The rotating sector technique has been applied to a study of the photochemical addition of bromotrichloromethane to ethylene in the gas phase.1 From these data the rate constant of trichloromethyl radical combination has been determined: CCl3˙+CCl3˙→C2Cl6, k6= 1010.9 1. mole–1 sec–1 independent of temperature in the range 77–173°C.