Temporary anion states of fluorine substituted benzenes probed by charge transfer in O2−·C6H6−xFx (x = 0–5) ion–molecule complexes

Abstract

The broadband photoelectron source realized by detaching O2−·X (X = neutral unsaturated molecule) complexes offers a unique opportunity to probe temporary anion states of the unsaturated species. Detachment of the ion molecule complex typically accesses a dissociative portion of the neutral potential, creating a continuum electron source that can undergo scattering with X. We present the application of this new approach to electron-neutral scattering toward a study of the series of fluorinated benzenes via photoelectron spectroscopy of O2−·C6H6−xFx (x = 0–6) measured with several photon energies. We compare these spectra to the reference O2−·hexane spectrum and observe evidence of temporary anion states of C6H6−xFx for species with x = 0–5 in the form of enhanced signal intensity at electron kinetic energies coinciding with the energies of the temporary anions. Furthermore, we observe autodetachment features in the x = 3, 5 spectra. Results of calculations on the isolated symmetric isomer of C6H3F3 suggest that the molecule cannot support a weakly-bound non-valence state that could be associated with the observed autodetachment. However, C6HF5− is predicted to support a valence bound state, which, if produced by charge transfer from O2− with sufficient vibrational energy, may undergo autodetachment. Finally, the [O2·C6F6]− spectrum is unique insofar as the spectrum is substantially higher in binding energy and qualitatively different from the x = 0–5 spectra. This result suggests much stronger interactions and charge delocalization between O2− and C6F6.

Trend in the Electron Affinities of Fluorophenyl Radicals ·C6H5-xFx (1 ≤ x ≤ 4)

“…The EA of the phenyl radical from ref is included, along with the origin of signal that is attributed to pentafluorophenide (blue X) in the PE spectrum of C 6 HF 5 – reported in ref . The green circles are the EAs of O 2 – ·C 6 H 6– x F x bimolecular complexes reported in ref . (b) Plot of the difference between the sum of the APT charges on the C atoms in the fluorobenzene backbone, excluding the radical center in the neutral or charge carrier in the anion, and the APT charge on the radical center (neutral, black squares), or the C atom carrying the excess charge (anion, red circles).…”

Probing Anion–Molecule Complexes of Atmospheric Relevance Using Anion Photoelectron Detachment Spectroscopy

“…In and of themselves, ion–molecule complexes (IMCs) have historically inspired active scientific exploration because of their importance in gas-phase reactions and photochemistry, − the properties and dynamics in aqueous electrolytic solutions, − and physical processes in planetary atmospheres. − Negatively charged complexes in particular have proven to be fertile ground for study using mass-selective photodetachment spectroscopies, with fundamental physical insights on the anions and their associated neutrals pouring from the laboratories engaged in these studies. − These species, like cationic IMCs, can accumulate numerous neutral molecules, forming noncovalently bound clusters, a topic explored in a recent review by Sanov …”

Autodetachment over Broad Photon Energy Ranges in the Anion Photoelectron Spectra of [O2–M]− (M = Glyoxal, Methylglyoxal, or Biacetyl) Complex Anions

“…In a related study, evidence of charge transfer to temporary anion states in the O 2 – ·C 6 H 6– x F x (0 ≤ x ≤ 5) IMCs was observed . The anion photoelectron (PE) spectra of these IMCs exhibited significant PE signal enhancements at electron kinetic energies corresponding to the C 6 H 6– x F x – temporary anion states, meaning that a charge transfer to fleeting O 2 ·C 6 H 6– x F x – states was affected via photoexcitation, in competition with direct detachment.…”

“…In a related study, evidence of charge transfer to temporary anion states in the O 2 − •C 6 H 6−x F x (0 ≤ x ≤ 5) IMCs was observed. 20 The anion photoelectron (PE) spectra of these IMCs exhibited significant PE signal enhancements at electron kinetic energies corresponding to the C 6 H 6−x F x − temporary anion states, meaning that a charge transfer to fleeting O 2 • C 6 H 6−x F x − states was affected via photoexcitation, in competition with direct detachment. In addition to the temporary anion states, several of the IMCs exhibited unexpected nonvalence bound anion states, the evidence for which was the distinct vibrational autodetachment signal observed near the zeroelectron kinetic energy limit of the spectra.…”