Raman and IR studies of polymorphism in n-hexanol at high pressure and low temperature

As one important organic molecule, the structure stability and polymorphism of n-hexanol (C6H14O) have been investigated at low temperature and high pressure using in situ Raman and infrared spectroscopy. The existence of three polymorphs is observed for n-hexanol in this work. The liquid n-hexanol converts to the monoclinic gamma-phase structure at 203 K and 0.8 GPa respectively. Additional changes are observed in spectra at 3.0 and 7.3 GPa, because of two additional phase transitions to monoclinic,beta-phase structures. In addition, conformational change between trans and gauche is also observed accompanied by the phase transitions. Moreover, hydrogen-bond formation and its response to the external pressure are confirmed from infrared spectra. Finally, the phase transitions under high pressure and low temperature are reversible. These results are helpful for understanding of structure transition under external condition for n-alcohols and other organic molecules. (C) 2017 Published by Elsevier B.V.