title: Dynamics of the reaction of C₃(a³Πu) radicals with C₂H₂: a new source for the formation of C₅H.
abstract: The reaction C3(a(3)Πu) + C2H2 → C5H + H was investigated at collision energy 10.9 kcal mol(-1) that is less than the enthalpy of ground-state reaction C3(X(1)Σg (+)) + C2H2 → C5H + H. C3(a(3)Πu) radicals were synthesized from 1% C4F6/He by pulsed high-voltage discharge. The title reaction was conducted in a crossed molecular-beam apparatus equipped with a quadrupole-mass filter. Product C5H was interrogated with time-of-flight spectroscopy and synchrotron vacuum-ultraviolet ionization. Reactant C3(a(3)Πu) and product C5H were identified using photoionization spectroscopy. The ionization thresholds of C3(X(1)Σg(+)) and C3(a(3)Πu) are determined as 11.6 ± 0.2 eV and 10.0 ± 0.2 eV, respectively. The C5H product is identified as linear pentynylidyne that has an ionization energy 8.4 ± 0.2 eV. The title reaction releases translational energy 10.6 kcal mol(-1) in average and has an isotropic product angular distribution. The quantum-chemical calculation indicates that the C3(a(3)Πu) radical attacks one of the carbon atoms of C2H2 and subsequently a hydrogen atom is ejected to form C5H + H, in good agreement with the experimental observation. As far as we are aware, the C3(a(3)Πu) + C2H2 reaction is investigated for the first time. This work gives an implication for the formation of C5H from the C3(a(3)Πu) + C2H2 reaction occurring in a combustion or discharge process of C2H2.
authors.affiliation: National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan.
authors.forename: Wen-Jian
authors.initials: WJ
authors.lastname: Huang
authors.affiliation: National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan.
authors.forename: Yi-Lun
authors.initials: YL
authors.lastname: Sun
authors.affiliation: National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan.
authors.forename: Chih-Hao
authors.initials: CH
authors.lastname: Chin
authors.affiliation: National Synchrotron Radiation Research Center (NSRRC), 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan.
authors.forename: Shih-Huang
authors.initials: SH
authors.lastname: Lee