Interplay of Open-Shell Spin-Coupling and Jahn-Teller Distortion in Benzene Radical Cation Probed by X-ray Spectroscopy

Marta L. Vidal, Michael Epshtein, Valeriu Scutelnic, Zheyue Yang, Tian Xue, Stephen R. Leone, Anna I. Krylov, Sonia Coriani

Research output: Contribution to journalArticlepeer-review

34 Scopus citations

Abstract

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 http://dx.doi.org/10.1021/acs.jpca.0c08736]. We show that the 1sC → πtransition 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.

Original languageEnglish
Pages (from-to)9532-9541
Number of pages10
JournalJournal of Physical Chemistry A
Volume124
Issue number46
DOIs
StatePublished - 19 Nov 2020
Externally publishedYes

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

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