Orientation of cations at the air/liquid interfaces of the salts of 1-butyl-3-methyl imidazolium with tetrafluoroborate and hexafluorophosphate is studied using infraredvisible sum frequency vibrational spectroscopy. For both salts, quantitative analyses show that the terminal methyl group of the butyl chain is polar-oriented with its symmetry axis aligned nearly vertical to the surface. 表面和頻光譜分析系統(tǒng)(SFG)