Photolysis of CH3C(O)CH3 at 248 and 266 nm: pressure and temperature dependent overall quantum yields

The overall quantum yield of photolysis of acetone (CH3C(O)CH3) at 248 and 266 nm was measured using the pulsed laser photolysis technique. The organic photo-fragment radicals CH3 and CH3CO were detected indirectly as Br atoms using time-resolved resonance fluorescence following their reaction with Br-2. Quantum yields for acetone photolysis were derived relative to COCl2 (at 248 nm) or Cl-2 (at 266 nm) in back-to-back experiments in which Cl atoms were scavenged by Br-2 to form Br. At 248 nm, experiments were carried out at pressures between 60 and 760 Torr of N-2 and at three temperatures: 224, 234 and 298 K. At this wavelength, the overall quantum yield was 0.98 +/- 0.10 and, within experimental uncertainty, was independent of pressure and temperature in the ranges covered. At 266 nm, experiments were restricted to 298 K, where the quantum yield was also close to unity, but with a weak dependence on bath gas pressure. These results confirm our previous room temperature, 266 nm dataset obtained using a different experimental approach in which the yield of CH3 was measured directly.