Ammonium Perchlorate and Ammonium Dihydrogen Phosphate as Energetic Materials: Comparison to Ammonium Nitrate

Ammonium perchlorate (NH4ClO4) and ammonium dihydrogen phosphate (NH4H2PO4) are investigated through laser ablation/matrix-assisted laser desorption ionization processes, anion photoelectron spectroscopy (PES), and density functional theory calculations. No parent anionic species are observed in the mass spectra of these two energetic species. Instead, abundant fragmentation ions for perchlorate are (NH4ClO4-H2O)-and ClO3- and those for dihydrogen phosphate are (NH4H2PO4-H2O)(-) and PO3-. Their vertical detachment energies and anionic structures are determined and identified through calculations. (NH4H2PO4-H3O)(-) is additionally detected through PES. Both NH4ClO4- and NH4H2PO4- parent anions possess a dipole bound extra electron distributed around the H atoms of the NH4 group. Based on the calculations, the fragmentation pathway for loss of H2O from either molecule involves detachment of two hydrogens from NH4 and one O from ClO4 or PO4H2. These current investigation results are compared to those previously established for NH4NO3, which include hydration, addition of H, isomerization, and reactive intermediate formation. The rich anion chemistry found for NH4NO3 is thereby further emphasized and characterized. This chemistry may well be responsible for NH4NO3's enhanced energetic properties.