In this work, we studied the coagulation process of two PAH clusters with diameter $\sim$2 nm using reactive molecular dynamics (MD) simulations. To describe the coagulation process quantitatively, the distance between the center of mass (COM) of the two PAH clusters, as well as the inter-cluster potential energy and kinetic energy of the COM of the clusters were calculated. Head-on coagulation efficiencies ($\eta$) of two PAH clusters at typical flame temperatures where soot inception is most likely to occur, i.e., 1500 K—2000 K, were determined based on hundreds of MD simulated trajectories. Our simulation results showed that $\eta$ decreases with increasing temperature, which is mainly due to the increased kinetic energy of atoms within the PAH clusters at higher temperature. In addition, introduction of surface $\sigma$-radical site fraction in the range of 0.01 to 0.1 can only moderately improve $\eta$ by $\sim$10% by forming carbon–carbon bonds between the two coagulating clusters, which suggests $\eta$ of incipient soot nanoparticles with surface $\sigma$-radicals in high temperature flame regions is very low even if with reactive coagulation taken into consideration.

在这项工作中，我们研究了两个直径为 $～$2  nm 使用反应性分子动力学 (MD) 模拟。为了定量描述凝结过程，计算了两个 PAH 簇的质心 (COM) 之间的距离，以及簇的 COM 的簇间势能和动能。正面凝固效率 ($\eta$) 在最有可能发生烟灰形成的典型火焰温度下，即1500  K-2000  K，基于数百个 MD 模拟轨迹确定了两个 PAH 簇。我们的模拟结果表明，$\eta$随温度升高而降低，这主要是由于在较高温度下 PAH 簇内原子的动能增加。此外，引入表面$\sigma$- 0.01 到 0.1 范围内的自由基位点分数只能适度改善 $\eta$ 经过 $～$10% 通过在两个凝结簇之间形成碳 - 碳键，这表明 $\eta$ 具有表面的初始烟灰纳米颗粒 $\sigma$- 即使考虑到反应凝固，高温火焰区域中的自由基也非常低。