Horikawa Yuka, Tokushima Takashi, Takahashi Osamu, Hoke Hiroshi, Takamuku Toshiyuki
Department of Physics and Information Science, Faculty of Science, Yamaguchi University , 1677-1 Yoshida, Yamaguchi 753-8512, Japan.
Soft X-ray Spectroscopy Instrumentation Unit, RIKEN SPring-8 Center , Sayo-cho, Sayo, Hyogo 679-5148, Japan.
J Phys Chem B. 2016 Aug 4;120(30):7480-7. doi: 10.1021/acs.jpcb.6b04132. Epub 2016 Jul 21.
Soft X-ray absorption spectroscopy (XAS) has been performed on the N K-edge of two imidazolium-based ionic liquids (ILs), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)amide ([C2mim][TFSA]) and 1-ethyl-3-methylimidazolium bromide ([C2mim][Br]), to clarify the electronic structures of the ILs. Soft X-ray emission spectroscopy (XES) has also been applied to the ILs by excitation at various X-ray energies according to the XAS spectra. It was possible to fully associate the XAS peaks with the XES peaks. Additionally, both XAS and XES spectra of the ILs were well reproduced by the theoretical spectra for a single-molecule model on C2mim and TFSA using density functional theory. The assignments for the XAS and XES peaks of the ILs were accomplished from both experimental and theoretical approaches. The theoretical XAS and XES spectra of C2mim and TFSA did not significantly depend on the conformations of the ions. The reproducibility of the theoretical spectra for the single-molecule model suggested that the interactions between the cations and anions are very weak in the ILs, thus scarcely influencing the electronic structures of the nitrogen atoms.
已对两种咪唑基离子液体（ILs），即1-乙基-3-甲基咪唑双（三氟甲基磺酰）酰胺（[C2mim][TFSA]）和1-乙基-3-甲基咪唑溴化物（[C2mim][Br]）的N K边进行了软X射线吸收光谱（XAS）分析，以阐明离子液体的电子结构。根据XAS光谱，还通过在各种X射线能量下激发，将软X射线发射光谱（XES）应用于离子液体。可以将XAS峰与XES峰完全关联起来。此外，使用密度泛函理论，对于C2mim和TFSA的单分子模型，离子液体的XAS和XES光谱均能很好地由理论光谱再现。离子液体的XAS和XES峰的归属是通过实验和理论方法完成的。C2mim和TFSA的理论XAS和XES光谱对离子构象的依赖性不显著。单分子模型理论光谱的再现性表明，离子液体中阳离子与阴离子之间的相互作用非常弱，因此几乎不会影响氮原子的电子结构。
