Cappa Christopher D, Smith Jared D, Messer Benjamin M, Cohen Ronald C, Saykally Richard J
Department of Chemistry, University of California, Berkeley, California 94720-1460, USA.
J Phys Chem B. 2006 Mar 23;110(11):5301-9. doi: 10.1021/jp054699c.
Oxygen K-edge X-ray absorption spectra (XAS) of aqueous chloride solutions have been measured for Li(+), Na(+), K(+), NH(4)(+), C(NH(2))(3)(+), Mg(2+), and Ca(2+) at 2 and 4 M cation concentrations. Marked changes in the liquid water XAS are observed upon addition of the various monovalent cation chlorides that are nearly independent of the identity of the cation. This indicates that interactions with the dissolved monovalent cations do not significantly perturb the unoccupied molecular orbitals of water molecules in the vicinity of the cations and that water-chloride interactions are primarily responsible for the observed spectral changes. In contrast, the addition of the divalent cations engenders changes unique from the case of the monovalent cations, as well as from each other. Density functional theory calculations suggest that the ion-specific spectral variations arise primarily from direct electronic perturbation of the unoccupied orbitals due to the presence of the ions, probably as a result of differences in charge transfer from the water molecules onto the divalent cations.
已测量了2M和4M阳离子浓度下，Li⁺、Na⁺、K⁺、NH₄⁺、C(NH₂)₃⁺、Mg²⁺和Ca²⁺的氯化物水溶液的氧K边X射线吸收光谱（XAS）。加入各种单价阳离子氯化物后，液态水XAS出现明显变化，这些变化几乎与阳离子的种类无关。这表明与溶解的单价阳离子的相互作用不会显著扰动阳离子附近水分子的未占据分子轨道，并且水 - 氯化物相互作用是观察到的光谱变化的主要原因。相比之下，加入二价阳离子会产生与单价阳离子情况不同且彼此也不同的变化。密度泛函理论计算表明，离子特异性光谱变化主要源于离子存在导致的未占据轨道的直接电子扰动，这可能是由于水分子向二价阳离子电荷转移差异所致。
