We present the first investigation of excited state dynamics by resonant Auger-Meitner spectroscopy (also known as resonant Auger spectroscopy) using the nucleobase thymine as an example. Thymine is photoexcited in the UV and probed with X-ray photon energies at and below the oxygen K-edge. After initial photoexcitation to a {pi}{pi}* excited state, thymine is known to undergo internal conversion to an n{pi}* excited state with a strong resonance at the oxygen K-edge, red-shifted from the ground state {pi}* resonances of thymine (see our previous study Wolf et al., Nat. Commun., 2017, 8, 29). We resolve and compare the Auger-Meitner electron spectra associated both with the excited state and ground state resonances, and distinguish participator and spectator decay contributions. Furthermore, we observe simultaneously with the decay of the n{pi}* state signatures the appearance of additional resonant Auger-Meitner contributions at photon energies between the n{pi}* state and the ground state resonances. We assign these contributions to population transfer from the n{pi}* state to a {pi}{pi}* triplet state via intersystem crossing on the picosecond timescale based on simulations of the X-ray absorption spectra in the vibrationally hot triplet state. Moreover, we identify signatures from the initially excited {pi}{pi}* singlet state which we have not observed in our previous study.
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