Evidence for a High‐Pressure Phase Transition of ε‐2,4,6,8,10,12‐Hexanitrohexaazaisowurtzitane (CL‐20) Using Vibrational Spectroscopy

The high‐pressure response of ε‐2,4,6,8,10,12‐hexanitrohexaazaisowurtizane (CL‐20) has been examined to 27 GPa in diamond anvil cells using vibrational spectroscopy. The results reveal evidence of an ε→γ pressure‐induced phase transition between 4.1 and 6.4 GPa and suggest the existence of a γ→ζ transition near 18.7 GPa. Several Raman and infrared frequencies were found to decrease in intensity as the phase boundaries are approached. An anomalous intensity increase was noted in the C N C infrared mode that is believed to result from an increase in the Raman cross‐section due to a stronger interlayer coupling under pressure.