The considerable level of uncertainty in the measured and calculated catalytic recombination coefficients of atomic oxygen (O) on silica (SiO₂) surfaces has posed a great challenge to the accurate prediction of heating load and thereby the weight-effective design for atmospheric hypersonic vehicles. This work conducts large-scale (in terms of reaction trajectories) reactive molecular dynamics simulations based on ReaxFF_SiO^GSI, a ReaxFF potential function tailored for O(gas)-SiO₂(surface) interactions to understand the chemical processes for the recombination of O for different SiO₂ surface structures. The applicability of the present ReaxFF-based molecular dynamics is validated by the density-functional-theory calculation through O adsorption on the same SiO₂ surface structures under investigation. An automatic data analyzer is developed to capture the reaction pathways and mechanisms from the vast amount of trajectories. It is found that the pathways of adsorption, active site formation, and recombination are sensitive to the surface structures. The overall recombination coefficient and its compositions from different reaction pathways vary considerably for different surface structures. We identify for the first time a reaction mechanism involving multiple active sites, which is more likely to occur than the single-site reactions and thus can potentially increase the recombination probability. These findings highlight the important role of surface structure in catalytic recombination reactions and provide a possible explanation for the huge discrepancy in the recombination coefficients from previous studies.

中文翻译：

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使用 ReaxFF 反应分子动力学揭示暴露于原子氧的二氧化硅表面的化学过程


二氧化硅 （SiO₂） 表面原子氧 （O） 的催化复合系数的测量和计算存在相当大的不确定性，这对热负荷的准确预测以及大气高超声速飞行器的减重设计构成了巨大挑战。这项工作基于 ReaxFF_SiO GSI 进行了大规模（就反应轨迹而言）反应分子动力学模拟，ReaxFF ^{SiO GSI} 是为 O（气体）-SiO₂（表面）相互作用量身定制的 ReaxFF 势函数，以了解不同 SiO₂ 表面结构的 O 复合的化学过程。通过对正在研究的相同 SiO₂ 表面结构的 O 吸附，通过密度泛函理论计算验证了当前基于 ReaxFF 的分子动力学的适用性。开发了一种自动数据分析器，用于从大量轨迹中捕获反应途径和机理。研究发现，吸附、活性位点形成和复合的途径对表面结构敏感。对于不同的表面结构，来自不同反应途径的总体复合系数及其组成差异很大。我们首次确定了涉及多个活性位点的反应机制，这比单位点反应更有可能发生，因此可能会增加重组概率。这些发现突出了表面结构在催化复合反应中的重要作用，并为与以往研究的复合系数的巨大差异提供了可能的解释。