Pathways to Interstellar Amides via Carbamoyl (NH2CO) Isomers by Radical-Neutral Reactions on Ice Grain Mantles

Abstract

Explaining the formation pathways of amides on ice-grain mantels is crucial to understanding the prebiotic chemistry in an interstellar medium. In this computational study, we explore different radical-neutral formation pathways for some of the observed amides (formamide, acetamide, urea, and N-methylformamide) via intermediate carbamoyl (NH2CO) radical precursors and their isomers. We assess the relative energy of four NH2CO isomers in the gas phase and evaluate their binding energy on small water clusters to discern the affinity that the isomers present to an ice model. We consider three possible reaction pathways for the formation of the carbamoyl radicals, namely, the OH + HCN, CN + H2O, and NH2 + CO reaction channels. We computed the binding energy distribution for the HCN and CH3CN precursors on an ice model consisting of a set of clusters of 22 water molecules each to serve as a starting point for the reactivity study on the ice surface. The computations revealed that the lowest barrier to the formation of an NH2CO isomer corresponds to the NH2 + CO reaction (12.6 kJ/mol). The OH + HCN reaction pathway results in the exothermic formation of the N-radical form of carbamoyl HN(C=O)H with a reaction barrier of 26.7 kJ/mol. We found that the CN + H2O reaction displays a high energy barrier of 70.6 kJ/mol. Finally, we also probed the direct formation of the acetamide radical precursor via the OH + CH3CN reaction and found that the most probable outcome on interstellar ices is the H-abstraction reaction to yield CH2CN and H2O. Based on these results, we believe that including alternative reaction pathways, leading to the formation of amides via the N-radical form of carbamoyl, would provide an improvement in the prediction of the amide abundances in astrochemical models, especially regarding the chemistry of star-forming regions.

Journal is ACS Earth Space Chem, 2024. ASAP (As Soon As Publishable)

References in corpus (13)

• Development of Novel Density Functionals for Thermochemical Kinetics
• An Ice Age JWST inventory of dense molecular cloud ices
• Testing grain-surface chemistry in massive hot-core regions
• Shedding light on the formation of the pre-biotic molecule formamide with ASAI
• Interstellar formamide (NH${}_2$CHO), a key prebiotic precursor
• Hydrogenation at low temperatures does not always lead to saturation: the case of HNCO
• The family of amide molecules toward NGC 6334I
• The GUAPOS project II. A comprehensive study of peptide-like bond molecules
• Binding Energy Evaluation Platform: A database of quantum chemical binding energy distributions for the astrochemical community
• Radiolysis of Amino Acids by Heavy and Energetic Cosmic Ray Analogs in Simulated Space Environments: $\alpha$-Glycine Zwitterion Form
• Amides inventory towards the G+0.693-0.027 molecular cloud
• Behavior of Hydroxyl Radicals on Water Ice at Low Temperatures
• Direct Determination of the Activation Energy for Diffusion of OH Radicals on Water Ice