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Theoretical study of reactions of N 2 O with NO and OH radicals
Author(s) -
Mebel A. M.,
Lin M. C.,
Morokuma K.,
Melius C. F.
Publication year - 1996
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/(sici)1097-4601(1996)28:9<693::aid-kin8>3.0.co;2-q
Subject(s) - chemistry , reaction rate constant , radical , ab initio , atmospheric temperature range , computational chemistry , molecule , activation energy , kinetic energy , kinetics , thermodynamics , organic chemistry , physics , quantum mechanics
The reactions of N 2 O 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 N 2 O + NO → N 2 + NO 2 (1) was found to proceed by direct oxygen abstraction and to have a barrier of 47 kcal/mol. The theoretical rate constant, k 1 = 8.74 × 10 −19 × T 2.23 exp (−23,292/T) cm 3 molecule −1 s −1 , is in close agreement with earlier estimates. The reaction of N 2 O 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 N 2 O + OH reaction is dominated by the N 2 + O 2 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 N 2 O + OH → N 2 + O 2 H (2A) and N 2 O + OH → HNO + NO (2B) are fitted by the following expressions: $$k_{2A}=2.15\times 10^{-26}\times T^{4.72}\exp(-18,400/T),$$ $$k_{2B}=1.96\times 10^{-28}\times T^{4.33}\exp(-12,623/T),$$ in units of cm 3 molecule −1 s −1 . Both N 2 O + NO and N 2 O + OH reactions are confirmed to enhance, albeit inefficiently, the N 2 O decomposition by reducing its activation energy. © 1996 John Wiley & Sons, Inc.