## 摘要

We have studied for the first time the kinetics and mechanism for the sublimation/decomposition of NH_{4}ClO_{4} by first-principles calculations, using a generalized gradient approximation with the plane-wave density functional theory. Supercells containing 4, 8, and 16 NH _{4}ClO_{4} units were used; the predicted enthalpic change for solid NH_{4}ClO_{4} to gaseous NH_{3} and HClO _{4} is 45.0 ± 1.5 kcal/mol. The calculated desorption activation energies for NH_{3}, HClO_{4}, and H_{3}N⋯ HOClO_{3} molecular complexes, individually, from the relaxed surface are 45.3, 43.5, and 28.1 kcal/mol, respectively. The rate constant for the dominant sublimation process desorbing H_{3}N⋯HOClO_{3} as a pair can be presented by k_{sub}.= 6.53 × 10^{12} exp (-28.8 kcal/mol/RT) s^{-1}, which is in reasonable agreement with available experimental data. Expectably, the decomposition of H _{3}N⋯HOClO_{3} (g) to NH_{3} (g) and HOClO _{3} (g) is considerably faster, about 1 × 10^{7} times greater than that for the sublimation process in the same temperature range. The rate constant for the gas-phase dissociation step can be expressed by 1.20 × 10^{15} exp (-14.6 kcal/mol/RT) sec^{-1}. This study further confirms that the activation energy for the sublimation of an ammonium salt is significantly lower than the enthalpic change and that the molecular complex of acid and base sublimes concurrently as a pair.

原文 | English |
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頁（從 - 到） | 14481-14485 |

頁數 | 5 |

期刊 | Journal of Physical Chemistry C |

卷 | 112 |

發行號 | 37 |

DOIs | |

出版狀態 | Published - 18 9月 2008 |