Molecules constituting nascent soot particles have been analyzed by two-step laser desorption laser ionization mass spectrometry. Three samples have been collected from a slightly sooting ethylene/air premixed flame with the aim to investigate soot composition in the transition from nucleated to just-grown soot particles. Sampling locations have been selected based on the evolution of the particle size distribution along the flame axis. The mass spectrometric results point to a strong evolution of the molecular composition. Just-nucleated soot is rich in polycyclic aromatic hydrocarbons (PAHs) dominated by medium sizes from 18 to 40 carbon atoms but containing sizes as large as 90 carbon atoms. Most abundant PAHs are in the form of peri-condensed structures. The presence of a large fraction of odd numbered carbon species shows that pentagonal cycles are a common feature of the detected population. Increasing the distance from the burner outlet, i.e., the particle residence time in flame, leads to an evolution of the chemical composition of this population with a major contribution of carbon clusters including also fullerenes up to about 160 carbon atoms. Our data support a scenario in which large PAHs containing pentagonal rings evolve very efficiently upon thermal processing by a series of dehydrogenation and isomerization processes to form fullerenes. This chemistry happens in the early steps of soot growth showing that carbonization is already active at this stage.

已经通过两步激光解吸激光电离质谱法分析了构成新生烟灰颗粒的分子。从轻微积灰的乙烯/空气预混火焰中采集了三个样品，目的是研究从成核到刚刚生长的烟灰颗粒转变过程中的烟灰成分。取样位置是根据沿火焰轴的颗粒尺寸分布的演变来选择的。质谱分析结果表明分子组成发生了强烈变化。刚刚成核的烟灰富含多环芳烃 (PAH)，主要是 18 到 40 个碳原子的中等尺寸，但也包含高达 90 个碳原子的尺寸。最丰富的 PAHs 以peri的形式存在- 压缩结构。大部分奇数碳物种的存在表明五边形循环是检测到的种群的共同特征。增加距燃烧器出口的距离，即，颗粒在火焰中的停留时间，导致该种群的化学组成发生变化，碳簇的主要贡献还包括高达约 160 个碳原子的富勒烯。我们的数据支持这样一种情况，在这种情况下，包含五边形环的大型多环芳烃在通过一系列脱氢和异构化过程形成富勒烯的热处理过程中非常有效地进化。这种化学反应发生在烟灰生长的早期阶段，表明碳化在这个阶段已经很活跃。