The past two decades have seen rapid developments in short-pulse X-ray sources, which have enabled the study of nuclear and electronic dynamics by ultrafast X-ray spectroscopies with unprecedented time resolution ranging from nanoseconds to attoseconds. In this Perspective, we discuss some of the major achievements in the study of nuclear and electronic dynamics with X-ray pulses produced by high-harmonic, free-electron-laser and synchrotron sources. The particular dynamic processes probed by X-ray radiation highlighted in this Perspective are electronic coherences on attosecond to femtosecond timescales, chemical reactions, such as dissociations, and pericyclic ring-openings, spin-crossover dynamics, ligand-exchange dynamics and structural deformations in excited states. X-ray spectroscopic probing of chemical dynamics holds great promise for the future owing to the ongoing developments of new spectroscopies, such as four-wave mixing, and the continuous improvements in emerging laboratory-based, high-harmonic sources and large-scale, facility-based, free-electron lasers.

在过去的二十年中，短脉冲X射线源得到了飞速发展，这使超快X射线光谱学能够以毫微秒的时间分辨率（从纳秒到十亿分之一秒）来研究核和电子动力学。在本《观点》中，我们讨论了在由高谐波，自由电子激光和同步加速器源产生的X射线脉冲研究核和电子动力学方面的一些主要成就。本透视图中突出显示的由X射线辐射探测到的特定动力学过程是：在十亿分之一秒至飞秒时间尺度上的电子相干性，化学反应（例如解离和周环开环），自旋交叉动力学，配体交换动力学和激发时的结构变形状态。