Pressure- and temperature-induced Raman spectral changes of 1-butyl-3-methylimidazolium tetrafluoroborate

In the present study, we have investigated the pressure- and temperature-induced Raman spectral changes of 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]). [bmim][BF4] did not crystallize at high pressures below 1.4GPa. Upon compression, spectral changes in the band due to the CH stretching mode of the alkyl chain are larger than those due to the imidazolium ring, indicating that the environment around the alkyl chain is significantly perturbed. On the other hand, the Raman spectral change of [bmim][BF4] upon cooling at ambient pressure is very small and no crystallization occurs down to 113K.