High Temperature Chemical Reactor

 

 

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Complementary to the crossed beam experiments, we developed in collaboration with Musahid Ahmed (Lawrence Berkeley National Lab) an experimental protocol to investigate the formation mechanisms of PAHs within a high temperature chemical reactor by simulating the combustion relevant conditions. Utilizing the indene molecule as a test case, we successfully conducted a directed synthesis of indene in situ in a continuous supersonic molecular beam through reaction of pyrolytically generated phenyl radicals (C6H5) with hydrocarbons (methylacetylene, allene) inside a heated silicon carbide tube (chemical reactor). Indene together with its acyclic isomers were then photoionized by vacuum ultraviolet (VUV) light from the Advanced Light Source at the Chemical Dynamics Beamline at various photon energies from 7.5 to 12.0 eV to record photoionization efficiency (PIE) curves. Based on known PIE curves of the PAH and their acyclic isomers, the recorded PIE curves were then simulated theoretically to extract the nature of the products formed and their branching ratios. Prior to this study, no experiment has been conducted in which an individual PAH was formed via a gas phase reaction under well-defined conditions in a high temperature chemical reactor. The data analysis of the phenyl/propylene system is in progress.

 

 

 

 

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The aromatic indene molecule (C9H8) together with its acyclic isomers (phenylallene, 1-phenyl-1-propyne, and 3-phenyl-1-propyne) were formed via a directed synthesis in situ utilizing a high-temperature chemical reactor under combustion-like conditions (300 Torr, 1200 to 1500 K) through the reactions of the phenyl radical (C6H5) with propyne (CH3CCH) and allene (H2CCCH2). The isomer distributions were probed utilizing tunable vacuum ultraviolet (VUV) radiation from the Advanced Light Source by recording the photoionization efficiency (PIE) curves at mass-to-charge of m/z = 116 (C9H8+) of the products in a supersonic expansion for both the phenyl-allene and phenyl-propyne systems; branching ratios were derived by fitting the recorded PIE curves with a linear combination of the PIE curves of the individual C9H8 isomers. Our data suggest that under our experimental conditions, the formation of the aromatic indene molecule via the reaction of the phenyl radical with allene is facile and enhanced compared to the phenyl - propyne system by a factor of about 7. Reaction mechanisms and branching ratios are explained in terms of new electronic structure calculations in collaboration with Alexander Mebel (Florida International University). Our newly developed high-temperature chemical reactor presents a versatile approach to study the formation of combustion-relevant polycyclic aromatic hydrocarbons (PAHs) under well-defined and controlled conditions

 

 

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