Energetics of ammonium perchlorate decomposition steps

Energy minima and enthalpies at 298 and 800 K were computed for 37 atoms, molecules and ions that have been implicated as intermediates in the thermal decomposition of ammonium perchlorate. These data permit the calculation of Delta H(298 K) and Delta H(800 K) for hundreds of reactions that may be involved; 39 of these are listed, and several possible decomposition pathways are outlined. The computations were carried out at the density functional B3PW91/6-311 + G(2df) level, which we found to be effective for systems containing several oxygen and/or chlorine atoms in close proximity. Delta H(298 K) and Delta H(800 K) are found to differ by less than 1.0 kcal mol(-1). We have identified an intermediate complex in the sublimation of ammonium perchlorate (believed to be the first decomposition step) which accounts for the activation energy of sublimation being considerably less than its overall enthalpy change. (C) 1998 Elsevier Science B.V. All rights reserved.