The “hole” story of water ionization The direct observation of the cationic hole H2O+ that is formed in liquid water after ionization has been a long-standing experimental challenge. Previous attempts using optical and ultraviolet techniques have failed to reveal its key spectroscopic signature during ultrafast transformation into a OH radical. Loh et al. address this gap by using intense, ultrafast x-ray pulses from an x-ray free electron laser at ∼530 electron volts. They found compelling evidence for the formation H2O+ and its decay to an OH radical by a proton transfer mechanism and elucidated the other fastest–time scale steps in the early-time dynamics of ionized liquid water. Science, this issue p. 179 Ultrafast soft x-ray pulses capture the early-time dynamics in ionized liquid water. Elementary processes associated with ionization of liquid water provide a framework for understanding radiation-matter interactions in chemistry and biology. Although numerous studies have been conducted on the dynamics of the hydrated electron, its partner arising from ionization of liquid water, H2O+, remains elusive. We used tunable femtosecond soft x-ray pulses from an x-ray free electron laser to reveal the dynamics of the valence hole created by strong-field ionization and to track the primary proton transfer reaction giving rise to the formation of OH. The isolated resonance associated with the valence hole (H2O+/OH) enabled straightforward detection. Molecular dynamics simulations revealed that the x-ray spectra are sensitive to structural dynamics at the ionization site. We found signatures of hydrated-electron dynamics in the x-ray spectrum.

中文翻译：

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观察水辐射分解中最快的化学过程

水电离的“洞”故事 直接观察电离后液态水中形成的阳离子空穴 H2O+ 一直是一项长期的实验挑战。之前使用光学和紫外线技术的尝试未能揭示其在超快转变为 OH 自由基期间的关键光谱特征。洛等人。通过使用来自约 530 电子伏特的 X 射线自由电子激光器的强、超快 X 射线脉冲来解决这一差距。他们发现了 H2O+ 的形成及其通过质子转移机制衰变成 OH 自由基的有力证据，并阐明了电离液态水早期动力学中的其他最快时间尺度步骤。科学，这个问题 p。179 超快软 X 射线脉冲捕获电离液态水中的早期动力学。与液态水电离相关的基本过程为理解化学和生物学中的辐射-物质相互作用提供了一个框架。尽管已经对水合电子的动力学进行了大量研究，但其由液态水电离产生的伙伴 H2O+ 仍然难以捉摸。我们使用来自 X 射线自由电子激光器的可调飞秒软 X 射线脉冲来揭示由强场电离产生的价空穴的动力学，并跟踪导致形成 OH 的主要质子转移反应。与价空穴 (H2O+/OH) 相关的孤立共振使检测变得简单。分子动力学模拟表明，X 射线光谱对电离位点的结构动力学很敏感。