The photolysis (visible and ultraviolet) of low-temperature argon matrices containing either chloroiodomethane/ozone or bromochloromethane/ozone has been studied by FTIR spectroscopy. Codeposition of ozone and chloroiodomethane in an argon matrix led to the formation of a weak complex, CH2ClI ... O-3, which, on irradiation with near infrared/visible light (lambda > 650 nm), formed iodosochloromethane CH2ClIO. Subsequent photolysis at shorter wavelength (lambda > 350 nm) produced hypoiodochloromethane CH2ClOI, a formyl chloride complex HC(O)Cl ... HI, and a carbon monoxide complex OC ... HCl ... HI. Subsequent Pyrex- (lambda > 290 nm) and quartz- (lambda > 240 nm) filtered irradiation increased the yield of the formyl chloride and carbon monoxide complexes. The photolysis of matrices containing bromochloromethane and ozone required much harsher conditions, i.e. ultraviolet irradiation for tens of hours, to produce any products, the first of which being the carbonyl complexes, HC(O)Cl ... HBr, HC(O)Br ... HCl, and COBrCl ... H-2. Subsequent photolysis produced the carbon monoxide complexes OC ... HCl ... HBr and OC ... HBr ... HCl. Thus by studying the reactions of ozone with these two disubstituted halomethanes it has been possible to extend the number of known species having I-O-x bonds and to detect a number of carbonyl ... HX and carbon mon oxide ...(HX)(HY) complexes in which the halogen atoms (X and Y) differ.