Hou Dingyu, You Xiaoqing
Center for Combustion Energy, Tsinghua University, Beijing, 100084, China.
Phys Chem Chem Phys. 2017 Nov 22;19(45):30772-30780. doi: 10.1039/c7cp04964a.
Hydrogen abstraction reactions of polycyclic aromatic hydrocarbons (PAH) by H atoms play a very important role in both PAH and soot formation processes. However, large discrepancies up to a few orders of magnitude exist among the literature rate constant values. To increase the reliability of the computed rate constants, it is critical to obtain highly accurate potential energy surfaces. For this purpose, we have investigated the energetics of hydrogen abstraction from benzene and naphthalene using both high level-of-theory quantum chemistry methods and a series of density functional theory (DFT) methods, among which M06-2X/6-311g(d,p) has the best performance with a mean unsigned deviation from the CCSD(T)/CBS calculations of 1.0 kcal mol for barrier heights and reaction energies. Thus, M06-2X/6-311g(d,p) has then been applied to compute the potential energy surfaces of the hydrogen abstraction reactions of a series of larger PAH. Based on the quantum chemistry calculations, rate constants are computed using the canonical transition state theory. The effects of the PAH size, structure, and reaction site on the energetics and rate constants are examined systematically. Finally, the hydrogen abstraction rate constants for application in PAH and soot surface chemistry models are recommended.
氢原子与多环芳烃（PAH）之间的氢提取反应在PAH和烟灰形成过程中都起着非常重要的作用。然而，文献中的速率常数数值存在高达几个数量级的巨大差异。为了提高计算速率常数的可靠性，获得高精度的势能面至关重要。为此，我们使用高水平理论量子化学方法和一系列密度泛函理论（DFT）方法研究了从苯和萘中提取氢的能量学，其中M06 - 2X/6 - 311g(d,p)表现最佳，其势垒高度和反应能量与CCSD(T)/CBS计算的平均绝对偏差为1.0 kcal/mol。因此，M06 - 2X/6 - 311g(d,p)随后被用于计算一系列更大PAH的氢提取反应的势能面。基于量子化学计算，使用正则过渡态理论计算速率常数。系统地研究了PAH尺寸、结构和反应位点对能量学和速率常数的影响。最后，推荐了适用于PAH和烟灰表面化学模型的氢提取速率常数。
