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arXiv 2107.06161physics.chem-ph
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溶质诱导液态水的定量电子结构和work-function变化

Quantitative electronic structure and work-function changes of liquid water induced by solute

Bruno Credidio, Michele Pugini, Sebastian Malerz, Florian Trinter, Uwe Hergenhahn, Iain Wilkinson, Stephan Thürmer, Bernd Winter

摘要:

定量液体喷射光电子能谱学的最新进展使得能够精确测定溶液中液体和物质的绝对尺度电子能量学。我们的主要目的是确定绝对最低的电离能的液态水,发现不同的溶质添加,并取决于溶质浓度。我们讨论了两种典型的盐水溶液,碘化钠(aq)和四丁基碘化铵,TBAI(aq),后者是一种强表面活性剂。相当不同的行为被揭示:在碘化钠(aq)的解决方案,水的1B 1能量增加了300毫电子伏后,增加浓度接近饱和浓度,而TBAI的能量减少约0.7电子伏特后,形成的表面层。溶质诱导的溶质结合能的影响进行量化,以及,推断从浓度依赖性的I-5 p峰能量的能量位移。对于碘化钠(水溶液),几乎相同的I-5 p位移被发现为水1b 1结合能,与TBAI(水溶液)的解决方案在相反的方向上发生较大的位移。我们表明,这一结果在碘化钠(aq)可以主要归因于水的电子结构在溶液中的散装的变化。与此相反,TBAI(aq)的1b 1能量的明显变化可能与溶液功函数的变化有关,这可能是由表面分子偶极子引起的。此外,对于这里研究的两种溶液,测得的水1b 1结合能可以与在高盐浓度下发生的广泛的溶液分子结构变化相关,其中在NaI(aq)的情况下,存在太少的水分子来水合单个离子,并且溶液采用晶体状相。我们还评论的浓度依赖的形状的3a 1轨道的液态水,这是一个敏感的签名水-水氢键相互作用。

英文摘要:

Recent advancement in quantitative liquid-jet photoelectron spectroscopy enables the accurate determination of the absolute-scale electronic energetics of liquids and species in solution. Our major objective is the determination of the absolute lowest-ionization energy of liquid water which is found to vary upon solute addition, and depends on the solute concentration. We discuss two prototypical aqueous salt solutions, NaI(aq) and tetrabutylammonium iodide, TBAI(aq), with the latter being a strong surfactant. Considerably different behavior is revealed: In the NaI(aq) solutions, water's 1b1 energy increases by 300 meV upon increasing the concentration near-saturation concentrations, whereas for TBAI the energy decreases by about 0.7 eV upon formation of a surface layer. The solute-induced effects on the solute binding energies are quantified as well, as inferred from concentration-dependent energy shifts of the I- 5p peak energy. For NaI(aq), an almost identical I- 5p shift is found as for the water 1b1 binding energy, with a larger shift occurring in the opposite direction for the TBAI(aq) solution. We show that this result in NaI(aq) can be primarily assigned to a change of water's electronic structure in the solution bulk. In contrast, apparent changes of the 1b1 energy for TBAI(aq) can be related to changes of the solution work function which could arise from surface molecular dipoles. Furthermore, for both of the solutions studied here, the measured water 1b1 binding energies can be correlated with the extensive solution molecular structure changes occurring at high salt concentrations, where in the case of NaI(aq), too few water molecules exist to hydrate individual ions and the solution adopts a crystalline-like phase. We also comment on the concentration-dependent shape of the 3a1 orbital of liquid water which is a sensitive signature of water-water hydrogen bond interactions.

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