水对室温离子液体表面阳离子取向影响的振动和频发生光谱

Sum frequency generation vibrational spectroscopy was used to determine the orientation of the cations in a
room-temperature ionic liquid at the air-liquid interface. The ionic liquid that was studied was 1-butyl-3-
methylimidazolium bis-trifluoromethylsulfonimide, [BMIM]+[imide]-. The orientation of the cation, [BMIM]+,
was studied as a function of water pressure in the vapor over the range of 10-5 to 200 Torr. At water pressures
below 10-4 Torr, the imidazolium ring was oriented parallel to the surface plane. On increasing the water
pressure to greater than 10-4 Torr, the imidazolium ring tipped up from the surface with an angle along the
surface normal of 40-55°. No water signal was observed in the spectra obtained at the water pressures studied
here. 表面和频光谱分析系统(SFG)