Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599, USA.
Sci Rep. 2017 Jan 13;7:40379. doi: 10.1038/srep40379.
Molecular behaviour of liquid water under proton irradiation is of great importance to a number of technological and medical applications. The highly energetic proton generates a time-varying field that is highly localized and heterogeneous at the molecular scale, and massive electronic excitations are produced as a result of the field-matter interaction. Using first-principles quantum dynamics simulations, we reveal details of how electrons are dynamically excited through non-equilibrium energy transfer from highly energetic protons in liquid water on the atto/femto-second time scale. Water molecules along the path of the energetic proton undergo ionization at individual molecular level, and the excitation primarily derives from lone pair electrons on the oxygen atom of water molecules. A reduced charge state on the energetic proton in the condensed phase of water results in the strongly suppressed electronic response when compared to water molecules in the gas phase. These molecular-level findings provide important insights into understanding the water radiolysis process under proton irradiation.
质子辐照下液态水的分子行为对于许多技术和医学应用都非常重要。高能质子会产生随时间变化的场，在分子尺度上高度局域和不均匀，并且由于场-物质相互作用会产生大量的电子激发。我们使用第一性原理量子动力学模拟，揭示了在阿秒/飞秒时间尺度上，高能质子在液态水中通过非平衡能量转移如何动态激发电子的细节。沿着高能质子路径的水分子在单个分子水平上发生电离，激发主要来自水分子中氧原子上的孤对电子。与气相中的水分子相比，水中高能质子的电荷状态降低会导致电子响应受到强烈抑制。这些分子水平的发现为理解质子辐照下的水辐射分解过程提供了重要的见解。
