Energetics of ammonium perchlorate decomposition steps

Energy minima and enthalpies at 298 and 800 K were computed for 37 atoms, m olecules and ions that have been implicated as intermediates in the thermal decomposition of ammonium perchlorate. These data permit the calculation o f Delta H(298 K) and Delta H(800 K) for hundreds of reactions that may be i nvolved; 39 of these are listed, and several possible decomposition pathway s 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 co ntaining several oxygen and/or chlorine atoms in close proximity. Delta H(2 98 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 fo r the activation energy of sublimation being considerably less than its ove rall enthalpy change. (C) 1998 Elsevier Science B.V. All rights reserved.