The rotational spectrum of an asymmetrically substituted isotopologue of the fluoroformyloxyl radical FC(16)O(18)O(•) with resolved fine and hyperfine structures were measured and analyzed for the very first time. The molecular parameters of this radical obtained from the spectral analysis were processed along with the symmetrical isotopologues FC(16)O2(•) and FC(18)O2(•) and accurate substitution geometry was attained. In addition to those, coupled cluster quantum chemistry calculations were used to scale the experimental parameters, and in this manner, trustworthy values of the equilibrium and ground state geometries were derived.