Interpretation of the Mechanism of a Thermal Decomposition from Photochemical Evidence

By analogy to diatomic molecules it is assumed that if in polyatomic molecules, a transition is permitted between two energy hypersurfaces in a radiative act, it is forbidden in a non-radiative process. The thermal decomposition, in acetaldehyde, yielding methane and carbon monoxide in a unimolecular primary process is shown consequently not to be allowed. However, the bimolecular and the catalyzed processes producing ultimate molecules in the primary act are permitted. The simultaneous occurrence of such a decomposition and a free radical mechanism of a Rice-Herzfeld type adequately account for many of the observations on the catalyzed and high pressure reactions by Hinshelwood and his co-workers, by Verhoek and by Letort.