Toward Unraveling Cyanopolyyne Surface Chemistry: A Preview on Isolated Systems From HC_{3}N to Ethyl Cyanide and Propylamine

TL;DR

This study investigates the hydrogenation reactions of cyanopolyynes, especially HC_{3}N, on ice grains in space using advanced computational methods, revealing pathways to molecules like vinyl cyanide, ethyl cyanide, and propylamine relevant to astrochemistry.

Contribution

It provides a detailed computational analysis of the reaction network of HC_{3}N on ice surfaces, offering new insights into interstellar surface chemistry of cyanopolyynes.

Findings

Hydrogen addition to the carbon chain at the opposite carbon atom of the cyano group has the lowest barriers.

Hydrogenation can lead to vinyl cyanide, ethyl cyanide, and propylamine.

Reactions on ice surfaces can be extrapolated to understand interstellar carbon chain chemistry.

Abstract

Cyanopolyynes, a family of nitrogen containing carbon chains, are common in the interstellar medium and possibly form the backbone of species relevant to prebiotic chemistry. Following their gas phase formation, they are expected to freeze out on ice grains in cold interstellar regions. In this work we present the hydrogenation reaction network of isolated HC_{3}N, the smallest cyanopolyyne, that consists over-a-barrier radical-neutral reactions and barrierless radical-radical reactions. We employ density functional theory, coupled cluster and multiconfigurational methods to obtain activation and reaction energies for the hydrogenation network of HC_{3}N. This work explores the reaction network of the isolated molecule and constitutes a preview on the reactions occurring on the ice grain surface. We find that the reactions where the hydrogen atom adds to the carbon chain at carbon atom opposite of the cyano-group give the lowest and most narrow barriers. Subsequent hydrogenation leads to the astrochemically relevant vinyl cyanide and ethyl cyanide. Alternatively, the cyano-group can hydrogenate via radical-radical reactions, leading to the fully saturated propylamine. These results can be extrapolated to give insight into the general reactivity of carbon chains on interstellar ices.