发表机构
Universität Heidelberg; Memorial University; American Museum of Natural History（海德堡大学; 纪念大学; 美国自然历史博物馆）
机构由 AI 辅助整理，请以论文原文为准。AI 中文总结
本研究通过动力学蒙特卡洛模型，发现气体-尘埃漂移对H2形成效率影响复杂：恒定粘附时漂移增强形成（效率0.3-0.4），能量依赖粘附时强漂移抑制形成（效率0.01-0.03），动态环境模型需考虑相对速度及粘附效应。
AI 中文摘要
分子氢主要形成于星际介质中的尘埃颗粒表面，在动态活跃的环境中，气体与尘埃之间可能产生相对运动。虽然H$_2$的形成对颗粒温度和表面性质的依赖性已被充分研究，但气体-尘埃漂移的影响却很少受到关注。我们研究了气体-尘埃漂移如何改变H$_2$的形成，重点关注漂移增强的氢原子碰撞速率与较高碰撞能量下粘附概率降低之间的竞争。我们使用事件驱动的动力学蒙特卡洛模型，跟踪球形硅酸盐和碳质颗粒上的单个氢原子，包括吸附、表面迁移、热脱附以及Langmuir-Hinshelwood（LH）和Eley-Rideal（ER）反应。漂移通过偏移的麦克斯韦速度分布来描述，我们比较了恒定粘附概率和依赖于碰撞能量的粘附概率两种情况。漂移导致吸附的H和H$_2$在颗粒表面的分布越来越各向异性。假设粘附概率恒定，增强的漂移通过更高的碰撞速率促进H$_2$的形成，效率可达$\epsilon=0.3-0.4$。而在能量依赖的粘附概率下，强漂移反而抑制了两种材料上的形成，将效率降低至$\epsilon=0.01-0.03$。碳质颗粒在比硅酸盐颗粒更高的尘埃温度下仍能保持高效形成。ER反应在所研究的大部分参数空间中占主导地位，并且在强漂移下变得越来越重要，因为表面种群减少抑制了LH反应。因此，气体-尘埃漂移下增强的碰撞速率并不一定增加H$_2$的形成。动态活跃环境的模型应同时考虑相对气体-尘埃速度及其对粘附概率的影响。
英文摘要
Molecular hydrogen is predominantly formed on dust-grain surfaces in the interstellar medium, where relative gas-dust motion can arise in dynamically active environments. While the dependence of H$_2$ formation on grain temperature and surface properties is well studied, the impact of gas-dust drift has received little attention. We investigate how gas-dust drift modifies H$_2$ formation, focusing on the competition between the drift-enhanced H-atom collision rate and reduced sticking at higher impact energies. We use an event-driven kinetic Monte Carlo model that follows individual H atoms on spherical silicate and carbonaceous grains, including adsorption, surface migration, thermal desorption, and Langmuir-Hinshelwood (LH) and Eley-Rideal (ER) reactions. Drift is described by a shifted Maxwellian velocity distribution, and we compare constant and impact-energy-dependent sticking probabilities. Drift produces increasingly anisotropic distributions of adsorbed H and H$_2$ formation across the grain surface. Assuming constant sticking, increasing drift enhances H$_2$ formation through the higher collision rate, with efficiencies up to $ε=0.3-0.4$. With energy-dependent sticking, strong drift instead suppresses formation on both materials, reducing efficiencies to $ε=0.01-0.03$. Carbonaceous grains remain efficient to higher dust temperatures than silicate grains. ER reactions dominate over most of the investigated parameter space and become increasingly important at strong drift as the reduced surface population suppresses LH reactions. Thus, enhanced collision rates under gas-dust drift do not necessarily increase H$_2$ formation. Models of dynamically active environments should account for both relative gas-dust velocities and their effects on sticking.
Comments14 pages, 13 figures, 4 tables
