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Table-Top X-ray Spectroscopy of Benzene Radical Cation

preprint
submitted on 13.08.2020 and posted on 13.08.2020 by Michael Epshtein, Valeriu Scutelnic, Zheyue Yang, Tian Xue, Marta L. Vidal, Anna Krylov, Sonia Coriani, Stephen Leone

Ultrafast table-top x-ray spectroscopy at the carbon K-edge is used to measure the x-ray spectral features of benzene radical cations (Bz+). The ground state of the cation is prepared selectively by two-photon ionization of neutral benzene, and the x-ray spectra are probed at early times after the ionization by transient absorption using x-rays produced by high harmonic generation (HHG). Bz+ is well known to undergo Jahn-Teller distortion, leading to a lower symmetry and splitting of the π orbitals. Comparison of the x-ray absorption spectra of the neutral and the cation reveals a splitting of the two degenerate π* orbitals as well as an appearance of a new peak due to excitation to the partially occupied π -subshell. The π* orbital splitting of the cation, elucidated on the basis of high-level calculations in a companion theoretical paper [Vidal et al, submitted to J. Phys. Chem. Lett.; ChemRxiv link: doi XXXXX], is discovered to be due to both the symmetry distortion and even more dominant spin coupling of the unpaired electron in the partially vacant π orbital (from ionization) with the unpaired electrons resulting from the transition from the 1sC core orbital to the fully vacant π* orbitals.


Funding

M.E., V.S., Z.Y., T.X., and S.R.L. - U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences (Contract No. DEAC02- 05CH11231), the gas phase chemical physics program through the Chemical Sciences Division of Lawrence Berkeley National Laboratory.

V.S. - Swiss National Science Foundation (P2ELP2_184414).

A.I.K. - Simons Fellowship in Theoretical Physics and Mildred Dresselhaus Award from CFEL/DESY, which supported her sabbatical stay in Germany.

M.L.V. and S.C. - DTU Chemistry and from the Independent Research Fund Denmark-Natural Sciences, DFF-RP2 grant no. 7014-00258B.

History

Email Address of Submitting Author

michaele@bgu.ac.il

Institution

Department of Chemistry, University of California, Berkeley, CA, 94720, USA

Country

United States

ORCID For Submitting Author

0000-0002-9149-3191

Declaration of Conflict of Interest

Anna Krylov is the President and a part-owner of Q-Chem, Inc.

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