Raaphorst Marten T, Enrique-Romero Joan, Lamberts Thanja
Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University, P.O. Box 9502,2300 RA Leiden, The Netherlands.
Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands.
ACS Earth Space Chem. 2025 May 15;9(6):1534-1543. doi: 10.1021/acsearthspacechem.5c00021. eCollection 2025 Jun 19.
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 HCN, the smallest cyanopolyyne, that consists of 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 HCN. This work explores the reaction network of the isolated molecule and constitutes a preview of the reactions occurring on the ice grain surface. We find that the reactions where the hydrogen atom adds to the carbon chain at the carbon atom opposite of the cyano group give the lowest and narrowest 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.
氰基多炔是一类含氮碳链，在星际介质中很常见，可能构成与益生元化学相关物种的骨架。在气相形成之后，它们预计会在寒冷的星际区域冻结在冰粒上。在这项工作中，我们展示了最小的氰基多炔——孤立的HCN的氢化反应网络，该网络由越过势垒的自由基-中性反应和无势垒的自由基-自由基反应组成。我们采用密度泛函理论、耦合簇理论和多组态方法来获得HCN氢化网络的活化能和反应能。这项工作探索了孤立分子的反应网络，并构成了冰粒表面发生反应的一个预览。我们发现，氢原子在氰基相对的碳原子处加到碳链上的反应具有最低且最窄的势垒。随后的氢化反应会生成与天体化学相关的丙烯腈和乙腈。另外，氰基可通过自由基-自由基反应氢化，生成完全饱和的丙胺。这些结果可以外推，以深入了解星际冰上碳链的一般反应活性。
