Ultrafast dynamics of 2-thiouracil investigated by time-resolved Auger spectroscopy

Abstract

We present time-resolved ultraviolet-pump x-ray probe Auger spectra of 2-thiouracil. An ultraviolet induced shift towards higher kinetic energies is observed in the sulfur 2p Auger decay. The difference Auger spectra of pumped and unpumped molecules exhibit ultrafast dynamics in the shift amplitude, in which three phases can be recognized. In the first 100 fs, a shift towards higher kinetic energies is observed, followed by a 400 fs shift back to lower kinetic energies and a 1 ps shift again to higher kinetic energies. We use a simple Coulomb-model, aided by quantum chemical calculations of potential energy states, to deduce a C-S bond expansion within the first 100 fs. The bond elongation triggers internal conversion from the photoexcited S2 to the S1 state. Based on timescales, the subsequent dynamics can be interpreted in terms of S1 nuclear relaxation and S1-triplet internal conversion.

Following excited-state chemical shifts in molecular ultrafast x-ray photoelectron spectroscopy

“…The experiment was performed at the FL24 beamline of the FLASH2 facility at DESY using the newly built URSA-PQ apparatus. A detailed description of the apparatus and the experiment can be found elsewhere 48 , 49 . In short, the apparatus includes a magnetic bottle time-of-flight electron spectrometer (MBES), a capillary oven to evaporate the 2-thiouracil samples at 150 °C and a paddle with beam diagnostics on top of the oven.…”

Data analysis procedures for time-resolved x-ray photoelectron spectroscopy at a SASE free-electron-laser

“…The data for this publication was collected during a FLASH2 beamtime in 2019. The 2-tUra sample was studied by means of time-resolved UV pump x-ray probe photoelectron spectroscopy using the URSA-PQ apparatus [6,39,40]. The molecule was excited with 269 nm light and probed with a delayed x-ray pulse with a photon energy of 272 eV, which is above the sulfur L 1 edge.…”

Core-Level Spectroscopy of 2-Thiouracil at the Sulfur L1- and L2,3-Edges Utilizing a SASE Free-Electron Laser

“…The data were obtained at the FL24 beamline of the FLASH2 free-electron laser (FEL) [37,38] as part of a more extensive investigation of the dynamics following UV excita-tion [20,21]. An instrument containing sample injection and a magnetic bottle-type electron spectrometer (URSA-PQ, German: Ultraschnelle Röntgenspektroskopie zur Abfrage der Photoenergiekonversion in Quantensystemen, English: Ultrafast X-ray spectroscopy for probing photoenergy conversion in quantum systems)-designed and built by the group at University of Potsdam-was connected to the beamline [25].…”

“…This particular advantage has been used to examine the 1 nπ* channel via UV-pump X-ray probe studies on thymine [18,19]. For 2-tUra, we used the sulfur L-edges to probe the local dynamics at the C-S bond using time-resolved Auger-Meitner spectroscopy [20]. In addition, we could attribute electronic states using the excited-state chemical shift (ESCS) resulting from the local charge at the sulfur atom probed in time-resolved X-ray photoelectron studies [21].…”