Dynamics of the reaction of C2 with C6H2: An implication for the formation of interstellar C8H

The reaction C-2 + C6H2 -> C8H + H was investigated for the first time. Reactant C-2 (C6H2) was synthesized from 1% C3F6/He (5% C2H2/He) by pulsed high-voltage discharge. We measured the translational-energy distribution, the angular distribution, and the photoionization spectrum of product C8H in a crossed molecular-beam apparatus using synchrotron vacuum-ultraviolet ionization. This reaction released average translational energy of 8.5 kcal mol(-1) corresponding to a fraction of 0.37 in translation. (CH)-H-8 was identified as octatetranyl based on the maximal translational-energy release 23 +/- 2 kcal mol(-1) and the ionization threshold 8.9 +/- 0.2 eV. Kinematic constraints can qualitatively account for the nearly isotropic angular distribution. The quantum-chemical calculations indicate that the exothermic reactions C-2 (X (1)Sigma(+)(g)/a (3)Pi(u)) + HC6H -> C8H + H can proceed without entrance and exit barriers, implying the importance in the cold interstellar medium. This work verifies that interstellar C8H can be formed through the C-2 + C6H2 reaction. (c) 2014 AIP Publishing LLC.