KRF LASER-INDUCED THERMAL-DECOMPOSITION OF 1,2-DICHLOROETHANE

The thermal decomposition of 1,2-dichloroethane to give vinyl chloride and hydrogen chloride has been reinvestigated at 703 K and the major features of this free-radical chain reaction found previously have been confirmed. A direct comparison of the pulsed KrF laser-induced process (248 nm) in the same static reactor at this temperature showed that a substantial increase in rate occurs even at low pulse-repetition rates (2 Hz). In an extended study of the laser-induced reaction at temperatures where thermal reaction is negligible (476-577 K), quantum yields of vinyl chloride formation have been measured to be between 3000 and 13000. Quantum yields decreased slightly with increasing pressure and showed an inverse square-root dependence on initial chlorine atom concentration. The major by-products were identified as ethene, ethyne, 1,2,3,4-tetrachlorobutane and 1,1,2-trichloroethane. At 577 K and 150 Torr, the quantum yield of ethene production is close to unity, indicating that under these conditions reaction (2) is essentially complete. [GRAPHICS] Computer modelling of a complete reaction mechanism involving the propagation steps (3) and (4) [GRAPHICS] was used to predict quantum yields of both vinyl chloride and the minor products.