The isomer distribution of C 6 H 6 products from the propargyl radical gas-phase recombination investigated by threshold-photoelectron spectroscopy.

The resonance-stabilization of the propargyl radical (C 3 H 3 ) makes it among the most important reactive intermediates in extreme environments and grants it a long enough lifetime to recombine in both terrestrial combustion media and cold molecular clouds in space. This makes the propargyl self-reaction a pivotal step in the formation of benzene, the first aromatic ring, to eventually lead to polycyclic aromatic hydrocarbons in a variety of environments. In this work, by producing propargyl radicals in a flow tube where propyne reacted with F atoms and probing the reaction products by mass-selected threshold-photoelectron spectroscopy (TPES), we identified eight C 6 H 6 products in total, including benzene. On top of providing the first comprehensive measurements of the branching ratios of the eight identified C 6 H 6 isomers in the propargyl self reaction products (4 mbar, 298 K conditions), this study also highlights the advantages and disadvantages of using isomer-selective TPES to identify and quantify reaction products.