Identification of Dihydropentalenes as Products of the Molecular-Weight Growth Reaction of Cyclopentadienyl Plus Propargyl

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The resonance-stabilized cyclopentadienyl (C 5 H 5 ) and propargyl (C 3 H 3 ) radicals are important precursors for polycyclic aromatic hydrocarbons (PAHs) and thus play a significant role in molecular-weight growth and soot formation processes under combustion conditions. In this work, we describe an experimental and theoretical investigation of the C 5 H 5 + C 3 H 3 reaction. Experimentally, we studied this reaction in a resistively heated microtubular SiC reactor at a controlled temperature of ∼1150 K and a pressure of 10–20 mbar. The reactants C 5 H 5 and C 3 H 3 were pyrolytically generated from anisole (C 6 H 5 OCH 3 ) and propargyl bromide (C 3 H 3 Br). We identified the reactants and the C 8 H 8 products isomer-selectively utilizing photoion mass-selected threshold photoelectron spectroscopy (ms-TPES). The experimentally observed predominant formation of dihydropentalenes over the ring-enlargement reaction to styrene is consistent with our theoretical predictions of the kinetics on the newly calculated C 8 H 8 potential energy surface. This work highlights dihydropentalenes as reactants in molecular-weight growth reactions and as potential building blocks in versatile routes for the formation of curved PAHs.