Direct measurements of the total rate constant of the reaction NCN plus H and implications for the product branching ratio and the enthalpy of formation of NCN

Fassheber, Nancy, Dammeier, Johannes and Friedrichs, Gernot (2014) Direct measurements of the total rate constant of the reaction NCN plus H and implications for the product branching ratio and the enthalpy of formation of NCN Physical Chemistry Chemical Physics, 16 (23). pp. 11647-11657.

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Abstract

The overall rate constant of the reaction (2), NCN + H, which plays a key role in prompt-NO formation in flames, has been directly measured at temperatures 962 K < T < 2425 K behind shock waves. NCN radicals and H atoms were generated by the thermal decomposition of NCN3 and C2H5I, respectively. NCN concentration-time profiles were measured by sensitive narrow-line-width laser absorption at a wavelength of lambda = 329.1302 nm. The obtained rate constants are best represented by the combination of two Arrhenius expressions, k(2)/(cm(3) mol(-1) s(-1)) = 3.49 x 10(14) exp(-33.3 kJ mol(-1)/RT) + 1.07 x 10(13) exp(+10.0 kJ mol(-1)/RT), with a small uncertainty of +/- 20% at T = 1600 K and +/- 30% at the upper and lower experimental temperature limits. The two Arrhenius terms basically can be attributed to the contributions of reaction channel (2a) yielding CH + N-2 and channel (2b) yielding HCN + N as the products. A more refined analysis taking into account experimental and theoretical literature data provided a consistent rate constant set for k(2a), its reverse reaction k(1a) (CH + N-2 -> NCN + H), k(2b) as well as a value for the controversial enthalpy of formation of NCN, Delta H-f(298K)degrees = 450 kJ mol(-1). The analysis verifies the expected strong temperature dependence of the branching fraction phi = k(2b)/k(2) with reaction channel (2b) dominating at the experimental high-temperature limit. In contrast, reaction (2a) dominates at the low-temperature limit with a possible minor contribution of the HNCN forming recombination channel (2d) at T < 1150 K.

Document Type: Article
Additional Information: Times Cited: 0 0
Research affiliation: Kiel University
UNSPECIFIED
OceanRep > The Future Ocean - Cluster of Excellence
Refereed: Yes
ISSN: 1463-9076
Projects: Future Ocean
Date Deposited: 30 Mar 2015 12:09
Last Modified: 21 Mar 2017 11:48
URI: http://eprints.uni-kiel.de/id/eprint/27494

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