Transient Resonant Auger-Meitner Spectra of Photoexcited Thymine

TL;DR

This study uses resonant Auger-Meitner spectroscopy to investigate the excited state dynamics of thymine, revealing internal conversion, intersystem crossing, and new spectral signatures of excited states with high temporal and spectral resolution.

Contribution

First application of resonant Auger-Meitner spectroscopy to thymine, providing detailed insights into excited state dynamics and identifying new spectral signatures of excited states.

Findings

Resolved Auger-Meitner spectra for excited and ground states.

Observed intersystem crossing from nπ* to triplet states.

Identified spectral signatures of initially excited ππ* singlet state.

Abstract

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.