The mechanism of evolution of polycyclic aromatic hydrocarbons (PAHs) into carbonaceous particles in combustion, atmosphere, and interstellar space has been the subject of intense debate. Recently, there has been emerging evidence supporting resonantly-stabilized radicals as key players in PAH growth. In this work, we build on this hypothesis and propose that, beyond a critical size, PAH reactivity can be assimilated to that of radicals. We found that odd-C-numbered PAHs embedding 5-membered rings rapidly lose a hydrogen atom to form resonantly-stabilized radicals in combustion conditions, while even-C-numbered PAHs react as open-shell rather than closed-shell molecules independently of temperature, as usually assumed. Acenes were used as molecular models of large even-C-numbered PAHs. The construction of a kinetic model including these findings allows to interpret experimental soot oxidation data otherwise irreconcilable with existing chemical kinetic mechanisms.

多环芳烃 (PAH) 在燃烧、大气和星际空间中演化为碳质颗粒的机制一直是激烈争论的主题。最近，有新的证据支持共振稳定的自由基是 PAH 增长的关键因素。在这项工作中，我们建立在这个假设的基础上，并提出，超出临界尺寸，多环芳烃反应性可以被同化为自由基的反应性。我们发现嵌入 5 元环的奇数 C 编号多环芳烃在燃烧条件下迅速失去一个氢原子以形成共振稳定的自由基，而偶数 C 编号多环芳烃作为开壳分子而不是闭壳分子与温度无关，正如通常假设的那样。并苯被用作大型偶数 C 编号多环芳烃的分子模型。