Flash Photolysis of Ethylene

The flash photolysis of ethylene has been studied at pressures from 1 to 20 torr and flash energies from 72 to 1800 J, with light of a broad spectral distribution from about 1550 to 1900 Å. The products were acetylene, hydrogen, ethane, propane, butane, methane, 1-butene, and propylene, in approximately decreasing order of importance. The primary processes are thought to have been C2H4+hν→C2H2+H2 (∼51%)and C2H4+hν→[C2H3*+H]→C2H2+2H (∼49%)in close agreement with the low-intensity photolysis at 1470 Å. A hydrogen-atom ``cracking'' mechanism followed by radical combination appears to account for the products. The formation of 1-butene and propylene indicates that some of the vibrationally excited vinyl radicals formed in the second primary process were stabilized by collision at the higher pressures and trapped by combination with methyl and ethyl radicals. About 12% of the vinyl radicals were stabilized by the addition of 600 torr of nitrogen.