丹麦奥胡斯大学Stapelfeldt, Henrik团队观察了氦滴离子溶剂化的基本步骤。相关研究成果于2023年11月8日发表在《自然》。

溶剂化是自然科学中普遍存在的现象。在宏观层面上，它通过热力学和化学反应动力学得到了很好的理解。在原子水平上，溶剂化的主要步骤是溶剂的单个分子或原子与溶质的分子或离子的吸引和结合。然而，这些步骤从未被实时观察到。

该文中，研究人员立即在液氦纳米滴的表面产生一个钠离子，并测量随时间变化而连续附着在离子上的溶剂原子数。研究发现前五个氦原子的结合动力学可以很好地用结合率为2.0 原子/皮秒的Poissonian过程来描述。该速率与溶剂化过程的时间依赖密度泛函理论模拟一致。此外，该测量能够估计从钠离子周围区域去除的能量作为时间的函数，表明总溶剂化能量的一半在4皮秒后耗散。

该实验方法为离子溶剂化的基准理论模型和阳离子-分子复合物形成的时间分辨测量开辟了可能性。观察到单个钠离子在液氦中的溶剂化过程的初始步骤，为离子溶剂化的基准理论描述开辟了可能性。

附：英文原文

Title: Observing the primary steps of ion solvation in helium droplets

Author: Albrechtsen, Simon H., Schouder, Constant A., Vias Muoz, Alberto, Christensen, Jeppe K., Engelbrecht Petersen, Christian, Pi, Mart, Barranco, Manuel, Stapelfeldt, Henrik

Issue&Volume: 2023-11-08

Abstract: Solvation is a ubiquitous phenomenon in the natural sciences. At the macroscopic level, it is well understood through thermodynamics and chemical reaction kinetics1,2. At the atomic level, the primary steps of solvation are the attraction and binding of individual molecules or atoms of a solvent to molecules or ions of a solute1. These steps have, however, never been observed in real time. Here we instantly create a single sodium ion at the surface of a liquid helium nanodroplet3,4, and measure the number of solvent atoms that successively attach to the ion as a function of time. We found that the binding dynamics of the first five helium atoms is well described by a Poissonian process with a binding rate of 2.0 atoms per picosecond. This rate is consistent with time-dependent density-functional-theory simulations of the solvation process. Furthermore, our measurements enable an estimate of the energy removed from the region around the sodium ion as a function of time, revealing that half of the total solvation energy is dissipated after four picoseconds. Our experimental method opens possibilities for benchmarking theoretical models of ion solvation and for time-resolved measurements of cation–molecule complex formation. The initial steps of the ion solvation process are observed for the solvation of a single sodium ion in liquid helium, opening possibilities for benchmarking theoretical descriptions of ion solvation.

DOI: 10.1038/s41586-023-06593-5

Source: https://www.nature.com/articles/s41586-023-06593-5