## Abstract

Potential energy surfaces for the reactions of NH_{3} with NO_{x} (x = 1, 2) have been studied by ab initio molecular orbital Gaussian 1 (G1) and Gaussian 2 (G2) methods. Both reactions have been shown to be endothermic and to proceed by the abstraction of a hydrogen atom from ammonia to produce NH_{2} and HNO_{x}. The calculated heats of reaction are in close agreement with experimental measurements. Reaction 1, NH_{3} + NO, does not have a reverse barrier at the G2 level of theory. Reaction 2, NH_{3} + NO_{2}, can occur by three channels, leading to HNO_{2} (2a), cis-HONO (2b), and trans-HONO (2c), and each mechanism involves the formation of NH_{2}·HNO_{2} or NH_{2}·HONO intermediate complexes. Mechanism 2b has been found to be dominant. Theoretical rate constants for (1), (2b); and their reverse reactions have been computed by VTST in conjunction with detailed balancing for the temperature range of 300-5000 K. The following least-squares fitted expressions are recommended for practical applications: k_{1} = 1.72 × 10^{-17}T^{1.73} e^{-28454/T}, k_{-1} = 6.02 × 10-^{1.63}T^{1.63} e^{630/T}, k_{2b} = 3.92 × 10^{-23}T^{3.41} e^{-11301/T}, k_{-2b} = 11.8 × 10^{-23}T^{3.02} e^{2487/T}, in cm^{3}/(molecule·s). The apparent activation energies calculated variationally for 300 ≤ T ≤ 1000 K, 58.3 and 25.6 kcal/mol for (1) and (2), respectively, agree well with experiments.

Original language | English |
---|---|

Pages (from-to) | 7517-7525 |

Number of pages | 9 |

Journal | Journal of physical chemistry |

Volume | 100 |

Issue number | 18 |

DOIs | |

State | Published - 2 May 1996 |