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 (lambda > 350 nm, lambda > 290 nm, and pi > 240 nm) have been examined using FT-IR spectroscopy. Ozonolysis occurs after irradiation at relatively long wavelengths, (lambda > 350 nm), due to the formation of an ozone(...)XCH=CHX (X = Br or Cl) pi 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, (OCHX)-H-... and OC...(HX)(2) (X = Br or Cl). However, the identification of a novel ketene species X-HC=C=O suggests that a further mechanism to the Criegee one is followed in the case of halogenated ethenes. Moreover the photochemically induced reaction of XCH==CHX deposited in oxygen matrices produced the similar photoproducts HC(O)X and (OCHX)-H-... as well as the ketene type species XHC=C=O, providing additional evidence that a further mechanism is being followed from that involved in ozonolysis. Two possible reaction pathways involving either the ozone molecule or oxygen atoms are discussed.