In the low frequency region of Fig. , four bands can be clearly identified: two overlapping bands in the region 1000-1100 cm -1 , one band in the region 1100-1200 cm -1 , and one band localized at 1300 cm -1 . The four bands see the participation of the three fragments of the molecule analyzed above, together with a contribution from the vibration of the CH bond that is not involved in the CH 3 fragment (see Fig. ).