Matrix studies on the photolytic reaction between ozone and hexafluoro-2-butyne have been performed at 11 K in argon and nitrogen matrices. The matrices were photolyzed with 640 and 642 nm light from a laser source, and with 254 nm light from a Hg are lamp. The final products of the reaction are perfluorobutanedione and bis (trifluoromethyl)ketene. An intermediate species was also observed. It has been identified as perfluoroacetylmethylmethylene, a ketocarbene. The ketocarbene was also trapped as trifluoromethyl trifluoroacetylketene, a ketoketene, when the matrix was doped with CO. Photolysis of the ketocarbene with 427 nm light results in the direct formation of the ketene. The ketocarbene and ketene form as a result of O atom addition to the butyne, whereas the butanedione appears to be predominantly produced by a reaction between the ketocarbene and O-2. Product distribution was found to depend greatly on both matrix material and ozone concentration. This is the first direct evidence of a ketocarbene as an intermediate in the O atom addition to an alkyne.