Energized complex quantum Rice-Ramsperger-Kassel analysis on reactions of NH2 with HO2, O2, and O atoms

Document Type

Article

Publication Date

1-1-1989

Abstract

The addition reactions of NH2 with HO2, O2, and O to form energized adducts have been analyzed as a chemically activated system by using a bimolecular version of the quantum Rice-Ramsperger-Kassel (QRRK) theory for temperatures from 200 to 1900 K and pressures from 0.001 to 10 atm with various bath gases. We predict that essentially 100% of the [NH2OOH] * adduct from the NH2 + HO2 reaction dissociates to the low-energy exit channel NH2O + OH over the above temperature and pressure regimes. Stabilization or isomerization of the complex and subsequent dissociation to HNO + H2O does not occur to any significant extent. This result suggests that NH2 + HO2 → NH2O + OH should be included in kinetic models for ammonia oxidation. Our calculations on the reaction of NH2 + O2 -NH2O2 are in agreement with the experimentally observed upper limits obtained in previous studies. We utilize the room-temperature upper limit rate constant data of Michael et al. to calculate an upper limit bond strength for NH2-OO of 12.5 kcal/mol. The isomerization barrier height NH2O2 ↔ HNOOH) in the NH2 + O2 reaction is shown to be dominant, below 600 K, for control of the principal reaction channel: NH2O + O versus HNO + OH. Above this temperature NH2O + O is calculated to be the primary product channel, further indicating that NH2O needs to be considered in high or moderate temperature ammonia oxidation reaction mechanisms. Branching ratios for the reaction of NH2 + O to NH + OH versus HNO + H products calculated from fundamental thermodynamic and kinetic principles are in remarkably good agreement with the experimental results of Dransfield et al. These branching ratios are nearly independent of pressure up to 10 atm but are somewhat dependent on exit channel barriers. Stabilization to NH2O is unimportant below 10 atm. © 1989 American Chemical Society.

Identifier

0000479094 (Scopus)

Publication Title

Journal of Physical Chemistry

External Full Text Location

https://doi.org/10.1021/j100340a009

ISSN

00223654

First Page

1058

Last Page

1065

Issue

3

Volume

93

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