National Food Research Institute, National Agriculture and Food Research Organization (NARO), Tsukuba, Ibaraki, 305-8642, Japan.
Phys Chem Chem Phys. 2012 Jun 14;14(22):8097-104. doi: 10.1039/c2cp40633k. Epub 2012 May 2.
The first electronic transition (Ã←X̃) of liquid water was studied from the perspective of the hydration of cations by analyzing the attenuated total reflection far-ultraviolet (ATR-FUV) spectra of the Group I, II, and XIII metal nitrate electrolyte solutions. The Ã←X̃ transition energies of 1 M electrolyte solutions are higher (Li(+): 8.024 eV and Cs(+): 8.013 eV) than that of pure water (8.010 eV) and linearly correlate with the Gibbs energies of hydration of the cations. The increases in the Ã←X̃ transition energies are mostly attributable to the hydrogen bond formation energies of water molecules in the ground state induced by the presence of the cations. The deviation from the linear relation was observed for the high charge density cations, H(+), Li(+), and Be(2+), which reflects that the electronic energies in the excited states are also perturbed. Quantum chemical calculations show that the Ã←X̃ transition energies of the water-cation complexes depend on the hydration structures of the cations. The calculated Ã←X̃ transition energies of the water molecules hydrating high charge density cations spread more widely than those of the low charge density cations. The calculated transition energy spreads of the water-cation complexes directly correlate with the widths of the Ã←X̃ transition bands measured by ATR-FUV spectroscopy.
本文从阳离子水合的角度，通过分析 I 族、II 族和 XIII 族金属硝酸盐电解质溶液的衰减全反射远紫外（ATR-FUV）光谱，研究了液态水的第一个电子跃迁（Ã←X̃）。1 M 电解质溶液的Ã←X̃跃迁能较高（Li(+)：8.024 eV 和 Cs(+)：8.013 eV），高于纯水（8.010 eV），且与阳离子的水合吉布斯能呈线性相关。Ã←X̃跃迁能的增加主要归因于阳离子存在时基态水分子氢键形成能的增加。对于高电荷密度阳离子 H(+)、Li(+)和 Be(2+)，观察到偏离线性关系，这反映出激发态的电子能也受到了干扰。量子化学计算表明，水-阳离子配合物的Ã←X̃跃迁能取决于阳离子的水合结构。计算得到的与高电荷密度阳离子结合的水分子的Ã←X̃跃迁能分布范围较广，而与低电荷密度阳离子结合的水分子Ã←X̃跃迁能分布范围较窄。水-阳离子配合物的计算跃迁能分布范围与 ATR-FUV 光谱测量得到的Ã←X̃跃迁带的宽度直接相关。
