Solvation dependence of valence electronic states of water diluted in organic solvents probed by soft X-ray spectroscopy
Solvation dependence of valence electronic states of water diluted in organic solvents probed by soft X-ray spectroscopy
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软 X 射线光谱探测有机溶剂中稀释水的价电子态的溶剂依赖性
DOI：
10.1039/c4cp00762j
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发表时间：
2014
影响因子：
3.3
通讯作者：
S. Shin
中科院分区：
文献类型：
--
作者：
T. Tokushima;Y. Horikawa;O. Takahashi;H. Arai;K. Sadakane;Y. Harada;Y. Takata;S. Shin
氢键的知识在许多科学领域都很重要。然而，有关氢键分子在液体和溶液中的电子状态的信息仍然有限。我们用X射线发射光谱和吸收光谱研究了常压下水在乙腈、3-甲基吡啶和乙二胺中占据和未占据价电子态的溶剂依赖性。根据光谱的直接比较，水在乙腈和3-甲基吡啶中未占据的2b2态的显著变化归因于偶极-偶极相互作用和给体氢键的不同。对于乙二胺溶液，在X射线吸收光谱的后边缘区域观察到峰结构的增强，在X射线发射光谱中被占据的1B1态的高能侧有明显的肩部结构。虽然乙二胺有两个氨基可以形成氢键作为质子供体，但研究结果表明，乙二胺的氨基在水分子之间的氢键中也起到了质子受体的作用。通过对三种有机溶剂的比较，还发现了与最低空位分子轨道4a1对应的前缘峰的系统峰强度变化。由于峰值强度随氢键数目的增加而减小，因此可以用氢键的共价性来解释这一结果。
Knowledge of hydrogen bonds is important in a wide range of scientific fields. However, information on the electronic state of hydrogen bonded molecules in liquids and solutions is still limited. We applied X-ray emission and absorption spectroscopy to observe the electronic state around oxygen of water and investigate the solvent dependence of occupied and unoccupied valence electronic states of water in acetonitrile, 3-methylpyridine, and ethylenediamine at room temperature under atmospheric pressure. Based on the direct comparison of the spectra, the pronounced variation of the unoccupied 2b2 state of water in acetonitrile and 3-methylpyridine was assigned to the difference of the dipole–dipole interaction and the donor hydrogen bond. For ethylenediamine solution, an enhancement of the peak structure in the post-edge region of X-ray absorption spectra and an evident shoulder structure on the higher energy side of the occupied 1b1 state in X-ray emission spectra were observed. Although ethylenediamine has two amino groups that can form the hydrogen bonds as a proton donor, the obtained results indicate that the amino groups of ethylenediamine also act as a proton acceptor in the hydrogen bond between water molecules. A systematic peak intensity variation of the pre-edge peak corresponding to the lowest unoccupied molecular orbital, 4a1, was also found through the comparison of three organic solvents. Since the peak intensity tends to decrease with increasing number of hydrogen bonds, the results can be interpreted by the covalency of hydrogen bonds.