Molecular mass growth through ring expansion in polycyclic aromatic hydrocarbons via radical\u2013radical reactions

Long Zhao,Alexander M Mebel,Bo Xu,A Hasan Howlader,Stanislaw F Wnuk,Musahid Ahmed,Alexander N Morozov,Ralf I Kaiser,Wenchao Lu

doi:10.1038/s41467-019-11652-5

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.

Highlights

Polycyclic aromatic hydrocarbons (PAHs) represent key molecular building blocks leading to carbonaceous nanoparticles identified in combustion systems and extraterrestrial environments
In the methyl–indenyl system, the data provide compelling evidence on the formation of molecules connected to molecular ions with mass-to-charge (m/z) ratios of 131, 130, 129, and 128 (Fig. 2b), which can be associated with 13CC9H10, C10H10, C10H9/13CC9H8, and C10H8, respectively
Our experiments reveal that the simplest representative of a PAH— naphthalene—can be formed via the reaction of the 1-indenyl radical with the methyl radical following isomerization and loss of two hydrogen atoms at elevated temperatures of 1425 K based on the decomposition temperatures of the radical precursor, which coincided with the maximum intensities of the products of interest

Summary

Introduction

Polycyclic aromatic hydrocarbons (PAHs) represent key molecular building blocks leading to carbonaceous nanoparticles identified in combustion systems and extraterrestrial environments. 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. In deep space, PAHs are rapidly destroyed by photolysis, galactic cosmic rays, and shock waves resulting in lifetimes of only a few 108 years[18] These time scales are significantly shorter than those for injection of PAHs into the interstellar medium by carbon rich Asymptotic Giant Branch (AGB) stars of 2 × 109 years[18]. Is our experimental methodology crucial in modelling combustion and astrochemical processes, it provides a strategy to study chemical reactions of radicals in general under high-temperature environments of relevance to synthesis and materials chemistry

Methods

Results

Conclusion