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

• Binding energies in relation to primary homolysis X-NO 2 bonds (X = C or N) • Length of the longest X-NO 2 bond in relation to binding energies • Binding energies N1s (N-NO 2 ) & O1s (NO 2 ) related to impact & spark sensitivities • Binding energies N1s (N-NO 2 ) & O1s (NO 2 ) related to maximal crystal density • Binding energies N1s (N-NO 2 ) & O1s (NO 2 ) related to detonation velocity • FTIR structural outputs related to binding energies of cocrystals 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 ( E bind ) 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 E bind values in both elements correlate with increasing enthalpy of formation and impact sensitivity. Electric spark sensitivity is directly proportional to O 1s E bind . Detonation velocity increases with E bind ; however, β-CL20/BCHMX composites and the O 1s E bind values of polynitro-polyazarenes (TACOT Z-BTX-TPT) show inverse trends. The relationship of N 1s E bind with the longest X –NO 2 bond ( X = C or N) in the molecule reflects nitro-group interactions with the rest of the molecule, whereas O 1s E bind is shaped by crystal packing. Relationships between E bind and crystal density have also been found and discussed. Additional correlations between N 1s E bind 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.