In-situ high pressure study of hydrogen-bonded energetic material N-nitropyrazole

The study investigated the behavior of N-nitropyrazole (1-NP, C 3 H 3 N 3 O 2 ) under high pressure using a diamond anvil cell, Raman spectroscopy, and simulation calculations. The pressure–volume relationship of the sample, molecular interactions, and changes in optical Raman were analyzed. The Raman experiments revealed abnormal vibration intensities and a discontinuity in peak position at 2.2 GPa. For instance, the C-H stretching vibration produces a new vibration peak under pressure, and the NO 2 torsion mode continues to red shift beyond 2.2 GPa. These observations suggest that the crystal’s phase transition results from the distortion of its hydrogen-bonded network structure. The pressure relief experiment confirms the reversibility of the phase transition.