The Isomer Distribution of CH Products from the Propargyl Radical Gas-phase Recombination Investigated by Threshold-photoelectron Spectroscopy

The resonance-stabilization of the propargyl radical (CH) 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 CH products in total, including benzene. On top of providing the first comprehensive measurements of the branching ratios of the eight identified CH 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.