Anomalous electronic structure of ionic liquids determined by soft x-ray emission spectroscopy: contributions from the cations and anions to the occupied electronic structure

K Kanai; T Nishi; T Iwahashi; Y Ouchi; K Seki; Y Harada; S Shin

doi:10.1063/1.3036925

Anomalous electronic structure of ionic liquids determined by soft x-ray emission spectroscopy: contributions from the cations and anions to the occupied electronic structure

J Chem Phys. 2008 Dec 14;129(22):224507. doi: 10.1063/1.3036925.

Authors

K Kanai¹, T Nishi, T Iwahashi, Y Ouchi, K Seki, Y Harada, S Shin

Affiliation

¹ Research Center for Materials Science, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan. kaname@mat.chem.nagoya-u.ac.jp

PMID: 19071928
DOI: 10.1063/1.3036925

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.