Photochemically Induced Reactions of Ozone with 1,2-Dibromoethene and 1,2-Dichloroethene: An FT-IR Matrix Isolation Study

Abstract

The co-deposition of ozone with the halogenated ethenes, 1,2-dibromoethene and 1,2-dichloroethene, in argon matrices and the subsequent photolysis cycles using radiation of different wavelengths (λ > 350 nm, λ > 290 nm, and λ > 240 nm) have been examined using FT-IR spectroscopy. Ozonolysis occurs after irradiation at relatively long wavelengths, (λ > 350 nm), due to the formation of an ozone···XCHCHX (X = Br or Cl) π complex upon deposition and is believed to follow the Criegee pathway because the expected HC(O)X (X = Br or Cl) intermediates are detected. The carbonyl species HC(O)X dissociate to form the carbon monoxide species, OC···HX and OC···(HX)2 (X = Br or Cl). However, the identification of a novel ketene species XHCCO suggests that a further mechanism to the Criegee one is followed in the case of halogenated ethenes. Moreover the photochemically induced reaction of XCHCHX deposited in oxygen matrices produced the similar photoproducts HC(O)X and OC···HX as well as the ketene type species XHCCO, ...