Institute for Molecular Science , Myodaiji, Okazaki 444-8585 , Japan.
SOKENDAI (The Graduate University for Advanced Studies) , Myodaiji, Okazaki 444-8585 , Japan.
J Phys Chem B. 2020 Feb 20;124(7):1259-1265. doi: 10.1021/acs.jpcb.0c00551. Epub 2020 Feb 10.
Chemical processes in solution are influenced by microheterogeneity (MH), where two liquids seem to be mixed in a macroscopic scale but are microscopically inhomogeneous. We have investigated one of the simplest MH systems, aqueous acetonitrile solution, using soft X-ray absorption spectroscopy (XAS). Molecular interactions of acetonitrile were revealed by C and N K-edge XAS at different concentrations, and those of solvent water were separately revealed by O K-edge XAS. The energy shift of the C≡N π* peak at the C K-edge shows three characteristic concentration regions and a phase-transition-like behavior between them. By comparing the energy shifts in XAS spectra with ab initio quantum chemical inner-shell calculations, we have determined local structures of acetonitrile-water mixtures in three concentration regions and found that the dipole interaction between acetonitrile and water is the key structure to emerge the MH state in the middle concentration region.
溶液中的化学过程受到微观不均匀性（MH）的影响，其中两种液体在宏观尺度上似乎混合在一起，但在微观上却是不均匀的。我们使用软 X 射线吸收光谱（XAS）研究了最简单的 MH 体系之一，即水-乙腈溶液。通过在不同浓度下的 C 和 N K 边 XAS，揭示了乙腈的分子相互作用，而溶剂水的分子相互作用则通过 O K 边 XAS 分别揭示。C 边的 C≡N π*峰的能量位移显示出三个特征浓度区域，它们之间具有类似相变的行为。通过将 XAS 谱中的能量位移与从头算量子化学内壳层计算进行比较，我们确定了三个浓度区域中乙腈-水混合物的局部结构，并发现乙腈和水之间的偶极相互作用是在中间浓度区域出现 MH 状态的关键结构。
