Saak Clara-Magdalena, Richter Clemens, Unger Isaak, Mucke Melanie, Nicolas Christophe, Hergenhahn Uwe, Caleman Carl, Huttula Marko, Patanen Minna, Björneholm Olle
Department for Physics and Astronomy, Uppsala University, Box 516, 751 20 Uppsala, Sweden.
Leibniz Institute of Surface Engineering (IOM), Permoserstr. 15, 04318 Leipzig, Germany.
Phys Chem Chem Phys. 2020 Feb 14;22(6):3264-3272. doi: 10.1039/c9cp06661f. Epub 2020 Jan 30.
Hydrogen bonding leads to the formation of strong, extended intermolecular networks in molecular liquids such as water. However, it is less well-known how robust the network is to environments in which surface formation or confinement effects become prominent, such as in clusters or droplets. Such systems provide a useful way to probe the robustness of the network, since the degree of confinement can be tuned by altering the cluster size, changing both the surface-to-volume ratio and the radius of curvature. To explore the formation of hydrogen bond networks in confined geometries, here we present O 1s Auger spectra of small and large clusters of water, methanol, and dimethyl ether, as well as their deuterated equivalents. The Auger spectra of the clusters and the corresponding macroscopic liquids are compared and evaluated for an isotope effect, which is due to proton dynamics within the lifetime of the core hole (proton-transfer-mediated charge-separation, PTM-CS), and can be linked to the formation of a hydrogen bond network in the system. An isotope effect is observed in water and methanol but not for dimethyl ether, which cannot donate a hydrogen bond at its oxygen site. The isotope effect, and therefore the strength of the hydrogen bond network, is more pronounced in water than in methanol. Its value depends on the average size of the cluster, indicating that confinement effects change proton dynamics in the core ionised excited state.
氢键导致在诸如水等分子液体中形成强大的、扩展的分子间网络。然而，对于在表面形成或限制效应变得显著的环境（如在团簇或液滴中）中该网络的稳健程度，人们了解得较少。这样的系统提供了一种有用的方法来探究网络的稳健性，因为可以通过改变团簇大小来调节限制程度，这会同时改变表面积与体积之比以及曲率半径。为了探索受限几何结构中氢键网络的形成，我们在此展示了水、甲醇和二甲醚的小团簇和大团簇以及它们的氘代等效物的O 1s俄歇光谱。对团簇和相应宏观液体的俄歇光谱进行了比较，并评估了同位素效应，该效应源于在核心空穴寿命内的质子动力学（质子转移介导的电荷分离，PTM-CS），并且可以与系统中氢键网络的形成相关联。在水和甲醇中观察到了同位素效应，但二甲醚没有，因为二甲醚在其氧位点不能提供氢键。同位素效应，进而氢键网络的强度，在水中比在甲醇中更明显。其值取决于团簇的平均大小，这表明限制效应改变了核心电离激发态下的质子动力学。
