The absorption characteristics of COF2both internal and external to the optical resonator of a CO2laser were investigated over pressure ranges 1–26 Torr. Injection of small amounts of COF2into the flow of an operating transfer chemical laser resulted in significant reductions in laser power. The absorption coefficient for COF2was obtained from experiments using a CO2laser with a line selection capability. For pure COF2in the pressure range 1–10 Torr, the strongest absorption was on theP(24) line yielding an absorption coefficient of — 0.005 cm−1Torr−1. When the COF2was diluted with N2, the absorption was found to decrease as the operating laser line moves away from the COF2absorption band centered at 965 cm−1(10.36 &mgr;m).