title: Anomalous electronic structure of ionic liquids determined by soft x-ray emission spectroscopy: contributions from the cations and anions to the occupied electronic structure.
abstract: Soft x-ray emission spectroscopy was used for elucidating the electronic structure of ionic liquids [C(4)mim](+)PF(6)(-) and [C(4)mim](+)OTf(-), where [C(4)mim](+) stands for methylbutylimidazolium cation and OTf(-) for the trifluoromethanesulfonate anion. Nonresonant spectra measured above N, O, and F 1s edges selectively probed the molecular orbitals (MOs) of the cation and anions. They give a clear evidence that the highest occupied molecular orbital of the [C(4)mim](+) cation contributes to the topmost occupied states of the ionic liquids [C(4)mim](+)PF(6)(-), while both cationic and anionic MOs contribute for the case of [C(4)mim](+)OTf(-). Resonant soft x-ray emission spectra at the N 1s edge of these ionic liquids revealed that the energy gap of [C(4)mim](+)PF(6)(-) is solely determined by the [C(4)mim](+) cation, in contrast to usual ionic crystals. The ionic liquids form a new class of the ionic materials from the viewpoint of the electronic structure.
authors.affiliation: Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan. kaname@mat.chem.nagoya-u.ac.jp
authors.forename: K
authors.initials: K
authors.lastname: Kanai
authors.forename: T
authors.initials: T
authors.lastname: Nishi
authors.forename: T
authors.initials: T
authors.lastname: Iwahashi
authors.forename: Y
authors.initials: Y
authors.lastname: Ouchi
authors.forename: K
authors.initials: K
authors.lastname: Seki
authors.forename: Y
authors.initials: Y
authors.lastname: Harada
authors.forename: S
authors.initials: S
authors.lastname: Shin