All ionic liquids used in this work were purchased from Iolitec and used without
further purification. They were dried under high vacuum (below 10-5 mbar) for several
days. Raman spectra as a function of temperature at atmospheric pressure were recorded
with a Jobin-Yvon T64000 triple monochromator spectrometer equipped with CCD.
The spectra were excited with the 647.1 nm line of a mixed argon-krypton Coherent
laser, and the spectral resolution was 2.0 cm-1. Raman spectra were obtained in 180o
scattering geometry with no selection of polarization of the scattered radiation.
Temperature control was achieved with an OptistatDN cryostat (Oxford Instruments).
The ionic liquids were cooled at a typical rate of 20 Kmin-1, waiting about 30 minutes
for equilibration before acquisition of the spectrum at each temperature.