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

Abstract

Reactions of the methylidyne (CH) radical with ammonia (NH 3 ), methylamine (CH 3 NH 2 ), dimethylamine ((CH 3 ) 2 NH), and trimethylamine ((CH 3 ) 3 N), have been investigated under multiple collision conditions at 373 K and 4 Torr. The reaction products are detected 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=CH 2 , 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 amino carbene 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.

Directed Gas-Phase Formation of Aminosilylene (HSiNH2;X1A′): The Simplest Silicon Analogue of an Aminocarbene, under Single-Collision Conditions

“…The profound effect by replacing a single carbon atom by silicon is depicted in Figure . The molecular geometries of methanimine (1) and aminomethylene (2) including the relative energies, bond distances, and angles were extracted from the literature. − …”

“…The distinct chemical bondings of silicon–nitrogen versus the isovalent carbon–nitrogen compounds are well expressed, when contemplating aminosilylene ( 3 ) and silanimine ( 4 ) with their carbon analogues methanimine ( 1 ) and aminomethylene ( 2 ) (Figure ). ,− Methanimine (H 2 CNH, 1 ) represents the global minimum and is thermodynamically more stable by 150 kJ mol –1 compared to the carbene structure aminomethylene (HNCH 2 , 2 ). The sequence of stability is reversed when replacing a carbon atom by silicon with aminosilylene (HSiNH 2 , 3 ) corresponding to the global minimum and silanimine (H 2 SiNH, 4 ) lying 70 kJ mol –1 higher in energy.…”

Formation of a Resonance-Stabilized Radical Intermediate by Hydroxyl Radical Addition to Cyclopentadiene

“…The reaction of OH with cyclopentadiene proceeds with a rate coefficient of 9.2 × 10 –11 cm –3 s –1 at room temperature. , Assuming pseudo-first-order approximation and a cyclopentadiene number density of 5.7 × 10 13 cm –3 , the characteristic time for the decay of the OH radical and rise of the primary products is of an order of 190 μs (rate of 5200 s –1 ). Reactions of primary products with remaining radicals or other photoproducts in the flow may lead to the formation of secondary products over the experimental reaction time with a slower formation. , It is therefore possible to discriminate between primary and secondary reactions by integrating mass spectra and photoion spectra over the first few milliseconds of reaction time. Products showing a slow initial formation will have a smaller contribution to the spectra.…”

“…Reactions of primary products with remaining radicals or other photoproducts in the flow may lead to the formation of secondary products over the experimental reaction time with a slower formation. 47,65 It is therefore possible to discriminate between primary and secondary reactions by integrating mass spectra and photoion spectra over the first few milliseconds of reaction time. Products showing a slow initial formation will have a smaller contribution to the spectra.…”

Low-Temperature Gas-Phase Formation of Methanimine (CH2NH; X1A′)─the Simplest Imine─under Single-Collision Conditions

“…Kinetic measurements were conducted by Zabarnick et al and Bocherel et al exploiting the PLP (pulse laser photolysis)–LIF (laser-induced fluorescence) method; these works revealed fast reaction rates of 2.21 × 10 –10 cm 3 s –1 at 23 K. In 2012, Blitz et al determined the hydrogen atom yield to be 0.89 ± 0.07 and combined these studies with high-level ab initio calculations. More recently, this reaction was investigated under multiple collision conditions at 373 K and 4 Torr in a flow reactor with the predominant formation of methanimine inferred …”