With use of vacuum-UV radiation from a synchrotron, gas-phase negative ions are detected by mass spectrometry following photoexcitation of SF5Cl. F-, Cl-, and SF5- are observed, and their ion yields recorded in the range 8-30 eV. F- and Cl- show a linear dependence of signal with pressure, showing that they arise from unimolecular ion-pair dissociation, generically written AB + hv -> C- + D+ (+ neutral(s)). F-is the strongest signal, and absolute cross sections are determined by calibrating the signal intensity with that of F- from SF6 and CF4. Resonances are observed and assigned to transitions to Rydberg states of SF5Cl. The Cl- signal is much weaker, despite the S-Cl bond being significantly weaker than the S-F bond. Appearance energies for F- and Cl- of 12.7 +/- 0.2 and 10.6 +/- 0.2 eV are determined. The spectra suggest that these ions form indirectly by crossing of Rydberg states of SF5Cl onto an ion-pair continuum.