The photolysis of methyl vinyl ketone at 308 nm

The photolysis of methyl vinyl ketone at small conversions has been studied at 308 nm and at temperatures from approximately 300 K to 475 K as a function of the partial pressures of methyl vinyl ketone, argon and oxygen. The main products of photolysis from 300 K to 435 K are propylene and carbon monoxide together with much smaller yields of methane. The absence of measurable yields of ethane, ethylene and 1,3-butadiene indicates that dissociation of methyl vinyl ketone to free radical products is unimportant under these conditions. At 475 K, small yields of ethane, ethylene and 1,3-butadiene were observed suggesting the increased importance of channels producing CH3 and C2H3 radicals which were not observable at the lower temperatures.The formation of propylene is quenched by methyl vinyl ketone, argon and oxygen. However, the yield of methane is increased by the addition of argon and oxygen but is reduced by increasing the pressure of methyl vinyl ketone. The maximum partial pressures of argon and oxygen used in these experiments were approximately 450 Torr. The maximum pressure of methyl vinyl ketone was limited by its vapour pressure to approximately 45 Torr. The markedly different variation in the yields of propylene and methane with changing pressure and with the addition of argon and oxygen suggests that propylene and methane are formed from different excited states of methyl vinyl ketone. These results are discussed within the context of the energetically accessible states of methyl vinyl ketone.