Similar to it's native counterpart; p-BQ, TFQ forms a metastable molecular anion at unusually high incident energies in electron attachment under single collision conditions. Transition state calculations are used for both p-BQ and TFQ to explore possible stabilization of the molecular anion through isomerization reactions, and stabilization through intramolecular vibrational energy redistribution (IVR) is discussed in relation to the electronic structure of these compounds. We also report exceptionally extensive and complex rearrangement reactions in dissociative electron attachment to TFQ and discuss possible reaction paths based on thermochemical threshold calculations. The observed fragmentation reactions can at large be described by two dissociation series, i.e., the formation of [TFQ − CO − nF]⁻ (n = 0, 1, 2 or 3) and [TFQ − 2CO − nF]⁻ (n = 0, 1, 2, 3 or 4). In the latter series we observe, at incident electron energy as low as ∼0.5 eV, the excision of two CO molecules followed by recombination of the remaining moiety to form an anionic carbon chain with two terminal CF₂ groups. To our knowledge such excision of two non-adjacent carbon atoms and recombination of the remaining moiety have not been observed before in low energy electron attachment.