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Gas-Phase Reactivity of the CN radical with methyl amines at low temperatures (23 - 297K) : a combined experimental and theoretical investigation

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Authors : C. Sleiman, G. El Dib, D. Talbi, and A. Canosa.

Abstract : The gas phase reactivity of the CN radical in the presence of dimethylamine (CH3)2NH and trimethylamine (CH3)3N has been investigated experimentally using a uniform supersonic expansion CRESU reactor coupled to the pulsed laser photolysis/laser-induced fluorescence technique. Rate constants have been obtained in the temperature range 23−297 K and were found to be independent of temperature for both reactants. A typical rate constant of 5 × 10−10 cm3 molecule−1 s−1 is representative of the full set of experiments. Additionally, ab initio calculations at the ROCCSD(T)/6-311++G (3df,2pd)//M062X/6-311++G(d,p) evel of theory have been carried out in order to determine the energy profiles along the reaction pathways. The paths corresponding to the hydrogen abstraction with the formation of HCN were found to be barrierless and very exothermic for the two studied reactions. Results are compared to previous works concerning the reactivity of CN with
ammonia NH3 and methylamine CH3NH2. The energy profile for the reaction
with methylamine has been revisited using the level of theory mentioned above. Calculations indicate that hydrogen abstraction is the major reaction pathway as well, in contradiction with a previous investigation claiming that the CN/CH3 substitution is the dominant exit channel.
Journal : Earth and Space Chemistry 2[10], 1047-1057 (2018).