Product Detection of the CH Radical Reactions with Ammonia and Methyl-Substituted Amines

• Published in: The journal of physical chemistry. A, Molecules, spectroscopy, kinetics, environment, & general theory Vol. 123; no. 11; pp. 2178 - 2193
• Main Authors: Bourgalais, Jeremy, Caster, Kacee L, Durif, Olivier, Osborn, David L, Le Picard, Sebastien D, Goulay, Fabien
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 21.03.2019
• Subjects: Alkyls; Chemical Physics; Chemical reactions; Chemical Sciences; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Molecular structure; Nitrogen; or physical chemistry; Photoionization; Physics; Theoretical and; Photoionization spectra; Amines; Advanced light sources; Linear combinations; Isomers; Product formation; Product detection; Light sources; Reaction products; Orthogonal acceleration; Ammonia; Photoionization; Amination; Reaction kinetics; Addition-elimination; Multiple collisions; Fighter aircraft; Mass spectrometry
• ISSN: 1089-5639; 1520-5215
• DOI: 10.1021/acs.jpca.8b11688

Reactions of the methylidyne (CH) radical with ammonia (NH3), methylamine (CH3NH2), dimethylamine ((CH3)2NH), and trimethylamine ((CH3)3N) have been investigated under multiple collision conditions at 373 K and 4 Torr. The reaction products are detected by using soft photoionization coupled to orthogonal acceleration time-of-flight mass spectrometry at the Advanced Light Source (ALS) synchrotron. Kinetic traces are employed to discriminate between CH reaction products and products from secondary or slower reactions. Branching ratios for isomers produced at a given mass and formed by a single reaction are obtained by fitting the observed photoionization spectra to linear combinations of pure compound spectra. The reaction of the CH radical with ammonia is found to form mainly imine, HNCH2, in line with an addition–elimination mechanism. The singly methyl-substituted imine is detected for the CH reactions with methylamine, dimethylamine, and trimethylamine. Dimethylimine isomers are formed by the reaction of CH with dimethylamine, while trimethylimine is formed by the CH reaction with trimethylamine. Overall, the temporal profiles of the products are not consistent with the formation of aminocarbene products in the reaction flow tube. In the case of the reactions with methylamine and dimethylamine, product formation is assigned to an addition–elimination mechanism similar to that proposed for the CH reaction with ammonia. However, this mechanism cannot explain the products detected by the reaction with trimethylamine. A CH insertion pathway may become more probable as the number of methyl groups increases.