考虑核量子效应的分子模拟揭示尘埃催化的H₂和HD形成中的能量分配
Energy Partitioning in Dust-catalyzed $\mathrm{H_2}$ and HD Formation Revealed by Molecular Simulations Considering Nuclear Quantum Effects
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中文总结 AI 辅助
研究人员通过环聚合物分子动力学模拟，揭示了尘埃催化H₂和HD形成时的能量分配规律，为星际介质中相关过程提供了微观依据。
中文摘要 AI 辅助
星际尘埃表面的分子氢形成是星际介质中的关键表面过程，但复合能量在基底与新生分子之间的重新分配仍知之甚少。本研究采用带机器学习力场的环聚合物分子动力学（RPMD），在T=25、50和100K条件下探究石墨烯上H₂和HD形成过程中的能量分配。我们聚焦于纳入核量子效应后，在裸露石墨表面被确定为主要低温通道的化学吸附氢复合路径。脱附分子保留了表面介导释放的有效能量的大部分，而石墨烯吸收了较小但不可忽略的部分，该分子保留分数在所研究的温度范围内几乎与温度无关。相比之下，形成后分子的动能分布随温度变化更显著：低温下振转运动占主导，而100K时质心平动愈发重要。H₂和HD表现出大致相似的总能量保留，仅在内部动能分配上存在适度的同位素依赖差异。这些结果为H₂/HD形成中表面介导的能量重新分配提供了能量分辨的微观图像，对高激发H₂线的形成泵浦特征、振动激发H₂化学，以及冷星际气体中平动热新生H₂对共存分子的碰撞激发具有启示意义。
英文摘要
Molecular hydrogen formation on interstellar dust grains is a key surface process in the interstellar medium, but the redistribution of the recombination energy between the substrate and the nascent molecule remains poorly understood. Here, we use ring-polymer molecular dynamics (RPMD) with a machine-learning force field to investigate energy partitioning during $\mathrm{H_2}$ and $\mathrm{HD}$ formation on graphene at $T=25, 50$ and $100 \mathrm{K}$. We focus on the chemisorbed-H recombination pathway previously identified as the dominant low-temperature channel on bare graphitic surfaces when nuclear quantum effects are included. The desorbing molecule retains the major fraction of the effective surface-mediated released energy, while graphene absorbs a smaller but non-negligible part. This molecular retention fraction is nearly temperature-independent over the investigated range. In contrast, the post-formation molecular kinetic-energy distribution changes more strongly with temperature: rovibrational motion dominates at low temperature, whereas center-of-mass translation becomes increasingly important at $100 \mathrm{K}$. $\mathrm{H_2}$ and $\mathrm{HD}$ exhibit broadly similar total energy retention, with only modest isotope-dependent differences in their internal kinetic-energy partitioning. These results provide an energy-resolved microscopic picture of surface-mediated energy redistribution in $\mathrm{H_2}$/$\mathrm{HD}$ formation, with implications for formation-pumping signatures in high-excitation $\mathrm{H_2}$ lines, vibrationally excited $\mathrm{H_2}$ chemistry, and collisional excitation of coexisting molecules by translationally hot nascent $\mathrm{H_2}$ in cold interstellar gas.
