Isomer-Dependent Electron Affinities of Fluorophenyl Radicals, •C6H5-xFx (2 ≤ x ≤ 4).

Di-, tri-, and tetrafluorophenyl radicals each have three regioisomers, several of which can form multiple distinct radical structures. We present the photoelectron spectra of the di-, tri-, and tetrafluorophenide regioisomer anions generated from their associated fluorobenzene precursors. By comparing the spectra to the results of density functional theory calculations, we determine that in cases where more than one possible radical isomer is possible for a given regioisomer (radicals formed from 1,2-difluorobenzene, 1,3-difluorobenzene, 1,2,3-trifluorobenzene, and 1,2,4-trifluorobenzene) the most stable anion corresponds to a less stable neutral, suggesting that the reactive C-center on these fluorine-substituted phenyl groups can be controlled by charge state. Full analyses of the spectra and computational results yield further insights into the differences between the electronic and molecular structures of the fluorophenyl radicals and their associated anions.

Anion Photoelectron Imaging Spectroscopy of C6HF5-, C6F6-, and the Absence of C6H2F4.

Substituents have a profound effect on the electronic structure of the benzene molecule. In this paper, we present new photoelectron spectra of the C5HF5- molecular anion, to test predictions [ Int. J. Quant. Chem. 2017, 188, e25504] that pentafluorobenzene has a positive electron affinity, as hexafluorobenzene was already known to have. The PE spectrum of C6HF5- exhibits a broad and vibrationally unresolved band due to significant differences between the structure of the anion and the neutral. The vertical detachment energy (VDE) of C5HF5- is determined to be 1.33 ± 0.05 eV, and the lowest binding energy at which the signal is observed is 0.53 ± 0.05 eV, which, if taken as the electron affinity, is in good agreement with the computed value. In addition, we attempted to generate intact C6H2F4- molecular ions using the 1,2,3,4-tetrafluorobenzene, 1,2,3,5-tetrafluorobenzene, and 1,2,4,5-tetrafluorobenzene precursors, as tetrafluorobenzene was predicted to have a near-zero but marginally positive electron affinity. Using a photoemission anion source, we were not able to produce the intact tetrafluorobenzene anion. Density functional theory calculations support a more detailed discussion of the impact of fluorine substitution on the electronic structure of these species.

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

The electron affinities (EAs) of a series of ·C6H5-xFx (1 ≤ x ≤ 4) fluorophenyl radicals are determined from the photoelectron spectra of their associated fluorophenide anions generated from C6H6-xFx (1 ≤ x ≤ 4) fluorobenzene precursors. The spectra show a near-linear incremental increase in EA of 0.4 eV/x. The spectra exhibit vibrationally unresolved and broad detachment transitions consistent with significant differences in the molecular structures of the anion and neutral radical species. The experimental EAs and broad spectra are consistent with density functional theory calculations on these species. While the anion detachment transitions all involve an electron in a non-bonding orbital, the differences in structure between the neutral and anion are in part due to repulsion between the lone pair on the C-center on which the excess charge is localized and neighboring F atoms. The C6H5-xFx- (2 ≤ x ≤ 4) spectra show features at lower binding energy that appear to be due to constitutional isomers formed in the ion source.

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

Complexes of anion-neutral pairs are prevalent in chemical and physical processes in the interstellar medium, the atmosphere, and biological systems, among others. However, bimolecular anionic species that cannot be described as simple ion-molecule complexes due to their competitive electron affinities have received less attention. In this study, the [O2-M]- (M = glyoxal, methylglyoxal, or biacetyl) anion photoelectron spectra obtained with several different photon energies are reported and interpreted in the context of ab initio calculations. The spectra do not resemble the photoelectron spectra of M- or O2- "solvated" by a neutral partner. Rather, all spectra are dominated by near-threshold autodetachment from what are likely transient dipole bound states of the cis conformers of the complex anions. Very low Franck-Condon overlap between the neutral M·O2 van der Waals clusters and the partial covalently bound complex anions results in low-intensity, broad direct detachment observed in the spectra. The [O2-glyoxal]- spectra measured with 2.88 and 3.495 eV photon energies additionally exhibit features at ∼0.5 eV electron kinetic energy, which is more difficult to explain, though there are numerous quasibound states of the anion that may be involved. Overall, these features point to the inadequacy of describing the complex anions as simple ion-molecule complexes.