Investigation of the initiatory reactivity of polynitro -amines and -arenes via X-ray photoelectron spectroscopy

The initiation reactivity of a wide range of polynitro compounds has been assessed via X-ray photoelectron spectroscopy (XPS). These compounds include nitramines (ε-CL20, β-CL20, BCHMX, TTAZ), six β-CL20/BCHMX coagglomerates (CACs) and eight highly thermostable “genuine” polynitroarenes (HNBP, ONT, NONA, DODECA, TENN, BTX, TPT and TACOT Z), all of which exhibit primary homolysis of the trigger bond. The binding energies (Ebind) of N 1s and O 1s electrons have been analyzed in relation to the enthalpy of formation, impact and electric-spark sensitivity, detonation velocity and crystal density. Higher Ebind values in both elements correlate with increasing enthalpy of formation and impact sensitivity. Electric spark sensitivity is directly proportional to O 1s Ebind. Detonation velocity increases with Ebind; however, β-CL20/BCHMX composites and the O 1s Ebind values of polynitro-polyazarenes (TACOT Z-BTX-TPT) show inverse trends. The relationship of N 1s Ebind with the longest X–NO2 bond (X = C or N) in the molecule reflects nitro-group interactions with the rest of the molecule, whereas O 1s Ebind is shaped by crystal packing. Relationships between Ebind and crystal density have also been found and discussed. Additional correlations between N 1s Ebind values and FTIR symmetric N–O stretching support the identification cocrystals in CACs. These findings highlight XPS as a valuable tool for probing initiation reactivity and intermolecular behavior in energetic materials.