Electron Radiolysis of Ammonium Perchlorate: A Reflectron Time-of-Flight Mass Spectrometric Study

Thin films of ammonium perchlorate (NH₄ClO₄) were exposed to energetic electrons at 5.5 K to explore the radiolytic decomposition mechanisms. The effects of radiolysis were monitored on line and in situ via Fourier transform infrared spectroscopy (FTIR) in the condensed phase along with electron impact ionization quadrupole mass spectrometry (EI-QMS) and single-photon photoionization reflectron time-of-flight mass spectrometry (PI-ReTOF-MS) during the temperature-programmed desorption (TPD) phase to probe the subliming molecules. Three classes of molecules were observed: (i) nitrogen bearing species [ammonia (NH₃), hydroxylamine (NH₂OH), molecular nitrogen (N₂), nitrogen dioxide (NO₂)], (ii) chlorine carrying molecules [chlorine monoxide (ClO), chlorine dioxide (ClO₂), dichlorine trioxide (Cl₂O₃)], and (iii) molecular oxygen (O₂). Decay profiles of the reactants along with the growth profiles of the products as derived from the infrared data were fit kinetically to obtain a reaction mechanism with the initial steps involving a proton loss from the ammonium ion (NH₄⁺) yielding ammonia (NH₃) and the decomposition of perchlorate ion (ClO₄^-) forming chlorate ion (ClO₃^-) plus atomic oxygen. The latter oxidized ammonia to hydroxylamine and ultimately to nitrogen dioxide. Molecular oxygen and nitrogen were found to be formed via recombination of atomic oxygen and multistep radiolysis of ammonia, respectively.