The photolysis of carbon suboxide in the presence of ethylene oxide with light of 2537 Å yields ethylene and traces of acetylene. Ethylene oxide reacts with :CCO four times as fast as ethylene oxide. With trimethylene oxide the products are ethylene, acetylene, propene, and cyclopropane. The overall rate is six times that with ethylene. The cyclopropane is formed with vibrational energy close to 82 kcal. mole^–1 and isomerizes to propene unless it is deactivated by collision.