Vacuum flash pyrolysis of bis(fluoroformyl) peroxide, FC(O)OOC(O)F, diluted in N-2, Ar, or Ne, yields on subsequent quenching of the products in a matrix at 10, 14, or 6 K, respectively, the fluoroformyloxyl radical, FCO2., in the X(2)B(2) ground state. It has been possible to record its infrared spectrum and to identify all bands by their photochemical behavior for the first time. The assignment of the six fundamental vibrations on the basis of C-2 upsilon symmetry (a(1) 1475, 960, 519; b(1) 1098, 474, b(2) 735 cm(-1); Ne matrix) was achieved by a normal coordinate analysis taking into account additional data of O-18- or C-13-labeled FCO2.. The experimental fundamental vibrations and the structural parameters derived from the vibrational data are compared to the results of ab initio and DFT (density functional theory) calculations. The visible spectrum of FCO2. isolated in a neon matrix agrees with the known gas phase spectrum. The origin of the B(2)A(1) <-- X(2)B(2) transition is observed at 13 103 cm(-1), and four fundamentals at 1607, 1117, 839, and 611 cm(-1) are detected due to the excited state species (B(2)A(1)). In a fast reaction with NO, the FCO2. radical quantitatively forms FNO and CO2. The anticipated intermediate FC(O)ONO is not observed.