一个完全ab Initio的动力蒙特卡洛方法,用于模拟星际冰粒地幔中的吸附和扩散:H2S的情况
Vittorio Bariosco1,2, Stefano Pantaleone2, Cecilia Ceccarelli3
1Departament de Quimica, Universitat Autònoma de Barcelona, 08193 Bellaterra, Catalonia, Spain.
概括
星际冰的扩散对于理解分子云化学是至关重要的. 这项研究表明,H2S扩散在20K以下是可以忽略不计的,影响了表面反应的天体化学模型.
科学领域:
- 天体化学是天体化学.
- 计算化学计算化学
- 表面科学是一门学科.
背景情况:
- 星际冰是冷分子云中的化学反应的关键地点.
- 了解这些冰块上的分子扩散对于精确的天体化学建模至关重要.
- 分子云中的低温显著限制了冰面上的分子运动.
研究的目的:
- 开发一个计算框架来量化无形固体水 (ASW) 上的吸附剂扩散.
- 研究H2S在ASW上的扩散及其对天体化学模型的影响.
- 评估星际冰物种的扩散障碍和结合能之间的关系.
主要方法:
- 一个结合密度函数理论 (DFT) 和动力蒙特卡洛 (kMC) 模拟的多尺度计算框架.
- 与DLPNO-CCSD-(T) 相比,对DFT的能量进行基准测试,以获得高精度.
- 在ASW上建造H2S的详细吸附点和过渡状态网络.
- 网格之外的kMC建模,以计算温度依赖的扩散系数,并模拟温度编程脱吸 (TPD).
主要成果:
- 在ASW上的H2S扩散在20K以下是可以忽略不计的,在10K时的扩散系数非常低.
- 在submonolayer条件下,表面扩散对TPD峰值位置的影响最小.
- 关于扩散障碍与结合能量的通用缩放因子是不适用的,因为它具有显著的变化.
- 在ASW上H2S的扩散障碍范围从0.1到27kJmol-1之间,中位数为5.4kJmol-1.1.
结论:
- 在典型的密集云层条件下,H2S的热扩散是微不足道的,这挑战了Langmuir-Hinshelwood表面反应机制.
- 一种适合所有人的方法来估计来自结合能量的扩散障碍,对于星际冰化学来说是不准确的.
- 天体化学模型需要统计上具有代表性的结合能和扩散障碍的分布,以提高表面扩散和反应性研究的准确性.
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