Low pressure pyrolysis at 600 K of bis(fluoroformyl) peroxide, FC(O)OOC(O)F, yields the fluorocarboxyl radical, FCO2, in a concentration high enough to allow its detection by millimeter wave and infrared spectroscopy. The radical was first identified from its high resolution infrared spectrum obtained using a Fourier transform infrared interferometer. Observation and identification of its millimeter wave (MMW) spectrum were made possible by reliable ab initio calculations at the level of open-shell coupled cluster theory using large basis sets. The excellent agreement between the experimental and theoretical results confirms the structure of the FCO2 radical and the efficiency of the synthesis. The analysis of the MMW spectrum has given a set of ground state parameters including rotational, quartic centrifugal distortion, fine and hyperfine constants. (C) 2003 American Institute of Physics.