High-pressure Raman scattering studies on hexamethylenetetramine

High-pressure Raman spectroscopic measurements have been carried out on hexamethylenetetramine (C6N4H12) up to pressures of 20 GPa. The evolution of Raman spectra at high pressures shows that the system undergoes two structural transitions around 1.4 and 12.5 GPa. The second phase transition around 12.5 GPa is associated with a large hysteresis indicating the first-order nature of the transition. Excessive broadening accompanied by considerable decrease in intensity of the internal modes above 15 GPa suggests that the system could be disordered above this pressure.