A VUV Photoionization Study of the Formation of the Indene Molecule and Its Isomers

Abstract

The aromatic indene molecule (C 9 H 8 ) 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, 1,200-1,500 K) through the reactions of the phenyl radical (C 6 H 5 ) with propyne (CH 3 CCH) and allene (H 2 CCCH 2 ). 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 (C 9 H 8 + ) 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 C 9 H 8 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 seven. Reaction mechanisms and branching ratios are explained in terms of new electronic structure calculations.Our newly developed high temperature chemical reactor presents a versatile approach to study the formation of combustion-relevant polycyclic aromatic hydrocarbons (PAHs) under welldefined and controlled conditions.

Formation of polycyclic aromatic hydrocarbons from bimolecular reactions of phenyl radicals at high temperatures

“…Indene, C 9 H 8 has been observed as a reaction product in a mixture of phenyl and allene or propyne. 22 Similar to naphthalene, it is detected in the present work without any secondary reactant being added. The IR/UV spectrum is given in Fig.…”

Reactivity of the Indenyl Radical (C9H7) with Acetylene (C2H2) and Vinylacetylene (C4H4)

“…The identification of the 1‐indenyl radical suggests that if the 2‐, 6‐, and 7‐indenyl radicals are formed via homolytic carbon‐bromine bond rupture, these radicals effectively isomerize within a few tens of microseconds, i. e. the residence time of the radicals within our chemical reactor . An alternative explanation for the non‐observation of the 2‐, 6‐, and 7‐indenyl radicals would be that they do not actually form in the first place from the bromoindenes used in the present experiment.…”

Gas‐Phase Synthesis of Triphenylene (C18H12)

“…The experiments were conducted at the Advanced Light Source (ALS) at the Chemical Dynamics Beamline (9.0.2.) exploiting a high‐temperature chemical reactor consisting of a resistively‐heated silicon carbide (SiC) tube of 20 mm length and 1 mm inner diameter ,,. This reactor is incorporated into a molecular beam apparatus operated with a Wiley‐McLaren reflectron time‐of‐flight mass spectrometer (Re‐TOF‐MS).…”