Lever Fabiano, Picconi David, Mayer Dennis, Ališauskas Skirmantas, Calegari Francesca, Düsterer Stefan, Feifel Raimund, Kuhlmann Marion, Mazza Tommaso, Metje Jan, Robinson Matthew S, Squibb Richard J, Trabattoni Andrea, Ware Matthew, Saalfrank Peter, Wolf Thomas J A, Gühr Markus
Deutsches Elektronen-Synchrotron DESY, Hamburg, 22607, Germany.
Heinrich-Heine University, Düsseldorf, 40225, Germany.
J Phys Chem Lett. 2025 Apr 24;16(16):4038-4046. doi: 10.1021/acs.jpclett.5c00544. Epub 2025 Apr 15.
The photophysics of nucleobases has been the subject of both theoretical and experimental studies over the past decades due to the challenges posed by resolving the steps of their radiationless relaxation dynamics, which cannot be described in the framework of the Born-Oppenheimer approximation (BOA). In this context, the ultrafast dynamics of 2-thiouracil has been investigated with a time-resolved NEXAFS study at the Free Electron Laser FLASH. Near Edge X-ray Absorption Fine Structure spectroscopy (NEXAFS) can be used to observe electronic transitions in ultrafast molecular relaxation. We performed time-resolved UV-pump/X-ray probe absorption measurements at the sulfur 2 (L1) and 2 (L2/3) edges. We are able to identify absorption features corresponding to the S2 () and S1 () electronic states. We observe a delay of 102 ± 11 fs in the population of the state with respect to the initial optical excitation and interpret the delay as the time scale for the S2 → S1 internal conversion. We furthermore identify oscillations in the absorption signal that match a similar observation in our previous X-ray photoelectron spectroscopy study on the same molecule.
在过去几十年里，由于解决核碱基无辐射弛豫动力学步骤所带来的挑战，而这无法在玻恩 - 奥本海默近似（BOA）框架内描述，其光物理一直是理论和实验研究的主题。在此背景下，利用自由电子激光FLASH的时间分辨近边X射线吸收精细结构（NEXAFS）研究了2 - 硫尿嘧啶的超快动力学。近边X射线吸收精细结构光谱（NEXAFS）可用于观察超快分子弛豫中的电子跃迁。我们在硫的2（L1）和2（L2 / 3）边缘进行了时间分辨紫外泵浦/ X射线探测吸收测量。我们能够识别出对应于S2（）和S1（）电子态的吸收特征。我们观察到相对于初始光激发，态的布居延迟为102±11 fs，并将该延迟解释为S2→S1内转换的时间尺度。此外，我们还识别出吸收信号中的振荡，这与我们之前对同一分子的X射线光电子能谱研究中的类似观察结果相符。
