The liquid phase photolysis of diethyl ketone has been studied in the temperature range from -35" to 95' C. The CO quantum yield a t 95' C. nras found to be close to unity. .At 28" C. decrease in intensity and addition of heptane led to a substantial increase of the CO and the ethane yields.The methyl ethyl ketone liquid phase photolysis a t temperatures between 5' and 75" C. led to the same observations. Arrhenius plots of Rp/Ru1/? [I<] ga\.e for both compounds a value of 5 k~a l . / mole.Gas phase studies in the temperature range of 0" to 60' C. confirmed the low CO quantum yield reported previously and showed evidence for disproportionation and recombinatioii reactions between ethyl and propionyl radicals.
EXPERIMENTALEastman Icodak Company methyl ethyl ketone and diethyl ketone (white label) were distilled through 10 theoretical plates with rejection of large head ancl tail fractions. Air was removed by bulb-to-bulb distillation in the vacuum line.Gas phase experiments were performed with a Hanovia (16A-13) SH type medium pressure lamp. The cylindrical quartz cell (5 cm. diameter, 10 cm. long) was completely filled with a nearly parallel light beam.The liquids were irradiated in a quartz cell of 5 cm. diameter and 0.05 cm. depth. The cell was provided with two outlets, one of which was sealed after filling, while the other was closed by a break seal which made it possible to attach the cell to the analysis system after each experiment. Between runs the cell was washed out with diethyl ketone and dried a t about 150' C. The irradiation was carried out in a thermostat consisting of a brass cylinder with evacuated double walls and double quartz windows. For experiments above room temperature an electric im~nersion heater was brought into distilled water, while for the low temperature experiments the thermostat was filled with methanol cooled by dry ice. In this way it was possible to maintain the temperature constant within half a degree.At 3130 A about 98% of the incident radiation is absorbed by the undiluted ketone.In order to compensate for this sharp absorption decrease throughout the cell, two Hanovia lamps were placed opposite each other with the cell fixecl in the center of the nearly parallel light beam.Except for experiments 1 and 2 Corning filters (9-53) were used to cut off wavelengths below 2800 A. The incident intensity was varied by means of copper gratings.After irradiation of the liquid the cell was attached to the analysis system, consisting of three traps and one modified Ward still. The CO-CHI fraction was removed a t solid nitrogen temperature and was analyzed by combustion over hot CuO. The C~H C -C~H~ fraction was taken off a t -lGOO C. CzH4 was determined by hydrogenation over a Ni