Crossed molecular beams experiments have been utilized to investigate the reaction dynamics between two closed shell species, i.e. the reactions of tricarbon molecules, C3(X1Σg+), with allene (H2CCCH2; X1A1), and with methylacetylene (CH3CCH; X1A1). Our investigations indicated that both these reactions featured characteristic threshold energies of 40–50 kJ mol−1. The reaction dynamics are indirect and suggested the reactions proceeded via an initial addition of the tricarbon molecule to the unsaturated hydrocarbon molecules forming initially cyclic reaction intermediates of the generic formula C6H4. The cyclic intermediates isomerize to yield eventually the acyclic isomers CH3CCCCCH (methylacetylene reaction) and H2CCCCCCH2 (allene reaction). Both structures decompose via atomic hydrogen elimination to form the 1-hexene-3,4-diynyl-2 radical (C6H3; H2CCCCCCH). Future flame studies utilizing the Advanced Light Source should therefore investigate the existence of 1-hexene-3,4-diynyl-2 radicals in high temperature methylacetylene and allene flames. Since the corresponding C3H3, C4H3, and C5H3 radicals have been identified via their ionization potentials in combustion flames, the existence of the C6H3 isomer 1-hexene-3,4-diynyl-2 can be predicted as well.
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