Low frequency Raman Spectroscopy and liquid structure of imidazolium based ionic liquids

I&EC 15

Hajime Okajima, okajima@chem.s.u-tokyo.ac.jp and Hiro-o Hamaguchi, hhama@chem.s.u-tokyo.ac.jp. Department of Chemistry, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
Low frequency Raman spectroscopy in the frequency region below 200cm-1 provides us with valuable information about intermolecular interactions in liquids and solutions.We applied this spectroscopy to butylmethylimidazolium based ionic liquids (bmimX) and some related molecular liquids, in order to reveal the liquid structure of ionic liquids.For bmimX and butylimidazole, we observed characteristic intense low frequency Raman bands around 100cm-1.In chloroform solutions, their intensities showed non-linear dependence on concentration,contrast to high frequency intra-molecular vibrational bands'.We discuss the cation, anion, concentration, and temperature dependence of these bands, in terms of inter-molecular dynamics of ionic liquids.