Temperature-dependence of the low-frequency spectrum of 1-pentyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide studied by optical Kerr effect spectroscopy

The spectrum of the ionic liquid, 1-pentyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, in the 0–250 cm−1 region was studied as a function of temperature from 280 to 393 K. The spectra were obtained by using optical Kerr effect spectroscopy. The intermolecular part of the spectrum can be decomposed into two components. The first spectral moments of both components decrease with temperature. However, the width of the low-frequency component decreases with temperature, while that of the high-frequency component increases and then remains constant above 323 K. This difference is interpreted as being due to the mixed intermolecular/intramolecular character of the high-frequency component.