AI 中文总结
该研究通过动力学蒙特卡洛模拟揭示碳质尘埃颗粒表面H₂的催化形成机制，明确其效率随温度、数密度的变化规律，证实尘埃催化H₂化学可与高红移恒星形成区的引力坍缩同步。
AI 中文摘要
我们采用动力学蒙特卡洛（KMC）模拟研究分子氢在碳质尘埃颗粒表面的形成过程，该模拟通过近期对10至250 K温度下蔻烯薄膜上H₂形成的实验室测量进行验证。模型采用三维非晶碳晶格，包含异质物理吸附（45±5 meV）和化学吸附（1.75±0.25 eV）位点，并在随机Gillespie事件驱动框架内同时追踪Langmuir–Hinshelwood（LH）和Eley–Rideal（ER）形成通道。该模型在实验不确定度内重现了测量的效率曲线，包括100-250 K下的等温（恒定表面温度）测量结果，还能正确描述LH与ER驱动过程之间随尘埃温度变化的相边界及观测到的转变。在星际介质条件（温度10-250 K，数密度n=10-10⁴ cm⁻³）下，模型预测形成效率ε（撞击H原子转化为H₂的比例）存在三个不同区域：10 K时扩散缓慢，ε≈0.06；20 K至80 K间LH通道占主导，ε≈0.28；150 K以上，化学吸附捕获的H原子维持ER平台，ε=0.19；LH向ER的转变发生在100-120 K之间，100 K时观测到16%的密度依赖型随机增强，这是速率方程模型无法捕捉的。在尘埃温度T_dust=60 K、数密度n=10³ cm⁻³时，我们得到H₂形成时间与自由下落时间的比值t_H₂/t_ff≈0.93，表明尘埃催化的H₂化学反应在高红移恒星形成环境中可与引力坍缩同步进行。
英文摘要
We use kinetic Monte Carlo (KMC) simulations to study molecular hydrogen formation on carbonaceous dust grain surfaces, validated against recent laboratory measurements of H$_2$ formation on coronene films at temperatures from 10 to 250 K. The model uses a three-dimensional amorphous carbon lattice with heterogeneous physisorption ($45 \pm 5$ meV) and chemisorption ($1.75 \pm 0.25$ eV) sites, and tracks both Langmuir--Hinshelwood (LH) and Eley--Rideal (ER) formation channels within a stochastic Gillespie event-driven framework. The model reproduces the measured efficiency curve within the experimental uncertainties, including the isothermal (constant surface temperature) measurements at 100 - 250 K. The simulations correctly describe the phase boundary between the LH and ER driven processes as functions of grain temperature and the observed crossover. Under interstellar medium conditions, 10 - 250 K and n = 10 - 10$^4$ cm$^3$, the model predicts three distinct regimes for the formation efficiency $ε$, the fraction of impinging H atoms released as H$_2$. At 10 K diffusion is slow and $ε\approx 0.06$. Between 20 K and 80 K, LH dominates and $ε\approx 0.28$. Above 150 K, an ER plateau at $ε= 0.19$ is sustained by chemisorption-trapped H atoms. The LH-to-ER crossover occurs between 100 and 120 K. At 100 K we observe a 16\% density-dependent stochastic enhancement, which rate-equation models cannot capture. At T$_{dust}$ = 60 K, n = 10$^3$ cm$^3$ we find the ratio of H$_2$ formation to free-fall time $t_{{\rm H}_2}/t_{\rm ff} \approx 0.93$, so dust-catalysed H$_2$ chemistry can keep pace with gravitational collapse in high-redshift star-forming environments.
Comments21 pages, 18 figures
