Fritz Haber Research Center for Molecular Dynamics, The Hebrew University of Jerusalem, Jerusalem 9190401, Israel.
J Chem Phys. 2022 Feb 7;156(5):054307. doi: 10.1063/5.0077000.
Hydrogen cyanide (HCN) and its isomer hydrogen isocyanide (HNC) are omnipresent in the interstellar medium (ISM). The ratio between the two isomers serves as an indicator of the physical conditions in different areas of the ISM. As such, the isomerization process between the two isomers has been extensively studied on the neutral potential energy surface. Moreover, HCN and HNC are thought to be precursors of important organic molecules, such as adenine. Here, we use quantum chemistry calculations and ab initio molecular dynamics simulations to focus on the chemistry that occurs upon ionization of pure HNC clusters. We demonstrate that upon ionization of HNC clusters, a distonic ion CN⋯HCNH is formed, and this formation is accompanied by HNC-to-HCN isomerization. Moreover, we show that the cluster environment and the network of hydrogen bonds are crucial for the isomerization process to occur and for the stabilization of the clusters. We demonstrate that, in contrast to HNC clusters, isomerization of ionized HCN clusters can occur only for the larger clusters. In addition, we discuss the formation of aminonitrile cation in the clusters and propose a barrierless route for diaminonitrile, a known precursor of amino acids and nucleobases, to form.
氰化氢 (HCN) 和它的异构体异氰化氢 (HNC) 普遍存在于星际介质 (ISM) 中。两种异构体之间的比例是不同 ISM 区域物理条件的指示物。因此，两种异构体之间的异构化过程在中性势能表面上得到了广泛的研究。此外，HCN 和 HNC 被认为是重要有机分子的前体，如腺嘌呤。在这里，我们使用量子化学计算和从头算分子动力学模拟来研究纯 HNC 团簇电离时发生的化学变化。我们证明，在 HNC 团簇的电离过程中，会形成一个离域离子 CN⋯HCNH，并且这种形成伴随着 HNC 到 HCN 的异构化。此外，我们表明团簇环境和氢键网络对于异构化过程的发生以及团簇的稳定化至关重要。我们证明，与 HNC 团簇相比，只有较大的团簇才能发生离子化 HCN 团簇的异构化。此外，我们还讨论了在团簇中形成氨基腈阳离子，并提出了一种无势垒的途径，用于形成二氨基腈，二氨基腈是氨基酸和核苷酸碱基的已知前体。
