Combined experimental and computational study of the reactivity of the methanimine radical cation (H2CNH˙+) and its isomer aminomethylene (HCNH2˙+) with propene (CH3CHCH2)

Abstract

The gas phase reactivity of the radical cation isomers H₂CNH˙⁺ (methanimine) and HCNH₂˙⁺ (aminomethylene) with propene (CH₃CHCH₂) has been investigated by measuring absolute reactive cross sections and product branching ratios, under single collision conditions, as a function of collision energy (in the range ∼0.07–11.80 eV) using guided ion beam mass spectrometry coupled with VUV photoionization for selective isomer generation. Experimental results have been merged with theoretical calculations to elucidate reaction pathways and structures of products. The H₂CNH˙⁺ isomer is over a factor two more reactive than HCNH₂˙⁺. A major channel from both isomers is production of protonated methanimine CH₂NH₂⁺via hydrogen-atom transfer reaction but, while H₂CNH˙⁺ additionally gives charge and proton transfer products, the HCNH₂˙⁺ isomer leads instead to protonated vinylimine CH₂CHCHNH₂⁺, produced alongside CH₃˙ radicals. The reactions have astrochemical implications in the build up of chemical complexity in both the interstellar medium and the hydrocarbon-rich atmospheres of planets and satellites.