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.
A new instrument dedicated to the kinetic study of low-temperature gas phase neutral-neutral reactions, including clustering processes, is presented. It combines a supersonic flow reactor with Vacuum Ultra-Violet (VUV) synchrotron photoionization time of flight mass spectrometry. A photoionphotoelectron coincidence detection scheme has been adopted to optimize the particle counting efficiency. The characteristics of the instrument are detailed along with its capabilities illustrated through a few results obtained at low temperatures (< 100 K) including a photoionization spectrum of n-butane, the detection of formic acid dimer formation as well as the observation of diacetylene molecules formed by the reaction between the C 2 H radical and C 2 H 2 .
This commentary addresses the anomalies in the results reported from the CRESU-SIS experiment at the Institute of Physics of Rennes, France. This experimental setup is dedicated to studying ion-molecule kinetic in the gas phase at very low temperatures using a uniform supersonic flow reactor. A reinterpretation of the latest study performed with this instrument highly suggests a dramatic decrease in flow density upon the injection of neutral reactants.In particular, these concerns can be related to the diffusion effects prevalent in the reported results on the vast majority of the kinetics experiments conducted with a uniform supersonic flow reactor. The scientific community in the field of low-temperature chemical kinetics in uniform supersonic flow would greatly benefit from being aware of and comprehending these highlighted anomalies because the evidence in this commentary calls into question many of the results published to date.
In spite of the considerable advances made by Cassini–Huygens in our understanding of Titan, many questions endure. In particular, the detailed processes that lead to the formation of haze aerosols in Titan’s atmosphere, found in high concentrations at low altitudes, are not well identified. Hydrocarbons, which are abundant constituents of Titan’s cold atmosphere originating from photochemical processes, may simultaneously condense on the surface of existing aerosols, nucleate and grow to generate new aerosol seeds. The relative importance of the various processes depends on several factors, including the saturation ratio. The dynamics of hydrocarbon condensation and nucleation in Titan’s atmosphere remains poorly known. Aiming to progress on these issues, we investigate here the kinetics of propane dimer formation at low temperature through state-of-the-art laboratory experiments combined with theoretical calculations. Our results provide an estimate of the rate coefficients, which are then employed to evaluate the abundance of propane dimers in the lower atmosphere of Titan. The mixing ratios of propane dimers inferred, with a maximum abundance of 10 cm−3 near 100 km, is found to be under the detection limit of the Composite Infrared Spectrometer of the Cassini spacecraft. Based on our results, homogeneous nucleation of the most abundant species appears not to be relevant for the growth of aerosols. Future studies should focus on homogeneous nucleation of polar molecules or alternatively on heterogeneous processes, which are usually more efficient.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.