The photolysis of acetaldehyde, diacetyl and acetone at high intensity

The photolysis of acetone, acetaldehyde and diacetyl have been investigated at absorbed intensities of the order 10-3Nhv cm-3s-1 which are greater by a factor of about 107than those normally used. Precautions were taken to keep the system nearly isothermal. Analysis of the products shows that, in this intensity region, reactions which are second order in radical concentration predominate, and no evidence was found of any reaction of radicals with the parent molecule. In the case of acetaldehyde this results in a complete change in the products, ethane formation being the main reaction of methyl, whilst in the photolysis of acetone and diacetyl only minor differences are observed. It has been possible to give a fairly complete account of all the analytical results and the intensity dependence of the product ratios in terms of reaction mechanisms which are logical extrapolations of the results of studies at low intensity. The simplifications resulting from the elimination of reactions with the parent molecule lead to information concerning the primary photochemical acts and those second-order radical reactions which are of minor importance at lower intensities.