Changes of structure and energy on the route from dioxetane to carbonyl products. A quantum chemical study

Energy diagrams, changes of geometry and bond orders were calculated semi-empirically for the thermolysis of 1,2-dioxetane. Stretching of the O-O bond, then of the C-C bond and distortion of the whole quadrangular structure make major, but different, contributions to the reaction coordinate on the path to formaldehyde. The activation barrier represents a vast region where the gaps between the ground and excited states are small, and this favours horizontal radiationless transitions leading to the excitation of a product. The results show that semi-empirical calculations may help to provide better insight into the nature and mechanism of the chemiluminescence excitation.