Unraveling ultrafast molecular processes initiated by energetic radiation provides direct information on the chemical evolution under extreme conditions. A prominent example is interstellar media where complex molecules such as polycyclic aromatic hydrocarbons (PAHs) are excited by energetic photons. Until recently, ultrafast dynamics following such excitations remained largely unexplored due to the lack of relevant technologies. Here, we use time-resolved mass spectrometry combining ultrashort femtosecond XUV and IR pulses, to investigate the dynamics induced by high-energy photon excitation in PAHs. We demonstrate that excited cations relax through a progressive loss of vibrational selectivity, created at the early-stage dynamics, and which represents the first steps of a complete intramolecular vibrational energy redistribution. This process is in competition with the recently revealed correlation-band dynamics. These results might have direct consequences for the development of XUV molecular physics and other fields such as astrochemistry.

中文翻译：

---

XUV激发的多环芳烃分子中的超快振动弛豫动力学

解开由高能辐射引发的超快分子过程提供了极端条件下化学演化的直接信息。一个突出的例子是星际介质，其中多环芳烃 (PAH) 等复杂分子被高能光子激发。直到最近，由于缺乏相关技术，这种激发后的超快动力学仍然在很大程度上未被探索。在这里，我们使用时间分辨质谱结合超短飞秒 XUV 和 IR 脉冲，研究 PAH 中高能光子激发引起的动力学。我们证明了激发的阳离子通过振动选择性的逐渐丧失而松弛，这是在早期动力学中产生的，这代表了完整的分子内振动能量重新分配的第一步。这个过程与最近揭示的相关带动态竞争。这些结果可能对 XUV 分子物理学和其他领域（如天体化学）的发展产生直接影响。