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Specific Anion Effects on Na+ Adsorption at the Aqueous Solution–Air Interface: MD Simulations, SESSA Calculations, and Photoelectron Spectroscopy Experiments
The Journal of Physical Chemistry B ( IF 2.8 ) Pub Date : 2017-11-10 00:00:00 , DOI: 10.1021/acs.jpcb.7b06981
Giorgia Olivieri 1 , Krista M. Parry 2 , Raffaella D’Auria 2 , Douglas J. Tobias 2 , Matthew A. Brown 1
Affiliation  

Specific ion effects of the large halide anions have been shown to moderate anion adsorption to the air–water interface (AWI), but little quantitative attention has been paid to the behavior of alkali cations. Here we investigate the concentration and local distribution of sodium (Na+) at the AWI in dilute (<1 M) aqueous solutions of NaCl, NaBr, and NaI using a combination of molecular dynamics (MD) and SESSA simulations, and liquid jet ambient pressure photoelectron spectroscopy measurements. We use SESSA to simulate Na 2p photoelectron intensities on the basis of the atom density profiles obtained from MD simulations, and we compare the simulation results with photoelectron spectroscopy experiments to evaluate the performance of a nonpolarizable force field model versus that of an induced dipole polarizable one. Our results show that the nonpolarizable force model developed by Horinek and co-workers (Chem. Phys. Lett. 2009, 479, 173–183) accurately predicts the local concentration and distribution of Na+ near the AWI for all three electrolytes, whereas the polarizable model does not. To our knowledge, this is the first interface-specific spectroscopic validation of a MD force field. The molecular origins of the unique Na+ distributions for the three electrolytes are analyzed on the basis of electrostatic arguments, and shown to arise from an indirect anion effect wherein the identity of the anion affects the strength of the attractive Na+–H2O electrostatic interaction. Finally, we use the photoelectron spectroscopy results to constrain the range of inelastic mean free paths (IMFPs) for the three electrolyte solutions used in the SESSA simulations that are able to reproduce the experimental intensities. Our results suggest that earlier estimates of IMFPs for aqueous solutions are likely too high.

中文翻译:

特定阴离子对水溶液-空气界面上的Na +吸附的影响:MD模拟,SESSA计算和光电子能谱实验

大型卤化物阴离子的特定离子效应已显示出一定程度的阴离子吸附到空气-水界面(AWI)的作用,但是对碱金属阳离子的行为却很少有定量关注。在这里我们调查钠(Na +)结合分子动力学(MD)和SESSA模拟以及液体喷射环境压力光电子能谱测量,在AWI中的NaCl,NaBr和NaI稀水溶液(<1 M)中进行测量。我们使用SESSA在MD模拟获得的原子密度分布的基础上模拟Na 2p光电子强度,并将模拟结果与光电子光谱实验进行比较,以评估非极化力场模型与感应偶极子极化模型的性能。 。我们的研究结果表明,不可极化力模型开发的Horinek和同事(化学物理快报, 2009479,173-183)准确预测娜的局部浓度和分布+所有三种电解质的AWI都接近于AWI,而可极化模型却没有。据我们所知,这是MD力场的第一个特定于界面的光谱验证。基于静电论点对三种电解质的独特Na +分布的分子起源进行了分析,结果表明这是由于间接阴离子效应引起的,其中阴离子的身份影响了有吸引力的Na + -H 2的强度。O静电相互作用。最后,我们使用光电子能谱结果来约束SESSA模拟中使用的三种能够再现实验强度的电解质溶液的非弹性平均自由程(IMFP)的范围。我们的结果表明,对于水溶液的IMFP的早期估计可能太高。
更新日期:2017-11-11
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