ISSN:
0538-8066
Keywords:
Chemistry
;
Physical Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
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 \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{{\rm N}_{\rm 2} {\rm O}} \, = \,6.4 \times 10^{- 21} {\rm T}^{{\rm 2}{\rm .6}} \exp (- 1860/{\rm T)cm}^{\rm 3} /{\rm s} $$\end{document} \documentclass{article}\pagestyle{empty}\begin{document}$$ k_{{\rm C} {\rm O}_{\rm 2}} \, = \,6.1 \times 10^{- 18} {\rm T}^{{\rm 2}{\rm .2}} \exp (- 13530/{\rm T)cm}^{\rm 3} /{\rm s} $$\end{document} for the temperature range 300-3000 K.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/kin.550230206
