title: Local structure at the air/liquid interface of room-temperature ionic liquids probed by infrared-visible sum frequency generation vibrational spectroscopy: 1-alkyl-3-methylimidazolium tetrafluoroborates.
abstract: The air/liquid interface of 1-alkyl-3-methylimidazolium tetrafluoroborates with the general formula [C(n)mim]BF(4) (n = 4-11) was studied using infrared-visible sum frequency generation (SFG) vibrational spectroscopy. The probability of the gauche defect per CH2-CH2 bond in the alkyl chain decreases as the number of carbon atoms in the alkyl chain increases. This observation suggests that the interaction between the alkyl chains is enhanced as the alkyl chain length becomes longer. The frequencies of the C-H stretching vibrational modes observed in the SFG spectra are higher than those of the corresponding peak positions observed in the infrared spectra of the bulk liquids. This shift is consistent with a structure in which the alkyl chain protrudes from the bulk liquid into the air. A local structure, which originates from the intermolecular interaction between the ionic liquid molecules, is proposed to explain these observations.
authors.affiliation: Research Center for Materials Science, Nagoya University, Nagoya 464-8602, Japan.
authors.forename: Toshifumi
authors.initials: T
authors.lastname: Iimori
authors.forename: Takashi
authors.initials: T
authors.lastname: Iwahashi
authors.forename: Kaname
authors.initials: K
authors.lastname: Kanai
authors.forename: Kazuhiko
authors.initials: K
authors.lastname: Seki
authors.forename: Jaeho
authors.initials: J
authors.lastname: Sung
authors.forename: Doseok
authors.initials: D
authors.lastname: Kim
authors.forename: Hiro-o
authors.initials: HO
authors.lastname: Hamaguchi
authors.forename: Yukio
authors.initials: Y
authors.lastname: Ouchi
mesh_terms: D000388:Air; D001881:Borates / Q000737:chemistry*; D052578:Ionic Liquids / Q000737:chemistry*; D012680:Sensitivity and Specificity; D013055:Spectrophotometry, Infrared / Q000379:methods; D013696:Temperature; D014732:Vibration
chemical_list: D001881:Borates; D052578:Ionic Liquids