The photoelectric effect is not truly instantaneous but exhibits attosecond delays that can reveal complex molecular dynamics^{1,2,3,4,5,6,7}. Sub-femtosecond-duration light pulses provide the requisite tools to resolve the dynamics of photoionization^8,9,10,11,12. Accordingly, the past decade has produced a large volume of work on photoionization delays following single-photon absorption of an extreme ultraviolet photon. However, the measurement of time-resolved core-level photoionization remained out of reach. The required X-ray photon energies needed for core-level photoionization were not available with attosecond tabletop sources. Here we report measurements of the X-ray photoemission delay of core-level electrons, with unexpectedly large delays, ranging up to 700 as in NO near the oxygen K-shell threshold. These measurements exploit attosecond soft X-ray pulses from a free-electron laser to scan across the entire region near the K-shell threshold. Furthermore, we find that the delay spectrum is richly modulated, suggesting several contributions, including transient trapping of the photoelectron owing to shape resonances, collisions with the Auger–Meitner electron that is emitted in the rapid non-radiative relaxation of the molecule and multi-electron scattering effects. The results demonstrate how X-ray attosecond experiments, supported by comprehensive theoretical modelling, can unravel the complex correlated dynamics of core-level photoionization.

光电效应并不是真正瞬时的，而是表现出阿秒延迟，可以揭示复杂的分子动力学^{1,2,3,4,5,6,7} 。亚飞秒持续时间的光脉冲提供了解决光电离动力学的必要工具^8,9,10,11,12 。因此，在过去的十年里，人们对极紫外光子的单光子吸收后的光电离延迟进行了大量的工作。然而，时间分辨核心级光电离的测量仍然遥不可及。阿秒桌面源无法提供核心级光电离所需的 X 射线光子能量。在这里，我们报告了核心级电子的 X 射线光电发射延迟的测量结果，延迟范围出乎意料地大，范围高达 700，就像在氧 K 壳层阈值附近的 NO 中一样。这些测量利用自由电子激光器的阿秒软 X 射线脉冲来扫描 K 壳阈值附近的整个区域。此外，我们发现延迟光谱经过丰富的调制，这表明了多种贡献，包括由于形状共振而导致的光电子瞬态俘获、与分子快速非辐射弛豫中发射的俄歇-迈特纳电子的碰撞以及多态性。电子散射效应。结果表明，在综合理论模型的支持下，X 射线阿秒实验如何能够揭示核心级光电离的复杂相关动力学。