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首页> 外文期刊>Proceedings of the National Academy of Sciences of the United States of America >Water surface is acidic
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Water surface is acidic

机译：水面呈酸性

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摘要

Water autoionization reaction 2H_2O → H_3O~- + OH~- is a textbook process of basic importance, resulting in pH = 7 for pure water. However, pH of pure water surface is shown to be significantly lower, the reduction being caused by proton stabilization at the surface. The evidence presented here includes ab initio and classical molecular dynamics simulations of water slabs with solvated H_3O~+ and OH~- ions, density functional studies of (H_2O)_(48)H~+ clusters, and spectroscopic isotopic-exchange data for D_2O substitutional impurities at the surface and in the interior of ice nanocrystals. Because H_3O~+ does, but OH~- does not, display preference for surface sites, the H_2O surface is predicted to be acidic with pH < 4.8. For similar reasons, the strength of some weak acids, such as carbonic acid, is expected to increase at the surface. Enhanced surface acidity can have a significant impact on aqueous surface chemistry, e.g., in the atmosphere.
机译：水的自电离反应2H_2O→H_3O〜-+ OH〜-是最重要的教科书过程，纯水的pH = 7。但是，纯水表面的pH值明显降低，其降低是由于表面的质子稳定引起的。这里提供的证据包括具有溶剂化的H_3O〜+和OH〜-离子的水板的从头算和经典分子动力学模拟，（H_2O）_（48）H〜+团簇的密度泛函研究以及D_2O的光谱同位素交换数据冰纳米晶体表面和内部的替代杂质。因为H_3O〜+确实有，但OH〜-没有显示出对表面位置的偏爱，所以H_2O表面预计在pH <4.​​8时呈酸性。由于类似的原因，预计某些弱酸（例如碳酸）的强度会在表面增加。表面酸度的提高可对例如大气中的水性表面化学产生重大影响。

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