A central motivation for the development of x-ray free-electron lasers has been the prospect of time-resolved single-molecule imaging with atomic resolution. Here, we show that x-ray photoelectron diffraction—where a photoelectron emitted after x-ray absorption illuminates the molecular structure from within—can be used to image the increase of the internuclear distance during the x-ray-induced fragmentation of an ${\mathrm{O}}_2$ molecule. By measuring the molecular-frame photoelectron emission patterns for a two-photon sequential $K$-shell ionization in coincidence with the fragment ions, and by sorting the data as a function of the measured kinetic energy release, we can resolve the elongation of the molecular bond by approximately 1.2 a.u. within the duration of the x-ray pulse. The experiment paves the road toward time-resolved pump-probe photoelectron diffraction imaging at high-repetition-rate x-ray free-electron lasers.

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使用X射线自由电子激光的分子破裂的光电子衍射成像

开发X射线自由电子激光器的主要动机是具有原子分辨率的时间分辨单分子成像的前景。在这里，我们证明了x射线光电子衍射（其中x射线吸收后发出的光电子从内部照亮了分子结构）可用于成像在x射线诱导的分子碎裂过程中核间距的增加。${\mathrm{Ø}}_2$分子。通过测量两个光子顺序的分子框架光电子发射图$ķ$-壳电离与碎片离子同时发生，并通过将数据作为测得的动能释放的函数进行排序，我们可以在X射线脉冲持续时间内将分子键的伸长解析为约1.2 au。该实验为在高重复率X射线自由电子激光器上实现时间分辨泵浦探测光电子衍射成像铺平了道路。