Fourier transform infrared spectra of the FO2 radical

Six infrared bands of FO₂ have been measured at high resolution using a fast-flow long-path absorption cell and a Fourier transform spectrometer. The bands have been analyzed to obtain accurate band origins, as well as rotational, centrifugal distortion, and spin-rotation parameters. In order of increasing wavenumber they are ν₃ at 579 cm⁻¹, ν₂ + ν₃ at 940 cm⁻¹, 2ν₃ at 1142 cm⁻¹, ν₁ at 1487 cm⁻¹, ν₂ + 2ν₃ at 1496 cm⁻¹, and 2ν₁ at 2948 cm⁻¹. Only ν₃ has been studied previously (by C. Yamada and E. Hirota, J. Chem. Phys. 80, 4694–4700 (1984)); the other bands are rotationally analyzed here for the first time. The ν₁ and ν₂ + 2ν₃ vibrations were found to be strongly mixed by Coriolis- and Fermi-type interactions and were thus analyzed simultaneously. 2ν₁ was also observed to be perturbed, but the perturbations were not analyzed. FO₂ now becomes one of the best-characterized unstable free radicals in terms of its rotation-vibration structure.