Structural Transformation and Chemical Stability of a Shock Compressed Insensitive High Explosive Single Crystal: Time-Resolved Raman Spectroscopy

Despite the considerable interest in insensitive high explosives (IHEs), real-time measurements to directly probe the molecular-level response of shock compressed IHE single crystals are lacking. To address this need, plate impact experiments were conducted to measure time-resolved Raman spectra for 1,1-diamino-2,2-dinitroethene (FOX-7) single crystals shock compressed to 20 GPa. Vibrational frequencies from 800 cm^-1 to 1500 cm^-1 were examined with 15 nanosecond time resolution at several peak stresses. At 4 – 6 GPa, two new Raman peaks appeared, consistent with onset of the α′ – ε structural transformation reported previously in static compression work. Raman results to 20 GPa showed neither additional transformations nor any indication of chemical decomposition, in marked contrast to the decomposition observed at lower stresses in shock compressed conventional HE single crystals. Our Raman results support the previous suggestion that strengthening of intra- and inter-molecular bonds, due to the α′ – ε transformation, plays a significant role in the insensitivity of FOX-7 single crystals to shock initiation. The present work provides the first experimental insight into the molecular-level response of a shock compressed IHE single crystal.