Molecular mass growth through ring expansion in polycyclic aromatic hydrocarbons via radical–radical reactions

Abstract

Polycyclic aromatic hydrocarbons (PAHs) represent key molecular building blocks leading to carbonaceous nanoparticles identified in combustion systems and extraterrestrial environments. However, the understanding of their formation and growth in these high temperature environments has remained elusive. We present a mechanism through laboratory experiments and computations revealing how the prototype PAH—naphthalene—can be efficiently formed via a rapid 1-indenyl radical—methyl radical reaction. This versatile route converts five- to six-membered rings and provides a detailed view of high temperature mass growth processes that can eventually lead to graphene-type PAHs and two-dimensional nanostructures providing a radical new view about the transformations of carbon in our universe.

Determination of absolute photoionization cross‐sections of some aromatic hydrocarbons

“…Figure 8 presents the PICSs of 2‐methylindene measured in this study. The measured photoionization threshold for 2‐methylindene is 7.79 ± 0.03 eV, which is slightly smaller than the value reported by Zhao et al 74 (7.90 ± 0.05 eV). The curvature of the PICS of 2‐methylindene is different from that of indene.…”

“…2‐Methylindene has been observed to be a critical intermediate in the ring expansion process from indene to naphthalene, 74 but no previous publication has reported its PICSs. Different from indene, 2‐methylindene is solid at room temperature.…”

PAH Growth in Flames and Space: Formation of the Phenalenyl Radical

“…enyl radical and naphthalene formation from indene (Figure 1b). 31,[40][41][42][43][44][45] Recently, calculations for the reaction of 1-acenaphthyl and methyl suggest that ring expansion of the five-membered ring occurs by methylation to produce 1H-phenalene and the phenalenyl radical 46 . Phenalenyl radical 47,48 is posited to play a role in soot inception and growth 33 .…”

PAH growth in flames and space: Formation of phenalenyl radical

“…H-loss, and this mechanism has been invoked to account for benzene formation from cyclopentadienyl radical and naphthalene formation from indene (Figure 1b). 31,[40][41][42][43][44][45] Recently, calculations for the reaction of 1-acenaphthyl and methyl suggest that ring expansion of the five-membered ring occurs by methylation to produce 1H-phenalene and the phenalenyl radical 46 . Phenalenyl radical 47,48 is posited to play a role in soot inception and growth 33 .…”