Electron Scattering and Electron Angular Anisotropy in Water and Aqueous Solution

该项目在国际合作中利用光电子能谱对液态水和水溶液中的电子散射机制及其对光电子角分布的影响提供了新的见解。电子散射对于理解慢电子和快电子的能量沉积、自由基形成和生物损伤，以及正确解释液态水和水溶液的光谱都是至关重要的。在过去的一年里，人们证明了水溶液中的表面活性分子(这里是全氟戊酸盐)可以通过光电子角分布(PADS)精确地绘制出来。电子散射以一种独特的方式改变了焊盘的特征，这种方式与探测深度唯一地联系在一起，一直到埃的分辨率。结合光电发射的化学特性，这一新技术为研究与大气化学相关的溶液的详细表面组成铺平了道路。最近的结果表明，电子散射对表面活性物质的影响不同于主体物质。来自表面的光电子在大块液体中不会受到散射，因此可以探测到低得多的动能。这种区别对于理解来自激光等低能源的光电子光谱是至关重要的，如果不考虑表面倾向和浓度，这可能会被误解。这些结果目前正在准备发表。此外，已经开发了一种获取水溶液功函数(表面电势)的方法，目前正在审查中。

The project gives new insights into electron scattering mechanisms in liquid water and aqueous solutions and its impact on photoelectron angular distributions using photoelectron spectroscopy in international collaboration. Electron scattering is crucial for understanding energy deposition, radical formation, and biological damage by slow and fast electrons, and a correct interpretation of spectra from liquid water and aqueous solutions.In the past year, it was demonstrated that surface-active molecules (here: perfluoropentanoate) in aqueous solution can be precisely mapped using photoelectron angular distributions (PADs). Electron scattering alters the PAD signature in a way that is uniquely linked to the probing depth down to an Angstrom resolution. Combined with the chemical specificity of photoemission, this novel technique paves the way to study the detailed surface composition of solutions relevant for, e.g., atmospheric chemistry.Recent results reveal that electron scattering affects surface-active species differently than bulk species. Photoelectrons from the surface do not suffer from scattering in the bulk liquid, and are thus detectable down to much lower kinetic energies. This distinction is crucial to understand photoelectron spectra from low-energy sources such as lasers, which might be misinterpreted if the surface-propensity and concentration is not considered. These results are currently prepared for publication.Furthermore, a method for accessing the work function (surface potential) of aqueous solutions has been developed and is currently under review.