A novel "site decompression technique" that takes advantage of specific pressure relaxation effects in cryogenic noble gas matrices was applied in a spectroscopic investigation of the two title compounds, resulting in virtually background-free, complete, high-resolution IR spectra with line widths of ca. 0.1 cm(-1). The compounds were prepared photo chemically in Ar and Ne matrices and, together with the related intermediates, fluorinated benzocyclopropenone and cyclopentadienylideneketene, characterized by IR and UV-visible absorption spectroscopy. Weak IR absorption bands observed at 1878 cm(-1) for perfluoro-o-benzyne and at 1866 cm(-1) for 3-fluoro-o-benzyne were assigned to CC triple bond stretching vibrations, corresponding to the transition at 1846 cm(-1) in the parent o-benzyne. The application of polarization spectroscopy on photooriented samples led to the determination of transition moment directions for most of the observed vibrational transitions. Absolute IR absorption intensities were also obtained. The assignments of the observed transitions were supported by the results of B3LYP/cc-pVDZ quantum chemical calculations.