近日，美国SLAC国家加速器实验室的James P. Cryan&Agostino Marinelli及其研究团队取得一项新进展。经过不懈努力，他们对X射线分子电离的阿秒延迟进行研究。相关研究成果已于2024年8月21日在国际权威学术期刊《自然》上发表。

该研究团队报道了对核心级电子X射线光发射延迟的测量结果，其延迟意外地大，在氧K壳层阈值附近的NO中，延迟时间长达700阿秒。这些测量利用了自由电子激光器产生的阿秒级软X射线脉冲，扫描了整个K壳层阈值附近的区域。

此外，研究人员发现延迟谱受到了丰富的调制，这表明存在多种影响因素，包括由于形状共振导致的光电子瞬态捕获、与在分子快速非辐射弛豫过程中发射的俄歇电子发生碰撞，以及多电子散射效应。研究结果表明，在全面的理论模型支持下，X射线阿秒实验能够揭示核心级光电离的复杂相关动力学。

据悉，光电效应并非真正瞬时发生，而是存在可揭示复杂分子动力学的阿秒级延迟。亚飞秒持续时间的光脉冲提供了解决光电离动力学所需的工具。因此，过去十年中，关于极端紫外光子单光子吸收后的光电离延迟，已经产生了大量的研究成果。然而，时间分辨的核心级光电离测量仍然无法实现。阿秒级台式光源无法提供核心级光电离所需的X射线光子能量。

附：英文原文

Title: Attosecond delays in X-ray molecular ionization

Author: Driver, Taran, Mountney, Miles, Wang, Jun, Ortmann, Lisa, Al-Haddad, Andre, Berrah, Nora, Bostedt, Christoph, Champenois, Elio G., DiMauro, Louis F., Duris, Joseph, Garratt, Douglas, Glownia, James M., Guo, Zhaoheng, Haxton, Daniel, Isele, Erik, Ivanov, Igor, Ji, Jiabao, Kamalov, Andrei, Li, Siqi, Lin, Ming-Fu, Marangos, Jon P., Obaid, Razib, ONeal, Jordan T., Rosenberger, Philipp, Shivaram, Niranjan H., Wang, Anna L., Walter, Peter, Wolf, Thomas J. A., Wrner, Hans Jakob, Zhang, Zhen, Bucksbaum, Philip H., Kling, Matthias F., Landsman, Alexandra S., Lucchese, Robert R., Emmanouilidou, Agapi, Marinelli, Agostino, Cryan, James P.

Issue&Volume: 2024-08-21

Abstract: The photoelectric effect is not truly instantaneous but exhibits attosecond delays that can reveal complex molecular dynamics. Sub-femtosecond-duration light pulses provide the requisite tools to resolve the dynamics of photoionization. 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 700as 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.

DOI: 10.1038/s41586-024-07771-9

Source: https://www.nature.com/articles/s41586-024-07771-9