Ab initio chemical kinetics for the NH2 + HNOx Reactions, Part I: Kinetics and Mechanism for NH2 + HNO

✍ Scribed by Shucheng Xu; M. C. Lin

• Publisher: John Wiley and Sons
• Year: 2009
• Tongue: English
• Weight: 435 KB
• Volume: 41
• Category: Article
• ISSN: 0538-8066
• DOI: 10.1002/kin.20453

✦ Synopsis

Abstract

The kinetics and mechanism for the reaction of NH~2~ with HNO have been investigated by ab initio calculations with rate constant prediction. The potential energy surface of this reaction has been computed by single‐point calculations at the CCSD(T)/6‐311+G(3__df__, 2__p__) level based on geometries optimized at the CCSD/6‐311++G(d, p) level. The major products of this reaction were found to be NH~3~ + NO formed by H‐abstraction via a long‐lived H~2~N⋅⋅⋅HNO complex and the H~2~NN(H)O radical intermediate formed by association with 26.9 kcal/mol binding energy. The rate constants for formation of primary products in the temperature range of 300–3000 K were predicted by variational transition state or RRKM theories. The predicted total rate constants at the 760 Torr Ar pressure can be represented by k~total~ = 3.83 × 10^−20^ × T^+2.47^exp(1450/T) at T = 300–600 K; 2.58 × 10^−22^ × T^+3.15^ exp(1831/T) cm^3^ molecule^−1^ s^−1^ at T = 600−3000 K. The branching ratios of major channels at 760 Torr Ar pressure are predicted: k~1~ + k~3~ + k~4~ producing NH~3~ + NO accounts for 0.59–0.90 at T = 300–3000 K peaking around 1000 K, k~2~ accounts for 0.41–0.03 at T = 300–600 K decreasing with temperature, and k~5~ accounts for 0.07–0.27 at T > 600 K increasing gradually with temperature. The NH~3~ + NO formation rate constant was found to be a factor of 3–10 smaller than that of the isoelectronic reaction CH~3~ + HNO producing CH~4~ + NO, which has been shown to take place by barrierless H‐abstraction without involving a hydrogen‐bonding complex as in the NH~2~ case. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 677–677, 2009