A far- and mid-infrared study of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) under high pressure

►We report the first high pressure far-IR study of HMX. ►HMX survives pressure cycling to at least 30 GPa. ►Observation of two possible phase transitions near 6 and 12 GPa. ►A phase transition is observed near 25 GPa (probably β → δ).