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Table-Top X-ray Spectroscopy of Benzene Radical Cation

preprint
submitted on 13.08.2020, 05:03 and posted on 13.08.2020, 09:40 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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