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Isomer-specific detection in the UV photodissociation of the propargyl radical by Chirped-Pulse mm-Wave spectroscopy in a Pulsed Quasi-Uniform Flow

Abstract

Isomer-specific detection and product branching fractions in the UV photodissociation of the propargyl radical is achieved through the use of chirped-pulse Fourier-transform mm-wave spectroscopy in a pulsed quasi-uniform flow (CPUF). Propargyl radicals are produced in the 193 nm photodissociation of 1,2-butadiene. Absorption of a second photon leads to H atom elimination giving three possible C3H2 isomers: singlets cyclopropenylidene (c-C3H2) and propadienylidene (l-C3H2), and triplet propargylene (3HCCCH). The singlet products and their appearance kinetics are directly determined by rotational spectroscopy, but due to the negligible dipole moment of propargylene, it is not directly monitored. However, we exploit the time-dependent kinetics of H-atom catalyzed isomerization to infer the branching to propargylene as well. We obtain the overall branching among H loss channels to be 80.2%(+1.8/-4.2):16.8%(+3.2/-1.3):2.9%(+1.1/-0.5) for 3HCCCH: c-C3H2: l-C3H2. Our findings are qualitatively consistent with the ab initio/RRKM calculations by Nguyen et al. in that the major channel in the photodissociation of the propargyl radical at 193 nm is due to 3HCCCH + H; however, a greater contribution to the energetically most favorable isomer, c-C3H2 + H is observed in this work. We do not detect the predicted HCCC+H2 channel, but place an upper bound on its yield of 1-2%.

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Publication details

The article was received on 12 Sep 2017, accepted on 13 Nov 2017 and first published on 13 Nov 2017


Article type: Paper
DOI: 10.1039/C7CP06211G
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    Isomer-specific detection in the UV photodissociation of the propargyl radical by Chirped-Pulse mm-Wave spectroscopy in a Pulsed Quasi-Uniform Flow

    B. Broderick, N. Suas-David, N. Dias and A. Suits, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP06211G

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