Ultrafast photo-ion probing of the relaxation dynamics in 2-thiouracil

TL;DR

This study uses ultrafast UV/UV pump-probe spectroscopy and VUV photoionization to investigate the relaxation dynamics and ionization channels of 2-thiouracil after UV excitation, revealing multiple decay processes and ionization mechanisms.

Contribution

It provides new insights into the ultrafast relaxation pathways and ionization channels of 2-thiouracil, combining pump-probe spectroscopy with synchrotron VUV studies.

Findings

Fragments appear via multi-photon processes at >11 eV

Observed decay times include sub-370 fs, 300-450 fs, and 220-400 ps

Results support the S2 -> S1 -> Triplet -> Ground decay pathway

Abstract

In this work we investigate the relaxation processes of 2-thiouracil after UV photoexcitation to the S2 state through the use of ultrafast, single-color, pump-probe UV/UV spectroscopy. We place focus on investigating the appearance and subsequent decay signals of ionized fragments. We complement this with VUV-induced disso-ciative photoionization studies collected at a synchrotron, allowing us to better understand and assign the ion-isation channels involved in the appearance of the fragments. We find that all fragments appear when single photons with energy > 11 eV are used in the VUV experiments and hence appear through 3+ photon-order processes when 266 nm light is used the UV/UV experiment. We also observe three major decays for the frag-ment ions: a sub-autocorrelation decay (i.e. sub-370 fs), a secondary ultrafast decay on the order of 300-450 fs, and a long decay on the order of 220 to 400 ps (all fragment dependent). These decays agree well with the previously established S2 -> S1 -> Triplet -> Ground decay process. Results from the VUV study also suggest that some of the fragments may be created by dynamics occurring on the excited cationic state. Keywords: thiouracil; uracil; pump-probe spectroscopy; ultrafast