Photolysis of acetaldehyde in presence of nitric oxide

Abstract

The initial rate of formation of nitrogen dioxide during and after the photolysis of acetaldehyde + nitric oxide mixtures is compared with that in the corresponding acetone system. It is shown that the thermal disproportionation of nitric oxide by the unstable species nitrosoacetaldehyde (CH₃·CONO) exhibits a decrease in order with respect to nitric oxide as the pressure of nitric oxide increases, and this effect is discussed. The dependence of the rate of production of nitrogen dioxide on the pressure of acetaldehyde and on I_a, the absorbed light, indicates that there are at least two sources of CH₃·CONO in the acetaldehyde system. It is suggested that a reaction of an excited singlet state of acetaldehyde leads to CH₃·CONO and that the intermediate, with a life-time of several seconds, formed by the reaction of triplet-state acetaldehyde with nitric oxide, also decomposes to produce CH₃·CONO. The latter source is responsible for the dark reaction observed.