AI 中文总结
研究结合关联成像、少飞秒测量与非绝热模拟，探明重水电离后分子氢形成的三条路径及对应时间，为关联电子激发与化学结果提供通用策略。
AI 中文摘要
从水分子中移除一个电子可促使其两个氢原子配对并以分子氢形式脱离。然而即便是这个基础反应，其完整路径仍未被探明，因为测量手段尚未能同时追踪电子与原子核的运动。结合关联光电子与离子成像、少飞秒泵浦-探测测量以及非绝热模拟，我们追踪了孤立重水（D₂O）分子中该反应的完整路径。反应采取间接路径，沿三条不同路径（直接、漫游和延迟）解离，直接分支和延迟分支的形成时间分别约为34飞秒和72飞秒。但键形成要求分子先打破自身对称性，只有随机不对称运动才能使锥形交叉点处发生电子态切换，在氧-氢键断裂前将两个氢原子结合。这些结果建立了从水中形成分子氢的时间分辨图像，并提供了一种通用策略，用于在从辐射损伤到制氢等场景中关联电子激发与化学结果。
英文摘要
Removing an electron from a water molecule can drive its two hydrogen atoms to pair up and depart as molecular hydrogen. However, even for this elementary reaction, the route from start to finish has remained hidden because measurements have yet to follow the electronic and nuclear motion simultaneously. Combining correlated photoelectron and ion imaging, few-femtosecond pump--probe measurements, and nonadiabatic simulations, we track the complete pathway in isolated heavy water (D$_2$O) molecules. The reaction takes an indirect route and dissociates along three distinct pathways (direct, roaming, and delayed) with formation times of about 34 and 72 femtoseconds for the direct and delayed branches. Yet bond formation requires the molecule to first break its own symmetry. Only random asymmetric motion enables the electronic-state switch at a conical intersection, joining the two hydrogen atoms before the oxygen--hydrogen bond breaks. These results establish a time-resolved picture of molecular hydrogen formation from water and provide a general strategy for linking electronic excitation to chemical outcomes in settings from radiation damage to hydrogen production.
