The reactions of N2O with NO and OH radicals have been studied using ab initio molecular orbital theory. The energetics and molecular parameters, calculated by the modified Gaussian-2 method (G2M), have been used to compute the reaction rate constants on the basis of the TST and RRKM theories. The reaction N2O + NO → N2 + NO2 (1) was found to proceed by direct oxygen abstraction and to have a barrier of 47 kcal/mol. The theoretical rate constant, k1 = 8.74 × 10-19 × T2.23 exp (-23,292/T) cm33 molecule-1 s-1, is in close agreement with earlier estimates. The reaction of N2O with OH at low temperatures and atmospheric pressure is slow and dominated by association, resulting in the HONNO intermediate. The calculated rate constant for 300 K ≤ T ≤ 500 K is lower by a few orders than the upper limits previously reported in the literature. At temperatures higher than 1000 K, the N2 O + OH reaction is dominated by the N2 + O2 H channel, while the HNO + NO channel is slower by 2-3 orders of magnitude. The calculated rate constants at the temperature range of 1000-5000 K for N2 O + OH → N2 + O2 H (2A) and N2 O + OH → HNO + NO (2B) are fitted by the following expressions: k2A = 2.15 × 10-26 X T-4.72 × exp(-18,400/T), k2B = 1.96 × 10-28 X T4.33 × exp(-12,623/T), in units of cm3 molecule-1 s-1. Both N2O + NO and N2O + OH reactions are confirmed to enhance, albeit inefficiently, the N2O decomposition by reducing its activation energy.
|Number of pages||11|
|Journal||International Journal of Chemical Kinetics|
|State||Published - Sep 1996|