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Interplay of open-shell spin-coupling and Jahn–Teller distortion in benzene radical cation probed by X-ray spectroscopy

Vidal, Marta L., Epshtein, Michael, Scutelnic, Valeriu, Yang, Zheyue, Xue, Tian, Leone, Stephen R., Krylov, Anna I. and Coriani, Sonia 2020. Interplay of open-shell spin-coupling and Jahn–Teller distortion in benzene radical cation probed by X-ray spectroscopy. The Journal of Physical Chemistry A 124 (46) , pp. 9532-9541. 10.1021/acs.jpca.0c08732

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We report a theoretical investigation and elucidation of the X-ray absorption spectra of neutral benzene and of the benzene cation. The generation of the cation by multiphoton ultraviolet (UV) ionization and the measurement of the carbon K-edge spectra of both species using a table-top high-harmonic generation source are described in the companion experimental paper [Epshtein, M.; et al. J. Phys. Chem. A]. We show that the 1sC → π transition serves as a sensitive signature of the transient cation formation, as it occurs outside of the spectral window of the parent neutral species. Moreover, the presence of the unpaired (spectator) electron in the π-subshell of the cation and the high symmetry of the system result in significant differences relative to neutral benzene in the spectral features associated with the 1sC → π* transitions. High-level calculations using equation-of-motion coupled-cluster theory provide the interpretation of the experimental spectra and insight into the electronic structure of benzene and its cation. The prominent split structure of the 1sC → π* band of the cation is attributed to the interplay between the coupling of the core → π* excitation with the unpaired electron in the π-subshell and the Jahn–Teller distortion. The calculations attribute most of the splitting (∼1–1.2 eV) to the spin coupling, which is visible already at the Franck–Condon structure, and we estimate the additional splitting due to structural relaxation to be around ∼0.1–0.2 eV. These results suggest that X-ray absorption with increased resolution might be able to disentangle electronic and structural aspects of the Jahn–Teller effect in the benzene cation.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Chemistry
Publisher: American Chemical Society
ISSN: 1089-5639
Last Modified: 27 Sep 2022 01:07

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