Gas Phase Far Ultraviolet Photolysis and Radiolysis of Vinyl Chloride

Quantum yie lds of the major products formed in the far ultraviole t photolys is of CH,C DCI (C2 H2 , C, HD , C,HoD, C, H2 D" and 1,3·C, H,D,) have been de termined at 147 nm (8.4 eV), 123.6 nm (10.0 eV), a nd 104.8106.7 nm 01.611.8 eV). The quantum yield of the s tab le vinyl rad icals which can be un· ambiguous ly asc ribed to the primary process (CH2CDCI + hll ~ CH,C D+ CI) is 0.3 a nd 0.05 at 147 and 123.6 nm, res pectively. The sharp decrease in the yie ld of vinyl radicals with the increase in e ne rgy of the incident photon beam is in part attributed to the decomposition of inte rnally excited vinyl radicals to give acetyle ne as a product. At 147 nm , the combined yield of acetylene plus vinyl rad icals is 0.95 ± 0.05. At the s horte r wa velengths, approximate ly one acetylene molecule is form ed per e lectronically excited vinyl chloride molecule. It is concluded that the dissociative process: C2 HaCI* ~ C,H, + H + CI, occurring via a C, Ha or C,H,CI inte rmediate adequate ly accounts for the reo active neutral s pecies form ed at higher photon e ne rgies. Isotopic labeling e xperime nts s how that the hyd rogen atoms are detached from both pos itions of the pare nt molecule. Ethylene which is a product over the entire wavelength range is in part formed via the reaction : H* + C,HaC I ~ C2H .. + CI, where H* represents a translationaUy excited hydrogen atom. The C2H2DC I+ ions formed at 104.8 106.7 nm with a quantum yie ld of 0.47 do not contribute to the form ation of acetylene or vinyl radical s. In the gas phase radiolysis of vinyl chloride, acetylene (G 1.5) is mainly formed in the di ssocia tion of ne utra l e lectronica ll y excited vinyl chloride molecules. From this value, we may es timate that the ratio of neutral excited molecules formation to ionization in the rad iolys is of vinyl chloride is 0.39. Vinyl ions, which a re also prod uced (G 0.280.35) react mainl y by addition to vi nyl chloride.