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Shock Tube Measurements of the Rate Constant of the Reaction NCN + O 2
Author(s) -
Faßheber Nancy,
Friedrichs Gernot
Publication year - 2015
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.20932
Subject(s) - chemistry , cyanogen , reaction rate constant , arrhenius equation , radical , thermal decomposition , singlet state , shock wave , photochemistry , shock tube , decomposition , adduct , analytical chemistry (journal) , kinetics , thermodynamics , activation energy , atomic physics , excited state , organic chemistry , physics , quantum mechanics
The rate constant of the comparably slow bimolecular NCN radical reaction NCN + O 2 has been measured for the first time under combustion relevant conditions using the shock tube method. The thermal decomposition of cyanogen azide (NCN 3 ) served as a clean high‐temperature source of NCN radicals. NCN concentration–time profiles have been detected by narrow‐bandwidth laser absorption atν ̃ = 30383.11 cm −1 . The experiments behind incident shock waves have been performed with up to 17% O 2 in the reaction gas mixture. At such high O 2 mole fractions, it was necessary to take O 2 relaxation into account that caused a gradual decrease of the temperature during the experiment. Moreover, following fast decomposition of NCN 3 and collision‐induced intersystem crossing of the initially formed singlet NCN to its triplet ground state, an unexpected and slow additional formation of triplet NCN has been observed on a 100‐μs timescale. This delayed NCN formation was attributed to a fast recombination of 1 NCN with O 2 forming a 3 NCNOO adduct acting as a reservoir species for NCN. Rate constant data for the reaction NCN + O 2 have been measured at temperatures between 1674 and 2308 K. They are best represented by the Arrhenius expressionk 2 / (cm 3mol− 1s − 1 ) = 1.3 × 10 12 exp ( − 97kJmol − 1R T ) , ( ± 57 % ) . No pressure dependence has been observed at pressures between 216 and 706 mbar.