Mechanical Engineering Graduate Seminar

Abstract

The presentation will overview recent theoretical studies of the reaction mechanisms and kinetics of the formation and growth of large polycyclic aromatic hydrocarbons (PAH) starting from small PAH containing two or three benzene rings. The Hydrogen Abstraction – aCetylene Addition (HACA), Hydrogen Abstraction – Vinylacetylene Addition (HAVA), and Phenyl Addition – Cyclodehydrogenation (PAC) mechanisms will be described eventually leading from two-ring naphthalene and biphenyl and three-ring phenanthrene toward coronene with seven six-membered rings via pyrene, triphenylene, benzo[e]pyrene, and benzo[ghi]perylene. We will also demonstrate how the incorporation of five-membered rings introduces curvature in the PAH structures making them three-dimensional and how the increasing curvature may eventually end up in the formation of a (nearly) spherical C₆₀ buckminsterfullerene molecule. In particular, the PAC reaction beginning from naphthalene produces fluoranthene which in turn undergoes two HACA sequences leading to corannulene C₂₀H₁₀. The latter is subjected to five consecutive HAVA series leading to C₄₀H₂₀ followed by five cyclodehydrogenation reactions on the edges of this molecule resulting in the C40 nanobowl (C₄₀H₁₀). Finally, the nanobowl can be shut by a nanolid (corannulene, C₂₀H₁₀) via a zipping mechanism involving a series of hydrogen abstraction – cyclodehydrogenation reactions. The theoretical electronic structure calculations of the potential energy surfaces involved in the reactions and the reaction kinetics are carried out along and are corroborated with experimental studies in R. Kaiser, M. Ahmed, and P. Hemberger’s groups using a pyrolytic chemical micro reactor with isomer-specific product identification employing the photoionization mass spectrometry (PIMS) and mass-selected threshold photoelectron spectroscopy (ms-TPES) with synchrotron light sources. An outlook on the further growth of carbonaceous nanostructures and soot inception in various conditions (combustion and astrochemistry) will be also given.

Bio

Alexander M. Mebel received his bachelor’s degree in physical chemistry at the Moscow Institute of Steel and Alloys in 1984 and his Ph.D. degree in physical chemistry at Kurnakov’s Institute of General and Inorganic Chemistry of Russian Academy of Science in 1990, in Moscow, Russia. After postdoctoral appointments in Germany, Japan, and USA, his first faculty appointment was at the Institute of Atomic and Molecular Sciences (Academia Sinica, Taiwan) in 1998, and in 2003 he joined the Department of Chemistry and Biochemistry of Florida International University in Miami, Florida, USA, where he is currently Professor of Chemistry. His current research interests include theoretical quantum chemical studies of mechanisms, kinetics, and dynamics of elementary chemical reactions related to combustion, atmospheric, and interstellar chemistry. In 2021, Alexander M. Mebel was elected as a The Combustion Institute Fellow for “for significant contributions to quantumchemical calculations of potential energy surfaces of complex reaction systems of immediate and central interest to combustion”.