title: Formation of Polyynes C4H2, C6H2, C8H2, and C10H2 from Reactions of C2H, C4H, C6H, and C8H Radicals with C2H2.
abstract: Some of the polyynes (HC2n+2H, 1 ≤ n ≤ 4) are observable in planetary atmospheres, interstellar space, and flames. Polyynes are proposed to play an important role in synthesis of large carbonaceous molecules. We explore the dynamics of reactions of C2nH (n = 1-4) radicals with C2H2 by interrogating time-of-flight spectra and photoionization efficiency spectra of products C2n+2H2. The reactions of n = 2-4 were investigated for the first time. The translational energy release is biased to low energy but extends to the energetic limit of product HC2n+2H + H, corresponding to a fraction of 0.34-0.36 on translational energy. Product C2n+2H2 has a deconvoluted ionization threshold in good agreement with the ionization energy of polyynes. The quantum chemical calculations support the experimental observations. This work verifies that the title reaction is an important source for formation of polyynes that have been observed in interstellar/circumstellar media and combustion processes.
authors.affiliation: Scientific Research Division, National Synchrotron Radiation Research Center , 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan.
authors.forename: Yi-Lun
authors.initials: YL
authors.lastname: Sun
authors.affiliation: Scientific Research Division, National Synchrotron Radiation Research Center , 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan.
authors.forename: Wen-Jian
authors.initials: WJ
authors.lastname: Huang
authors.affiliation: Scientific Research Division, National Synchrotron Radiation Research Center , 101 Hsin-Ann Road, Hsinchu Science Park, Hsinchu 30076, Taiwan.
authors.forename: Shih-Huang
authors.initials: SH
authors.lastname: Lee
keywords: crossed molecular beams; photoionization; reaction dynamics; synchrotron radiation; time-of-flight