The influence of phase transformations on the frequencies of molecular vibrations in films of 2-methylbenzimidazole perchlorate С$_8$Н$_8$N$_2$–HClO$_4$

Films of 2-methylbenzimidazolium perchlorate С$_8$Н$_8$N$_2$–HClO$_4$ (MBI-HClO$_4$) were grown on sapphire Al$_2$O$_3$(0001) substrates. The frequencies of molecular vibrations of MBI-HClO$_4$ were studied during phase transitions from the ionic crystal (IC) state to the intermediate phase and to the ionic liquid (IL) phase. Raman spectra were obtained in the range of 80–3300 cm$^{-1}$, as well as infrared absorption and reflectance (FTIR) spectra in the range of 650–5000 cm$^{-1}$. It was shown that in the IL phase, as in the IR phase, the MBI molecule remains protonated as the MBI-H$^+$ cation, and perchloric acid is present as the ClO$_4^-$ anion. Analysis of the FTIR spectra showed that the ionic liquid crystal state is realized in the intermediate phase.