Jubert Léana, Martínez-Bachs Berta, Pareras Gerard, Rimola Albert
Departament de Química, Universitat Autònoma de Barcelona, Bellaterra 08193, Catalonia, Spain.
Accademia delle Scienze di Torino, Via Maria Vittoria, 3, 10123 Torino, Italy.
Phys Chem Chem Phys. 2025 Jul 7. doi: 10.1039/d5cp01585e.
Molecular hydrogen (H) stands as the most abundant molecule within the interstellar medium (ISM), primarily originating from the coupling of two H atoms on the surfaces of dust grains. The role of dust grains during the H formation is of third bodies, dissipating the nascent reaction energy and thereby stabilizing the newly formed molecule and preventing it from dissociating back. Whether the formed H remains adsorbed or not on the surface (in this latter case undergoing chemical desorption, CD) largely depends on the type of grain and its capability to absorb the reaction energy excess. In diffuse interstellar clouds, dust grains are typically bare and are composed primarily of silicates or carbonaceous materials, while in denser regions they are covered in ices mostly of water. While water-ice-covered grains have been elucidated to be efficient third bodies, the behavior of carbonaceous grains is still unknown. In this study, molecular dynamics (AIMD) simulations are employed to analyze how the reaction energy is distributed between the newly formed H and a large graphene slab, as a model of carbonaceous grains in diffuse clouds, and assess the feasibility of CD. The results indicate that only a fraction of the reaction energy is absorbed by the surface, leaving the newly formed H with sufficient internal energy for CD to occur.
分子氢（H₂）是星际介质（ISM）中最丰富的分子，主要源于尘埃颗粒表面两个氢原子的耦合。尘埃颗粒在H₂形成过程中起到第三体的作用，消散新生反应能量，从而稳定新形成的分子并防止其解离回去。形成的H₂是否仍吸附在表面（在后一种情况下会发生化学解吸，CD）很大程度上取决于颗粒的类型及其吸收多余反应能量的能力。在弥漫星际云中，尘埃颗粒通常是裸露的，主要由硅酸盐或碳质材料组成，而在密度较大的区域，它们被 mostly of water 冰覆盖。虽然已阐明被水冰覆盖的颗粒是有效的第三体，但碳质颗粒的行为仍然未知。在本研究中，采用分子动力学（AIMD）模拟来分析反应能量如何在新形成的H₂和作为弥漫云中碳质颗粒模型的大石墨烯平板之间分布，并评估化学解吸的可行性。结果表明，只有一部分反应能量被表面吸收，使新形成的H₂具有足够的内能以发生化学解吸。 注：原文中“ices mostly of water”表述有误，推测可能是“ices mostly of water ice”，翻译时按推测内容翻译为“被水冰覆盖”。
