Gas Phase Far Ultraviolet Photolysis and Radiolysis of Vinyl Chloride.

Abstract
Quantum yields of the major products formed in the far ultraviolet photolysis of CH2CDCl (C2H2, C2HD, C2H3D, C2H2D2, and 1,3-C4H4D2) have been determined at 147 nm (8.4 eV), 123.6 nm (10.0 eV), and 104.8-106.7 nm (11.6-11.8 eV). The quantum yield of the stable vinyl radicals which can be unambiguously ascribed to the primary process (CH2CDCl + hv → CH2CD + Cl) is 0.3 and 0.05 at 147 and 123.6 nm, respectively. The sharp decrease in the yield of vinyl radicals with the increase in energy of the incident photon beam is in part attributed to the decomposition of internally excited vinyl radicals to give acetylene as a product. At 147 nm, the combined yield of acetylene plus vinyl radicals is 0.95 ±0.05. At the shorter wavelengths, approximately one acetylene molecule is formed per electronically excited vinyl chloride molecule. It is concluded that the dissociative process: C2H3Cl* → C2H2 + H + Cl, occurring via a C2H3 or C2H2Cl intermediate adequately accounts for the reactive neutral species formed at higher photon energies. Isotopic labeling experiments show that the hydrogen atoms are detached from both positions of the parent molecule. Ethylene which is a product over the entire wavelength range is in part formed via the reaction: H* + C2H3Cl → C2H4 + Cl, where H* represents a translationally excited hydrogen atom. The C2H2DC1+ ions formed at 104.8 - 106.7 nm with a quantum yield of 0.47 do not contribute to the formation of acetylene or vinyl radicals. In the gas phase radiolysis of vinyl chloride, acetylene (G ~ 1.5) is mainly formed in the dissociation of neutral electronically excited vinyl chloride molecules. From this value, we may estimate that the ratio of neutral excited molecules formation to ionization in the radiolysis of vinyl chloride is 0.39. Vinyl ions, which are also produced (G ~ 0.28-0.35) react mainly by addition to vinyl chloride.

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