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The photoelectron (PE) spectra of C6F5X– (X = Cl, Br, I) and computational results on the anions and neutrals are presented and compared to previously reported results on C6F6– [McGee, C. J. J. Phys. Chem. A 2023, 127, 8556–8565.]. The spectra all exhibit broad, vibrationally unresolved detachment transitions, indicating that the equilibrium structures of the anions are significantly different from the neutrals. The PE spectrum of C6F5Cl– exhibits a parallel photoelectron angular distribution (PAD), similar to that of the previously reported C6F6– spectrum, while the PE spectra of C6F5Br– and C6F5I– have isotropic PADs, and also exhibit a prominent X– PE feature due to photodissociation of C6F5X– resulting in X– formation. Identification of the C6F5X– detachment transition origins, which is equivalent to the neutral electron affinity (EA), in all three cases is difficult, since the broadness of the detachment feature is accompanied by vanishingly small detachment cross section near the origin. Upper limits on the EAs were determined to be 1.70 eV for C6F5Cl, 2.10 eV for C6F5Br, and 2.00 eV for C6F5I, all significantly higher than the 0.76 eV upper limit determined for C6F6 with the same experiment. The broad detachment transitions are consistent with computational results, which predict very large differences between the neutral and anionic C–X (X = Cl, Br, I) bond lengths. Based on differences between the MBIS atom charges in the anions and neutrals, the excess charge in the anion is on the unique C atom and X, in contrast to the nonplanar C2v structured C6F6– anion, for which the charge is delocalized over the molecule. In C6F5Cl–, the C–Cl bond is predicted to be bent out of the plane, while both C6F5Br– and C6F5I– are predicted to be planar on average. The impact of the interruption of the symmetry in the hexafluorobenzene neutral and anion on the molecular and electronic structure of C6F5X/C6F5X– is considered, as well as the possible dissociative state leading to X– (X = Br, I) formation, and the nature of the C–X bond.
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Photoelectron Imaging Spectroscopy of C 6 Cl x F 6–x – ( x = 2, 3, 5) and C 2 Cl 4 – Anions: Charge Localization or Delocalization─That Is the Question
- Award ID(s):
- 2053889
- PAR ID:
- 10701765
- Publisher / Repository:
- American Chemical Society
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry A
- Volume:
- 130
- Issue:
- 9
- ISSN:
- 1089-5639
- Page Range / eLocation ID:
- 1837 to 1850
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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