Exploration of Gas-Liquid Interfaces for Liquid Water and Methanol Using Extreme Ultraviolet Laser Photoemission Spectroscopy
Exploration of Gas-Liquid Interfaces for Liquid Water and Methanol Using Extreme Ultraviolet Laser Photoemission Spectroscopy
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使用极紫外激光光电发射光谱法探索液态水和甲醇的气液界面
DOI：
10.1021/acs.jpcb.1c04765
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发表时间：
2021
期刊：
影响因子：
--
通讯作者：
T. Suzuki
中科院分区：
文献类型：
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作者：
Y. Yamamoto;T. Ishiyama;A. Morita;T. Suzuki
我们提出了一个研究使用极紫外（EUV）光电子能谱的价电子结构的水溶液和甲醇溶液使用10 kHz EUV光源的基础上高次谐波产生和磁瓶飞行时间电子光谱仪。在这项研究中，所观察到的光谱的两个方面是突出的。一个是垂直电离能（VIE）的变化作为溶质浓度的函数，这是密切相关的表面偶极子在气液界面的液体。实验结果表明，液态水的VIE随NaCl和NaI浓度的增加而略有增加，随NaOH浓度的增加而减小。液体甲醇的VIE也被发现与NaI略有变化。另一方面，四丁基碘化铵（TBAI）和丁胺（BA）明显降低VIE的液态水，这是由于形成的双电层（EDL）的气-液界面处的分离溶质。作为这一点的证据，当BA水溶液的pH降低到质子化BA时，VIE位移逐渐减小，因为质子化BA移动到本体中以抑制EDL的影响。我们用分子动力学模拟计算了这些溶液的表面势，结果支持了我们对实验结果的解释。另一个观察结果是溶剂的单个光电子带的相对能量和形状的变化，这与电离溶剂分子的第一溶剂化壳层的结构和成分的改变有关。所有溶质在高浓度下都会引起光电子能谱的变化，其中最突出的变化之一是液体水的3a 1带和液体甲醇的7a′带的分裂程度，这对液体中的氢键是敏感的。3a 1分裂随着NaI、NaCl和NaOH浓度的增加而减少，表明Na+渗透到氢键网络中与水分子的非键电子配位。另一方面，TBAI和BA引起的3a 1分裂的变化较小。这些光谱特征的充分解释有待广泛的量子化学计算，超出了本研究的范围。然而，这些结果说明了极紫外激光光电子能谱的液体界面和溶液化学的探索的强大潜力。
We present a study using extreme UV (EUV) photoemission spectroscopy of the valence electronic structures of aqueous and methanol solutions using a 10 kHz EUV light source based on high-order harmonic generation and a magnetic bottle time-of-flight electron spectrometer. Two aspects of the observed spectra are highlighted in this study. One is variation of the vertical ionization energy (VIE) for liquids as a function of the solute concentration, which is closely related to surface dipoles at the gas–liquid interface. The experimental results show that the VIE of liquid water increases slightly with increasing concentrations of NaCl and NaI and decreases with NaOH. The VIE of liquid methanol was also found to change slightly with NaI. On the other hand, tetrabutylammonium iodide (TBAI) and butylamine (BA) clearly reduce the VIE for liquid water, which is attributed to the formation of an electric double layer (EDL) by segregated solutes at the gas–liquid interface. As evidence for this, when the pH of an aqueous BA solution is reduced to protonate BA, the VIE shift gradually decreases because the protonated BA moves into the bulk to suppress the influence of the EDL. We computed the surface potentials for these solutions using molecular dynamics simulations, and the results supported our interpretation of the experimental results. Another observation is the variation of the relative energy and shape of individual photoelectron bands for solvents, which is related to alteration of the structure and constituents of the first solvation shell of ionized solvent molecules. All of the solutes cause changes in the photoelectron spectra at high concentration, one of the most prominent of which is the degree of splitting of the 3a1band for liquid water and the 7a′ band for liquid methanol, which are sensitive to hydrogen bonding in the liquids. The 3a1splitting decreases with the increasing concentration of NaI, NaCl, and NaOH, indicating that Na+penetrates into the hydrogen-bonding network to coordinate to a nonbonding electron of a water molecule. On the other hand, TBAI and BA cause smaller changes in the 3a1splitting. Full interpretation of these spectroscopic features awaits extensive quantum chemical calculations and is beyond the scope of this study. However, these results illustrate the strong potential of EUV laser photoemission spectroscopy of liquids for exploration of interfacial and solution chemistry.