Abstract The recombination reaction Cl+ FSO 3+ M→ FSO 2 OCl+ M has been studied by ArF excimer laser photolysis-visible absorption spectroscopy in the pressure range 24–708 Torr of the bath gases He and CF 4 at 297 K. For M= CF 4 the limiting high-pressure rate constant is (6.0±0.7)× 10− 11 cm 3 molecule− 1 s− 1. Small fall-off effects are apparent for He diluent. An analysis of the in terms of the statistical adiabatic channel model leads to α/ ...