Höfft Oliver, Borodin Andriy, Kahnert Uwe, Kempter Volker, Dang Liem X, Jungwirth Pavel
Technische Universität Clausthal, Institut für Physik und Physikalische Technologien, Leibnizstr. 4, D-38678 Clausthal-Zellerfeld, Germany.
J Phys Chem B. 2006 Jun 22;110(24):11971-6. doi: 10.1021/jp061437h.
Surface segregation of iodide, but not of fluoride or cesium ions, is observed by a combination of metastable impact electron spectroscopy (MIES) and ultraviolet photoelectron spectroscopy (UPS(HeI)) of amorphous solid water exposed to CsI or CsF vapor. The same surface ionic behavior is also derived from molecular dynamics (MD) simulations of the corresponding aqueous salt solutions. The MIES results show the propensity of iodide, but not fluoride, for the surface of the amorphous solid water film, providing thus strong evidence for the suggested presence of heavier halides (iodide, bromide, and to a lesser extent chloride) at the topmost layer of aqueous surfaces. In contrast, no appreciable surface segregation of ions is observed in methanol, neither in the experiment nor in the simulation. Furthermore, the present results indicate that, as far as the thermodynamic aspects of solvation of alkali halides are concerned, amorphous solid water and methanol surfaces behave similarly as surfaces of the corresponding liquids.
通过对暴露于碘化铯或氟化铯蒸汽中的非晶态固态水进行亚稳碰撞电子能谱（MIES）和紫外光电子能谱（UPS(HeI)）的组合观测，发现存在碘离子的表面偏析现象，但氟离子或铯离子不存在这种现象。相应盐水溶液的分子动力学（MD）模拟也得出了相同的表面离子行为。MIES结果表明，碘离子而非氟离子倾向于在非晶态固态水膜的表面，从而为在水表面最顶层存在较重卤化物（碘离子、溴离子以及程度稍轻的氯离子）提供了有力证据。相比之下，在甲醇中，无论是实验还是模拟，均未观察到明显的离子表面偏析现象。此外，目前的结果表明，就碱金属卤化物溶剂化的热力学方面而言，非晶态固态水和甲醇表面的行为与相应液体的表面行为相似。
