Mercury Photosensitized Reaction of Cyclo-octatetraene and the Comparison with the Direct Photochemical Reaction

The reaction products of both the mercury photosensitized reaction and the direct photochemical reaction are the same, i.e. acetylene, benzene, orange-colored liquid (presumably bicyclo form of C8H8), polymer and a trace of styrene; the noncondensable products at liquid nitrogen temperature such as hydrogen and methane were not detected. A quantitative experiment has been made on the decomposition reaction, in which cyclo-octatetraene shows a similar behavior to ethylene in the pressure dependence of the quantum yield. The quantum yields of the decomposition are of the same magnitude in both the mercury photosensitized and the direct photochemical reaction. The result shows that the two reactions proceed via the same excited state (probably triplet), directly or indirectly. An investigation has also been made on the polymerization reaction, for which the total pressure change and the absorption spectrum of the reaction products have been examined in the course of the reaction. It is concluded that the polymerization takes the place via orange-colored liquid as an intermediate. In the study of the reaction of hydrocarbons with Hg(63P1) atom a great deal of evidence has now been accumulated which shows the fact that the reaction always accompanies hydrogen production. The mercury photosensitized reaction of cyclooctatetraene is one of the rare exceptions in this generality.