Photoelectron Imaging Spectroscopy of C₆Cl_xF_6-x^- (x = 2, 3, 5) and C₂Cl₄^- Anions: Charge Localization or...

New photoelectron (PE) spectra of C₆Cl_xF_6-x^- (x = 2, 3, 5) are presented and compared with previously reported PE spectra of C₆F₆^- and C₆ClF₅^-, along with the known properties of C₆Cl₆^-. Based on a recent theoretical study [J. Phys. Chem. A 2024, 128, 8072-8079], anions of the mixed perchlorofluorobenzenes have competing molecular and electronic structures: one in which the electron is localized in a single C-Cl σ* orbital, resulting in a structure with a uniquely elongated C-Cl bond, and the other in which the excess charge is more delocalized, resulting in a more symmetric anion. In all cases, the experimental PE spectra are consistent with the former, with the exception of C₆Cl₅F^-, the spectrum of which is not consistent with calculations on either structure. The adiabatic electron affinities of the neutrals are difficult to ascertain from the anion PE spectra because of vanishingly small signal near the origin. However, the vertical detachment energies are determined to be 3.20(10) eV for C₆Cl₂F₄^-, 3.09(5) eV for C₆Cl₃F₃^-, and 1.85(10) eV for C₆Cl₅F^-. The VDEs of C₆Cl₂F₄^- and C₆Cl₃F₃^- are similar to the previously reported VDE of C₆ClF₅^-, 2.95 eV [J. Phys. Chem. A 2024, 128, 5646-5658], and significantly higher than the previously reported VDE determined from the PE spectrum of C₆F₆^-, 1.60 eV, measured on the same instrument [J. Phys. Chem. A 2023, 127, 556-8565]. To further benchmark the computational methods and gain insights into the relationship between the anionic structures in which the excess charge is localized in a single C-Cl σ* orbital and the delocalized structure, we measured the PE spectrum C₂Cl₄^-, which exhibited a VDE consistent with the computed structure in which the excess charge is localized in a single C-Cl σ* orbital, and which was the computed lowest energy structure of C₂Cl₄^-. We further explore the relationship between localized and delocalized structures in this molecular anion and C₆Cl₅F^-.