Institut für Physik und Astronomie, Universität Potsdam, 14476, Potsdam, Germany.
Institut für Chemie, Universität Potsdam, 14476, Potsdam, Germany.
Nat Commun. 2022 Jan 11;13(1):198. doi: 10.1038/s41467-021-27908-y.
The conversion of photon energy into other energetic forms in molecules is accompanied by charge moving on ultrafast timescales. We directly observe the charge motion at a specific site in an electronically excited molecule using time-resolved x-ray photoelectron spectroscopy (TR-XPS). We extend the concept of static chemical shift from conventional XPS by the excited-state chemical shift (ESCS), which is connected to the charge in the framework of a potential model. This allows us to invert TR-XPS spectra to the dynamic charge at a specific atom. We demonstrate the power of TR-XPS by using sulphur 2p-core-electron-emission probing to study the UV-excited dynamics of 2-thiouracil. The method allows us to discover that a major part of the population relaxes to the molecular ground state within 220-250 fs. In addition, a 250-fs oscillation, visible in the kinetic energy of the TR-XPS, reveals a coherent exchange of population among electronic states.
光子能量在分子中转化为其他能量形式伴随着电荷在超快时间尺度上的移动。我们使用时间分辨 X 射线光电子能谱（TR-XPS）直接观察电子激发分子中特定位置的电荷运动。我们通过激发态化学位移（ESCS）扩展了传统 XPS 中的静态化学位移的概念，ESCS 将电荷与势模型联系起来。这使我们能够将 TR-XPS 光谱反演到特定原子上的动态电荷。我们通过使用硫 2p 芯电子发射探测来研究 2-硫代尿嘧啶的 UV 激发动力学，展示了 TR-XPS 的强大功能。该方法使我们能够发现大部分分子在 220-250fs 内弛豫到分子基态。此外，在 TR-XPS 的动能中可见的 250fs 振荡揭示了电子态之间的人口相干交换。
