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X-Ray Transient Absorption Reveals the 1Au (Nπ*) State of Pyrazine in Electronic Relaxation

submitted on 04.02.2021, 19:53 and posted on 05.02.2021, 12:53 by Valeriu Scutelnic, Shota Tsuru, Mátyás Imre Pápai, Zheyue Yang, Michael Epshtein, Tian Xue, Eric Haugen, Yuki Kobayashi, Anna Krylov, Klaus Braagaard Møller, Sonia Coriani, Stephen Leone
Electronic relaxation in organic chromophores often proceeds via states not directly accessible by photoexcitation. We report on the photoinduced dynamics of pyrazine that involves such states, excited by a 267 nm laser and probed with X-ray transient absorption spectroscopy in a table-top setup. In addition to the previously characterized 1B2u (ππ*) (S2) and 1B3u (nπ*) (S1) states, the participation of the optically dark 1Au (nπ*) state is assigned by a combination of experimental X-ray core-to-valence spectroscopy, electronic structure calculations, nonadiabatic dynamics simulations, and X-ray spectral computation. Despite 1Au (nπ*) and 1B3u (nπ*) states having similar energies at relaxed geometry, their X-ray absorption spectra differ largely in transition energy and oscillator strength. The 1Au (nπ*) state is populated about 200 femtoseconds after electronic excitation and plays a key role in the relaxation of pyrazine to the ground state.


V.S., M.E., T.X., E.H., Z.Y. 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).

S.T. - European Union's Horizon 2020 research and innovation program under the Marie Skłodowska-Curie Grant Agreement No. 713683 (COFUNDfellowsDTU).

S.C., M.P. and K.B.M. - Danish Council for Independent Research (now Independent Research Fund Denmark), Grant Nos. 7014-00258B (S.C.), 4002-00272 (M.P., K.B.M.), 014-00258B (M.P., K.B.M.), and 8021-00347B(M.P., K.B.M.).

A.I.K. - U.S. National Science Foundation (No. CHE-1856342).


Email Address of Submitting Author


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


United States

ORCID For Submitting Author


Declaration of Conflict of Interest

The authors declare the following competing financial interest: A.I.K. is the president and a part owner of Q-Chem, Inc.