Carbon Atom Condensation on NH₃–H₂O Ices. An Alternative Pathway to Interstellar Methanimine and Methylamine

Abstract

The recent discovery of the nature and behavior of carbon atoms interacting with interstellar ices has prompted a number of investigations on the chemistry initiated by carbon accretion on icy interstellar dust. In this work, we expand the range of processes promoted by carbon accretion to the chemistry initiated by the interaction of this atom with ammonia (NH 3 ) using quantum chemical calculations. We found that carbon addition to the ammonia molecule forms a rather stable radical, CNH 3 , that is easily hydrogenated. The complete hydrogenation network is later studied. Our calculations reveal that while conversion to simpler molecules like HCN and HNC is indeed a possible outcome promoted by H-abstraction reactions, methylamine is also easily formed (CH 3 NH 2 ). In fact, the stability of methylamine against hydrogen abstraction makes this molecule the preferred product of the reaction network. Our results serve as a stepping stone toward the accurate modeling of C-addition reactions in realistic astrochemical kinetic models.

The Complex (Organic) Puzzle of the Formation of Hydrogen Cyanide and Isocyanide on Interstellar Ice Analogues

“…Indeed, reactivity of radicals with molecular hydrogen has been shown to outweigh that of atomic hydrogen, despite the usual presence of activation barriers. − Interestingly, HNC was not observed in the experiments by Borget et al, which can be explained by the reaction 7 having a barrier of 56–70 kJ mol –1 in the gas phase. , Recently, Molpeceres et al demonstrated that hydrogenation and H-abstraction reactions on the intermediate formed after the chemisorption of carbon atoms on ammonia in water ices lead to a competition between the formation of CH 3 NH 2 and the isomers HCN and HNC.…”