Orientation of cations at the air/liquid interfaces of the salts of 1-butyl-3-methyl imidazolium with tetrafluoroborate and hexafluorophosphate is studied using infrared-visible 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. (C) 2004 Elsevier B.V. All rights reserved.