PRESSURE-DEPENDENCE OF RAMAN AND INFRARED-SPECTRA OF ALPHA, BETA, GAMMA AND DELTA-OCTAHYDRO-1,3,5,7-TETRANITRO-1,3,5,7-TETRAZOCINE

The Raman and infrared spectra are reported of the α-, β-, γ-, and δ-polymorphs of HMX (octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine) under pressure using a diamond anvil cell (DAC). The stability to pressure or the pressure-induced phase transitions were determined for each polymorph. Sample pressures up to 10 kbar were used in the Raman experiments; infrared spectra were recorded at pressures up to 54 kbar. The observed behavior of the polymorphic forms is as follows: β-HMX is stable up to 54 kbar and α-HMX is stable up to 42 kbar. γ-HMX converts to β-HMX at 5.5 kbar, and δ-HMX converts to a mixture of α- and β-HMX at pressures below 0.5 kbar. No new polymorphs were produced under pressure. An inverse relationship exists between temperature and pressure effects; the polymorph most stable at low temperature and having the smallest volume (β-HMX) is the most stable at high pressure. The infrared spectra (600-1700 cm-1) of the solid HMX polymorphs at ambient pressure are reported for the first time without matrix effects. The -CH2- and -NO2 vibrational regions (>1200 cm-1) in the absence of the KBr matrix, and with the increased resolution obtained in the DAC, show minor differences from the KBr spectra reported in the literature. © 1978 American Chemical Society.