Kinetics of CN reactions with N2O and CO2

Niann-Shiah Wang, D. L. Yang, Ming-Chang Lin*, C. F. Melius

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Scopus citations

Abstract

The rate constants for the reaction of CN with N2O and CO2 have been measured by the laser dissociation/laser‐induced fluorescence (two‐laser pump‐probe) technique at temperatures between 300 and 740 K. The rate of CN + N2O was measurable above 500 K, with a least‐squares averaged rate constant, k = 10−11.8±0.4 exp(−3560 ± 181/T) cm3/s. The rate of CN + CO2, however, was not measurable even at the highest temperature reached in the present work, 743 K, with [CO2] ⩽ 1.9 × 1018 molecules/cm3. In order to rationalize the observed kinetics, quantum mechanical calculations based on the BAC‐MP4 method were performed. The results of these calculations reveal that the CN + N2O reaction takes place via a stable adduct NCNNO with a small barrier of 1.1 kcal/mol. The adduct, which is more stable than the reactants by 13 kcal/mol, decomposes into the NCN + NO products with an activation energy of 20.0 kcal/mol. This latter process is thus the rate‐controlling step in the CN + N2O reaction. The CN + CO2 reaction, on the other hand, occurs with a large barrier of 27.4 kcal/mol, producing an unstable adduct NCOCO which fragments into NCO + CO with a small barrier of 4.5 kcal/mol. The large overall activation energy for this process explains the negligibly low reactivity of the CN radical toward CO2 below 1000 K. Least‐squares analyses of the computed rate constants for these two CN reactions, which fit well with experimental data, give rise to (Formula Presented.) (Formula Presented.) for the temperature range 300–3000 K.

Original languageEnglish
Pages (from-to)151-160
Number of pages10
JournalInternational Journal of Chemical Kinetics
Volume23
Issue number2
DOIs
StatePublished - 1 Jan 1991

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